Ankle and Foot 47 - Department of Radiology - University of ...

Ken L. Schreibman 

Richard Bruce 

Ankle and Foot 47 

This chapter is intended to serve as a practical approach to 

imaging the ankle and foot using computed tomography 

(CT) and magnetic resonance imaging (MRI). Rather than 

providing an exhaustive review of the literature, we illustrate 

the anatomic structures and common pathologic 

processes seen with CT and MRI scans. In addition, we have 

included discussions regarding the techniques for obtaining 

these scans, including the CT and MR protocol sheets 

we use daily in the Radiology Department of the University 

of Wisconsin in Madison (UW). The most up-to-date versions 

of these protocol sheets are available for free download 

at www.schreibman.info. Throughout this chapter, we 

have endeavored to include references to review articles for 

readers who wish to explore topics in more detail. The 

images and content of this chapter are based on Dr. 

Schreibman’s lecture series. 

Anatomy 

• Tarsal Bones 

• Gross Anatomy of the Tarsal Bones 15 

Talus 

Figures 47-1 through 47-4 are photographs of cadaveric 

bones arranged to illustrate the relationships of the major 

tarsal bones and joints. Figure 47-1 represents the bones 

we typically cover when scanning the distal tibia/ankle/ 

foot. Central to all this is the talus, labeled Ta. (The label 

abbreviations in Fig. 47-1 will be consistent throughout all 

figures.) Indeed, the word talus is Latin for “ankle,” indicating 

that early anatomists considered the talus the center of 

the ankle. Understanding the articulations between the 

talus and the surrounding bones is the key to understanding 

the anatomy of the ankle and foot. 

Two views of the talus are shown in Figure 47-2. The 

dome is the broad, curved articular surface on the top of 

the talus. (The specimen in Fig. 47-2 has an osteochondral 

lesion centrally in the medial edge of the talar dome. 

Osteochondral lesions are discussed later in the chapter.) 

The head is the rounded process at the anterior aspect of 

the talus, and it articulates with the navicular bone. The 

body of the talus comprises everything between the dome 

and head. The dome of the talus along with the distal ends 

of the tibia and fibula make up the ankle joint (Fig. 47-3). 

(Ankle joint is the preferred name of this joint in the radiology 

and orthopedic surgery literature, rather than “tibiotalar 

joint” or “crural joint.”) 

Mortise 

The flat talar dome articulates with the flat surface at the 

distal end of the tibia known as the plafond. Plafond is an 

architectural term meaning “a ceiling formed by the underside 

of a floor.” In essence, the plafond is the ceiling of the 

ankle joint, formed by the floor of the tibia. The ankle joint 

is bounded on the sides by the inner articular surfaces of 

the medial and lateral malleoli. The plafond and malleoli 

together form a rectangular opening called the mortise into 

which the talar domes fit, analogous to a mortise-andtenon 

joint in woodworking. The ankle mortise is a remarkably 

sturdy joint. Like the hip and knee joints, the ankle 

must bear our entire body weight with every step. But 

although it is common for primary osteoarthritis to affect 

the hips and knees of many of us as we age, it is uncommon 

to have primary osteoarthritis of the ankle. 

The joint between the distal tibia and fibula is called 

the syndesmosis. Syndesmosis is a Greek term meaning “to 

bind together,” and in general a syndesmosis joint is held 

together by thick connective ligaments. (Most joints in the 

body, including the ankle and subtalar joints, are synovial 

joints in that they are enclosed by a synovium-lined capsule 

that creates synovial fluid.) The distal fibula, just above the 

lateral malleolus, fits into a shallow groove in the adjacent 

tibia, and this relationship is best visualized in the axial 

plane of a CT scan. 

Subtalar Joint 

The talus articulates with the tibia from above and with the 

navicular in front. It is at the undersurface of the talus 

where it articulates with the calcaneus that things get complicated. 

This joint below the talus is called the subtalar 

joint, which is preferred over “talocalcaneal joint.” Figure 

47-4 illustrates the three facets that make up the subtalar 

joint. In Figure 47-4A to D, the talus and calcaneus were 

attached using colored modeling clay. In Figure 47-4E, the 

two bones have been disarticulated and the talus flipped 

2207 

Ch047-A05375.indd 2207 

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2208 VII Imaging of the Musculoskeletal System 

over, displaying the talar and calcaneal articular surfaces of 

the posterior, middle, and anterior facets of the subtalar 

joint in red, blue, and green, respectively. 

The posterior facet is the largest and is the primary 

weight-bearing portion of the subtalar joint. At the anterolateral 

corner of the posterior facet, the talus comes to an 

acutely angled corner, the lateral process of the talus. When 

the subtalar joint experiences an extreme axial load, such 

as when a person falls from a height or undergoes a deceleration 

injury in a motor vehicle collision, the pointy 

lateral process of the talus acts like a wedge, splitting 

and fracturing the calcaneus. 13 Calcaneal fractures tend to 

extend into the posterior facet, and when imaging calcaneal 

fractures we obliquely angle our coronally reformatted 

CT slices to be perpendicular to the posterior facet. 

The middle facet is defined by the sustentaculum tali, 

a shelflike projection from the anteromedial portion of the 

calcaneus that supports the middle of the talus. Sustentaculum 

in Latin means “a supporting structure.” The flexor 

hallucis longus tendon passes under the sustentaculum 

tali. The middle facet of the subtalar joint is a completely 

separate articulation from the posterior facet. When injecting 

contrast (often mixed with anesthetic) into the posterior 

facet of the subtalar joint, we do not expect it to 

communicate with the middle facet. Across the middle 

facet of the subtalar joint is one of the two most common 

locations for tarsal coalitions to occur, the other being 

between the anterior process of the calcaneus and the 

lateral pole of the navicular. 

Unlike the posterior and middle facets, the anterior 

facet is not well defined and may even be absent. When 

present, the anterior facet is a smooth continuation of the 

middle facet, extending under the head of the talus. Directly 

lateral to the anterior and middle facet is the sinus tarsi, an 

area devoid of bone and filled primarily with fat. 

• Anatomic Divisions 

Figure 47-5 is a three-dimensionally reformatted CT image 

showing the anatomic divisions between the tarsals and 

metatarsals. The hindfoot consists of the talus and the calcaneus 

and is separated from the midfoot by the Chopart* 

joint, a smooth continuation between the talonavicular 

and calcaneocuboid joints. The midfoot consists of the 

other five tarsal bones, the navicular, the cuboid, and the 

three cuneiforms. The forefoot consists of the metatarsals 

and phalanges and is separated from the midfoot by the 

tarsometatarsal joint, also known as the Lisfranc † joint. Along 

Figure 47-1. Gross anatomy of the tarsals and surrounding bones. 

Ti, tibia; Fi; fibula; Ta, talus; Ca, calcaneus; ST, sustentaculum tali; 

N, navicular; Cu, cuboid; 1, 2, and 3, refer respectively to the first, 

second, and third cuneiforms (sometimes referred to as the medial, 

intermediate, and lateral cuneiforms, respectively); I, II, III, IV, and V 

refer to the first through fifth metatarsals, respectively. 

*François Chopart (1743-1795), a pioneer in urology, was known for the particular 

attention he gave to recording his numerous clinical observations. Thus, it 

is somewhat surprising that he never wrote about the midtarsal amputation that 

bears his name almost three centuries later. He performed this surgery only once, 

on August 21, 1791, to resect a presumed liposarcoma of the foot. The approach 

was based on Chopart’s knowledge of the anatomy of the midfoot and was published 

by his student, Laffiteau, in 1792. 

† Jacques Lisfranc (1790-1847) was a very aggressive surgeon who wrote 

extensively and described many new procedures, including disarticulation of the 

shoulder, excision of the rectum, and amputation of the cervix. At age 23 he joined 

Napoleon’s army as a battlefront surgeon, a setting where amputations were the 

norm. Military surgeons (of the period) were not given the calm and unhurried 

atmosphere necessary for the task of laboriously picking out bone splinters and 

bits of clothing from gaping wounds. Locating the open ends of severed arteries 

and tying them off in the smoke of battle or by flickering candlelight was an enormous 

problem. Although some wounds did not themselves dictate amputation, it 

often had to be done because the patient could not otherwise survive the rigors 

of transport to the rear. The mind did not have time to reason. Experience and 

cold-bloodedness counted for more than talent. Everything had to be done with 

prompt and decisive action. In 1815, the final year of the war, Lisfranc wrote a 50- 

page paper describing his technique for performing a partial amputation of the 

foot at the tarsometatarsal joint, with the sole being preserved to make the flap. 

The technique was used to treat forefoot gangrene from frostbite. Lisfranc was 

widely known for his ability to amputate a foot in less than a minute, an important 

skill in that preanesthesia era. 


9/9/2008 5:33:08 PM

47 Ankle and Foot 2209 47 

Figure 47-2. Gross anatomy of the talus as viewed 

from the top and medial sides. The green arrows show 

an osteochondral lesion of the talus (OLT) in the 

medial edge of the dome. 

Figure 47-3. Gross anatomy of the ankle joint. 

A, The plafond (dotted line) is the transverse cortical 

articular surface at the distal end of the tibia. The 

mortise is the rectangular opening consisting of the 

plafond as well as the inner cortical articular surfaces 

(solid lines) of the medial malleolus (MM) and lateral 

malleolus (LM). B, The talar dome fits into the ankle 

mortise. The joint between the distal tibia and fibula is 

the syndesmosis (black bracket). 

A 

B 

the Lisfranc joint is a common site for fracture-dislocations 

to occur, particularly in diabetic patients with peripheral 

neuropathy. Figure 47-5 illustrates how the base of the 

second metatarsal (II) sticks down like a keystone, disrupting 

the otherwise relatively smooth tarsometatarsal joint. 

For this reason dislocations along the Lisfranc joint are 

typically accompanied by fractures across the base of the 

second metatarsal. 

• Cross-sectional Anatomy of the Tarsal Bones 

Figure 47-6 is a series of straight axial images through the 

ankle and hindfoot, from proximal (see Fig. 47-6A) to 

distal (see Fig. 47-6F). The straight axial plane is well suited 

to examine the syndesmosis (see Fig. 47-6B, arrow). The 

two joints that make up the Chopart joint, the talonavicular 

joint (see Fig. 47-6D) and the calcaneocuboid joint 

(see Fig. 47-6F), are also well profiled in the axial plane. 

However, the ankle and subtalar joints are not well profiled 

in the axial plane, and because examination of these two 

joints is usually the primary indication for requesting a CT 

of the ankle or hindfoot, other reformatted planes are 

required. 

Figure 47-7 is a series of straight sagittal images through 

the hindfoot, from lateral (see Fig. 47-7A) to medial (see 

Fig. 47-7C). Nearly all of the joints are profiled in the sagittal 

plane, including the ankle joint, the calcaneocuboid 

and talonavicular joints, and the posterior and middle 

facets of the subtalar joint. The only joint not well seen in 

the sagittal plane is the syndesmosis, but this is easily seen 

in the axial plane. The lateral sagittal images are also useful 

for visualizing the lateral process of the talus and the anterior 

process of the calcaneus (compare Fig. 47-7A with 

Fig. 47-4C). 

Figure 47-8 is a series of oblique coronal images 

through the hindfoot, from posterior (see Fig. 47-8A) to 

anterior (see Fig. 47-8D). This plane best profiles the subtalar 

joint, and the broad posterior facet can be followed 


9/9/2008 5:33:12 PM


A 

C 

Figure 47-4. Various views of the gross anatomy of 

the subtalar joint. A, Medial view. ST, sustentaculum 

tali. B, Inferior medial view. ST, sustentaculum tali. 

C, Lateral view. LPT, lateral process of talus; APC, 

anterior process of calcaneus. D, Anterior lateral view 

looking into the sinus tarsi (asterisk). E, The subtalar 

joint has been disarticulated: left, talus (flipped over); 

right, calcaneus. The articular surfaces of the three 

facets of the subtalar joint are coated with colored 

modeling clay: posterior (red), middle (blue), anterior 

(yellow). 

B 

D 

E 

Figure 47-5. Three-dimensional CT scan illustrating anatomic 

divisions of the foot. The Chopart joint separates the hindfoot (talus [Ta] 

and calcaneus [Ca]) from the midfoot (navicular [N], cuboid [Cu], and 

the three cuneiforms [1, 2, 3]). The Lisfranc joint separates the midfoot 

from the forefoot (metatarsals and phalanges). 


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A B C 

Figure 47-6. Straight axial images through the ankle 

and hindfoot, proximal (A) to distal (F). A, Proximal to 

syndesmosis. Fi, fibula; Ti, tibia. B, Through the 

syndesmosis (arrow). Fi, fibula; Ti, tibia. C, Through the 

top of the mortise. LM, lateral malleolus; MM, medial 

malleolus; Ta, talus. D, Through the sustentaculum tali 

(ST). Ca, calcaneus; N, navicular; Ta, talus; TNJ, 

talonavicular joint. E, Through the level where the 

calcaneus gets close to the navicular (arrowhead) but 

does not normally form a joint. If there were an 

articulation here, or osseous bridging, that would be 

tarsal coalition. Ca, calcaneus; Cu, cuboid. Numerals 

indicate cuneiforms. F, Through the calcaneocuboid 

joint (CCJ). Ca, calcaneus; Cu, cuboid. Roman numerals 

indicate metatarsals. 

D E F 

over several 3-mm slices (see Fig. 47-8A). As the posterior 

facet ends the middle facet begins, as defined by the sustentaculum 

tali (see Fig. 47-8B). When the oblique coronal 

slices are properly angled, the middle facet appears horizontally 

oriented (see Fig. 47-8C). The sinus tarsi is the 

cone of soft tissues directly lateral to the middle facet. 

Anterior to the subtalar joint, the round head of the talus 

is seen as a circle forming the talonavicular joint (see Fig. 

47-8D). This demarcates the Chopart joint, the division 

between the hindfoot and midfoot. 

• Ankle Tendons 

There are 10 tendons that cross the ankle joint. For imaging 

purposes, these tendons can be clustered into four groups 

based on their anatomic locations, as illustrated by the 

colored curved lines drawn atop three-dimensional CT 

images in Figure 47-9. The anterior tendons are the anterior 

tibial, the extensor hallucis longus, and the extensor 

digitorum longus (see Fig. 47-9A). Posteriorly, there are the 

Achilles and plantaris tendons (see Fig. 47-9B). Laterally, 

the peroneus longus and peroneus brevis tendons pass 

under the lateral malleolus (see Fig. 47-9C). Medially, the 

posterior tibial and flexor digitorum longus tendons pass 

under the medial malleolus, whereas the flexor hallucis 

longus passes under the sustentaculum tali (see Fig. 47-9D 

and E). 

On MRI, ankle tendons are best appreciated in cross 

section in the direct axial plane (Fig. 47-10). The oblique 

coronal plane (Fig. 47-11) is a good secondary plane to 

observe the medial and lateral tendons as they course 

under the malleoli. Normal tendons should appear uniformly 

black on all imaging sequences and have a sharply 

defined interface with adjacent fatty soft tissues. Any 

increased signal in a tendon on a T2-weighted image indicates 

the presence of pathology, typically an intrasubstance 

tear. In addition, more than a trace amount of fluid around 

an ankle tendon is abnormal, indicating inflammation or 

some other pathologic process. The exception to this is the 

flexor hallucis longus, which can normally contain some 

fluid in its tendon sheath. 

• Anterior Tendons 

Normal Anatomy 

The normal anterior tibial tendon serves as a useful internal 

standard with which to compare the size of the other 

ankle tendons. The anterior tibial is normally the largest 


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A 

B 

C 

Figure 47-7. Straight sagittal images. Ca, calcaneus; Cu, cuboid; 

N, navicular; Ta, talus; Ti, tibia. A, Through the lateral hindfoot, 

profiling the calcaneocuboid joint (CCJ), the ankle joint (AJ), and the 

posterior facet of the subtalar joint (P-STJ). The brown arrow points 

to the lateral process of the talus (LPT), and the red arrow points to 

the anterior process of the calcaneus (APC). Fractures through these 

pointed bony projections are often difficult to see on radiographs 

and are typically worked up with CT. B, Through the middle of the 

hindfoot, profiling the talonavicular joint (TNJ), the ankle joint (AJ), 

and the posterior facet of the subtalar joint (P-STJ). The middle facet 

of the subtalar joint (M-STJ) can now be seen. C, Through the medial 

hindfoot, now profiling the middle facet, above the sustentaculum 

tali (ST). Straight alignment should normally be present between the 

talus, navicular, medial cuneiform (1), and first metatarsal (I). 

A B C D 

Figure 47-8. Oblique coronal images through the hindfoot, posterior (A) to anterior (D). Ca, calcaneus; Fi, fibula; ST, sustentaculum tali; Ta, talus; 

Ti, tibia. A, This plane best profiles the posterior facet of the subtalar joint (red arrow). The ankle mortise (yellow line) can be appreciated in the 

oblique coronal plane but would be better profiled in the mortise coronal plane. B, This oblique slice is just anterior to the ankle joint, where the 

posterior facet of the subtalar joint is ending (red arrow) and the middle facet is beginning (blue arrow). C, The oblique coronal slices are angled 

correctly if the middle facet of the subtalar joint (blue arrow) has a horizontal orientation. The cone of soft tissues lateral to the middle facet is the 

sinus tarsi (asterisk). D, The junction of the hindfoot and midfoot is at the round head of the talus at the talonavicular joint (circle). 


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A B C 

D 

E 

Figure 47-9. The 10 ankle tendons are illustrated as colored lines drawn over three-dimensional CT images. A, Anterior view of the anterior 

tendons: anterior tibial (AT; red), extensor hallucis longus (EHL; green), and extensor digitorum longus (EDL; blue). B, Posterior view of the 

posterior tendons: Achilles (Ach; light blue) and plantaris (yellow). Also labeled are the medial pole of the navicular (N) and the sustentaculum tali 

(ST). C, Posterolateral view of the lateral tendons: peroneus brevis (PB; dark purple) inserting into the base of the fifth metatarsal, and peroneus 

longus (PL; light purple) wrapping under the cuboid. Medial (D) and posterior (E) views of the medial tendons, illustrating the “Tom, Dick, and 

Harry” mnemonic: the posterior tibial (PT; red) wraps under the medial malleolus and inserts on the medial pole of the navicular (N); the flexor 

digitorum longus (FDL; blue) runs behind the PT, under N, and out to the second to fifth toes; and the flexor hallucis longus (FHL; green) runs 

behind the talus, wraps under the sustentaculum tali (ST), crosses under the FDL at the master knot of Henry, and passes between the two great 

toe sesamoids (white arrows), inserting on the distal phalanx. 

tendon in axial cross section, except the Achilles 

tendon. 42 

The anterior tendons extend, uncrossed, over the ankle 

joint and foot (see Fig. 47-9A). The anterior tibial is the 

most medial of the three anterior tendons. It extends along 

the medial aspect of the great toe tarsometatarsal joint to 

insert on the plantar aspect of the base of the first metatarsal 

and the adjacent medial cuneiform bone. The extensor 

hallucis longus is the middle of the three anterior tendons, 

proceeding straight to its insertion at the dorsal base of the 

great toe distal phalanx. The most lateral of the three anterior 

ankle tendons is the extensor digitorum longus. At the 

level of the midfoot, the extensor digitorum longus fans 

out into four separate tendon slips, which, in turn, proceed 

along the forefoot to insert at the dorsal bases of the second 

through fifth middle and distal phalanges. 21,31 

Whereas the anterior tibial and extensor digitorum 

longus tendons can be followed over a series of axial 

images (see Fig. 47-10), it is common to lose visualization 

of the extensor hallucis longus tendon as it curves anterior 

to the midfoot (see Fig. 47-10C). This is in part due to 

“magic-angle” effects. 7 It is important not to misinterpret 

this lack of visualization as a rupture of the extensor hallucis 

longus tendon, a condition that is exceedingly rare. 


9/9/2008 5:33:31 PM


A 

B 

C 

D 

Figure 47-10. MRI of normal ankle tendons in the straight axial plane. Ach, Achilles tendon; AT, anterior tibial tendon; EDL, extensor digitorum 

longus tendon; EHL, extensor hallucis longus tendon; FDL, flexor digitorum longus tendon; FHL, flexor hallucis longus tendon. PB, peroneus brevis 

tendon; PL, peroneus longus tendon; PT, posterior tibial tendon; A&N (artery and nerve) points to the dotted circle surrounding the neurovascular 

bundle that includes the posterior tibial artery and nerve. A, Just above the syndesmosis. B, Through the tip of the medial malleolus. C, One slice 

distal to B there is loss of the dark signal from the EHL tendon. D, Image through the talonavicular joint demonstrates the PT tendon inserting on 

the navicular (N), and the FHL tendon passing under the sustentaculum tali (ST). At this level, the EDL is dividing into separate tendon slips. 


9/9/2008 5:33:33 PM


A 

B 

C 

Figure 47-11. MRI of normal ankle tendons in the oblique 

coronal plane. FDL, flexor digitorum longus tendon; FHL, 

flexor hallucis longus tendon; PB, peroneus brevis tendon; 

PL, peroneus longus tendon; PT, posterior tibial tendon. 

A, Through the posterior facet of the subtalar joint. 

B, Through the middle facet of the subtalar joint. ST, 

sustentaculum tali. A&N (artery and nerve) points to 

the dotted circle surrounding the neurovascular bundle that 

includes the posterior tibial artery and nerve. C, Through the 

talonavicular joint. At this level, the PT tendon has divided 

into separate slips. The white line with the round end points 

to the portion of the PT that inserts onto the medial pole of 

the navicular (N). The white line with the square end points 

to the portion of the PT that passes under the navicular. This 

patient has an os peroneum, which is why the PL tendon 

appears enlarged and gray at this level (dark gray arrow). 

The lack of edematous signal along the course of the extensor 

hallucis longus on T2-weighted images should reassure 

the radiologist there is no pathologic process. 

Injury 

Tears of the anterior ankle tendons are rare, and if the 

patient indicates that the point of maximal tenderness is 

directly over the anterior tendons, it is prudent to search 

for other causes for pain, such as an unsuspected stress 

fracture (Fig. 47-12). 

Ganglion cysts can arise from any synovium-lined 

structure, including the anterior ankle tendons. Figure 

47-13 shows a synovial cyst arising from and partially 

enveloping the anterior tibial tendon. 

• Posterior Tendons 


For anatomic purposes, the Achilles and plantaris tendons 

together make up the posterior group. The Achilles tendon 

is the largest tendon in the body, originating in the midcalf 

at the junction of the two heads of the gastrocnemius 

muscle and the soleus muscle, and inserts onto the back 

of the calcaneal tuberosity. Unlike the anterior, medial, 


9/9/2008 5:33:35 PM


A 

B 

C 

D 

Figure 47-12. The patient is a 45-year-old with pain over the dorsum of the midfoot, indicated by the marker (m). Axial proton-density– 

weighted (A) and T2-weighted (B) images well demonstrate normal anterior tibial (AT) and extensor digitorum longus (EDL) tendons. The extensor 

hallucis longus (EHL) tendon, which was well seen and normal on more proximal slices, is not seen on this slice, although it should be just below 

the marker. Could this be a rare EHL tear? The lack of edema in (B) argues against this diagnosis. The answer is revealed on the sagittal T1- 

weighted (C) and T2-weighted fat-suppressed (D) images: there is a navicular stress fracture (black arrow). The normal Achilles tendon (Ach) is 

uniform in thickness and dark signal in both sagittal sequences and has a sharp interface with the adjacent Kager’s fat pad. A portion of the 

normal AT tendon is seen, as well as a normal amount of fluid in the retrocalcaneal bursa (white arrowhead in D). 

and lateral ankle tendons, all of which are surrounded by 

synovial sheaths, the Achilles is surrounded by thin layers 

of filmy fibrous tissue with fine internal blood vessels, 

called the paratenon or paratendon. This paratenon is analogous 

to synovium in that it provides nutrients for the 

tendon, but because the Achilles tendon does not change 

its axis of motion, there is no need for the lubrication function 

of synovium. Thus, there should never be any fluid 

seen around a normal Achilles tendon. 

Directly anterior to the Achilles tendon is a triangular 

fat pad described radiographically by Kager in 1939. 26 

Kager’s fat pad is located in the retromalleolar region and 

is defined anteriorly by the posterior aspect of the tibia and 

posteriorly by the Achilles tendon, with the base being the 


9/9/2008 5:33:37 PM


Figure 47-13. Synovial cyst of 

the anterior tibial tendon in a 23- 

year-old. Axial (A) and sagittal (B) 

T2-weighted images demonstrate 

the cystic outpouching (white 

arrow) of the synovial sheath 

surrounding the anterior tibial 

tendon (black arrow). The tendon 

itself is normal. 

A 

B 

proximal aspect of the calcaneus. The space contained 

within this triangle is filled with fatty tissue, producing a 

well-defined lucent triangle that can be seen on lateral 

radiographs of the ankle (Fig. 47-14A). On rupture of the 

Achilles tendon, this space becomes poorly demarcated, 

and the normally lucent fatty tissue space becomes obscured 

(see Fig. 47-21A). 

The Achilles tendon is easily evaluated by physical 

examination as well as by MRI or ultrasonography. 23 In the 

sagittal plane, the Achilles tendon should appear uniformly 

straight and black on T1-weighted images (Fig. 47-14B) 

as well as on fluid-sensitive images (Fig. 47-14C). There 

should be a sharp interface between the Achilles tendon 

and Kager’s fat pad directly ventral to it. A normal retrocalcaneal 

bursa may be present just in front of the Achilles 

tendon (white arrowhead, Figs. 47-12D and 47-14C). The 

normal retrocalcaneal bursa should measure less than 

6 mm superior to inferior, 3 mm medial to lateral, and 

2 mm anterior to posterior. 41 Any fluid behind the Achilles 

tendon, in a retro-Achilles bursa, is abnormal. In the axial 

plane, the Achilles tendon should appear flattened in the 

anteroposterior direction. Distally, the ventral margin of 

the tendon becomes concave, with upturned corners resembling 

a smile (see Fig. 47-10D). 

Injury 

For practical purposes, the plantaris tendon is seldom clinically 

relevant in the ankle. Tears of the plantaris tendon 

tend to occur high in the calf, at the plantaris musculotendinous 

junction, and have been called “tennis leg.” By 

MRI, plantaris tears present as fluid tracking along the 

length of the calf, between the underlying soleus and more 

superficial gastrocnemius muscles (Fig. 47-15). Figure 

47-16 illustrates a chronically swollen and scarred posterior 

tibial tendon, with its cross-sectional area greater than 

that of the normal anterior tibial tendon. 

Ruptures of the Achilles tendon are usually diagnosed 

clinically, often by the patients themselves. Patients can 

often recall the exact instant the Achilles ruptured, describing 

the sensation “as if someone kicked me.” The classic 

Achilles tendon rupture occurs with forced dorsiflexion of 

the planted foot, such as occurs in basketball or other 

jumping sports. The classic patient is a middle-age 

“weekend warrior” who leads a sedentary life and attempts 

to participate in sports, perhaps with younger players, 

without an adequate warm-up. Of all the tendons of the 

foot and ankle, the Achilles is the only one for which disorders 

have a male predominance. Complete ruptures of 

the Achilles tendon typically occur at one of two locations. 

One site is low, 3 to 5 cm just proximal to the calcaneal 

insertion (Fig. 47-17). This is a relatively hypovascular 

watershed region. The other site is relatively high, up at the 

musculotendinous junction (Fig. 47-18). These more proximal 

tears may require that the imaging coil be repositioned 

around the lower calf rather than around the ankle 

to visualize the torn and retracted proximal end (Fig. 

47-19). When it is clinically apparent to all that the Achilles 

tendon is completely ruptured, confirmation with MRI 

is usually unnecessary. However, imaging with MRI or 

ultrasonography is used to measure the tendinous gap 

between the retracted ends of a complete tear. 

Partial tears of the Achilles tendon are usually intrasubstance 

tears, and edema-sensitive images reveal increased 

signal in a swollen, abnormally rounded tendon (Fig. 

47-20). Partial tears can also present as nearly complete 

ruptures, with only a few remaining fibers intact (Fig. 

47-21). In these cases, abnormal fluid can be seen surrounding 

the intact fibers, within the distended paratenon 

(see Fig. 47-21E). Imaging with MRI or ultrasonography is 

used to assess the extent of partial tears. 

An Achilles tendon that has undergone internal healing 

and scar formation from a prior intrasubstance tear tends 


9/9/2008 5:33:38 PM


Figure 47-14. Normal Achilles tendon in a 14-year-old with a calcaneal 

stress fracture. A, Lateral radiograph shows the normal sharp interface 

between the lucent Kager’s fat pad and the semiradiopaque Achilles 

tendon (white arrows). The sclerosis in the calcaneal tuberosity (black 

arrowheads) is more subtle radiographically. B, Midsagittal T1-weighted 

image shows the sharp interface between the normal, bright Kager’s fat 

pad and the normal, straight and uniformly dark Achilles tendon (Ach), 

which is uniform in thickness throughout its length. The dark line running 

perpendicular to the trabeculae in the calcaneal tuberosity is the stress 

fracture (black arrowheads). C, Midsagittal inversion recovery image 

reveals no abnormally increased signal in the uniformly dark Achilles 

tendon. A normal amount of fluid is present in the retrocalcaneal bursa 

(white arrowhead). There is bone marrow edema throughout the calcaneus 

as a response to the stress fracture in the tuberosity. 

A 

B 

C 


9/9/2008 5:33:39 PM


A 

B 

Figure 47-15. Plantaris tear in a 71-year-old who, while playing tennis, heard a “snap” and experienced sudden onset of posterior calf pain. 

A, Coronal T2-weighted fat-suppressed images through both calves reveal a band of edema tracking between the left calf muscles (white 

arrowheads). B, Axial T2-weighted fat-suppressed images taken at the level of the dotted line in A show the edema tracking between the left 

soleus (S) and the gastrocnemius (G) muscles. 

A B C 

Figure 47-16. Stenosing tenosynovitis of the posterior tibial tendon (PT) in a 57-year-old with chronic medial ankle pain. These are straight 

axial images, obtained at the same level, with different sequences. A, T1-weighted image shows loss of the normal sharp fat–tendon interface 

around the PT (arrowhead). B, Proton-density–weighted image shows that the chronically swollen and scarred PT is larger in axial cross section 

than the normal anterior tibial tendon (AT). C, T2-weighted image shows that the tissue surrounding the PT is not fluid but the chronic fibrotic 

scarring of stenosing tenosynovitis. 


9/9/2008 5:33:41 PM


Figure 47-17. Complete Achilles tendon rupture in 

a 41-year-old with history of renal transplantation and 

steroid use, who experienced acute posterior ankle 

pain 5 days earlier when bending over while 

gardening. Sagittal T1-weighted (A) and T2-weighted 

fat-suppressed (B) images reveal the complete 

Achilles tendon tear at the critical zone, 3 to 5 cm 

proximal to the calcaneal insertion. The arrows show 

the torn ends of the retracted fibers. C, Axial T1- 

weighted image through the tear reveals no intact 

Achilles tendon fibers (arrowhead). Incidentally noted 

is the intact plantaris tendon (arrow). 

A 

B 

C 

Figure 47-18. Complete Achilles tendon rupture in 

a 38-year-old who, while playing volleyball, felt a 

sudden “pop” and pain “like getting hit in the back of 

the leg.” A, Midsagittal T1-weighted image shows that 

the tear occurred at the musculotendinous junction 

(white arrow). B, Midsagittal T2-weighted fatsuppressed 

image shows the torn ends of the 

retracted fibers (arrows). This Achilles tendon tear 

required surgical repair. 

A 

B 


9/9/2008 5:33:43 PM


Figure 47-19. Complete Achilles tendon rupture at 

the musculotendinous junction in a 52-year-old. A, An 

initial set of sagittal images was obtained with the 

extremity coil centered on the heel, which was too low 

to include the proximal end of the tear. B, The coil was 

repositioned proximal to the ankle joint to include the 

musculotendinous junction. The marker (m) is at the 

palpable defect. 

A 

B 

Figure 47-20. Intrasubstance tear of the Achilles 

tendon in a 54-year-old with a history of rheumatoid 

arthritis and several months of persistent heel pain. 

T2-weighted fat-suppressed images in the sagittal (A) 

and axial (B) planes reveal that the distal Achilles 

tendon is abnormally swollen with increased 

intrasubstance signal (black arrow). An incidental 

finding is an abnormal amount of fluid in the posterior 

tibial tendon sheath (white arrow in B). 

A 

B 

to retain its thickened fusiform shape. However, unlike the 

acute intrasubstance tear, a healed Achilles tendon does 

not contain internal signal (Fig. 47-22). 

• Medial Tendons 


The classic mnemonic “Tom, Dick, and Harry” is useful for 

remembering the order of the medial ankle tendons; T 

represents the posterior tibial tendon, D the flexor digitorum 

longus tendon, and H the flexor hallucis longus 

tendon. By changing the emphasis to “Tom, Dick, ANd 

Harry,” with the AN standing for the posterior tibial artery 

and nerve, it is easier to remember the neurovascular 

bundle that runs between the flexor digitorum longus 

and flexor hallucis longus tendons (see Figs. 47-10 and 

47-11). 

The posterior tibial tendon runs directly behind and 

under the medial malleolus, proceeds medial to the talus, 

and inserts on the medial pole of the navicular (see Fig. 

47-10D). At this insertion site there is a focal osseous 

prominence, called the navicular tubercle. The bulk of the 

posterior tibial tendon inserts on the navicular tubercle, 

although smaller slips of tendon pass under the navicular 

(see Fig. 47-11C) to insert on the plantar aspects of all three 

cuneiforms as well as the bases of the second through 

fourth metatarsals. 

The flexor digitorum longus tendon runs directly 

behind the posterior tibial tendon, although these two 

tendons maintain individual tendon sheaths. The flexor 

digitorum longus tendon extends plantar to the bones of 

the midfoot, crossing superficially to the flexor hallucis 

longus tendon. This crossover point has been called the 

master knot of Henry, 24 and the sheaths of these two flexor 

tendons communicate at this point. Distally, the flexor 

digitorum longus divides into separate tendon slips that 

insert on the plantar bases of the second through fifth 

distal phalanges. 


9/9/2008 5:33:45 PM


A 

Figure 47-21. Near-complete 

Achilles tendon rupture in a 

54-year-old who, while playing 

racquetball, felt a pain “like being 

kicked in the back of the heel.” 

A, Lateral radiograph shows 

obscuration of the normally lucent 

Kager’s fat pad. B, Midsagittal T1- 

weighted image shows only a few 

remaining intact Achilles tendon 

fibers (arrow). C, Midsagittal T2- 

weighted fat-suppressed image 

shows the retracted ends of the 

torn fibers (black arrows). White 

arrow shows the few remaining 

fibers. D, Axial T1-weighted image 

through the level of the 

syndesmosis shows the markedly 

thinned intact Achilles tendon 

fibers (arrow). E, Axial T2-weighted 

fat-suppressed image at the same 

level shows bright abnormal fluid 

in the abnormally thickened and 

distended paratenon (arrowheads). 

White arrow shows the thinned 

intact Achilles tendon fibers. This 

Achilles tear ultimately required 

surgical repair. 

B 

C 

D 

E 


9/9/2008 5:33:47 PM


Figure 47-22. A 57-year-old with 

an Achilles tendon that has healed 

with chronic scarring. Axial T1- 

weighted (A), axial T2-weighted 

(B), and sagittal T2-weighted (C) 

images reveal that the distal 

Achilles tendon is too round and 

thick but contains no increased 

signal. 

A 

B 

C 

The flexor hallucis longus muscle is a posterior structure 

originating from the lower two thirds of the back of 

the fibula. The musculotendinous junction extends distally 

to the level of the ankle joint, and the proximal end of the 

tendon passes through a groove along the posterior talus. 

Whereas the posterior tibial and flexor digitorum longus 

tendons pass under the medial malleolus, the flexor hallucis 

longus tendon passes under the sustentaculum tali. 

The flexor hallucis longus then crosses deep to the flexor 

digitorum longus, extends under the first metatarsal, and 

passes between the two great toe sesamoids, to insert on 

the plantar base of the distal phalanx (see Fig. 47-9D 

and E). 

A 

Medial 

malleolus 

B 

Injury 

Of the three medial ankle tendons, the posterior tibial is 

the most prone to tear, characteristically along the portion 

that curves around the medial malleolus. The posterior 

tibial tendon is relatively hypovascular in this region. 39 

This region of the tendon is also susceptible to mechanical 

wear as the tendon rubs against the medial malleolus (Fig. 

47-23). If the surrounding tendon sheath does not provide 

adequate lubrication, such as in stenosing tenosynovitis 

or rheumatoid pannus formation, this frictional wear 

increases. Perhaps because of these longitudinal frictional 

stresses, the posterior tibial tendon tends to tear with a 

longitudinal split, rather than the transverse rupture seen 

in Achilles tendon tears. When imaged in the axial plane, 

a longitudinal split in the posterior tibial tendon resembles 

two individual tendons. This longitudinally split posterior 

tibial tendon, when grouped with the flexor digitorum and 

hallucis longus tendons, has been called the four-tendon 

sign (Fig. 47-24). 

Tenosynovitis refers to inflammation between the 

tendon and the surrounding synovial sheath. This is often 

a chronic irritative process, more commonly affecting 

C D E 

Figure 47-23. Illustration of posterior tibial tendon mechanical 

wear becoming a longitudinal tear. A, Medial view of the posterior 

tibial tendon (PT; red) as it wraps over the medial malleolus and 

under the flexor digitorum longus tendon (FDL; blue). The PT is 

susceptible to mechanical wear as it rubs back and forth (as indicated 

by the double-headed black arrow) between the underlying medial 

malleolus (gray lightning bolts) and the overlying FDL (white lightning 

bolts). B, A more anterior view of a partially torn PT as it might appear 

if it were laid flat. The tendon is thickened and butterflied open, with 

the gray region representing abnormal internal signal. (The dashed 

line represents the location of cross sections C to E). C to E, MRI cross 

sections of the PT only (now shown as a black ellipse), taken in the 

axial or oblique coronal plane through the longitudinal tear as it 

develops. In C, there is a gray wedge of abnormally increased 

signal along the inner aspect of the flattened PT (black ellipse). 

In D, tendinopathy (gray wedges) now involves the outer and inner 

surfaces of the PT. In E, the wedges of tendinopathy have progressed 

to a longitudinal tear, giving the appearance in cross section that the 

PT is two tendons. 


9/9/2008 5:33:49 PM


A B C 

Figure 47-24. Longitudinal split in the posterior tibial tendon (PT) in a 39-year-old. Shown are the same straight axial images obtained through 

the tip of the medial malleolus (MM). A, T1-weighted image well demonstrates the anatomy of the tendons as well as the neurovascular bundle 

(dotted oval). B, Proton-density–weighted image shows what appears to be four medial tendons, the four-tendon sign, where 1 and 2 are the two 

halves of the split PT, and 3 and 4 are the normal flexor digitorum longus (FDL) and flexor hallucis longus (FHL) tendons. C, T2-weighted image 

demonstrates not bright fluid but gray scar (gray arrowhead) around the split PT, suggesting that this is chronic stenosing tenosynovitis. There is 

an abnormal amount of fluid in the FDL sheath (black arrowhead), suggesting active tenosynovitis here. The fluid in the FHL sheath (white 

arrowhead) is within normal limits for this tendon only. 

A 

B 

Figure 47-25. Active posterior tibial tenosynovitis in a 46-year-old with chronic pain in the distribution of the posterior tibial tendon (PT). 

A, Straight axial proton-density–weighted image demonstrates that the PT is intact and contains no abnormal internal signal. The PT is slightly 

larger in cross section than the normal anterior tibial tendon, and there is loss of the normal fat signal around the tendon (gray arrowhead). 

B, Straight axial T2-weighted image at the same level reveals an abnormal amount of fluid in the posterior tibial tendon sheath (black arrowhead), 

indicating active tenosynovitis. 


9/9/2008 5:33:51 PM


A B C 

Figure 47-26. Chronic posterior 

tibial stenosing tenosynovitis in a 

57-year-old with chronic pain in 

the distribution of the posterior 

tibial tendon (PT). (This is the 

same patient as in Fig. 47-16; these 

straight axial images are two slices 

distal to those.) T1-weighted (A), 

proton-density–weighted (B), and 

T2-weighted (C) images all show 

abnormally dark signal (gray 

arrowhead) around the PT. 

women than men, particularly workers who are on their 

feet all day, such as waitresses and sales clerks. In the ankle, 

tenosynovitis most frequently occurs in the posterior tibial 

tendon and in the two peroneal tendons. Even when these 

tendons are intact, their tendon sheaths and surrounding 

soft tissues should be carefully examined. An abnormal 

amount of fluid in the tendon sheath indicates active tenosynovitis 

(Fig. 47-25). Dark, fibrous tissue around the 

tendon suggests chronic scarring or stenosing tenosynovitis 

(Fig. 47-26). Rheumatoid pannus can also be demonstrated 

by MRI (see Fig. 47-55) and should enhance if 

intravenous contrast is administered. It has been suggested 

that these inflammatory conditions of the tendon sheath 

can be ameliorated by therapeutic tenography. 40 

• Lateral Tendons 

Laterally, the peroneus brevis and longus tendons share a 

common sheath as they pass under the lateral malleolus. 

Distal to the lateral malleolus, the tendons are enveloped 

with individual sheaths. The peroneus brevis tendon 

extends along the lateral aspect of the midfoot and inserts 

on the tuberosity at the lateral base of the fifth metatarsal. 

The peroneus longus tendon passes through a groove in 

the plantar surface of the cuboid, crosses under the midfoot 

deep to the master knot of Henry, and extends medially to 

insert on the plantar aspect of the medial cuneiform and 

the base of the first metatarsal, just lateral to the anterior 

tibial tendon insertion site. 

A trick for identifying the peroneal tendons is to think 

of the lateral malleolus as a race track (Fig. 47-27). The 

peroneus brevis, being the shortest, hugs the inside curve 

and is thus closest to the fibula. The peroneus longus 

follows the outside of the curve, running posterior and 

inferior to the peroneus brevis. 

Unlike the medial ankle tendons, which are normally 

round or oval in axial cross section, the peroneus brevis 

Figure 47-27. Coronal MRI (left) and graphic representation in the 

sagittal plane (right) demonstrate the relationship of the peroneal 

tendons to the lateral malleolus (LM); the peroneus brevis (PB) is 

closer to the distal fibula than is the peroneus longus (PL). 

can normally appear flattened as it passes around the 

lateral malleolus. The presence of increased signal in 

the substance of the tendon, or the presence of fluid in the 

surrounding sheath, aids in the diagnosis of pathology of 

the peroneal tendons. It is often helpful to examine the 

peroneal tendons over multiple slices, using several imaging 

planes and sequences (Fig. 47-28). 


9/9/2008 5:33:52 PM


A B C 

Figure 47-28. Longitudinal split 

of the peroneus brevis tendon (PB) 

in a 62-year-old. Straight axial T1- 

weighted (A), proton-density (PD)– 

weighted (B), and T2-weighted 

images through the syndesmosis. 

The PB (black arrow) is well seen 

on T1 and PD weighting, located 

between the lateral malleolus (LM) 

and the peroneus longus tendon 

(PL). At this level, the PB has a 

normal flattened appearance. 

However, the T2-weighted image 

shows an abnormal amount of 

fluid in the common peroneal 

tendon sheath (white arrowhead). 

Straight axial T1-weighted (D), PDweighted 

(E), and T2-weighted (F) 

images through the LM. At this 

level, the PB is abnormally 

flattened to such an extent that it is 

draped over the PL, best seen on 

the PD image (E). Straight axial T1- 

weighted (G), PD-weighted (H), and 

T2-weighted (I) images distal to 

the LM. 

D E F 

G H I 


9/9/2008 5:33:54 PM


J K L 

M 

N 

Figure 47-28, cont’d The marker (m) indicates the site of maximal tenderness. At this level, the PB is split into two pieces (black arrows), 

separated by the intact PL (white arrow). Oblique coronal T1-weighted (J), PD-weighted (K), and T2-weighted (L) images anterior to the LM, 

through the pain marker (m). All three sequences show increased signal in the PB (black arrow) as opposed to the normal black signal in the PL 

(white arrow). Although the “magic angle” can artifactually increase the intratendinous signal on the short TE sequences (T1 and PD), magic angle 

does not affect the long TE T2-weighted sequence. Thus, the bright signal in the PB on the T2-weighted image represents a true intrasubstance 

tear. The abnormal fluid in the common peroneal tendon sheath (white arrowhead) indicates active tenosynovitis. M and N, Far lateral sagittal 

inversion recovery images demonstrate the abnormal fluid in the common peroneal tendon sheath (white dotted rectangle) as well as the edema 

in the swollen PB (black dotted rectangle). 


9/9/2008 5:33:56 PM


• Ankle Ligaments 14 

There are three sets of ligaments around the ankle joint. 

Laterally there are the syndesmotic ligaments and the 

lateral capsular ligaments. The syndesmotic ligaments 

consist of the thin anterior tibiofibular ligament and the 

broader posterior tibiofibular ligament. These ligaments 

are typically best seen in the straight axial plane (Fig. 

47-29A), although they may be seen in the coronal 

plane if a single image serendipitously cuts though one 

(Fig. 47-29C). It is these syndesmotic ligaments that are 

disrupted in a Weber type C ankle fracture (see Fig. 

47-60C). 

The lateral capsular ligaments consist of the thin anterior 

talofibular ligament and the broader posterior talofibular 

ligament, both of which are transversely oriented and 

thus best seen in the straight axial plane (Fig. 47-29B), and 

the longitudinally oriented calcaneofibular ligament, best 

seen in the coronal plane (Fig. 47-29D). 

Of the lateral ankle ligaments, the anterior ones are 

more subject than the posterior ones to tearing from twisting 

injuries (Fig. 47-30). 

A 

B 

C 

D 

Figure 47-29. The normal lateral ankle ligaments. These are all T1-weighted images obtained using a high-resolution 512 acquisition matrix, in 

the same normal volunteer as in Figure 47-10. A, Axial image through the bottom of the syndesmosis shows the two syndesmotic ligaments: the 

anterior tibiofibular ligament (ATiFL; white arrow) and the posterior tibiofibular ligament (PTiFL; black arrow). B, Axial image two slices distal to A, 

through the top of the talar dome, shows two of the three lateral capsular ligaments: the anterior talofibular ligament (ATaFL; white arrowhead) 

and the posterior talofibular ligament (PTaFL; black arrowhead). C, Coronal image through the back of the ankle joint shows the PTiFL (black 

arrow) running between the posterior malleolus of the talus and the fibula. D, Coronal image two slices anterior to C shows the PTaFL (black 

arrowhead) running between the back of the talus and the fibula. Also seen is a portion of the third of the three lateral capsular ligaments, the 

calcaneofibular ligament (CFL; gray arrowhead). 


9/9/2008 5:33:57 PM


Figure 47-30. Tears of the anterior lateral ankle 

ligaments in a 47-year-old. Straight axial protondensity 

(PD)–weighted (A) and T2-weighted fatsuppressed 

(B) images through the syndesmosis show 

disruption of the anterior tibiofibular ligament (arrow). 

Straight axial PD-weighted (C) and T2-weighted fatsuppressed 

(D) images through the top of the ankle 

mortise show an interruption (arrowhead) of the 

anterior talofibular ligament. 

A 

B 

C 

D 

Medially, the ankle joint is stabilized by a group of 

ligaments that fan out from the distal tip of the medial 

malleolus in a triangular configuration and collectively are 

called the deltoid ligament. When viewed in the coronal 

plane (Fig. 47-31), the deltoid ligament can be seen to 

consist of deep fibers that insert on the medial process of 

the talus and superficial fibers that insert on the calcaneus 

at the sustentaculum tali. Injuries of the deltoid ligament 

tend to be sprains* rather than complete ruptures, although 

they may be accompanied by bone marrow edema (Fig. 

47-32) or even avulsion fractures. 

Unlike the ankle tendons, which when visualized by 

MRI can be followed over a series of sequential slices in 

several planes, the ankle ligaments are usually seen on only 

*”Sprains” are defined as stretching or tearing of ligaments and are due to 

twisting injuries. “Strains” are defined as stretching or tearing of muscles, often at 

the musculotendinous junction, and are caused by sudden and powerful contractions 

or from overuse. 

one or two slices in a single imaging plane. And when they 

are seen in a piecemeal fashion on two images, it can be 

difficult to determine whether the two halves of the ligament 

are continuous. Certainly, seeing fluid extending 

through or around the ankle ligament helps confirm the 

diagnosis of a tear, but at the UW our sports medicine clinicians 

and orthopedic surgeons do not use MRI to evaluate 

the ankle ligaments. They rely on physical examination, 

and sometimes stress radiographs, to assess the functional 

integrity of the ankle ligaments, ordering MRI primarily for 

the bones and tendons. 

There are many accessory ossicles that can be present 

throughout the skeleton, and these are well documented 

in the encyclopedic text by Keats. 27 Many of these normal 

variants can be found in the feet. Three of the most commonly 

found accessory ossicles in the feet are the os trigonum 

posterior to the talus, the accessory navicular medial 

to the navicular bone, and the os peroneum plantar to the 

calcaneocuboid joint. Although in the vast majority of 

people these are nothing more than asymptomatic inci- 


9/9/2008 5:34:00 PM


dental findings, in rare circumstances they are painful 

normal variants, conditions that can be difficult to diagnose 

and difficult to treat. 

Figure 47-31. The normal medial ankle ligaments on a T1-weighted 

image obtained using a high-resolution 512 acquisition matrix. This 

coronal image is located just behind the middle facet of the subtalar 

joint. (This image is seven slices anterior to Fig. 47-29D). The 

magnified dashed box to the right shows the superficial and deep 

components of the deltoid ligament. The broader deep fibers (black 

arrow) run from the medial malleolus (MM) to the medial process of 

the talus. The more slender superficial fibers (white arrow) run from 

the MM to the calcaneus at the sustentaculum tali (ST). Also shown is 

the flexor retinaculum (open arrowheads), forming the roof of the 

tarsal tunnel atop the three medial tendons (T, posterior tibial; D, 

flexor digitorum longus; H, flexor hallucis longus) and the posterior 

tibial neurovascular bundle (dotted oval). 

• Os Trigonum Syndrome 

The os trigonum is a common accessory ossicle located 

directly behind the talus, at the posterior end of the 

subtalar joint, adjacent to where the flexor hallucis longus 

wraps around the back of the talus. The os trigonum develops 

as a separate ossification center. During growth this 

fuses to the talus in most people, but in 5% to 15% of 

normal feet it remains nonunited and is variable in size 

and shape. There are no radiographic findings in a patient 

with symptomatic os trigonum syndrome, 44 although the 

diagnosis can be made with MRI by demonstrating marrow 

edema in the os trigonum and the adjacent talus 

(Fig. 47-33). 

• Accessory Navicular Syndrome 

The accessory navicular bone (os tibiale externum) is a 

common normal variant found adjacent to the medial pole 

of the navicular in approximately 10% of the population. 

As previously mentioned under “Medial Tendons,” the 

medial pole of the navicular is the primary insertion site 

of the posterior tibial tendon (see Figs. 47-10D and 

47-11C). Small accessory navicular bones are called type 1 

and are simply sesamoid bones in the substance of the 

posterior tibial tendon (Fig. 47-34). The posterior tibial 

tendon still inserts normally on the navicular, and the type 

1 accessory navicular bones are of no clinical significance. 

Larger accessory navicular bones are called type 2 (Fig. 

47-35), and with these the posterior tibial tendon inserts 

onto the accessory navicular, rather than on the navicular 

Figure 47-32. Deltoid ligament sprain in an 18-yearold. 

Mortise coronal T1-weighted (A) and T2-weighted 

fat-suppressed (B) images show abnormally increased 

signal in the deep deltoid (black arrow). There is bone 

marrow edema at its insertion site on the medial talus 

(arrowhead). The superficial deltoid (white arrow) is 

intact. 

A 

B 


9/9/2008 5:34:01 PM


A 

B 

Figure 47-33. Os trigonum syndrome in an 11-yearold 

competitive Irish dancer. Lateral view of the 

symptomatic left ankle (A) shows a small os trigonum, 

a common normal variant. The asymptomatic right 

side (B) is shown for comparison. C, Midsagittal T1- 

weighted image shows the small os trigonum (arrow). 

D, Corresponding sagittal inversion recovery image 

shows bone marrow edema in the os trigonum (arrow) 

as well as in the adjacent talus (arrowhead). E, Straight 

axial proton-density–weighted image shows the 

irregular cleft (arrowhead) between the os trigonum 

and the talus. Well seen are the normal structures 

in the tarsal tunnel: the posterior tibial tendon (T), 

flexor digitorum longus tendon (D), neurovascular 

bundle (&), and flexor hallucis longus tendon (H). 

F, Corresponding axial T2-weighted fat-suppressed 

image shows bone marrow edema in the os trigonum 

(arrow) and in the adjacent talus (arrowhead). 

C 

D 

E 

F 


9/9/2008 5:34:03 PM


Figure 47-34. Normal type 1 (small) accessory 

navicular (arrow in dashed magnified box). 

Figure 47-35. Normal type 2 (large) accessory 

navicular (white arrow in dashed magnified box). 

Incidentally seen is a normal os peroneum (black 

arrow). 

bone itself. Patients with this normal variation are typically 

asymptomatic unless they have a fracture through the 

normal fibrous union between the navicular and accessory 

navicular. A painful accessory navicular syndrome can be 

diagnosed by MRI by the presence of marrow edema in the 

accessory navicular and the adjacent navicular bone, especially 

if this corresponds to the point of maximum pain 

(Fig. 47-36). Normally, there should be a solid fibrous 

union between the type 2 accessory navicular and the 

navicular. The presence of a line of fluid between 

these bones is abnormal and indicates a pseudarthrosis, 

another MRI finding in accessory navicular syndrome 


• Os Peroneum Syndrome 

The os peroneum is a common sesamoid bone located in 

the peroneus longus tendon as it passes under the cuboid. 

In rare cases, this normal ossicle can become inflamed and 

painful. Chronic inflammation can be suspected radiographically 

if the os peroneum is abnormally sclerotic, 

although this finding is subjective. A more objective finding 


9/9/2008 5:34:04 PM

A 

C 

E 

B 

D 

F 

Figure 47-36. Accessory navicular syndrome in 

a 20-year-old with focal pain directly over the left 

medial navicular. A, Standing anteroposterior 

radiograph of the asymptomatic right foot shows 

an elongated medial pole of an otherwise normal 

navicular (arrow). This has been referred to as a 

cornuate navicular and as a type 3 accessory navicular. 

B, Standing anteroposterior radiograph of the 

symptomatic left foot barely reveals the type 2 

accessory navicular (arrow in the magnified dashed 

box). C, Far-medial sagittal T1-weighted image well 

shows the posterior tibial tendon (T) inserting onto 

the type 2 accessory navicular (A), as well as the 

fibrous union (arrowhead) between it and the 

navicular bone (N). D, Corresponding sagittal 

inversion recovery image shows subcortical edema 

(arrows) on both sides of this fibrous union. 

E, Oblique coronal T1-weighted image through the 

round head of the talus (Ta) shows the marker (m) 

indicating that the site of focal tenderness is directly 

over the abnormal articulation between the type 2 

accessory navicular (A) and the navicular bone (N). 

F, Corresponding coronal T2-weighted fat-suppressed 

image shows subcortical edema (arrows) on both 

sides of this abnormal articulation. G, Oblique axial 

T1-weighted image shows that the marker (m) 

indicating the site of focal tenderness is directly over 

the abnormal articulation between the type 2 

accessory navicular (A) and the navicular bone (N). 

H, Corresponding axial T2-weighted fat-suppressed 

image shows subcortical edema (arrows) on both 

sides of this abnormal articulation. 

G 

H 


9/9/2008 5:34:06 PM


B 

A 

C 

D 

Figure 47-37. Accessory navicular syndrome in a 38-year-old. A, Anteroposterior radiograph shows a type 2 accessory navicular (white arrow 

in magnified gray dashed box). B, On the lateral radiograph, the accessory navicular can faintly be seen through the anterior calcaneus (open 

arrow in magnified white dashed box). Axial (C) and far-medial sagittal (D) T2-weighted fat-suppressed images reveal a line of fluid (white 

arrowhead) indicating an abnormal joint where there should be a solid fibrous union between the navicular (N) and accessory navicular (A). 

The far-medial sagittal image shows the posterior tibial tendon (T) inserting on the type 2 accessory navicular. 

of os peroneum syndrome is edema in and around the 

small ossicle, best shown with an edema-sensitive MRI 

sequence targeted to the lesion (Fig. 47-38). 

• Os Calcaneus Secondarius 

Os calcaneus secondarius is an occasionally seen normal 

variant that resides between the anterior process of the 

calcaneus (APC) and the lateral pole of the navicular (Fig. 

47-39). It is discussed in more detail later. 

Imaging Protocol 

All imaging of the ankle and foot must begin with radiographs. 

Traumatic fractures are the most common cause 

of ankle and foot pain, and radiographs are the quickest 

and least expensive imaging modality for the detection 

and follow-up of these fractures. However, the question 

often arises as to which imaging modality should be 

obtained next if radiographs do not sufficiently delineate 

the fracture or do not demonstrate the cause of symptoms. 


9/9/2008 5:34:07 PM


A 

B 

Figure 47-38. Os peroneum syndrome in a 58-yearold 

who developed chronic lateral foot pain after 

ballroom dancing. (Case courtesy of Edwin Rogers, 

MD.) Oblique (A) and lateral (B) radiographs reveal an 

os peroneum (white arrow) below the calcaneocuboid 

joint, a common normal variant. C, Far-lateral sagittal 

T1-weighted image shows the peroneus longus 

tendon (PB), wrapping around the lateral malleolus 

(LM), toward the base of the fifth metatarsal (5). 

Behind and below the PB is the peroneus longus 

tendon (PL). D, Sagittal T1-weighted image one slice 

medial to C. Here, the PL is passing under the 

calcaneus (Ca) and cuboid (Cu). Directly plantar to 

the calcaneocuboid joint is the os peroneum (black 

arrow), a sesamoid of the PL. (The os peroneum is 

difficult to see on this T1-weighted image because its 

edematous bone marrow is dark.) E, Corresponding 

inversion recovery image of slice at D demonstrates 

bone marrow edema throughout the os peroneum 

(arrow). 

Continued 

C 

D 

E 


9/9/2008 5:34:10 PM


F G H 

Figure 47-38, cont’d F, Coronal 

T1-weighted slice through the os 

peroneum (arrow) shows its 

marrow to be darker than that of 

the other bones. G, T2-weighted 

image without fat suppression, 

corresponding coronal slice to (F). 

This sequence is not particularly 

edema sensitive, and the marrow 

signal of the os peroneum (arrow) 

is isointense to that of the other 

bones. H, Corresponding coronal 

inversion recovery image of slice 

at F and G. This sequence is so 

fluid sensitive it shows marrow 

edema not only in the os 

peroneum (arrow) but also in the 

adjacent cuboid (arrowhead). 

I, Axial T1-weighted image through 

the bottom of the foot shows the 

os peroneum (arrow). J, Axial 

inversion recovery image 

corresponding to slice at I shows 

the bone marrow edema in the os 

peroneum (arrow). K, Bone scan, 

both-feet-on-detector view, shows 

increased activity in the os 

peroneum (arrow) of the left foot. 

The normal right foot is included 

for comparison. To help with 

localization, also included is an 

axial scout MRI (L) showing the os 

peroneum (arrow). 

I 

J 

K 

L 


9/9/2008 5:34:12 PM


Figure 47-39. The os calcaneus secondarius (OCS) 

is an occasionally seen normal variant that resides 

between the anterior process of the calcaneus (APC) 

and the lateral pole of the navicular (N). 

Radiographs 

Figure 47-40. 

Flow chart for imaging ankle and foot (see text). 

CT 

MRI US NM 

Assess cortex 

• Fractures 

-Calcaneus 

-Distal tibia 

-Lateral 

process of talus 

• Arthritis 

• Fusions 

• Coalitions 

-Osseous 

-Nonosseous 

Everything else 

• Tendons 

-Tears 

-Tenosynovitis 

• Masses 

-Soft tissue 

-Osseous 

• Bone pathology 

-Occult fracture 

-Osteochondral 

lesions 

-Infection 

• Tendons 

-Achilles 

• Toes 

-Morton’s 

-Plantar plate 

• Masses 

-Vascularity 

-Cyst vs solid 

• Foreign bodies 

-Wood 

• Screening 

-Sesamoid 

• Charcot 

Figure 47-40 is a flow chart outlining which modalities we 

use to image various pathologic processes. 

CT is used when we specifically need to assess 

bone cortex. The ability to reformat CT data into twodimensional 

cross-sectional images in any plane desired 

makes it the ideal modality to assess the intra-articular 

extent of fractures, especially complex fractures involving 

the distal tibia or calcaneus. This is particularly helpful to 

orthopedic surgeons as part of their presurgical planning. 

CT data can also be volume rendered into threedimensional 

projections to show the alignment of comminuted 

fractures. CT is also useful for showing fractures 

that are difficult to see radiographically, such as the lateral 

process of the talus or the anterior process of the calcaneus. 

CT can be used to show arthritic narrowing of joints that 

are difficult to visualize radiographically, such as the subtalar 

joint. In patients who have undergone a surgical 

arthrodesis in an attempt to fuse a painful arthritic joint 

who remain symptomatic, CT can show the degree of bone 

fusion at the cortical level. CT is also the best modality to 

show the abnormal bone cortex in cases of tarsal coalition, 

both solid osseous and nonosseous coalitions. 

MRI is essentially used for everything else. MRI is the 

best way to evaluate all of the ankle tendons at once for 

tears or tenosynovitis. It is the best way to evaluate masses 

arising from either the soft tissues or bones of the extremities. 

MRI is extremely sensitive for the detection of bone 

marrow and soft tissue edema/inflammation, and as such 

is it useful for the detection of conditions that may be 

radiographically occult, including stress fractures, osteochondral 

lesions, and infection. 

Ultrasonography (US) can be used to perform a 

focused examination of the soft tissues of the ankle or foot. 

Unlike MRI, which images all of the ankle bones and 

tendons at once, US is used when we wish to examine one 

specific tendon. US is particularly useful when we wish to 

examine a torn Achilles tendon in a dynamic fashion to 

see how much the tendinous gap opens between plantar 


9/9/2008 5:34:13 PM


flexion and dorsiflexion. US is used to evaluate small 

superficial structures that are sometimes difficult to see on 

MRI, such as Morton’s neuromas or the plantar plate. US 

can also be used to characterize soft tissue masses, particularly 

to assess the degree of vascularity or to determine if 

the mass is cystic or solid. US is also extremely sensitive 

for the detection of subcutaneous foreign bodies in the 

extremities, particularly wooden splinters, which can be 

difficult to detect with radiographs, CT, or MRI. (A discussion 

of US of the ankle and foot is beyond the scope of 

this chapter.) 

Nuclear medicine (NM) plays a limited role when it 

comes to imaging the ankle and foot, although in certain 

circumstances a bone scan can be helpful. Fractures of the 

sesamoid bones of the great toe tend to be less conspicuous 

on MRI than on bone scans, especially when the both-feeton-detector 

view is used. In neuropathic feet in which 

radiographs show Charcot changes of collapse and bone 

fragmentation, a bone scan combined with a white blood 

cell scan can be as sensitive and more specific for the detection 

of osteomyelitis than MRI. (A discussion of nuclear 

medicine is beyond the scope of this chapter.) 

• Radiography 

Because radiographs are a necessary first step in the workup 

of the ankle or foot, let us now briefly review how these 

should be obtained. 

• Ankle Radiography 

Ankle radiographs can be either weight bearing or non– 

weight bearing, depending on the preference of the ordering 

clinician. A standard radiographic ankle series consists 

of three projectional views: anteroposterior (AP), mortise, 

and lateral (Fig. 47-41). The mortise view is similar to the 

AP view, with the leg internally rotated 15 degrees to obtain 

a better profile of the ankle mortise. 

When obtaining radiographs of the ankle, it is important 

that the technologist include the base of the fifth 

metatarsal on at least one view. Patients with fractures of 

the base of the fifth metatarsal clinically present complaining 

of lateral ankle pain, and this can cause the clinician 

to request radiographs of the ankle rather than of the foot. 

Figure 47-41 is such a case, where the Jones* fracture can 

be seen at the edge of the lateral view. 

*Sir Robert Jones (1857-1933) was the father of orthopedic surgery in England 

and revolutionized the care of wounded soldiers during World War I. An early 

proponent of x-rays, Jones imaged the transverse extra-articular fracture across 

the proximal diaphysis of the fifth metatarsal just a few months after Röntgen published 

“On a New Kind of Rays” (December 28, 1895). Jones first described this 

fracture after having sustained such an injury himself “whilst dancing.” (This was 

not ballroom dancing; rather it was “dancing in a circle round the tent pole” with 

his military colleagues. There was no mention as to whether alcohol was involved.) 

He subsequently identified this fracture on radiographs of two other patients and 

published his series of three in the Annals of Surgery in 1902, “Fracture of the Base 

of the Fifth Metatarsal Bone by Indirect Violence.” 

• Foot Radiography 

It is preferable to obtain radiographs of the foot with the 

patient standing to visualize the bones in their weightbearing 

alignment. 5 AP and oblique views (Fig. 47-42A and 

B) can be obtained by placing the x-ray cassette on the floor 

and having the patient stand on the cassette while the x-ray 

beam is pointed downward. It is important to closely scrutinize 

the alignment of the tarsometatarsal joints on both 

of these views when assessing for a Lisfranc fracturedislocation. 

Normally, the first metatarsal should line up 

perfectly with the first (medial) cuneiform, the second 

metatarsal with the middle cuneiform, the third metatarsal 

with the third cuneiform, and the fourth and fifth metatarsals 

with the cuboid. 

The standing lateral view of the foot (Fig. 47-42C) is 

somewhat more difficult to obtain because it is usually not 

possible to lower the x-ray tube all the way down to the 

floor. Consequently, we use a set of wooden steps (Fig. 47- 

43). This elevates the feet to a level where the x-ray beam 

can be oriented horizontally while the cassette is held 

between the feet. Figure 47-44 is an example of differences 

that can be seen between standing and non–weight-bearing 

views. 

• Computed Tomography 

• Overview 

Bone CT protocols have evolved as scanner technology has 

progressed. In the broadest terms, a CT gantry consists of 

a spinning ring on which is mounted an x-ray tube. The 

tube emits a fan-shaped x-ray beam, aimed through the 

center of the ring to an array of x-ray detectors mounted 

on the other side. The patient lies on a padded table that 

moves through the spinning gantry. With early generations 

of single-slice CT scanners the gantry would spin clockwise 

one rotation, then stop and spin counter-clockwise one 

rotation to prevent tangling of the power cables supplying 

the x-ray tube. The patient table would be stationary during 

each of the scanning rotations while the gantry was spinning 

and the tube was emitting x-rays. The table would 

move between gantry rotations and stop at each slice position. 

These were the days of true CAT, in which “A” stood 

for “axial,” and scans consisted only of a series of axial 

slides. Scans were relatively slow because time was lost 

stopping the gantry’s clockwise momentum to reverse its 

rotation. 

With the innovation of slip-ring technology, tangled 

power cables were eliminated and the gantry could spin in 

one direction continuously while the table moved continuously 

through it. Thus, helical CT (also known as spiral CT, 

analogous to a spiral-sliced ham) was born. Now the data 

stream coming out of the x-ray detectors no longer represents 

individual axial slices, but rather a continuous volume 

of patient imaging information. The raw data are then 

reconstructed into a series of axial slices that we refer to as 


9/9/2008 5:34:14 PM


Figure 47-41. Non–weight-bearing radiographic 

ankle series in a 37-year-old with lateral ankle pain 

after an acute inversion injury. Anteroposterior view 

(A) and mortise view (B) demonstrate a normal 

appearance of the ankle joint. C, The lateral ankle view 

reveals no abnormalities of the hindfoot. (The region 

outlined by the dashed rectangle is magnified and 

displayed to the right). Close inspection of the base of 

the fifth metatarsal on the lateral view of the ankle 

reveals a proximal diaphyseal fracture, a Jones 

fracture (arrow). Fractures of the base of the fifth 

metatarsal often present clinically as lateral ankle 

pain. The technologist must be careful always to 

include the base of the fifth metatarsal on at least one 

view of all ankle radiographic series. 

A 

B 

C 

the source images. Because of its volumetric nature, helical 

data can be reconstructed at any slice width, and with any 

interval spacing between slices. These axial source images 

can then be reformatted into two-dimensional slices in any 

desired plane and of any desired width, or into threedimensional 

volume-rendered images. In the past decade, 

single-slice helical scanners have evolved into multislice 

scanners, able to acquire larger volumes of patient data 

with each gantry rotation. This technology has largely been 

driven by the desire to scan the entire chest within a single 

breath-hold and the coronary arteries in a single heartbeat. 

Although a multislice CT scanner is not absolutely required 

for bone CT, covering the desired volume faster minimizes 

artifacts related to patient motion as well as minimizing 

the amount of time the patient has to lie still on the 

scanner table. 

Thus, the modern bone CT scan consists of the acquisition 

of three sets of imaging data. The raw data tend not to 

be archived; they are temporarily stored on the scanner’s 

hard drive and are overwritten as the hard drive becomes 

full (often after 24 hours). The source images are reconstructed 

from the raw data using a variety of filtered backprojection 

algorithms. These images are oriented in a plane 

axial to the scanner gantry. Once the raw data are overwritten, 

no additional source images can be reconstructed; 

thus, it behooves the CT technologist to create whichever 

source image data sets are needed for future reformats. 

These source images can be viewed by the radiologist as 

desired and can be sent to the picture archiving and communications 

system (PACS) for short- or long-term storage. 

However, the multiplanar two- and three-dimensional images 

reformatted from the source images are the ones primarily 

used for diagnostic and planning purposes and ultimately 

sent to the PACS for archiving. 

Achieving the highest-resolution two-dimensional 

reformatted images requires the source images to be 


9/9/2008 5:34:15 PM


A 

B 

Figure 47-43. Method of obtaining weight-bearing lateral view. In 

most radiology departments the x-ray tube cannot be lowered to the 

floor. Weight-bearing lateral views can be obtained by having the 

patient stand on a wooden box. The central x-ray beam (dashed 

arrow) passes through the foot, from lateral to medial, striking the 

x-ray cassette held upright between the feet. 

C 

Figure 47-42. Weight-bearing radiographic foot series in an 

asymptomatic 41-year-old male volunteer. A, Anteroposterior view; 

B, oblique view; C, lateral view. The upward-pointing white arrow was 

placed by the technologist to indicate the patient was standing. The 

heel spur (black arrow in C) at the origin of the plantar fascia is of 

doubtful clinical significance in this normal volunteer who has never 

had heel pain. (This person is not standing on screws, but on the 

wooden box in Figure 47-43, held together by screws.) 

reconstructed into relatively thin slices, often the width of 

a detector element. To minimize the stair-step quantization 

artifact that can occur between axial slices, the source 

images should be reconstructed at intervals such that they 

overlap each other. We have found that a 50% overlap 

(interslice interval equals one-half slice width) works well. 

We use an edge-enhanced reconstruction algorithm (called 

a “bone” algorithm by some CT manufacturers) to yield 

two-dimensional reformatted images with sharp cortical 

detail. 

Thin and overlapping source images also yield good 

three-dimensional reformatted images. However, threedimensional 

images by their nature represent a smooth 

rendering of the volumetric data, and edge-enhanced 

source images can yield excessively noisy threedimensional 

images. We create a second set of source 

images, using a smoothing reconstruction algorithm (called 

a “standard” algorithm by some manufacturers) for threedimensional 

reformatting. 

Depending on the length of the body part being 

scanned, the thin overlapping source images may consist 

of hundreds, or sometimes thousands, of images—twice 

that if both edge-enhanced and smoothed data sets are 

created. At our institution we choose to store these source 

images permanently on our PACS, although we save them 

in a separate imaging folder from the multiplanar reformatted 

images, which typically consist of merely dozens of 

images per plane. 

• Protocol for Foot, Ankle, and Tibia (Distal) 

Scanning Technique 

At the UW we have developed our “F/A/T” protocol—a single 

scanning protocol that allows us to create multiplanar 

reformatted images optimized to visualize the foot, 

ankle, and distal tibia. (The latest versions of all the 

UW musculoskeletal protocol sheets can be viewed 

and downloaded for free at www.Radiology.Wisc.Edu/ 

MSKprotocols.) 

The patient is positioned supine on the CT table, with 

legs straight, feet together in the center of the gantry, and 

toes pointing up at the ceiling (Fig. 47-45A). We typically 

scan through both ankles and feet simultaneously because 

this position is most comfortable for the patient and allows 

us to compare the injured side with the contralateral 

normal side when questions arise regarding subtle alignment 

abnormalities. Unless the contralateral foot contains 


9/9/2008 5:34:17 PM


Figure 47-44. Importance of weight-bearing view. 

A, Non–weight-bearing lateral view, obtained 

portably. On this image, the long axis of the talus 

(dashed white line) is parallel to the long axis of the 

first metatarsal (dashed black line), suggesting normal 

alignment. B, Same patient as in A, obtained upright at 

a follow-up clinic visit 3 months later. On this weightbearing 

lateral view, the long axis of the talus (solid 

white line) is now angled downward relative to the 

first metatarsal (solid black line). This indicates that 

the patient has a nonrigid flat-foot deformity (pes 

planus), demonstrable only with weight bearing. 

A 

B 

A 

B 

C 

Figure 47-45. A, The patient is positioned supine on the CT table 

with her legs straight, feet together, toes pointing to the ceiling. 

B, Example of a foot holder we built to help keep patients’ feet 

centered in the CT scanner in neutral position. C, In lieu of a 

dedicated foot holder, we have used a box. 

metal, including it in the scanning field-of-view (FOV) 

does not cause excessive streak artifacts and does not 

increase the radiation exposure to organs in the torso. 

Securing the patient’s feet to a dedicated holder (Fig. 

47-45B) or to a box (Fig. 47-45C) helps to hold the feet in 

neutral position and to prevent motion during the scan. 

Scout views are obtained in both the AP and lateral 

projections (Fig. 47-46). The scanning FOV should be 

set wide enough to include both the right and left lateral 

malleoli; for most patients this is less than 25 cm. The 

coverage should begin superior to both syndesmoses 

and extend below the calcanei. In cases of pilon fractures, 

which are comminuted fractures involving the plafond, 

coverage is extended superiorly to include more of the 

distal tibia. We typically scan using 120 kVp at less than 

200 mA. 


9/9/2008 5:34:22 PM


Figure 47-46. Anteroposterior (A) and lateral 

(B) scout CT views. The scanning field should cover 

both ankles and should extend from above the 

syndesmosis to below the calcaneus (white 

rectangles). In cases of pilon fractures, more of the 

distal tibia is covered (dashed rectangle). 

A 

B 

We can achieve the highest resolution on the reformatted 

images by reconstructing the source images at a width 

equal to the width of the narrowest detector. The reconstruction 

interval between source images is equal to onehalf 

the detector width, and this allows for a 50% overlap 

between slices. We reconstruct two sets of source images; 

one uses an edge-enhanced bone algorithm for the twodimensional 

multiplanar reformatted images, the other a 

smoothing standard algorithm for reformatting in threedimensions. 

Both sets of source images are sent to the 

PACS for archival storage and can be accessed any time in 

the future if additional two- or three-dimensional reformatted 

images are desired. Because these thin overlapping 

slices yield hundreds of source images, we store these 

source images on the PACS in their own folder—a folder 

separate from where we store the reformatted images, 

which are images most of us primarily view. 

Reformatting Technique 

At the UW we have identified at least 15 different ways that 

we are commonly asked to create two-dimensional reformatted 

images of the ankle and foot. These are delineated 

on our downloadable protocol sheets, portions of which 

are shown in Figure 47-47. The reformatting protocols are 

centered on the anatomic divisions illustrated in Figures 

47-5 and 47-48. 

Ankle/Distal Tibia Protocol. Our ankle/distal tibia protocol 

(see Fig. 47-47A) is centered on the ankle joint. This 

protocol is used for scanning fractures of the distal tibia 

(e.g., pilon, malleoli, triplane, juvenile Tillaux) or of the 

talar dome (e.g., osteochondral lesions). Using a midsagittal 

reference image, straight axial images are created in a 

plane parallel to the bottom of the foot. Then, using an 

axial reference image through the top of the ankle mortise, 

mortise coronal and mortise sagittal images are created 

parallel and perpendicular to an imaginary line through 

the anterior cortex of the medial and lateral malleoli. For 

distal tibial fractures, we find that creating reformatted 

images that are 3 mm thick at 3-mm intervals (no gap or 

overlap between reformatted slices) yields crisp images 

that do not appear noisy. However, for osteochondral 

lesions of the talar dome, our surgeons prefer that the 

mortise coronal and mortise sagittal images be reformatted 

at 1 mm, yielding images of higher resolution but also with 

more noise. 

Hindfoot/Midfoot Protocol. Our hindfoot/midfoot protocol 

(see Fig. 47-47B) is centered on the Chopart joint and 

is used to evaluate hindfoot fractures (e.g., calcaneus, talar 

body) and the subtalar joint (e.g., tarsal coalitions). Using 

an axial reference image, straight sagittal images are reformatted 

along a plane parallel to the long axis of the foot. 

The other three planes are reformatted off a midsagittal 

reference image. Straight axial images are reformatted in a 

plane parallel to the bottom of the foot. Oblique coronal 

and oblique axial images are reformatted in planes both 

perpendicular and parallel to the posterior facet of the 

subtalar joint. 

Forefoot/Midfoot Protocol. Our forefoot/midfoot protocol 

(see Fig. 47-47C) is primarily used to assess the alignment 

of the Lisfranc joint and the integrity of the adjacent 

bones. We find that it works best to create reformatted 

images in three planes relative to the first metatarsal shaft. 

A sagittal reference image that best delineates the entire 

length of the first metatarsal is selected. Long-axis and 

short-axis planes are reformatted both parallel and perpendicular 

to the sagittal length of the first metatarsal. The 

third plane, sagittal to the first metatarsal, is best obtained 

off an axial reference image that has been obliqued to 

include the entire length of the first metatarsal. 

Navicular Protocol. Our dedicated navicular protocol 

(see Fig. 47-47D) is used to assess the healing of a known 

navicular fatigue fracture that has perhaps been previously 

diagnosed by MRI. Because these navicular fatigue fractures 

tend to be incomplete hairline cracks, we increase the resolution 

by creating thin (1 mm) reformatted images in a 

small (6 cm) FOV. Oblique coronal and oblique axial 


9/9/2008 5:34:23 PM


A Ankle/distal tibia (centered on ankle joint) 

1. Straight axial (off a sagittal) 

Standard: 3 × 3 mm 

For OLT: 3 × 3 mm 

2. Mortise coronal (off an axial) 

3 × 3 mm 

1 × 1 mm 

3. Mortise sagittal (off an axial) 

3 × 3 mm 

1 × 1 mm 

B Hindfoot/midfoot (centered on Chopart joint) 

1. Straight sagittal (off an axial) 


2. Oblique coronal (off a sagittal) 

3 × 3 mm 

3. Straight axial (off a sagittal) 

3 × 3 mm 

4. Oblique axial (off a sagittal) 

3 × 3 mm 

C Forefoot/midfoot (centered on Lisfranc joint) 

All planes are relative to 1st metatarsal 

1. Axial (long axis) (off a sagittal) 


2. Short axis 

(off a sagittal) 

3 × 3 mm 

3. Sagittal 

(off an axial; may 

have to oblique 

reference image 

to see 1st metatarsal) 

3 × 3 mm 

D Navicular (stress fracture) 

Reformat 6 cm FOV 

Reformat 1 × 1 mm 

1 and 2. Coronal and axial 

(off a sagittal) 

3. Sagittal (off 

an axial) 

Figure 47-47. These are portions of our University of Wisconsin foot/ankle/distal tibia (F/A/T) protocol sheet. A, Ankle/distal tibia protocol. 

This protocol is appropriate for distal tibial fractures (pilon, malleoli, triplane, and juvenile Tillaux) and for talar dome fractures (osteochondral 

lesions of the talus [OLT], osteochondritis dissecans). B, Hindfoot/midfoot protocol. This protocol is appropriate for hindfoot fractures (calcaneus, 

talar body, and subtalar joint) and for tarsal coalitions. C, Forefoot/midfoot protocol. This protocol is appropriate for forefoot fractures (Lisfranc 

dislocation, metatarsals). D, Navicular protocol. 


9/9/2008 5:34:25 PM


Figure 47-48. Anatomic division and major joints shown on a 

sagittal CT. The joint between the tibia (Ti) and talus (Ta) is the ankle 

joint (AJ), shown with the yellow line. The joint between the talus and 

calcaneus (Ca) is the subtalar joint; the posterior facet (P-STJ) is shown 

with the red line. The Chopart joint, shown with the curved blue line, 

separates the hindfoot from midfoot. The Lisfranc joint, shown with 

the angled green line, separates the midfoot from forefoot. 

images are reformatted off a sagittal reference image, and 

oblique sagittal images are reformatted off an axial reference 

image. 

• Magnetic Resonance Imaging 

• Coils and Markers 

When imaging the ankle or foot with MR, it is vital to 

understand the clinical question that the scan is being requested 

to address. No one standardized protocol can 

answer all possible questions. The imaging planes, 

sequences, and even the selection of which coil to use will 

vary depending on the clinical circumstances. Whenever 

possible, an extremity coil should be used. We use a dedicated 

foot and ankle coil (Fig. 47-49) that incorporates a 

chimney-like extension so that the toes can be included in 

the FOV. This chimney design also helps to hold the 

patient’s foot and ankle in a neutral position, that is, with 

the bottom of the foot perpendicular to the tibia, as it 

would be if the patient were standing. Some designs of 

knee coils have an open top that allows the toes to protrude 

(Fig. 47-50A). Custom cushioned inserts (Fig. 

47-50B) help to keep the heel immobilized and centered 

in the coil. Although the neutral positioning shown in 

Figure 47-50A is fine for imaging the ankle and hindfoot, 

it would not be appropriate for the phalanges. When it is 

necessary to image the toes, and a foot coil as in Figure 

47-49 is not available, the knee coil can be used with the 

patient’s foot held in plantar flexion. In these circumstances, 

the technologist should see if having the patient 

lie prone makes it more comfortable to maintain plantar 

Figure 47-49. This dedicated foot and ankle coil incorporates a 

chimney-like extension (arrow) so that the phalanges can be included 

in the field of view. 

flexion. Also, patients tend to feel less claustrophobic when 

prone. Sometimes we have to be creative in our coil selection 

to accommodate the patient’s physical limitations 


We encourage our technologists to place a marker over 

the sight of maximal tenderness or near a nonhealing ulcer. 

Markers can be helpful to draw the attention of both the 

technologist acquiring the images and the radiologist interpreting 

the images. Do not be dissuaded when the patient 

initially points to a wide area, such as across the midfoot 

or around the malleoli. This is typical. Instead, ask the 

patient to point to one spot with one finger—which, when 

encouraged, they usually can do. The marker should be 

placed there. Such a marker needs to be conspicuous on 

all imaging sequences, including fat-suppressed sequences, 

and should be placed on the patient in such a way as 

not to deform the contour of the skin. Although markers 

are commercially available,* generic capsules containing 

vitamin E or docusate sodium (Colace) are often used. 

• Scanning Technique 

Imaging Planes 

We use at least nine standard imaging planes in our foot 

and ankle MRI protocols (Fig. 47-52). The exact slice thickness, 

interslice gap, and FOV should be optimized to take 

advantage of the characteristics of the MRI scanner and coil 

being used. The parameters used at the UW for our GE 

1.5-T scanners are spelled out in detail on our MRI scanning 

parameters and protocols sheets, the most up to 

date of which can be found at our website (http://www. 

Radiology.Wisc.Edu/MSKprotocols). 

*IZI Multi-Modality Radiographic Markers, IZI Medical Products, 7020 

Tudsbury Road, Baltimore, MD 21244; (410) 594-9403; http://www.izimed.com. 

Beekley MR-Spots, Beekley Corporation, 150 Dolphin Road, Bristol, CT 06010; 

(860) 583-4700; http://www.beekley.com. 


9/9/2008 5:34:27 PM


A 

Figure 47-50. A knee coil can be used to scan the ankle. A, The open top on this knee coil allows the toes to extend through the coil while 

keeping the foot in neutral position. B, A customized foam pad (white arrow) helps immobilize the hindfoot being scanned. A second pad next to 

the coil (black arrow) give the contralateral foot a place to rest. 

B 

A 

B 

C 

D 

Figure 47-51. Example of a patient who could not be positioned in the foot or knee coil. This is a 41-year-old with paraplegia from spina bifida 

who is essentially frozen in the fetal position. The clinical concern was for infection in and around the ankle joint. Because the patient was 

physically unable to straighten her legs, we could not use the foot coil. Instead, we used a torso coil and covered the leg and ankle. A, Lateral 

radiograph shows soft tissue swelling. B, T1-weighted, large field-of-view image covering the entire leg as well as the ankle. Because of difficulty 

positioning the patient, a portion of the other leg is also within the coil. C, Inversion recovery image shows no bone marrow edema but diffuse 

edema of the subcutaneous fat. D, T1-weighted image with fat suppression after the administration of intravenous gadolinium shows diffuse 

enhancement of the subcutaneous fat, indicative of cellulitis. The lack of enhancement and edema in the bone marrow exclude osteomyelitis. The 

gray arrow points to inadequate fat suppression at the edge of the coil, a common occurrence with large fields of view. 

The straight sagittal plane (see Fig. 47-52A) is our survey 

plane, and it is usually the first plane acquired in all of our 

ankle and foot MRI protocols. Most of the other imaging 

planes are acquired relative to a straight sagittal reference 

image. The straight sagittal slices are set up off an axial scout 

image and are oriented parallel to the long axis of the foot. 

At least two axial orientations are typically used. 

Straight axial slices (see Fig. 47-52B) are set up off a straight 

sagittal reference image, either a sagittal scout image or 

one of the midsagittal slices from the preceding acquisition. 

The straight axial slices should be roughly perpendicular 

to the long axis of the tibia and if the ankle is 

held in the neutral position will be roughly parallel to 

the bottom of the foot. The slices should begin well proximal 

to the level of the malleoli and extend distal to 

the calcaneus. This is our primary plane for imaging the 


9/9/2008 5:34:31 PM


A 

B 

C 

D 

E 

F 

G 

H 

I 

Legend on opposite page. 


9/9/2008 5:34:33 PM

47 Ankle and Foot 2247 47 

ankle tendons and is also useful for the ankle ligaments 

and syndesmosis. 

Oblique axial slices (see Fig. 47-52C) are set up off the 

same straight sagittal reference image as previously but are 

oriented parallel to the long axis of the metatarsals. This is 

our primary plane for imaging the tarsal bones, and the 

slices should include all of the tarsals from the back of the 

calcaneus through the metatarsal bases. 

There are at least three ways to orient slices in the 

coronal plane. Least commonly used is the straight coronal 

plane (see Fig. 47-52D). These slices are set up off a sagittal 

reference image, are oriented roughly perpendicular to the 

plantar aponeurosis, and are used primarily when evaluating 

the plantar fascia. 

Oblique coronal slices (see Fig. 47-52E) are used much 

more often then straight coronal slices and are set up off 

the same sagittal reference slice as previously. The oblique 

coronal slices are oriented perpendicular to the posterior 

facet of the subtalar joint. (See Fig. 47-7 to review the 

anatomy of the posterior facet of the subtalar joint.) This 

is a good secondary plane to evaluate the tendons and 

tarsals, and the slices should include all of the hindfoot 

and midfoot. 

Mortise coronal slices (see Fig. 47-52F) are set up off 

a straight axial reference image taken through the top of 

the talar dome. This axial reference image can be either an 

axial scout image or one of the straight axial slices from a 

preceding acquisition. The slices are aligned parallel to a 

line drawn between the medial and lateral malleoli. This 

is one of the primary planes used for imaging osteochondral 

lesions of the talus (OLTs), and it is also good for 

looking at the malleoli and the ankle ligaments. 

Mortise sagittal slices (see Fig. 47-52G) are set up off 

the same straight axial reference image as previously, and 

the slices are oriented perpendicular to the mortise coronal 

slices. This, rather than the straight sagittal plane, is the 

survey plane we use for OLTs. 

With regard to the forefoot, we have found that there 

is come confusion among technologists as to the coronal 

and axial planes, and to avoid potential ambiguity we refer 

to the short-axis and long-axis planes relative to the metatarsals. 

Short-axis images are obtained off a straight sagittal 

reference image and are oriented perpendicular to the long 

axis of the metatarsals (see Fig. 47-52H). This yields a series 

of short-axis slices that cut transversely through the metatarsals 

and phalanges, an example of which is shown in 

Figure 47-52I. This is a good plane to evaluate for bone 

marrow edema in the forefoot. 

Long-axis images are obtained off a short-axis reference 

image through the metatarsals and are oriented to 

include all five, or at least four, metatarsals on individual 

slices (see Fig. 47-52I). This is the best way to obtain a 

side-by-side comparison of the metatarsals and is used 

when evaluating for stress fractures or osteomyelitis. 

Figure 47-52. The standard imaging planes we use for MRI of the foot and ankle. The white lines represent the orientation, but not the actual 

number or spacing, of the slices. A, Straight sagittal slices are set up off an axial scout image and are oriented parallel to the long axis of the foot. 

(Using a cushioned foot holder, as in Figs. 47-49 and 47-50, helps keep the foot in place relative to the scanner.) This is our survey plane, and it is 

the first plane acquired in all of our ankle and foot MRI protocols. Most of the other imaging planes are acquired relative to a straight sagittal 

reference image. B, Straight axial slices are set up off a straight sagittal reference image, either a sagittal scout image or one of the midsagittal 

slices acquired in A. The straight axial slices should be roughly perpendicular to the long axis of the tibia and, if the ankle is held in the neutral 

position, will be roughly parallel to the bottom of the foot. The slices should begin well proximal to the level of the malleoli and extend distal to 

the calcaneus. This is our primary plane for imaging the ankle tendons. C, Oblique axial slices are set up off the same straight sagittal reference 

image as in B and are oriented parallel to the long axis of the metatarsals. This is our primary plane for imaging the tarsal bones, and the slices 

should include all of the tarsals from the back of the calcaneus through the metatarsal bases. (Although the field of view can be enlarged to 

include the metatarsals and phalanges in their entirety, we prefer to use the short-axis and long-axis planes delineated in H and I when the 

clinical question involves the forefoot.) D, Straight coronal slices, set up off a sagittal reference image, are used primarily when evaluating the 

plantar fascia and should be oriented roughly perpendicular to the plantar aponeurosis. E, Oblique coronal slices are used much more often then 

straight coronal slices and are set up off the same sagittal reference slice as in B. The oblique coronal slices are oriented perpendicular to the 

posterior facet of the subtalar joint. (Refer to Fig. 47-7 to review the anatomy of the posterior facet of the subtalar joint.) This is a good secondary 

plane to evaluate the tendons and tarsals, and the slices should include all of the hindfoot and midfoot. F, Mortise coronal slices are set up off a 

straight axial reference image taken through the top of the talar dome. This axial reference image can be either an axial scout image or one of the 

straight axial slices acquired in B. The slices are aligned parallel to a line drawn between the medial and lateral malleoli. This is one of the 

primary planes used for imaging osteochondral lesions of the talus (OLT), and it is also good for looking at the malleoli and the ankle ligaments. 

G, Mortise sagittal slices are set up off the same straight axial reference image as in F, and the slices are oriented perpendicular to the mortise 

coronal slices. This is the survey plane for OLT. (The marker [m] indicates the site of maximal tenderness.) With regard to the forefoot, we prefer 

to refer to the short-axis and long-axis planes, rather than coronal or axial, to avoid ambiguity. H, Short-axis images are obtained off a straight 

sagittal reference image and are oriented perpendicular to the long axis of the metatarsals. A short-axis image through the metatarsals is shown in 

I. I, Long-axis images are obtained off a short-axis reference image through the metatarsals and are oriented to try to include all five, or at least 

four, metatarsals on individual slices. This is the best way to obtain a side-by-side comparison of the metatarsals and is used when evaluating for 

stress fractures or osteomyelitis. 

Ch047-A05375.indd 2247 

9/9/2008 5:34:33 PM


Figure 47-53. Comparison of T2-weighted, fatsuppressed 

(A) and inversion recovery (B) MRIs in a 

35-year-old with plantar fasciitis. Both of these sagittal 

images of the calcaneus delineate the plantar 

aponeurosis (open arrowheads), as well as the edema 

in the adjacent heel fat pad (white arrowheads) and in 

the bone marrow at its origin (white arrow). 

A 

B 

Protocols 

Our ankle/foot MRI protocols call for acquiring images in 

three of the standard planes and typically take 45 to 60 

minutes. We start with straight sagittal images to survey the 

bones. For an ankle MRI, the FOV needs to include the 

distal tibia and fibula, all of the tarsal bones, and the bases 

of the metatarsals. For a foot MRI, the FOV needs to include 

all of the phalanges, all of the metatarsals, and the midfoot 

tarsal bones back to the Chopart joint. In cases in which 

the area of clinical concern is vague, the sagittal FOV can 

be enlarged to include the ankle and forefoot. When they 

are available, the radiologist should check these first sets 

of sagittal survey images, particularly the edema-sensitive 

sequence. If the radiologist observes edema in the talar 

dome, images can then be acquired in the mortise coronal 

and mortise sagittal planes (our OLT protocol). If there is 

edema elsewhere in the tarsal bones, oblique axial and 

oblique coronal images are acquired (our tarsal stress fracture 

protocol). If the marrow edema is in a metatarsal, this 

is usually best demonstrated with short- and long-axis 

images (our metatarsal stress fracture protocol). If no bone 

marrow edema is found, we generally proceed with our 

tendon protocol (straight axial and oblique coronal) unless 

some other site is clinically requested. 

Sequences 

Because detecting abnormally edematous signal in the 

bones, tendons, and surrounding soft tissues is the key to 

all musculoskeletal MRI, we run edema-sensitive sequences 

in all the planes we image. This can be either a fatsuppressed 

fast-spin echo T2-weighted sequence or an 

inversion recovery sequence. Although for the most part 

these two sequences are equivalent (Fig. 47-53), we find 

that we get the best images when we use inversion recovery 

for the straight sagittal survey plane and T2-weighted 

sequences in all other planes. 

T1-weighted images, being inherently fat sensitive, 

well demonstrate the normal fat in yellow bone marrow 

as well as the subcutaneus fat and the deeper fat between 

muscles and tendons. We use T1 weighting in all imaging 

planes whenever the tendons are not the primary site of 

interest. 

When the tendons are the site of clinical concern, 

we use proton-density–weighted images, along with T2- 

weighted sequences, in the straight axial and oblique 

coronal planes. The straight axial plane well images all 10 

of the ankle tendons in cross section at and above the level 

of the ankle joint. The oblique coronal plane well images 

the medial and lateral ankle tendons in cross section as 

they curve under the malleoli. Tears in the substance of the 

ankle tendons are usually best seen with proton-density– 

weighted images (Fig. 47-54). However, because protondensity–weighted 

images are relatively insensitive for fluid, 

they should always be read side-by-side with edemasensitive 

images to look for abnormal amounts of fluid in 

the tendon sheaths, indicative of active tenosynovitis. 

• Use of Contrast 

Although the intravenous administration of a gadoliniumbased 

contrast agent (IVGd) is not needed for most 

musculoskeletal MRI, there are particular circumstances in 

which its use is invaluable.* 

Whenever possible, we use IVGd when there is a clinical 

concern for an inflammatory arthropathy or synovitis, 

such as in rheumatoid arthritis (Fig. 47-55). The IVGd 

causes T1 signal enhancement of the hypervascularized 

inflammatory synovium (pannus) but not of the adjacent 

synovial fluid, a distinction that may not otherwise be seen 

on noncontrast T1-weighted or T2-weighted images. 

Likewise, we prefer to use IVGd whenever possible in 

cases of infection. IVGd can help distinguish an enhancing 

phlegmon from a nonenhancing pus pocket. Also, IVGd 

can distinguish cellulitis, which demonstrates contrast 

enhancement of the edematous skin, from “nonspecific 

edema from other causes” that does not enhance. 

*During the year leading up to the publication of this chapter, the U.S. Food 

and Drug Administration (FDA) has issued warnings describing the risk for nephrogenic 

systemic fibrosis (NSF) after exposure to gadolinium-containing contrast 

agents in patients with acute or chronic severe renal insufficiency. Information 

can be found at http://www.fda.gov/cder/drug/infopage/gcca. Before any contrast 

agent is administered to any patient, that patient should be screened in 

accordance to your institution’s policies. 


9/9/2008 5:34:34 PM


Figure 47-54. Peroneus brevis 

tear in a 62-year-old. This is a sideby-side 

comparison of the same 

straight axial slice acquired using 

T1-weighted (A), proton-density 

(PD)–weighted (B), and T2- 

weighted (C) images. Although T1 

shows the fat best and T2 shows 

the fluid best, PD shows the 

tendons best, particularly the 

abnormally increased signal in the 

split/abnormally flattened 

peroneus brevis tendon (white 

arrowhead). 

A 

B 

C 

A 

B 

Figure 47-55. Comparison of T2 weighting with 

fat suppression (A) and T1 weighting with fat 

suppression after intravenous gadolinium (B) in a 65- 

year-old with rheumatoid arthritis. The bright T2 

signal in A in the posterior tibial (white arrow) and 

flexor digitorum longus (white arrowhead) tendon 

sheaths is shown to be enhancing pannus in B. In 

comparison, the bright T2 signal in A adjacent to the 

extensor digitorum longus (black arrow) and the 

anterolateral ankle joint (black arrowhead) is shown to 

be nonenhancing fluid surrounded by a thin rim of 

enhancing synovium in B. 

We sometimes use IVGd when we detect a soft tissue 

mass that is bright on T2-weighted sequences and we wish 

to confirm whether it is solid (Fig. 47-56) or cystic (Fig. 

47-57). IVGd is also useful for the detection of Morton’s 

neuroma by MRI (Fig. 47-58). At UW, we prefer to image 

Morton’s neuroma with ultrasonography rather than 

MRI. 36 

The contrast-enhanced tissue can be made all the more 

conspicuous on T1-weighted images by suppressing the 

signal from fat, and we use fat suppression on nearly all of 

our postcontrast images. When there is a concern that the 

degree of fat suppression may not be uniform throughout 

the image, fat-suppressed T1-weighted images can be 

obtained before the administration of IVGd to be compared 

side-by-side with the postcontrast fat-suppressed T1- 

weighted images. 

Ankle and Foot Injuries 

• Ankle Mortise Fractures 

• Malleoli/Syndesmosis 12 

Fractures of the medial and lateral malleoli are commonly 

the result of twisting injury of the talus in ankle mortise. 

Radiographs are usually sufficient for the management of 

what are typically simple fractures. CT axial images through 


9/9/2008 5:34:35 PM


A 

B 

Figure 47-56. Schwannoma in a 67-year-old. 

A, Lateral radiograph shows a round soft tissue mass 

posterior to the talus. B, Sagittal T1-weighted image 

shows the mass to be homogeneously relatively dark, 

with no invasion into the overlying subcutaneus fat or 

the underlying talus. C, Sagittal inversion recovery 

image shows the mass to be heterogeneously bright. 

This is the classic appearance of a schwannoma. 

D, Sagittal T1-weighted fat-suppressed image after 

intravenous gadolinium administration shows 

heterogeneous enhancement, confirming that this is a 

vascularized mass and not a cyst. 

C 

D 

A 

C 

B 

D 

Figure 47-57. Synovial cyst in a 51-year-old. 

A, Lateral radiograph shows a round soft tissue mass 

dorsal to the metatarsals. B, Sagittal T1-weighted 

image shows the mass to be homogeneously relatively 

dark. C, Sagittal T2-weighted fat-suppressed image 

shows the mass to be homogeneously bright. This is 

the classic appearance of a simple cyst. There is a 

small lobule distal to the main cyst. D, Sagittal T1- 

weighted fat-suppressed image after intravenous 

gadolinium (IVGd) shows enhancement of only the 

thin synovial lining but not the cyst fluid. Short-axis 

T1-weighted (E), T2-weighted fat-suppressed (F), and 

T1-weighted fat-suppressed post-IVGd (G) images 

through the cyst demonstrate the same signal 

characteristics as in the sagittal plane. The gray arrows 

in F and G indicate areas of inadequate fat 

suppression near the fifth toe. 

E 

F 

G 


9/9/2008 5:34:38 PM


A 

B 

C 

Figure 47-58. Morton’s neuroma in a 44-year-old: short-axis images 

through the second metatarsal head. The marker (m) indicates the site 

of maximum tenderness. A, T1-weighted image demonstrates a small 

lobule of decreased signal (black arrow) between and below the heads 

of the second and third metatarsals. Morton’s neuromas are seldom 

more conspicuous than this on T1-weighted images. B, T2-weighted 

fat-suppressed images of Morton’s neuromas usually show little (open 

arrowhead), if any, edema. C, The administration of intravenous 

gadolinium makes the vascularized Morton’s neuroma (arrow) much 

more conspicuous on this T1-weighted fat-suppressed image. 

both ankles are useful when the integrity of the syndesmosis 

is questioned. To understand the mechanism of syndesmotic 

injury, we find it is helpful to review the Weber* 

staging system for ankle fractures. 

Figure 47-59 shows two models of the ankle mortise. 

On the left is a skeleton model showing the relationship 

of the talus to the malleoli and syndesmosis. On the right 

is a schematic. The tibia is connected to the fibula by the 

intraosseous membrane (IOM), a sheet of connective tissue 

that runs along the length of the diaphyses. Where the 

distal fibula fits into a groove in the distal tibia is the syndesmosis. 

The syndesmotic ligaments, the anterior and 

posterior tibiofibular ligaments, maintain the integrity of 

this syndesmotic joint. The integrity of the ankle joint is 

maintained laterally by the anterior and posterior talofibular 

ligaments, and medially by the deltoid ligament. 

Figure 47-60 illustrates how either inversion or eversion 

rotational injuries to the talus cause both avulsive 

and compressive forces on the malleoli. Figure 47-60A 

illustrates a Weber type A injury, radiographically on the 

left and schematically on the right. As the talus undergoes 

an inversion rotational injury, it applies avulsive pulling 

forces on the lateral side of the mortise and compressive 

pushing forces on the medial side. The lateral avulsive 

forces may cause strain or tearing of the talofibular ligaments, 

or they may cause an avulsion fracture through the 

lateral malleolus, pulling it off the fibular shaft. Conversely, 

the compressive forces on the medial side can fracture 

through the medial malleolus, pushing it away from the 

*Bernhard Georg Weber (1927-2002), a Swiss orthopedist, nearly gave up 

medicine and surgery to pursue his dream of becoming an architect. During his 

surgical training in Zurich, though, he recognized that orthopedics would satisfy 

his interest in medicine and technology and his need for artistic expression. 

Besides fracture treatment, he designed a new hip prosthesis and developed a 

tibial realignment osteotomy procedure to treat prematurely degenerated knees. 

In fact, he underwent this realignment procedure himself bilaterally to enable him 

to continue with two of his passions, skiing and tennis. His skill at skiing was such 

that he was certified as a championship instructor. 

Figure 47-59. Models of the ankle mortise. Left, 

Skeletal model. Right, Schematic. The intraosseous 

membrane (IOM) is shown in yellow. The syndesmotic 

ligaments, the anterior and posterior tibiofibular 

ligaments (Tib-Fig Lig), are modeled in green. The 

anterior and posterior talofibular ligaments (Talo-Fib 

Lig) are modeled in purple. The deltoid ligament (Delt 

Lig) is shown in blue. LM, lateral malleolus; MM, 

medial malleolus. 


9/9/2008 5:34:40 PM


A 

B 

Figure 47-60. Weber injuries. Structures are as 

identified in Figure 47-59. A, Weber type A. Left, 

Anteroposterior radiograph of the ankle showing 

medial displacement of the talus relative to the tibia, a 

horizontal avulsion fracture through the lateral 

malleolus, and a vertically oriented compression 

fracture through the medial malleolus. Right, 

Schematic showing the mechanism of a Weber type A 

ankle fracture. As the talus undergoes an inversion 

rotational injury, it applies avulsive pulling forces on 

the lateral side of the mortise and compressive 

pushing forces on the medial side. B, Weber type B. 

Left, Anteroposterior radiograph of the ankle showing 

lateral displacement of the talus relative to the tibia, a 

horizontal avulsion fracture through the medial 

malleolus, and an obliquely vertically oriented 

compression fracture through the distal fibular, below 

the level of the syndesmosis. Right, Schematic showing 

the mechanism of a Weber type B ankle fracture. As 

the talus undergoes an eversion rotational injury, it 

applies avulsive pulling forces on the medial 

malleolus and compressive pushing forces on the 

fibula. C, Weber type C. Left, Anteroposterior 

radiograph of the ankle showing a horizontal avulsion 

fracture through the medial malleolus and an 

obliquely vertically oriented compression fracture 

through the distal fibular, above the level of the 

syndesmosis. The syndesmosis is disrupted and 

abnormally widened, with no overlap between the 

tibia and fibula. Right, Schematic showing the 

mechanism of a Weber type C ankle fracture. This is 

the same as a Weber type B, except now the 

compressive forces extend through the syndesmosis, 

tearing the tibiofibular ligaments and the distal 

intraosseous membrane (IOM), with the oblique 

fracture higher up on the fibula. (If the compressive 

forces extend proximally up the length of the IOM, 

fracturing through the proximal fibula up near the 

knee, this is referred to as a Maisonneuve fracture 

[not illustrated].) 

C 


9/9/2008 5:34:45 PM


Figure 47-61. CT of Weber type C injury. A, Axial 

images through both ankles show the abnormally 

widened left syndesmosis (black arrows) compared 

with the width of the contralateral normal right 

syndesmosis (white arrows). B, Mortise coronal 

image shows widened syndesmosis (black arrows) 

and the high fibula fracture (white arrow), 

characteristic of a Weber type C injury. 

A Right 

Left 

B 

tibial plafond. Radiographically, avulsion fractures can be 

distinguished from compression fractures by the orientation 

of the fracture margins. Avulsion fractures are horizontally 

oriented, in a direction roughly perpendicular to 

the lines of force. Compression fractures are more obliquely 

or vertically oriented, in the same direction as the force. 

This principle is the key to understanding the Weber 

fractures. 

Figure 47-60B illustrates a Weber type B injury, radiographically 

on the left and schematically on the right. Here 

the talus is undergoing an eversion rotational injury, with 

the avulsive pulling forces on the medial malleolus and the 

compressive pushing forces on the lateral side. The medial 

avulsive forces may cause strain or tearing of the deltoid 

ligaments, or they may cause a horizontal avulsion fracture 

through the medial malleolus. The compressive forces on 

the lateral side cause a vertically oblique fracture through 

the fibula. If the fibular fracture is distal to the syndesmosis 

it is characterized as a Weber type B. The syndesmotic ligaments 

and IOM remain intact. 

Figure 47-60C illustrates a Weber type C injury, radiographically 

on the left and schematically on the right. This 

is the same mechanism as a Weber type B injury, except 

now the compressive lateral forces extend through the syndesmosis, 

tearing the tibiofibular ligament as well as the 

distal IOM. In this case the obliquely oriented fibula fracture 

will be higher up, above the level of the syndesmosis. 

Identifying this high fibula fracture is important to recognizing 

that the syndesmotic ligaments are disrupted, 

because radiographically the syndesmosis may not appear 

abnormally widened if not stressed. 

Indeed, sometimes the fibula fracture is so high that it 

occurs through the proximal fibula, near the knee joint, 

and is thus not imaged on ankle radiographs. This is 

referred to as a Maisonneuve* fracture and can be sus- 

*Jules Germain François Maisonneuve (1809-1897), a French surgeon and a 

student of Guillaume Dupuytren, was the first to describe external rotation as a 

contributing mechanism in the production of ankle fractures. 

pected when the ankle radiographs demonstrate an avulsion 

fracture through the medial malleolus without an 

accompanying fibula fracture. If you cannot tell from ankle 

radiographs whether you are looking at a Weber type B or 

C, this is a clue that you may be looking at a Maisonneuve, 

and radiographs that include the entire length of the fibula 

should be obtained. 

Determining the integrity of the syndesmosis is an 

important surgical consideration because syndesmotic 

injuries usually require screw fixation. When the integrity 

of the syndesmosis is unclear based on physical examination 

and radiographs, a CT scan can be helpful (Fig. 

47-61). Scanning in the axial plane through both ankles 

simultaneously allows for side-by-side comparison of the 

widths of the injured and uninjured syndesmoses. 

• Fracture through the Tibial Plafond 

Intra-articular fractures through the tibial plafond often 

require surgical open reduction with internal fixation 

(ORIF) to restore the anatomic alignment of the articular 

surfaces, and multiplanar reformatted CT scans are often 

instrumental in such surgical planning. Three fractures in 

particular that typically come to CT are the pilon 10 fracture 

in adults, and the juvenile Tillaux 35 and triplane 38 fractures 

in adolescents. 

Pilon Fracture 

Pilon fractures are any tibial fracture that involves the distal 

articular plafond and are typically the result of an axial 

loading force. Pilon is French for “pestle,” an instrument 

used for crushing or pounding, and was first used to describe 

this fracture in 1911 by Étienne Destot, the father of 

radiology in France. When they are the result of a highenergy 

injury, such as a fall from height or a high-speed 

motor vehicle front-end collision, pilon fractures can 

produce significant comminution with multiple displaced 

fracture fragments. Although these comminuted fractures 

invariably require internal fixation, they are typically not 


9/9/2008 5:34:46 PM


surgical emergencies. The patients with significantly displaced 

fractures may go to the operating room the day of 

the injury for traction reduction and external fixation to 

restore relative alignment to the mortise, and then wait 

several days for the swelling of the surrounding soft tissues 

to reduce before returning to the operating room for the 

more anatomic ORIF of the pilon fracture. This means that 

these patients typically receive their CT scans during this 

interim period, after the external fixator is in place. However, 

as illustrated in Figure 47-62, such external fixation hardware 

is no impediment to obtaining the CT images the 

surgeon requires. To maintain alignment between the hindfoot 

and leg, the surgeon will percutaneously drill thick 

metal pins through the calcaneus (white arrows in Fig. 47- 

62A, B, and D) and through the tibia proximal to the fracture 

(this pin is not seen in Fig. 47-62). These pins are 

rigidly attached by metal clamps (white arrowheads in Fig. 

47-62A and B) to nonmetallic connecting bars (gray arrows 

in Fig. 47-62A to C). It is these nonmetallic bars that span 

the length of the fracture and maintain the tibia length. 

Because these nonmetallic bars are made of materials 

(usually carbon fiber) that block very few x-rays from reaching 

the detectors, they are nearly radiolucent and cause no 

CT streak artifacts (see Fig. 47-62C). The metal pin-bar 

clamps block many x-rays from reaching detectors and thus 

will cause some CT streak artifacts. However, because the 

clamps are always placed proximal and distal to the pilon 

fracture, they never cause any CT streak artifacts across the 

reformatted fracture margins (see Fig. 47-62B and D). Using 

our standard bone CT scanning protocol of thin/overlapping 

slices, metallic streak artifacts are often not appreciable. 

Notice the good visualization of the calcaneus cortex 

in Figure 47-62B and D, which is only minimally affected 

by streaking caused by the metal pin-bar clamps. 

Juvenile Tillaux Fracture 

Juvenile Tillaux fractures are Salter-Harris type 3 fractures.* 

These fractures have a characteristic appearance, particularly 

on CT. The fracture is the result of an external rotation 

force pulling on the anterior tibiofibular ligament, causing 

avulsion of the anterolateral corner of the distal tibial 

epiphysis (Fig. 47-63A). These fractures always occur laterally 

because the distal tibial physis fuses from medial to 

lateral as a child matures (Fig. 47-63B). As such, juvenile 

Tillaux fractures occur exclusively in adolescents in whom 

the lateral growth plates have not yet fused, usually between 

the ages of 12 and 15 years. Coronal and sagittal images 

are useful to demonstrate the degree of displacement particularly 

at the articular surface (Fig. 47-63B and C, white 

arrow). While minimally displaced juvenile Tillaux fractures 

are usually treated nonoperatively, fractures displaced 

more than 2 mm should have orthopedic consultation and 

surgery to restore the congruity of the joint surface. 

Triplane Fracture 

Triplane fractures are Salter-Harris type 4 fractures. Like the 

juvenile Tillaux fracture, triplane fractures occur in adolescents 

in whom the lateral growth plates have not yet fused. 

When minimally displaced, triplane fractures can be difficult 

to see radiographically, and frontal and lateral views are 

needed to appreciate their multiplanar nature (Fig. 47-64A 

to C): the epiphysis fracture running vertically in a sagittal 

orientation (plane 1), the physeal fracture running horizontally 

in the axial plane (plane 2), and the metaphyseal fracture 

running obliquely vertically in a coronal orientation 

(plane 3). Multiplanar CT scans are ideally suited to visualize 

these fractures in all planes (Fig. 47-64D to F) and often 

reveal more deformity of the articular surface than would 

be anticipated from radiographs alone. 

• Talar Fractures 3,47 

Talar fractures can be thought of as either traumatic or 

insidious. Traumatic fractures are considered surgical emergencies 

because of the high risk of avascular necrosis, and 

patients usually go straight from the emergency department 

to the operating room without stopping at CT (although 

CT scans of displaced fractures of the body of the talus can 

be dramatic; Fig. 47-65). Even with anatomic internal fixation, 

avascular necrosis sometimes occurs, and CT can be 

useful to confirm the presence of abnormal medullary sclerosis 

suspected radiographically (Fig. 47-66). 

• Osteochondral Lesions of the Talus 

Fractures of the talar dome are insidious. They typically 

occur at the medial edge or posterolateral corners of the 

talar dome and are thought to be the result of an impaction 

of the talar dome on the tibial plafond during an inversion 

or eversion twisting injury. Refer to the illustrations of 

Weber injuries (see Fig. 47-60). Because they involve the 

cortical bone and the overlying articular hyaline cartilage, 

they are referred to as osteochondral fractures. A gross example 

is indicated by the green arrow in Figure 47-2. Osteochondral 

fractures notoriously occur on convex articular surfaces, 

including the femoral condyles of the knee and 

capitellum of the elbow. Generically, these fractures have 

been referred to by many names, including osteochondral 

defect, osteochondral lesion, and osteochondritis dissecans. The 

last term is the oldest and perhaps the most misleading, 

for although the suffix “itis” by definition implies inflammation, 

histologically these lesions have not been shown 

to be inflammatory. We prefer the term osteochondral lesions 

of the talus, to distinguish them from osteochondral lesions 

at other sites. 

*The Salter-Harris system is applied to fractures that involve the growth plate 

(physis) at the ends of skeletally immature bones. Type 1 refers to simple transverse 

fractures that involve the physis only. Type 2, the most common, refers to 

fractures that involve the physis and the adjacent metaphysis. Type 3 fractures 

extend from the physis through the epiphysis at the end of the bone, typically disrupting 

the articular surface at a joint. Type 4 fractures involve the epiphysis, the 

physis, and the metaphysis. Type 5 fractures are rare and are crush injuries to the 

growth plate. Text continued on p. 2260 


9/9/2008 5:34:47 PM


A 

B 

C 

D 

Figure 47-62. Pilon fracture. A, Anteroposterior radiograph showing an external fixation device. The radiopaque hardware that could 

potentially cause streak artifacts on CT—the thick metal pin through the calcaneus (white arrows), the distal pin-bar clamps (white arrowheads), 

and the proximal pin-bar clamps (black arrowheads)—are below and above the pilon fracture and thus will not be in the axial CT scanning plane 

through the fracture. The longitudinal carbon fiber connecting bars are barely radiopaque, and as such they are barely discernible on this 

radiograph (gray arrows). These will cause no CT streak artifacts. B, Coronal plane CT scan. The carbon fiber connecting bars (gray arrows) cause 

no CT streak artifacts across the fractures. The CT streak artifacts from the metal percutaneous pin (white arrows) and pin-bar clamps (white 

arrowheads) are all distal to the pilon fracture and only minimally effect visualization of the calcaneus cortex. C, Axial plane CT scan through the 

level of the fractured plafond. The carbon fiber connecting bars (gray arrows) cause no CT streak artifacts across the fractures. D, Sagittal plane 

showing the talar dome impacted into a large cortical gap in the plafond. This is the type of visual information the surgeon needs to plan the open 

reduction and internal fixation. The white arrow shows the percutaneous pin passing through the calcaneus. 


9/9/2008 5:34:49 PM


A 

B 

C 

Figure 47-63. Juvenile Tillaux fracture in a 13-year-old who reported hearing or feeling a snap when, during cheerleading, she landed very 

forcefully on the left foot with the ankle twisted. A Salter-Harris type 3 fracture was seen on outside radiographs (not shown). A CT series was 

requested to assess the degree of fracture displacement. A, Axial CT image through both distal tibial physes demonstrates the avulsion fracture of 

the left anterolateral quadrant (sad face). B, Coronal CT image shows the Salter-Harris type 3 fracture with a longitudinal component through the 

epiphysis (arrow) and a transverse component through the unfused lateral physis (white arrowheads). The fused medial physis is indicated by the 

black arrowheads. C, Sagittal CT image shows the Salter-Harris type 3 fracture with a longitudinal component through the epiphysis (arrow) and a 

transverse component through the unfused physis (arrowheads). Because CT showed that the fracture fragments were displaced more than 2 mm, 

open reduction and internal fixation was performed electively 1 week after the injury. Postoperatively the patient did well after being non–weight 

bearing in a cast for 6 weeks and in a weight-bearing boot for 4 weeks. 


9/9/2008 5:34:50 PM


A 

B 

C 

Figure 47-64. Triplane fracture in a 13-year-old who twisted an ankle in a sledding accident. Non–weight-bearing anteroposterior (A) and 

mortise (B) radiographs. When minimally displaced, the fracture margins can be difficult to see on radiographs. The black arrow points to the 

epiphysis fracture, running vertically in the sagittal plane (plane 1). The white arrow points to the physis fracture, running horizontally in the axial 

plane (plane 2). C, Lateral non–weight-bearing radiograph. The arrow points to the physis fracture, running horizontally in the axial plane. The 

arrowheads point to the metaphysis fracture, running obliquely vertically in the coronal plane (plane 3). 

Continued 


9/9/2008 5:34:51 PM


E 

D 

F 

Figure 47-64, cont’d D to F, CT scanning was performed after closed reduction and casting to assess the degree of fracture displacement. 

D, Axial CT scan. The avulsion fracture of the anterolateral quadrant (sad face) resembles the juvenile Tillaux fracture (see Fig. 47-63A). The 

surrounding plaster cast causes no streak artifacts and helps to immobilize the patient’s ankle during scanning. E, Coronal CT scan. The black 

arrow points to the epiphysis fracture, running vertically in the sagittal plane (plane 1). The white arrow points to the physis fracture, running 

horizontally in the axial plane (plane 2). F, Sagittal CT scan. The arrow points to the physis fracture, running horizontally in the axial plane (plane 

2). The arrowheads point to the metaphysis fracture, running obliquely vertically in the coronal plane (plane 3). These images clearly showed the 

surgeons that the closed reduction still had unacceptable displacement, and open reduction and internal fixation was performed the next day. 

After surgery, the patient was non–weight bearing in a cast for 4 weeks and was pain free after 1 week in a walking boot. 


9/9/2008 5:34:53 PM

A 

B 


Figure 47-65. CT scan of a 69-year-old patient 

transferred to our emergency department after having 

undergone nonsurgical reduction and casting of an 

open ankle fracture-dislocation. The patient was sent 

for CT to better visualize the fracture. A, In the axial 

plane, we recognize the head of the talus (h-Ta) by its 

articulation with the navicular (N), but the body of the 

talus behind the head is missing. Small collections of 

air, seen as black on CT, are scattered around the 

fracture fragments, indicating that this was an open 

fracture. B, The coronal plane shows no talus between 

the tibia (Ti) and calcaneus (Ca). C, The sagittal plane 

tells the whole story: the body of the talus (b-Ta) has 

been sheered off the head and posteriorly displaced 

behind the ankle mortise. 

C 

A 

B 

Figure 47-66. Development of avascular necrosis 

(AVN) of the talus after trauma in a 25-year-old who 

was transferred to our emergency department with 

the ankle already in a cast. A, Our initial casted lateral 

radiograph revealed a vertical fracture (arrowhead) 

through the body of the talus. Because of the risk of 

AVN with talus fractures, the patient was immediately 

taken to the operating room. B, Intraoperative 

radiograph reveals anatomic reduction of the fracture 

with two screws. No sclerosis is present in the talus. 

C, On a lateral radiograph obtained 8 weeks later, the 

body of the talus appears more sclerotic than the 

surrounding bones. D, Midsagittal CT scan obtained 5 

days after the CT scan in part C revealed a broad band 

of sclerosis in the talar dome and body, characteristic 

of AVN. 

C 

D 


9/9/2008 5:34:54 PM


A 

B 

Figure 47-67. Acute talar dome fracture in 

a 23-year-old who fell from a ladder. A and B, 

Anteroposterior and mortise radiographs in which the 

cortical fracture of the lateral corner of the talar dome 

is so nondisplaced it is barely discernible (arrow). C 

and D, Mortise coronal CT images obtained the same 

day well demonstrate the cortical fragment (arrow) as 

well as the full extent of the fracture (arrowheads). 

C 

D 

Radiology and Computed Tomography 

Although the development of a symptomatic OLT can 

often be traced to a specific injury, radiographs are usually 

read as normal early on. In part, this is because many of 

these fractures are so nondisplaced that they can be difficult 

to see radiographically (Fig. 47-67). But sometimes, 

even in retrospect, the initial radiographs truly are negative, 

and it may take months for the OLT to be radiographically 

apparent (Fig. 47-68). At the UW we have a special 

reformatting protocol just for such talar dome fractures 

(see Fig. 47-47A) that includes 1-mm-thin slices reformatted 

with no gaps in the mortise coronal and mortise sagittal 

planes. 

Magnetic Resonance Imaging and Staging 

Although CT is good at showing a displaced fragment and 

the size of the talar dome defect, MRI is better at showing 

the integrity of the overlying articular hyaline cartilage 

and the underlying bone marrow. Edema-sensitive MRI is 

used to detect OLTs that are radiographically occult and 

also is used to stage known OLTs to assess for healing 

potential or need for surgery. 

Several staging systems have been proposed. In 1959, 

Berndt, 8 an orthopedic surgeon from the Cleveland Clinic, 

working with Harty, an anatomist from the University of 

Pennsylvania, analyzed 24 cases of what they called “transchondral 

fractures of the talus.” In the process of tabulating 

their data, “an arbitrary classification was developed to 

aid understanding of the mechanism of the fracture and 

to help in determining the appropriate treatment.” This 

staging system was based solely on the radiographic appearance 

of the fracture: 

Stage I: A small compression fracture 

Stage II: Incomplete avulsion fragment 

Stage III: Complete avulsion without displacement 

Stage IV: Avulsed fragment displaced within the joint 

Thirty years later, Anderson and colleagues 2 from Australia 

modified this staging system based on the MRI 

appearance of the fracture. Anderson called stage I “subchondral 

trabecular compression” and defined it as radiographically 

negative, but with bone marrow edema on MRI 

(Fig. 47-69). Anderson called stage II “incomplete separation 

of the fragment,” requiring demonstration of an intact 

attachment by either CT or MR (Fig. 47-70). Anderson 

added a stage IIA, “formation of a subchondral cyst” (Fig. 

47-71). Stage IIA cysts are thought to develop from stage I 

injuries with post-traumatic necrosis of bone and subsequent 

resorption of the necrotic trabeculae, leaving behind 

a subchondral cyst. Anderson stage III, “unattached, undisplaced 

fragment,” is the same as Berndt and Harty stage III. 

Anderson noted, “In the T2 weighted image, the presence 

of synovial fluid around a large fragment can help to differentiate 

between stages II and III.” However, Anderson 

went on to question the utility of MRI over CT in making 

this determination (Fig. 47-72). Anderson stage IV, “displaced 

fragment,” is the same as Berndt and Harty stage IV 


Around the same time as Anderson but half a world 

away, De Smet and coworkers 19 from the University of 

Wisconsin, Madison, were correlating surgical and MRI 

findings and dividing OLTs into stable or unstable lesions. 

Stable fragments were defined as being fixed firmly 

with fibrous tissue or fibrocartilage, and these patients 

were thought not to need surgery. Unstable fractures are 

those that can be shown by MRI to be partially attached or 

unattached, and these fractures were thought to require 

more aggressive treatment with surgery or prolonged 

immobilization. De Smet showed that the key factor in 

distinguishing stability from instability by MRI is the 

presence of bright signal on T2-weighted images at the 

interface between the fragment and the donor site. In unattached 

fragments this signal was as bright as fluid, and 

surgery confirmed that these fragments were surrounded 


9/9/2008 5:34:57 PM


A 

C 

B 

D 

Figure 47-68. Osteochondral lesion (OLT) in a 9- 

year-old with right ankle pain, without any specific 

trauma. A, Mortise radiograph, even in retrospect, is 

negative for a lesion in the medial talar dome. B, Nine 

months later, the same mortise view reveals a subtle 

lesion in the medial talar dome (arrows). C and D, CT 

scans obtained 1 month after the radiograph in part B 

well demonstrate the medial osteochondral lesion of 

the talus (open and black arrows). The difference 

between C and D is the way the images were 

reformatted: C was reformatted using our hindfoot 

protocol (3 × 3 mm in the oblique coronal plane), 

whereas D was reformatted using our specialized OLT 

protocol (1 × 1 mm in the mortise coronal plane). The 

thinner, 1-mm reformatted images yield edges with 

sharper margins. E, Mortise coronal reformatted CT 

well shows the extent of the OLT (black arrows). 

F, Axial source images through both ankles 

demonstrate not only the symptomatic OLT in the 

posterior medial corner of the right talar dome (black 

arrows), but an asymptomatic OLT in the posterior 

medial corner of the left talar dome (white arrows). 

The patient was treated conservatively and was 

asymptomatic bilaterally. LM, lateral malleolus; MM, 

medial malleolus; Ta, talus. 

E 

F 


9/9/2008 5:34:59 PM


Figure 47-69. Anderson stage I osteochondral 

lesion of the talus—subchondral trabecular 

compression. Mortise coronal T1-weighted (A) and 

T2-weighted fat-suppressed (B) images show bone 

marrow edema (arrows) emanating from the lateral 

corner of the talar dome. The overlying cortex and 

cartilage are intact. (Courtesy of Richard Kijowski, 

MD.) 

A 

B 

Figure 47-70. Anderson stage II osteochondral 

lesion of the talus—incomplete separation of 

fragment. A, Mortise radiograph; B, mortise coronal CT 

scan; C, mortise coronal T1-weighted MRI; D, mortise 

coronal T2-weighted fat-suppressed MRI. The black 

arrow points to the fragment and the black 

arrowheads to the donor site. The white arrow in B 

and D shows where the fragment is still attached to 

the donor site. (Courtesy of Richard Kijowski, MD.) 

A 

B 

C 

D 


9/9/2008 5:35:01 PM

A 

B 


Figure 47-71. Anderson stage IIA osteochondral 

lesion of the talus—formation of a subchondral cyst. 

A, Mortise radiograph; B, mortise coronal CT scan; 

C, mortise coronal T1-weighted MRI; D, mortise 

coronal T2-weighted fat-suppressed MRI. All images 

show the subcortical cyst of the medial talar dome 

with a thin sclerotic border (black arrows). The 

overlying cortex is intact except for a small focal 

irregularity (short white arrow). There is edema of the 

underlying bone marrow (long white arrow). (Courtesy 

of Richard Kijowski, MD.) 

C 

D 

Figure 47-72. Anderson stage III osteochondral 

lesion of the talus—unattached, undisplaced 

fragment. A, Mortise radiograph; B, mortise coronal CT 

scan; C, mortise coronal T1-weighted MRI; D, mortise 

coronal T2-weighted fat-suppressed MRI. All images 

show the unattached nondisplaced fragment (short 

arrows). Arrowheads point to the donor site. Long 

arrow points to edema at the donor site. (Courtesy of 

Richard Kijowski, MD.) 

A 

B 

C 

D 


9/9/2008 5:35:02 PM


Figure 47-73. Anderson stage IV osteochondral 

lesion of the talus—displaced fragment. A, Mortise 

radiograph; B, mortise coronal CT scan; C, mortise 

coronal T1-weighted MRI; D, mortise coronal T2- 

weighted fat-suppressed MRI. All images show the 

displaced fragment (arrowheads) as well as the talar 

donor site (short arrows). Long arrows point to marrow 

edema at the donor site. (Courtesy of Richard 

Kijowski, MD.) 

A 

B 

C 

D 

by joint fluid. In the partially attached fragments, the 

interface line was more irregular and not as bright as fluid, 

and at surgery this was found to represent loose granulation 

tissue. The stable lesions did not have increased T2 

signal at their interface (Fig. 47-74). De Smet also found 

several patients with “focal oval or spherical lesions 

resembling cysts,” similar to the Anderson stage IIA lesions. 

These were all at the bases of unstable lesions, although 

at surgery these were found to be filled with loose granulation 

tissue rather than fluid. De Smet speculated that 

“these defects were traumatic cysts that were filled by the 

reactive tissue forming at the unstable interface.” De Smet 

also noted that the signal within the fragment, whether 

high, normal, or low on T2-weighted images, was not 

useful in distinguishing stable from unstable lesions (Fig. 


These seminal works by Anderson and De Smet and 

colleagues point out the need for close communication 

between radiologists and orthopedic surgeons with regard 

to imaging and managing patients with OLT. 

Once the diagnosis of OLT has been established, the 

decision as to whether to treat the patient conservatively 

or surgically often comes down to determining whether the 

fracture is stable and has a potential for continued healing, 

or unstable and at risk of dislocating. 

• Lateral Process of Talus 

The lateral process of the talus (LPT) is the pointed anterolateral 

corner of the posterior facet of the subtalar joint, 

indicated by the brown arrow on gross Figure 47-4C and 

on sagittal CT Figure 47-7A. LPT fractures are the result of 

trauma, often athletic trauma. Snowboarding, in particular, 

is so often cited that fractures of the LPT are also referred 

to as snowboarder’s ankle. 48 The LPT fracture lines tend to be 

transversely oriented (Fig. 47-76), although vertically oriented 

LPT fractures can occur (Fig. 47-77). LPT fractures 

are often difficult to see radiographically (Fig. 47-78A) and 

are best imaged with CT. Because LPT fractures are typically 

transversely oriented in the axial plane, they are best visualized 

in the sagittal (Fig. 47-78B) and oblique coronal 

planes (Fig. 47-78C) to appreciate the size of the fracture 

fragment as well as the extension of the fracture line into 

the subtalar joint. Like OLT, LPT fractures are often diagnosed 

months after injury, and reports in the orthopedic 

literature state that “40% are missed at initial presentation.” 

It is incumbent on anyone who looks at radiographs 

of the ankle to scrutinize the LPT on all views because these 

fractures can be subtle and sometimes are seen only on 

frontal views (Fig. 47-79). 

Text continued on p. 2269 


9/9/2008 5:35:03 PM


Figure 47-74. Osteochondral lesion of the talus 

(OLT) in a 26-year-old with a remote history of an 

ankle strain, with diffuse ankle pain for the past year. 

Anteroposterior (A) and mortise (B) radiographs 

demonstrate the OLT of the medial talar dome (open 

arrow). MRI was obtained 1 week later. C, Mortise 

coronal T1-weighted image demonstrates the OLT of 

the medial talar dome (open arrow). D, The 

corresponding mortise coronal T2-weighted fatsuppressed 

image shows no bright signal around the 

OLT, indicating that it is stable. 

A 

B 

C 

D 


9/9/2008 5:35:05 PM

2266 VII Imaging of the Musculoskeletal System 47 Ankle and Foot 2266 47 

Figure 47-75. Osteochondral lesion of the talus 

(OLT) in a 14-year-old with ankle pain. 

Anteroposterior (A) and mortise (B) radiographs 

demonstrate a subtle OLT of the medial talar dome 

(open arrow). MRI was obtained 2 months later. 

C, Coronal T1-weighted image demonstrates the OLT 

of the medial talar dome (open arrow). D, The 

corresponding coronal T2-weighted fat-suppressed 

image shows a bright line of fluid (arrows) around the 

OLT, indicating it is unstable. 

A 

B 

C 

D 

A 

B 

Figure 47-76. Lateral process of the talus (LPT) fracture in a 17-year-old gymnast who landed awkwardly after a vault. A, Lateral radiograph 

demonstrates the slightly displaced, transversely oriented LPT fracture (arrowheads). B, Sagittal CT confirms the LPT fracture (arrowheads) seen in 

A. Given the relatively small size of this fracture, the patient was treated nonoperatively with casting and then with physical therapy. (This scan 

was performed using an older protocol, with source images 1 mm thick at 1-mm intervals. This lack of overlap yields reformatted images with 

some stair-step artifacts that can be seen in the metatarsal shaft. This artifact can be avoided by reconstructing source images with a 50% overlap.) 


9/9/2008 5:35:07 PM


Figure 47-77. Subtle lateral process of the talus (LPT) fractures in a 

28-year-old who sustained multiple injuries from a motor vehicle 

collision. Lateral radiograph demonstrates a minimally displaced, 

vertically oriented LPT fracture (arrowhead). 

A 

Figure 47-78. Fracture of lateral process of the talus 

(LPT) in a 22-year-old who walked away from a motor 

vehicle collision and presented 1 day later with ankle 

pain. A, Lateral radiograph does not clearly 

demonstrate the fracture. Incidentally noted is an os 

trigonum (white arrow) and a bone island (black 

arrow), both of no clinical significance. B and C, CT 

scans obtained the same day as A, reformatted in the 

direct sagittal (B) and oblique coronal (C) planes. Both 

planes well demonstrate the transverse LPT fracture, 

with extension into the posterior facet of the subtalar 

joint (arrowheads). The patient did well after 6 weeks 

of non–weight bearing, and no surgery was required. 

B 

C 


9/9/2008 5:35:09 PM


A 

D 

B 

E 

C 

Figure 47-79. Fracture of lateral 

process of the talus (LPT) in a 45- 

year-old who was the driver in a 

front-end automobile collision. 

A, Lateral radiograph does not 

clearly demonstrate the LPT 

fracture. There is a small ossicle 

(gray arrow) just behind the 

subtalar joint that could be 

mistaken for an os trigonum but is 

in fact a small fragment off the 

posterior corner of the talus. 

B, Mortise radiograph shows a tiny 

ossicle (white arrow) between the 

LPT and lateral malleolus, too 

small to characterize. C, 

Anteroposterior radiograph 

reveals the large LPT fragment 

(white arrow) as well as a medial 

fragment (open arrow). D and E, CT 

scans obtained the same day as 

the radiographs, reformatted 

in the oblique coronal plane, 

perpendicular to the subtalar joint. 

D, Image through the middle facet 

of the subtalar joint (M-STJ) shows 

the large LPT fragment (arrow). 

E, A more posterior image 

demonstrates the LPT fracture 

extending into the posterior facet 

(arrowhead), as well as the 

separate fragment off the medial 

talus (arrow). Surgery was 

performed 1 week later, after the 

soft tissue swelling had 

diminished. Lateral (F) and mortise 

(G) radiographs were obtained 

after the LPT fracture was repaired 

with two screws. (There is also a 

Mitek suture anchor in the lateral 

malleolus.) 

F 

G 


9/9/2008 5:35:11 PM

• Calcaneal Fractures 6,18,33 


The calcaneus is the most commonly fractured tarsal bone, 

with fractures typically occurring as the result of traumatic 

axial loading, such as can occur with a front-end automotive 

collision or falling from a height and striking the 

ground feet first. Here in Wisconsin, we have hunters falling 

from their tree-mounted deer stands. As a clinical aside, 

patients who present to the emergency department with 

bilateral calcaneal fractures should also be evaluated for 

lumbar spine fractures at the time of the initial trauma 

workup. The same traumatic axial loading that drives the 

talus into the calcaneus also drives the lumbar vertebrae 

together, and the risk of a lumbar burst fracture with fragments 

retropulsed into the vertebral canal is high. An 

example of the workup of such a patient with nondisplaced 

lumbar fractures is outlined in Figure 47-80. 

Calcaneal fractures can usually be recognized on the 

lateral radiograph by the presence of lucent fracture lines 

and displaced fragments (see Fig. 47-80A) or by a compression 

deformity of the calcaneus with flattening of “Böhler’s* 

angle” (see Fig. 47-80B). 9 When calcaneal fractures are 

identified, it is important to evaluate for related injuries. 

Lumbar compression fractures related to axial loading 

forces are particularly associated with calcaneal fractures. 

At the UW it is typical for severely traumatized patients to 

receive a contrast-enhanced CT scan of the abdomen and 

pelvis as part of the initial trauma workup (see Fig. 

47-80C). Although this scan is designed to reconstruct the 

raw data into large FOV images that are relatively thick 

(5 mm) to assess for soft tissue organ injury, the same raw 

data can also be reconstructed into images centered on the 

spine with a smaller FOV and thinner (1 mm), overlapping 

slices (see Fig. 47-80D). These thin, overlapping source 

images can then be reformatted into sagittal (see Fig. 47- 

80E) and other planes. Although CT images of the spine 

are well suited to demonstrate the presence or absence of 

cortical fragments displaced into the vertebral canal as well 

as the overall alignment of the spine, MRI is used to visualize 

epidural hematomas and other possible soft tissue 

causes for neural compromise. T1-weighted (see Fig. 47- 

80F) and proton-density–weighted (see Fig. 47-80G) 

images are less sensitive to bone marrow edema than are 

fat-suppressed T2-weighted (see Fig. 47-80H and I) or 

inversion recovery images. 

With traumatic axial loading, the wedge-shaped LPT is 

driven into the calcaneus at the angle of Gissane, fracturing 

and depressing the calcaneus (see Fig. 47-80J; Fig. 47-81B). 

This fracture invariably involves the calcaneal articular 

surface of the posterior facet of the subtalar joint (see Figs. 

47-80K and 47-81C). The fracture then propagates inferiorly 

and medially (see Fig. 47-81C), involving the sustentaculum 

tali and the middle facet to varying degrees (see 

Figs. 47-80L and 47-81D). Assessment of the integrity of the 

middle facet of the subtalar joint is an important part of 

preoperative surgical planning. Surgeons prefer to operate 

on the calcaneus from the lateral side, meaning that they 

will not directly visualize the middle facet and sustentaculum 

tali. Thus, they require the preoperative CT scan to 

show them these structures. For this reason, the oblique 

coronal plane, angled perpendicular to the subtalar joint, is 

the primary imaging plane in the assessment of calcaneal 

fractures. Our CT hindfoot/midfoot reformatting protocol 

(see Fig. 47-47B) also includes straight sagittal and straight 

and oblique axial images to assess for extension into the 

calcaneocuboid joint (see Fig. 47-81E). 

One additional clinical point regarding calcaneal fractures: 

they tend not to be surgical emergencies. Surgeons 

typically wait for several days after the initial trauma for 

the soft tissue swelling to decrease before operating. Therefore, 

the preoperative CT scan of the calcaneus does not 

need to be performed emergently when there may be other, 

more serious injuries that need to be addressed. 

• Anterior Process of the Calcaneus 

The APC is the upper outer corner of the calcaneus where 

it articulates with the cuboid, indicated by the orange box 

on gross Figure 47-4C and the red arrow on sagittal CT 

Figure 47-7A. Like LPT fractures, APC fractures can be easily 

overlooked, and this structure should be carefully scrutinized 

on all lateral radiographs of the ankle and foot (Fig. 

47-82). APC fractures are more common in women and 

are the result of an inversion injury while the foot is in 

plantar flexion, such as when wearing high-heeled shoes. 

Even when APC fractures are only minimally displaced 

they have a tendency for nonunion despite prolonged 

immobilization (Fig. 47-83). CT is useful for both detecting 

these fractures and following their progress. 

One potential pitfall in the diagnosis of an APC fracture 

is the os calcaneus secondarius, an occasionally seen 

normal variant that resides between the APC and the lateral 

pole of the navicular (see Fig. 47-39). The os calcaneus 

secondarius can be thought of as a forme fruste of tarsal 

coalition, and it should not articulate with the cuboid as 

the APC does. CT can be used to distinguish an acute 

APC fracture from the normal-variant accessory ossicle 


• Lisfranc Dislocation 

Dislocations along the tarsometatarsal joint are not uncommon. 

These can be the result of severe acute trauma, but 

the Lisfranc joint is also a common site for dislocation in 

diabetic patients with peripheral neuropathy. As mentioned 

in a footnote earlier in this chapter, Jacques Lisfranc 

was a very aggressive surgeon in Napoleon’s army, and 

although he did not describe the dislocation that now 

*Lorenz Böhler (1885-1973) is most notable as the creator of modern accident 

surgery. He was the head of the AUVA-Hospital in Vienna, Austria, that was later 

named for him. This hospital was an international model during his time as the 

leading surgeon there. Text continued on p. 2277 


9/9/2008 5:35:11 PM


C 

A 

D 

B 

Figure 47-80. Bilateral calcaneal 

fractures in a 25-year-old who 

fell from a three-story parking 

garage, landing feet first. Lateral 

radiographs of the left (A) and 

right (B) ankles were obtained. In 

the left ankle, lucent fracture lines 

are clearly seen (arrowheads). In 

the right ankle, Böhler’s angle is 

flattened (compare with part N, 

after open reduction and internal 

fixation [ORIF]). As part of the 

trauma workup, a CT scan of the 

abdomen and pelvis was 

performed, hence the presence of 

oral contrast in the colon on the 

anteroposterior scout image (C). 

Because of the mechanism causing 

bilateral calcaneal fractures, it was 

necessary to evaluate the lumbar 

spine for fractures. The same raw 

data from the large field-of-view 

(FOV) scan of the abdomen and 

pelvis were reconstructed into 

thin, overlapping, small FOV 

images centered on the lumbar 

spine as source images (D). The 

arrowheads point to a fracture 

through the anterosuperior end 

plate of L1. E, Sagittal reformatted 

CT image of the lumbar spine 

shows the thin fracture through the 

anterosuperior corner of L1 

(arrowhead). F and G, MR sagittal 

T1- and proton-density–weighted 

images do not well demonstrate 

the L1 fracture. 

E F G 


9/9/2008 5:35:13 PM


H 

J 

I 

LPT 

Figure 47-80, cont’d H and I, 

MR sagittal and coronal fatsuppressed 

T2-weighted images 

show bone marrow edema 

throughout the superior halves of 

the L1 and L2 vertebral bodies. 

The next day, a CT scan was 

performed through both ankles 

simultaneously and reformatted in 

multiple planes for each ankle 

individually using our hindfoot 

protocol. Displayed are images of 

the right calcaneus. J, Sagittal 

image through the lateral process 

of the talus (LPT). The calcaneus is 

fractured just below the LPT, 

where the wedge-shaped LPT was 

driven into the calcaneus at the 

angle of Gissane. The small back 

spots with the fractured calcaneus 

are air, indicating that this was 

an open fracture that was 

subsequently reduced. Coronal 

oblique images through the 

posterior (K) and middle (L) facets 

of the subtalar joint were obtained. 

These calcaneal fractures typically 

begin with impaction from the LPT, 

and there is extension into the 

posterior facet (white arrowhead). 

In this patient, the fracture also 

extends through the sustentaculum 

tali (ST) into the middle facet 

(black arrowhead). 

Continued 

M-STJ 

LPT 

P-STJ 

ST 

K 

L 


9/9/2008 5:35:15 PM


Böhler’s 

angle 

CCJ 

N 

M 

Figure 47-80, cont’d M, Axial image through the 

calcaneocuboid joint (CCJ) shows that this joint is not 

involved in this patient. N, After ORIF of the calcaneal 

fracture, Böhler’s angle is restored (compare with B). 


9/9/2008 5:35:17 PM


LPT 

N 

APC 

A 

B 

LM 

M-STJ 

ST 

C 

D 

E 

CCJ 

Figure 47-81. Calcaneal fracture in a 40-year-old who fell 

from a 4-foot ladder, landing on the heel. A, Lateral 

radiograph shows a calcaneal fracture. B, CT scan in the 

sagittal plane shows where the lateral process of the talus 

(LPT; black arrow) drove into the calcaneus, causing wide 

separation of the posterior facet of the subtalar joint 

(bidirectional arrow). Incidentally seen is a nonosseous tarsal 

coalition (arrowheads) between the anterior process of the 

calcaneus (APC) and the navicular (N). C, CT scan in the 

coronal oblique plane through the posterior facet of the 

subtalar joint demonstrates the typical inferomedial direction 

of the fracture (dashed arrow). There are often laterally 

displaced fragments (black arrow). Normally, none of the 

calcaneus should be below the lateral malleolus (LM). D, CT 

scan in the coronal oblique plane through the middle facet 

(arrow) shows that in this patient the sustentaculum tali (ST) 

is in one large piece and that the fracture does not extend 

into the middle facet. E, Axial CT scan through the 

calcaneocuboid joint (CCJ) shows involvement of this joint 

(arrowhead). 


9/9/2008 5:35:19 PM


APC 

Figure 47-82. Anterior process of the calcaneus (APC) fracture in a 

48-year-old who fell while standing on a picnic table, sustained a 

twisting injury to the foot. This lateral radiograph was obtained in the 

emergency department the next day. The arrowheads in the magnified 

dashed box show the minimally displaced lucent fracture lines through 

the APC. The patient did well after nonoperative treatment with a non– 

weight-bearing cast for 12 weeks. 

A 

C 

B 

D 

Figure 47-83. Anterior process of the calcaneus 

(APC) fracture in a 29-year-old who tripped down 

some steps. A, Oblique, non–weight-bearing foot 

radiograph shows a nondisplaced APC fracture (white 

arrowheads in magnified dashed box). B, Radiographs 

6 months later show that the APC fracture is still 

unhealed. CT scans were also obtained on the same 

day as the initial radiographs. C, Source axial images 

through both hindfeet reveal the minimally displaced 

transverse fracture (white arrowheads in dotted 

magnified box) of the left APC. The contralateral right 

foot serves as a useful normal comparison when both 

feet are included in the small scanning field of view. 

D, Sagittal reformatted image shows the ACP fracture 

disrupting the superior cortex (arrow). The acute 

fracture margins are not corticated. The patient was 

initially treated conservatively, including 4 months of 

non–weight bearing and 4 months with a bone 

stimulator. When the patient remained symptomatic 

7 months later, a repeat CT scan was requested. 


9/9/2008 5:35:21 PM


E 

F 

G 

H 

Figure 47-83, cont’d E, The axial source images reveal that the transverse fracture remains nonunited (arrowheads in magnified dashed box). 

F, The sagittal image shows that the fracture margins are becoming sclerotic and corticated (arrow), a sign of nonunion. Because CT confirmed the 

clinical suspicion that the APC fracture was not healing, surgical intervention was warranted. G, Oblique radiograph obtained portably in the 

recovery room immediately after open reduction and internal fixation shows the lucent fracture line (arrowheads) bridged by a Whipple-type 

Herbert screw. H, Oblique radiograph obtained 9 months after surgery reveals that the fracture lines are essentially healed and barely discernible 

(arrowheads). 


9/9/2008 5:35:22 PM


A 

B 

C 

Figure 47-84. Anterior process of the calcaneus (APC) fracture in a 34-year-old who presented to the urgent care clinic 1 day after a minor 

motor vehicle collision, complaining of pain along the lateral midfoot. A, Lateral radiograph shows the small APC fracture resembling an os 

calcaneus secondarius (arrowheads in magnified dashed box). CT scans were obtained the next day. B, Sagittal scan through the APC 

demonstrating sharp, noncorticated, margins (arrowheads in dotted magnified box) on the vertically oriented fracture. C, The axial source scan 

confirms that this is an acute fracture with sharp but nonsclerotic margins (arrowheads in dashed magnified box). 


9/9/2008 5:35:23 PM


Figure 47-85. Example of a Lisfranc amputation 

in a 53-year-old who has had chronic peripheral 

neuropathy of unknown cause since 16 years of age. 

Lateral (A), anteroposterior (B), and (C) oblique 

radiographs. Cu, cuboid; 1, 2, and 3 indicate the first, 

second, and third cuneiforms. 

A 

B 

C 

bears his name, he did describe an amputation along the 

tarsometatarsal joint, an example of which is shown in 

Figure 47-85. 

In a Lisfranc dislocation, the second to fifth metatarsals 

are dislocated laterally, or dorsolaterally, relative to the 

tarsal bones. The Lisfranc dislocations are subdivided into 

two categories based on what happens to the first metatarsal 

relative to the other four. If the first metatarsal dislocates 

laterally along with the second to fifth metatarsals, it 

is called homolateral (Fig. 47-86). If the first metatarsal 

diverges from the other four metatarsals, remaining aligned 

with the medial cuneiform (Fig. 47-87), or if the first 

metatarsal dislocates medially (Fig. 47-88), it is called 

divergent. 

When a Lisfranc fracture is grossly displaced, a CT scan 

is not needed to confirm the diagnosis. However, because 

the exact location of dislocated metatarsals may be difficult 

to discern based solely on radiographs, a threedimensionally 

reformatted CT scan may prove useful in 

presurgical planning (see Figs. 47-86H and 47-87F and G). 

The three-dimensional nature of these dislocations can 

best be appreciated by creating a series of three-dimensional 

images rotated along longitudinal and transverse 

axes and played as a movie loop on the PACS. We find that 

a series of 36 images, each 10 degrees apart, works well. 

When only minimally displaced, Lisfranc dislocations 

can be difficult to discern radiographically, and close attention 

should be paid to the Lisfranc joint on all views of the 

foot. Normally there is perfect alignment between the first 

metatarsal base and first (or medial) cuneiform, between 

the second metatarsal and the second (or middle) cuneiform, 

and between the third metatarsal and the third (or 

lateral) cuneiform. Also, the bases of the fourth and fifth 

metatarsals should be perfectly aligned with their individual 

facets on the cuboid (see Fig. 47-86A and B). One clue 

that a nondisplaced Lisfranc dislocation may be present is 

fracture fragments off the base of the second metatarsal. As 

shown on the three-dimensional CT in Figure 47-5, the 

base of the second metatarsal extends more proximally 

across the Lisfranc joint than do the other metatarsals. 

Thus, when dislocations occur along the Lisfranc joint, it 



9/9/2008 5:35:24 PM


C 

A 

B 

D 

E 

Figure 47-86. Example of progression from normal to neuropathic Lisfranc dislocation. The patient was 49 years of age at presentation and had 

diabetes mellitus. Anteroposterior (A) and oblique (B) radiographs reveals normal anatomic alignment between the first (1), second (2), and third 

(3) cuneiforms and the first (I), second (II), and third (III) metatarsals, as well as between the cuboid (Cu) and the fourth (IV) and fifth (V) 

metatarsals. C, Lateral radiograph shows normal alignment between the midfoot and forefoot. Arterial calcifications (arrow) are present, consistent 

with the patient’s history of diabetes. The patient returned 2.5 years later. He had been having episodes of passing out and falling, although he did 

not remember these episodes well. He did not remember injuring himself, and because of peripheral neuropathy he had no sensation in his foot. 

He first noticed swelling and blisters on his foot the morning the following radiographs were taken. He ambulated normally without the assistance 

of a walker or cane. Anteroposterior (D) and oblique (E) radiographs illustrate a homolateral Lisfranc dislocation, with lateral dislocations of all 

five metatarsals. The first metatarsal (I) is not articulating with the first cuneiform (1) but is instead articulating with the second cuneiform (2). The 

base of the second metatarsal (II; arrowhead) is not articulating with anything. 


9/9/2008 5:35:26 PM


F 

G 

H 

Figure 47-86, cont’d F, Lateral radiograph shows the dorsal dislocation of the second metatarsal (arrowhead). A CT scan was obtained to 

understand better the extent of the dislocation. G, Axial oblique scan shows that none of the metatarsals are articulating with their appropriate 

tarsals. In cases of complex fracture-dislocations, three-dimensional (3D) reformatted images can help in understanding the relative locations of 

the bones. H, This 3D image as viewed from above shows lateral displacement of all five metatarsals, and dorsal dislocation of the second through 

fourth metatarsals. 


9/9/2008 5:35:28 PM


A 

B 

C 

E 

D 

Figure 47-87. Divergent Lisfranc dislocation in a 34-year-old who was the front passenger in a motor vehicle accident. Radiographs were 

obtained in the emergency department. Anteroposterior (A) and oblique (B) views of the foot reveal lateral dislocation of the second through fifth 

metatarsals. The white arrow points to a fragment fractured off the base of the second metatarsal. The black arrowhead points to the base of the 

fourth metatarsal, which is not articulating with anything. C, The Lisfranc dislocation is less obvious on the lateral view, although the base of the 

fourth metatarsal (black arrowhead) is not articulating with anything. A closed reduction was attempted at the bedside but was unsuccessful. 

D and E, CT scans were obtained to aid in surgical planning. Straight axial (long-axis) (D) and coronal oblique (long-axis) (E) images through the 

Lisfranc joint show that none of the metatarsals (II to V) is articulating properly with its respective tarsal bone. Cu, cuboid; N, navicular. 


9/9/2008 5:35:29 PM


Figure 47-87, cont’d F and G, Three-dimensional 

reformatted views help in understanding the 

multiplanar nature of the Lisfranc dislocation. 

F, Viewed from above, the second through fifth 

metatarsals can be seen to be dislocated dorsally and 

laterally. G, The view from below the foot (“Star Wars” 

view) shows a large fragment off the base of the 

second metatarsal (white arrow) and a smaller 

fragment off the third metatarsal (black arrow). 

Postoperative anteroposterior (H), oblique (I), and 

lateral (J) radiographs show that seven screws were 

required to restore the anatomic alignment of the 

Lisfranc joint. 

F 

G 

H 

I 

J 


9/9/2008 5:35:31 PM


A 

B 

D 

C 

Figure 47-88. Divergent Lisfranc dislocation in a 22-year-old who was driving on the highway when struck by another car going the wrong way. 

The patient also sustained a fracture of the contralateral femoral shaft. Anteroposterior (A) and oblique (B) radiographs demonstrate medial 

dislocation of the first metatarsal and lateral dislocation of the second through fourth metatarsals. The patient was taken to the operating room for 

open reduction and internal fixation of the femoral fracture with an intramedullary nail. Once the patient was fully anesthetized, the surgeon was 

able to apply longitudinal traction on the first ray and achieve closed anatomic reduction of the Lisfranc joint. C, Oblique port intra-operative 

radiograph. D, The patient returned to the operating room 1 week later, after the swelling had diminished, for elective fixation of the Lisfranc joint. 

is common for a base of the second metatarsal to be 

sheared off or avulsed. In some cases, axial oblique CT 

images can help to demonstrate subtle offsets at the 

tarsometatarsal joints, particularly when compared with 

the normal contralateral side (Fig. 47-89). In other cases, 

the dislocations along the Lisfranc joint may be manifest 

only when a lateral stress is applied to the forefoot. In these 

patients, the nonstressed CT scan may fail to demonstrate 

the degree of potential displacement (Fig. 47-90). 

• Arthritis 45 

The hallmarks of osteoarthritis—nonuniform joint space 

narrowing accompanied by the formation of osteophytes, 


9/9/2008 5:35:32 PM


LEFT 

LEFT 

A 

B 

C 

Figure 47-89. Subtle Lisfranc dislocation in a 39-year-old who fell backward down a 3-foot wall and injured the left foot. The patient bicycled 

home and continued to walk on this foot for 3 days before coming to the emergency department, concerned because the pain was not 

diminishing. Anteroposterior (A) and oblique (B) non–weight-bearing radiographs were obtained. Close scrutiny of the Lisfranc joint on the 

oblique view (dashed box) reveals small fractures off the bases of the second and first metatarsals (arrowheads). The Lisfranc joint appears 

anatomically aligned. The presence of the fragments along the Lisfranc joint raised the concern that this may represent a Lisfranc dislocation. 

C and D, CT scans were performed to assess the integrity of the tarsometatarsal joint. C, Axial oblique scan through both medial Lisfranc joints. 

In the normal right foot there is anatomic alignment across the first, second, and third cuneiform-metatarsal joints. In the injured left foot there 

is lateral subluxation of the first (white arrow) and third (black arrow) metatarsals as well as small fragments off the second metatarsal (white 

arrowhead) and second cuneiform (black arrowhead). D, Axial oblique scan, slightly more plantar and more angled than C, through the lateral 

tarsometatarsal joint. On the normal right side the articular surfaces of the fifth metatarsal (V) and the cuboid (Cu) are aligned (white arrows). 

On the left, the lateral corner of the fifth metatarsal (black arrow) is laterally displaced relative to the cuboid’s impacted lateral corner (open 

arrowhead). These findings confirmed that the patient had sustained a disruption of the Lisfranc joint, which was treated with a boot and non– 

weight bearing. 

D 


9/9/2008 5:35:34 PM


Figure 47-90. Subtle Lisfranc dislocation in a 56- 

year-old, nondiabetic patient who mis-stepped from 

a high curb and landed awkwardly, injuring the foot. 

A, Initial radiograph shows the fracture off the base of 

the second metatarsal (arrow). The alignment of the 

Lisfranc joint is relatively maintained. Because of the 

degree of soft tissue swelling, the patient was initially 

treated with a boot. B, Axial CT scan obtained 5 days 

later showed the second metatarsal fracture to be 

essentially nondisplaced and the first and second 

tarsometatarsal joints to be in anatomic alignment. 

When the soft tissue swelling subsided 4 days later, 

the boot was exchanged for a cast. C, Postcasting 

anteroposterior radiograph reveals that there is lateral 

displacement of the first (white arrow) and second 

(black arrow) metatarsals. Because this demonstrated 

that the Lisfranc joint was not stable, 3 days later the 

patient was taken to the operating room for open 

reduction and internal fixation (D). 

A 

B 

C 

D 

subcortical sclerosis, and subcortical round lucencies called 

geodes—are typically well seen radiographically. But some 

joints, such as the ankle and subtalar joints, can be difficult 

to profile radiographically, and in such cases CT should be 

well able to demonstrate all these osteoarthritic changes 


• Rheumatoid Arthritis 

For rheumatoid arthritis, we prefer MRI to CT when crosssectional 

imaging is required. MRI after the administration 

of intravenous contrast well demonstrates abnormally vas- 

cularized synovium and thickened pannus (see Fig. 47-55) 

as well as small cortical erosions before they become radiographically 

apparent. 

• Gout 

Gout is uric acid crystal deposition arthropathy with a 

predilection for the foot, particularly the first metatarsophalangeal 

joint. The cortical erosions caused by gout form 

slowly and can take as long as a decade to be manifest 

radiographically. These erosions are classically described as 

being well circumscribed with sharp overhanging edges. 

The diagnosis of gout is confirmed when an aspirate of 


9/9/2008 5:35:35 PM


A 

Figure 47-91. CT scan of osteoarthritis in a 71-yearold 

patient. A, Axial scan through the tops of both 

ankle joints demonstrates nonuniform narrowing of 

the medial ankle mortise bilaterally (black arrows). 

Many small geodes with well-circumscribed, 

corticated margins (black arrowheads) are seen in 

both talar domes. B, Coronal scan demonstrates 

nonuniform narrowing medially in both mortises 

(black arrows), subcortical geodes (black arrowheads), 

and subcortical sclerosis (white arrowheads). 

C, Sagittal scan demonstrates nonuniform joint space 

narrowing (black arrows) as well as a small anterior 

osteophyte (white arrow). 

B 

C 


9/9/2008 5:35:37 PM


Figure 47-92. A 34-year-old man came to the 

emergency department complaining of acute 

onset of nontraumatic pain of his left great toe. 

A, Anteroposterior radiograph of the left foot, with the 

area in the dashed box magnified to the right. A thin, 

white, curved line was observed just outside the 

lateral diaphyseal cortex of the first metatarsal 

(ellipse). Initially, this was mistakenly thought to 

present a periosteal reaction from the first metatarsal, 

rather than what it truly was: an eroded lateral 

sesamoid. There is also a marginal erosion of the 

medial first metatarsal head (white arrow). B, Axial CT 

scan through the sesamoids of the great toes 

bilaterally shows two normal sesamoids on the right, 

whereas on the left only a thin shell of the eroded 

lateral sesamoid remains (ellipse). 

A 

B 

joint fluid reveals strongly negative birefringent crystals 

under a polarizing microscope. CT is seldom used in the 

workup of gout. However, CT scans of the feet obtained 

for other reasons may unexpectedly reveal the finding of 

gout (Fig. 47-92). 

• Arthrodesis 

When the chronic pain from severe arthritis cannot be 

controlled medically, a surgical arthrodesis may be 

desirable. Once solid bony fusion across the joint has been 

achieved, that fused joint should be pain free. And even 

though the patient no longer has any motion at that joint 

after arthrodesis, before arthrodesis the joint may have 

been so limited by pain and lack of articular hyaline cartilage 

that the patient may have had very little functional 

range of motion to begin with. 

When patients remain symptomatic after an attempted 

arthrodesis, CT can be used to assess the degree of solid 

bony bridging, if any. Although there may be several metal 

plates and screws within the scanning FOV, these tend to 

cause relatively little CT streak artifact, especially when 


9/9/2008 5:35:38 PM

C 

D 


Figure 47-92, cont’d C, Shortaxis 

(coronal) CT scan confirms the 

erosion of the left lateral sesamoid 

(ellipse) as well as an erosion in 

the adjacent metatarsal head 

(arrow). D, Axial CT scan proximal 

to B reveals the marginal erosion 

seen radiographically in the left 

medial first metatarsal head (white 

arrow) and an erosion in the right 

second cuneiform (black arrow). 

Both erosions have well-defined, 

slightly sclerotic margins with 

sharp overhanging edges, 

characteristic of gout. Aspiration 

of the patient’s left great toe 

metatarsophalangeal joint yielded 

uric acid crystals. 

the source images consist of thin, overlapping slices 


• Tarsal Coalitions 17,32 

The term coalition comes from the verb “coalesce,” which 

means “to grow together and form a union.” These abnormal 

unions are either osseous, in which there is a solid cortical 

bridge between the bones, or nonosseous, in which there 

is a fibrous or cartilaginous union between the bones. 

Although abnormal bone coalitions have been reported 

throughout the body, certain locations predominate. In the 

wrist, for example, carpal coalitions usually occur between 

the lunate and triquetrum. In the hindfoot, tarsal coalitions 

most commonly occur across the middle facet of the 

subtalar joint, and between the APC and the lateral pole 

of the navicular. 46 An example of the latter was already seen 

as an incidental finding in Figure 47-81B. 

The subtalar joint complex consists of the subtalar 

joint itself and the talonavicular and calcaneocuboid joints. 

These joints function in unison during the gait cycle, and 

limitation of motion of any one of these joints limits the 

motion of the other joints. 37 The clinical syndrome of tarsal 

coalition consists of pain and reduced or absent subtalar 

motion, as well as pes planus (flat-foot) and peroneal 

muscle spasm (clonus on inversion stress). 4,43 The exact 

cause of the peroneal spasm is uncertain; however, peroneal 

muscle tightness is the result of tarsal coalition, not 

the cause. Symptoms usually manifest between 12 and 16 

years of age and worsen with increasing age. Conservative 

treatment options include anti-inflammatory medication 

and a trial of reduced activity, cast immobilization, and 

molded orthoses. If conservative treatment fails, surgical 

options include resection of the coalition and arthrodesis 

if secondary osteoarthritis has developed. 

According to the literature, tarsal coalitions are bilateral 

in 50% to 60% of cases. However, in searching our 

database for examples for this chapter, we found that bilaterality 

was the rule. Perhaps because our CT protocol 

entails scanning both feet, we are apt to find asymptomatic 

coalitions and other incidental variants, such as the os 

calcaneus secondarius (a forme fruste of calcaneonavicular 

coalition), in the contralateral foot (Fig. 47-94). 

A talar beak is an indirect sign of a tarsal coalition. Seen 

best radiographically on the lateral view (Fig. 47-95A) or 

on a sagittal CT (Fig. 47-95C), the talar beak is not part of 

the coalition but a result of it. The altered biomechanics 

across the talonavicular joint can result in a traction spur 

(enthesophyte) arising from the dorsal head of the talus. 



9/9/2008 5:35:40 PM


A B C 

Figure 47-93. Attempted 

arthrodesis. The patient is a 68- 

year-old farmer who injured his 

ankle 6 years earlier when he misstepped 

getting off his tractor. He 

underwent arthrodesis surgery 3 

years ago, and this was revised 1 

year ago because of failure of 

fusion. The patient is experiencing 

persistent pain. Anteroposterior 

(A), mortise (B), and lateral (C) 

radiographs reveal a plate and 

several screws across the ankle 

mortise and syndesmosis. 

Although the metal obscures 

visualization of portions of the 

mortise, no bony fusion is seen 

medially (black arrowheads). 

D and E, CT scans were requested 

to see if any fusion was present. 

Mortise coronal (D) and mortise 

sagittal (E) images clearly show no 

bony bridging throughout the 

ankle mortise (black arrowheads). 

D 

E 


9/9/2008 5:35:41 PM


Figure 47-93, cont’d Although 

there are some metallic streak 

artifacts, the resolution is high 

enough to visualize the widely 

spaced cancellous threads of the 

lag screw in the talus (white arrow) 

and the narrowly spaced cortical 

threads of the syndesmotic screw 

(white arrowhead). One operation 

and 16 months later, 

anteroposterior (F), mortise (G), 

and lateral (H) radiographs no 

longer demonstrate residual 

lucency along the mortise. Mortise 

coronal (I) and mortise sagittal (J) 

CT scans now reveal solid bony 

fusion between the tibia (Ti), talus 

(Ta), and fibula (Fi). 

F G H 

I 

J 


9/9/2008 5:35:43 PM


A 

Figure 47-94. Calcaneonavicular coalition in an 11- 

year-old with right foot pain. A, Oblique radiograph 

shows the abnormal joint in this nonosseous coalition 

(arrowheads in magnified dashed box). B, Axial 

oblique CT scan through the bottoms of the talar 

heads (H) shows the symptomatic coalition on the 

right foot (black arrowhead) between the elongated 

anterior process of the calcaneus (APC) and the 

navicular (N). Incidentally seen is an asymptomatic 

coalition on the left (white arrowhead) between the 

abnormally broad APC and the navicular. C, Axial 

oblique CT scan slightly plantar to B. On the right foot 

is the symptomatic abnormal joint (arrowhead) 

between the broad APC and the navicular. On the left 

is an extra bone, an os calcaneus secondarius (OCS), 

articulating with both the APC and navicular. 

B 

C 


9/9/2008 5:35:45 PM


D 

E 

F 

G 

Figure 47-94, cont’d D, Sagittal CT scan of the right foot shows the nonosseous coalition (arrowhead) between the navicular and APC. E, Sagittal 

CT scan of the left foot shows the OCS between the navicular and APC. Surgery was elected. F and G, Fluoroscopic spot views were obtained at the 

beginning (F) and end (G) of the resection. The pointer in F is a metal instrument that the surgeon uses to localize the coalition fluoroscopically. 

The white rectangle in G outlines the resection site. H, Postoperative radiograph shows the calcaneus and navicular no longer in contact with each 

other (white rectangle). 

H 


9/9/2008 5:35:47 PM


A 

B 

C 

D 

E 

F 

Figure 47-95. Tarsal coalition in a 29-year-old radiology resident with a long history of bilateral foot pain. The pain is worse on the right, is 

aggravated by athletics, and was improved with custom orthoses. A, Lateral radiograph of the more symptomatic right ankle reveals a talar beak 

(arrow). B, Lateral radiograph of the less symptomatic left ankle shows no enthesophyte arising from the dorsal head of the talus. Oblique 

radiographs of the right (C) and left (D) feet reveal no coalition between the calcaneus and navicular (bidirectional arrows). E, Sagittal CT scan of 

the right foot reveals the talar beak (arrow) as well as a portion of the solid osseous coalition across the subtalar joint (arrowhead). F, CT scan in 

the coronal oblique plane through the middle facets of both subtalar joints demonstrates solid osseous coalition across the right middle facet 

(white arrowheads). There is also a nonosseous coalition of the left middle facet (black arrowheads), as manifest by a joint that is abnormally 

broad with irregular, noncongruent articular surfaces. 


9/9/2008 5:35:49 PM

A 

C 

B 

D 


Figure 47-96. Calcaneonavicular coalition seen 

radiographically in this 21-year-old who has been 

complaining of left ankle pain for at least 7 years. On 

physical examination, the subtalar range of motion of the 

left foot is half that of the asymptomatic right. A, Oblique 

radiograph of the asymptomatic right midfoot shows the 

normal relationship between the calcaneus (Ca) and 

navicular (N), with no contact between them. B, Oblique 

radiograph of the symptomatic left foot shows the 

abnormal joint (arrowheads) between the calcaneus and 

navicular. This is a nonosseous coalition. Lateral 

radiographs of the right (C) and left (D) ankles reveal 

elongated anterior processes of the calcaneus bilaterally 

(arrows). These bilateral “ant-eater” signs suggest that 

the patient has an asymptomatic calcaneonavicular 

coalition on the right that was not radiographically 

apparent on the oblique view (A). 

Talar beaks occur less frequently with nonosseous coalition 

because some subtalar motion remains. 

• Calcaneonavicular Coalition 

Of the two common locations for tarsal coalitions, calcaneonavicular 

coalitions can often be seen radiographically 

on the oblique view (Fig. 47-96). Normally, the calcaneus 

and navicular do not touch (see Fig. 47-96A); it is abnormal 

any time they get close enough to each other to form 

a joint (see Fig. 47-96B), let alone a solid bony bridge. 

Another radiographic indication of a calcaneonavicular 

coalition is the presence of an elongated APC, sometimes 

called an ant-eater sign (Fig. 47-96C and D). An elongated 

APC and an asymptomatic calcaneonavicular coalition 

may be seen as incidental findings on radiographs and CTs 

obtained for other reasons. And although an elongated 

APC may not cause a symptomatic coalition, it may be at 

increased risk of fracture (Fig. 47-97). 

• Talocalcaneal Coalition 

Talocalcaneal coalitions, which occur across the middle 

facet of the subtalar joint, are difficult to demonstrate with 

conventional radiographs because these radiographs do not 

well profile the middle facet. For this reason, coronal CT 

images obliqued to be perpendicular to the subtalar joint 

are the key imaging plane (Fig. 47-95F). With osseous coalitions, 

solid bony ankylosis is present across the middle facet 

(see Fig. 47-95F, white arrowheads). Nonosseous coalitions 

across the middle facet are not difficult to recognize by CT 

because they do not look like the flat, uniform middle facet 

we typically see on coronal oblique CT. In nonosseous 

coalitions, the articular surfaces are not smooth or congruous 

and tend to have an overgrown appearance (see Fig. 

47-95F, black arrowheads). An additional example of nonosseous 

middle facet coalition is shown in Figure 47-98. 

• Tarsal Tunnel Syndrome 

The tarsal tunnel in the ankle is analogous to the carpal 

tunnel in the wrist. Both are spaces confined by the underlying 

bones and overlying fibrous ligaments through which 

pass tendons, blood vessels, and nerves. The roof of the 

tarsal tunnel is the flexor retinaculum, a broad, fibrous 

band extending between the medial malleolus and the 

medial tubercle of the calcaneus (Fig. 47-99A). These retinacular 

fibers help prevent the medial tendons from 

becoming dislocated and can be identified on highresolution 

images (Fig. 47-99B; see Fig. 47-31). Because the 

tarsal tunnel is a relatively tight space, otherwise innocuous 

volume-occupying lesions, such as synovial cysts (Fig. 


9/9/2008 5:35:50 PM


A 

B 

C 

Figure 47-97. Anterior process of the calcaneus (APC) fracture in a 51-year-old who was playing a jumping game. The patient, who was wearing 

sandals, landed awkwardly and felt a large “pop” after forcefully inverting the foot. A, Lateral radiograph obtained when the patient came into the 

emergency department the next day revealed the previously asymptomatic elongated APC (arrows). Careful scrutiny also reveals disruption of 

the cortex (arrowhead), indicating a nondisplaced APC fracture. B and C, CT scans were obtained the same day. Sagittal (B) and axial (C) scans 

revealed the APC fracture (black arrowheads) as well as the incidental finding of a calcaneonavicular nonosseous coalition (white arrowhead; 

N, navicular). The patient was treated nonoperatively with a non–weight-bearing cast. When no healing was seen radiographically 9 weeks later, 

an ultrasonic bone stimulator was used. Five weeks after that, healing was evident radiographically. Twenty-three weeks later, the injury was 

essentially asymptomatic. 

47-100), small nerve sheath tumors, focal synovitis, or 

rarely even varicose veins, can potentially impinge on the 

posterior tibial nerve. 22,30 

• Stress Injuries 

When the foot is subjected to new or excessive forces, such 

as a change in physical activity or an increased level of 

workout, certain bones may be subjected to a disproportionate 

amount of the increased stress and exhibit a stress 

response. The pattern of stress response depends on which 

bone is involved and how long it has been untreated. 

Figure 47-98. Bilateral nonosseous coalitions of the middle facet of 

the subtalar joint in an 8-year-old. Coronal CT scan reveals an 

abnormal vertical orientation of the right middle facet (white arrow). 

On the left, the talar-side middle facet has an abnormal rounded 

cortical surface (black arrow). 

• Navicular Stress Fractures 34 

Navicular stress fractures begin at the dorsal, central, proximal 

navicular where it articulates with the head of the talus 


9/9/2008 5:35:51 PM


Tarsal 

tunnel 

Flexor 

retinaculum 

B 

A 

Figure 47-99. Location of the tarsal tunnel. A, Illustration of the location of the tarsal tunnel (arrow), deep to the flexor retinaculum. 

(Artist, M. Schenk, MS, CMI.) B, Axial high-resolution T1-weighted image shows the medial neurovascular bundle (dotted ellipse) deep to the 

flexor retinaculum (arrows). 

Figure 47-100. Tarsal tunnel containing a synovial 

cyst (arrow): axial (A) and sagittal (B) T2-weighted fatsuppressed 

images. 

A 

B 

(Fig. 47-101A). These fractures tend to be the result of 

repetitive injuries rather than a specific traumatic event. In 

our practice, such fatigue injuries are commonly seen in 

college athletes. Often the athlete’s prognosis and the 

length of time needed to rest the fatigue injury depend on 

whether the cortex is broken. When MRI demonstrates just 

bone marrow edema without a breach in the cortex, these 

will be radiographically occult, and our sports medicine 

physicians prefer we use the term stress reaction. We use 

stress fracture to refer to bones that exhibit a discrete line 

extending through the cortex by MRI, CT, or plain radiography 

(Figs. 47-102 and 47-103). 

Although navicular fatigue fractures may be suspected 

clinically, initial radiographs are often negative, and MRI 

is the next imaging study ordered to confirm the diagnosis. 

As with most stress fractures, MRI is more sensitive than 

CT for the detection of the bone marrow edema that develops 

before the cortex breaks (see Fig. 47-101). But MRI, 

owing to its exquisite sensitivity to marrow edema, may be 

too sensitive to assess fracture healing. At the UW we have 


9/9/2008 5:35:53 PM


A 

C 

B 

D 

Figure 47-101. Navicular stress reaction in a 

36-year-old avid runner who had recently begun 

marathon training. The markers (m) indicate the 

proximal and distal extents of the patient’s pain. 

A, Sagittal T1-weighted MRI shows abnormally dark 

bone marrow in the dorsal half of the navicular 

(arrow). B, Sagittal inversion recovery (IR) image, 

being more sensitive for edema, shows abnormally 

bright signal throughout the navicular (arrows). 

C, Long-axis, oblique axial T1-weighted image shows 

abnormally dark bone marrow in the central third of 

the navicular, emanating from the proximal articular 

surface adjacent to the head of the talus (arrow). 

D, Fat-suppressed T2-weighted image in the same 

plane, being more sensitive for edema, shows 

abnormally bright signal throughout the navicular 

(arrows). E, Short-axis, oblique coronal T1-weighted 

image just distal to the talonavicular joint shows 

abnormally dark bone marrow in the dorsal central 

portion of the navicular (arrow). F, Fat-suppressed 

T2-weighted image at that same location, being more 

sensitive for edema, shows abnormally bright signal 

throughout the navicular (arrows). None of these MRIs 

demonstrates a discrete fracture line, and we call this 

a stress reaction rather than a stress fracture. 

E 

F 


9/9/2008 5:35:55 PM


Figure 47-102. Navicular fatigue (stress) fracture 

in a 16-year-old who developed midfoot pain while 

cross-country skiing. A, Anteroposterior radiograph of 

the foot reveals a subtle nondisplaced fracture in the 

middle third of the navicular (arrowhead in magnified 

dashed box). MRI was obtained 4 days later. Axial 

oblique T1- (B) and fat-suppressed T2-weighted (C) 

images reveal a discrete fracture in the middle third of 

the navicular (arrowhead) as well as diffuse bone 

marrow edema. 

Continued 

A 

B 

C 

developed a specific CT protocol that reformats the images 

in thin, 1-mm slices using a small, 6-cm FOV centered on 

the navicular (see Fig. 47-47D). 

Whether seen by CT or MRI, navicular fatigue injuries 

begin at the dorsal, central, proximal navicular where it 

articulates with the head of the talus. This is illustrated by 

the black arrows pointing to the dark regions of bone 

marrow on the T1-weighted images in the stress reaction 

in Figure 47-101. More fluid-sensitive fat-suppressed T2- 

weighted or inversion recovery images show bone marrow 

edema emanating from this dorsal/central/proximal site. 

This is illustrated by the white arrows in Figure 47-101. 

When stress reactions progress to stress fractures, the cortical 

disruption starts at the dorsal/central/proximal site 

on the navicular and propagates in a plantar direction 

vertically in the sagittal plane (see Fig. 47-102) or in an 

oblique sagittal plane (see Fig. 47-103). Because of the 

primarily sagittal orientation of these fractures, they may 

be difficult to appreciate on sagittal CT images and are 

better seen on oblique coronal (see Fig. 47-102F) and 

oblique axial (see Fig. 47-102G) images. Because they tend 

to be nondisplaced incomplete fractures, they are best seen 

on images that are reformatted into a small FOV with thin 

slices. Because these patients may undergo serial CT scans 

to follow the progress of fracture healing, it is useful to 

have a standard protocol (as in Fig. 47-47D) to help retain 

uniform reformatting parameters from one scan to the next 

(see Fig. 47-103C to F). 


9/9/2008 5:35:56 PM


D 

E 

Figure 47-102, cont’d Coronal oblique T1- (D) and 

fat-suppressed T2-weighted (E) images show that this 

is an incomplete fracture, beginning from the dorsal 

cortex (arrowhead) and extending inferiorly in the 

sagittal plane, but not extending completely to the 

plantar cortex. A CT scan obtained 2 months later, 

reformatted using a 6-cm field of view in the oblique 

coronal (F) and oblique axial (G) planes, reveals that 

the fracture remains nonunited (arrowhead) and the 

bones are diffusely osteopenic from the patient’s 

being non–weight bearing. 

F 

G 

• Calcaneal Stress Fractures 

Calcaneal stress fractures occur in a characteristic location, 

arising from the posterior third of the calcaneal tuberosity 

beginning at the superior cortex a few centimeters anterior 

to the Achilles insertion, and extending inferiorly and 

slightly anteriorly, running perpendicular to the trabeculae. 

When radiographically apparent, these fractures are seen as 

a white sclerotic line on the lateral view (Fig. 47-104A). On 

MRI, calcaneal stress fractures are seen as a black line on 

sagittal T1-weighted images (Fig. 47-104B) surrounded by 

bone marrow edema on fat-suppressed T2-weighted (Fig. 

47-104C) and inversion recovery (Fig. 47-104D) images. 

Figure 47-105 is a an example of a calcaneal stress fracture 

that was subtle on initial radiographs and was ultimately 

imaged using CT, a nuclear medicine bone scan, and MRI. 

• Plantar Fasciitis 

Plantar fasciitis is a stress reaction occurring at the origin 

of the plantar aponeurosis from the calcaneus, typically at 

the medial calcaneal tubercle. Degenerative changes from 

repetitive microtrauma in the origin of the plantar fascia 

cause traction periostitis and microtears, resulting in pain 

and inflammation. Plantar fasciitis is the most common 

cause of pain in the inferior aspect of the heel, and the 

diagnosis is typically made based on clinical symptoms 

and physical examination revealing tenderness along the 

medial calcaneal tuberosity. The relationship between 

plantar fasciitis and heel spurs has never been firmly established. 

Most patients with plantar fasciitis respond to conservative 

treatments that include calf stretching, orthoses, 

nonsteroidal anti-inflammatory medication, ultrasonic 

therapy, and occasionally casting. Patients with atypical 

clinical presentations or who fail conservative therapies 

may benefit from MRI to determine if their pain is indeed 

related to the plantar fascia or to some other etiology such 

as a tarsal stress fracture. An MRI of plantar fasciitis reveals 

edema around the origin of the aponeurosis. The plantar 

fascia itself may be abnormally thickened, and there may 

be edema in the underlying calcaneal bone marrow (Fig. 

47-106; see Fig. 47-53). 

• Metatarsal Stress Fractures 

Metatarsal stress fractures occur at such characteristic locations 

that some carry eponyms. 

Jones Fracture. The Jones fracture occurs at the proximal 

metadiaphysis of the fifth metatarsal and is seen radiographically 

as a transverse lucency (see Fig. 47-41C). 

Although Jones fractures can be caused by a single traumatic 

injury, they are commonly seen as the result of repet- 



9/9/2008 5:35:57 PM


A 

B 

C 

D 

E 

Figure 47-103. Navicular stress fracture in a 20-year-old college decathlete complaining of lateral ankle pain not localized to the navicular. An 

MRI requested to evaluate the ankle joint found no abnormalities in or around the ankle but revealed abnormal bone marrow signal limited to the 

navicular. Coronal oblique T1- (A) and fat-suppressed T2-weighted (B) images, just distal to the talonavicular joint, reveal the dark fracture line 

extending from the dorsal cortex (arrowhead) in a plantar-lateral direction. Serial CT scans using our navicular protocol were ordered to follow the 

progress of healing. Shown here is the same coronal oblique slice, just distal to the talonavicular joint, from scans taken over a period longer than 

1 year. C, The first CT scan, obtained 2 months after the MRI, during which time the patient was non–weight bearing on this foot and using an 

ultrasonic bone stimulator. The fracture (white arrowhead) is very narrow, with indistinct, noncorticated margins, suggesting that it is healing. 

D, The second CT scan, obtained 1 month after C, during which time the patient was weight bearing in a boot and using the bone stimulator. The 

fracture line (gray arrowhead) is much less distinct, consistent with continued interval healing. E, The third CT scan, obtained 3 months after 

D, during which time the patient resumed his training regimen. The fracture line (dark gray arrowhead) is now barely discernible. F, The final CT 

scan was obtained 9 months after E, when the patient’s symptoms returned. The fracture (black arrowhead) has recurred along the original 

fracture lines, which are now wider and more distinct than on the first CT scan (C). 

F 


9/9/2008 5:35:59 PM


A 

B 

C 

D 

Figure 47-104. Calcaneal stress fracture in a 62-year-old. A, Lateral radiograph shows a sclerotic band (black arrowheads) in the characteristic 

position of a calcaneal stress fracture, perpendicular to the trabeculae (white arrowheads). Incidentally seen is an os peroneum (arrow), a 

common normal variant. B, Midsagittal T1-weighted image shows the characteristic well-defined black line (arrowheads) of a calcaneal stress 

fracture. C, The corresponding midsagittal T2-weighted fat-suppressed (T2FS) image also shows the dark fracture line (arrowheads) as well as 

surrounding bone marrow edema. D, Sagittal inversion recovery (IR) image shown for comparison with the T2FS image (C). On the IR image, the 

normal fatty bone marrow is very dark, making the bone marrow edema more conspicuous. Arrowheads show the calcaneal stress fracture. 


9/9/2008 5:36:00 PM


A 

B 

C 

Figure 47-105. Calcaneal stress fracture in a 14-year-old cross-country runner. A, Lateral radiograph shows a subtle sclerotic band (arrowheads 

in the magnified dashed box). CT scans in the axial (B) and sagittal (C) planes show the sclerotic line in the right calcaneus (arrowheads). The 

normal left calcaneus is included for comparison. 

Continued 


9/9/2008 5:36:01 PM


D 

E 

F 

G 

Figure 47-105, cont’d Bone scan images, both-feet-on-detector (D) and lateral (E) views, show increased activity in the right calcaneal 

tuberosity. Incidentally noted is normal activity in the distal tibial physis (arrowheads) in this skeletally immature patient. Midsagittal T1-weighted 

(F) and T2-weighted fat-suppressed (G) images show the characteristic well-defined black line (arrowheads) of a calcaneal stress fracture, as well 

as edema in the surrounding bone marrow. 


9/9/2008 5:36:02 PM


A 

B 

C 

D 

E 

Figure 47-106. Plantar fasciitis in a 52-year-old with chronic bilateral heel pain. The left (A to C) and right (D to F) hindfeet were scanned 

individually. A, Sagittal T1-weighted image reveals thickening of the plantar fascia (white arrows). B, The corresponding sagittal inversion 

recovery (IR) image reveals edema (white arrowhead) deep to the plantar fascia (white arrow). Open arrow points to OS trigonum. C, Coronal T2- 

weighted fat-suppressed image demonstrates a line of fluid (white arrowhead) as well as some focal bone marrow edema (black arrowhead) deep 

to the origin of the plantar fascia (white arrow). (“med” and “lat” represent the medial and lateral sides of the image, respectively.) Incidentally 

seen is a normal os trigonum (open arrow in A to C) with bone marrow signal isointense to the normal bone marrow in the other bones. D, Sagittal 

T1-weighted image of the contralateral right foot also demonstrates a thickened plantar fascia (arrows). The calcaneal bone marrow edema is less 

conspicuous than on more fluid-sensitive sequences. E, The corresponding IR images reveal extensive bone marrow edema along the plantar 

portion of the calcaneus (arrowheads). F, Coronal T2-weighted fat-suppressed image shows the bone marrow edema (white arrowhead) radiating 

from the medial-plantar surface of the calcaneus, at the origin of the plantar fascia. 

F 


9/9/2008 5:36:03 PM


B 

C 

A 

Figure 47-107. Early Jones fracture in a 21-year-old college athlete. A, On the initial anteroposterior radiograph of the base of the fifth 

metatarsal there is a very subtle periosteal reaction (white arrow). There is a questionable lucency (open arrowheads) extending transversely 

through the lateral cortex. B, Far lateral sagittal inversion recovery (IR) image reveals bone marrow edema throughout the fifth metatarsal. 

C, Sagittal IR image through the asymptomatic fourth metatarsal for comparison revealed normal dark marrow signal. Because of the high 

propensity for Jones fractures to have delayed union or nonunion, elective internal fixation with a lag screw was performed the next day. 

D, Follow-up anteroposterior radiograph 2 weeks later reveals bone resorption (arrowheads) along the questionable lucency in A, part of the 

normal early healing response. Subsequent radiographs (not shown) demonstrated solid bony bridging 1 month later. 

D 

itive stress in athletes, or as in the case of Sir Robert Jones, 

“whilst dancing.” 25 The Jones fracture is well recognized to 

have a high rate of nonunion or delayed union because of 

the relative hypovascularity of this portion of the fifth 

metatarsal, prompting orthopedic surgeons to recommend 

early screw fixation. MRI is useful in confirming the diagnosis 

when it is suspected in athletes with radiographically 

occult injuries (Fig. 47-107). 

March Fracture. The march fracture is found most commonly 

in the mid- to distal diaphysis of the second metatarsal 

and less often in the third. Unlike the Jones fracture, 

which occurs in high-performance athletes, stress fractures 

in the second and third metatarsals occur in individuals 

who have previously led relatively sedentary lifestyles, then 

suddenly increase their level of activity. This fracture was 

first reported by Breithaupt in 1855, 11 when he described 

foot pain and swelling in military recruits in the Prussian 

army who were forced to go on long marches—hence the 

name “march fracture.” This was of course 40 years before 

Röntgen’s discovery of x-rays. The first radiographic reports 

of march fractures were in 1897.* Radiographically, the 

*In his 2006 academic dissertation for the University of Helsinki, Bone Stress 

Injuries of the Foot and Ankle (http://ethesis.helsinki.fi/julkaisut/laa/kliin/vk/ 

sormaala/bonestre.pdf), Sormaala cites these two references: 

Schulte: Die sogenannte Fussgeschwulst. Arch Klin Chir 1897;55:872. 

Stechow: Fussödem und Röntgenstrahlen. Deutsche Militärärztliche Zeitschrift 

1897;26:465-471. 

second and third metatarsals respond to stress by forming 

a periosteal reaction, although this may be imperceptible 

or subtle early on (Fig. 47-108). Edema-sensitive MRI 

reveals abnormally bright marrow signal in the diaphysis 

as well as bright periosteal reaction outside the cortex. 

• Sesamoid Stress Fractures 

Sesamoid stress fractures are notoriously difficult to diagnosis 

radiographically. Perhaps because of their varying 

presence and appearance, radiologists tend to have a “blind 

spot” when it comes to the sesamoids. However, when 

looking at the sesamoids of the first metatarsophalangeal 

joint, there are some helpful statistics to keep in mind. 

Although the other sesamoid bones of the foot are present 

in less than 10% of people, the two sesamoids plantar to 

the head of the first metatarsal are present in 100% of the 

population. 16 Absence of either the medial (tibial) or lateral 

(fibular) sesamoids is always abnormal, and a destructive 

process should be considered (see Fig. 47-92). And 

although a multipartite medial sesamoid bone is a common 

normal variant found in 13% to 30% of the population, a 

multipartite lateral sesamoid bone is an uncommon variant, 

found in only 1% of normal feet. 

When symptoms are referable to the lateral sesamoid 

and radiographs reveal it to be multipartite, this should be 

diagnosed as a fracture (Fig. 47-109). Additional diagnostic 

imaging should not be required, although MRI or a nuclear 


9/9/2008 5:36:04 PM


A 

Figure 47-108. Second metatarsal stress fracture in 

a 22-year-old who developed foot pain during a 1- 

week vacation in which the patient did a lot of walking 

in sandals. A, Oblique radiograph reveals a periosteal 

reaction along the medial cortex (white bracket in 

magnified dashed box). B, Long-axis T1-weighted 

image through the second metatarsal well illustrates 

the anatomy, but not the pathology. C, Corresponding 

long-axis T2-weighted fat-suppressed image reveals 

bone marrow edema throughout the second 

metatarsal diaphysis, the thickened medial cortex/ 

periosteum, and edema of the adjacent medial soft 

tissues. Short-axis T1-weighted (D) and T2-weighted 

fat-suppressed (E) images through the metatarsal 

shafts reveal edema in the second metatarsal bone 

marrow and in the adjacent medial soft tissues 

overlying the periosteal reaction. Sagittal T1-weighted 

(F) and inversion recovery (G) images through the 

marker (m) indicating the site of maximal tenderness 

show edema in and around the second metatarsal. 

B 

C 

D 

E 

F 

G 


9/9/2008 5:36:06 PM


A 

B 

D 

C 

E 

Figure 47-109. Fracture of the lateral sesamoid in a 34-year-old who complained of localized pain plantar and lateral to the first metatarsal 

head, made worse with weight bearing and extension of the great toe, for 1.5 years before the diagnosis was made. Anteroposterior (A), oblique 

(B), and sesamoid (C) radiographs all clearly show the transverse split across the lateral sesamoid of the great toe. A bipartite lateral sesamoid is 

an uncommon variant, present in only 1% of the population, and when symptomatic should be interpreted as a fracture. Short-axis T1-weighted 

(D) and inversion recovery (E) images through the marker (m) indicating the site of maximum pain show normal bone marrow signal in the medial 

sesamoid (white arrow) and bone marrow edema in the lateral sesamoid (black arrow). 

medicine bone scan could be obtained if confirmation is 

necessary. 

Fractures of the medial sesamoid are more difficult to 

diagnose radiographically because this sesamoid is not 

infrequently multipartite in normal people. Here radiographs 

are of limited value, and more sensitive imaging 

modalities are often required. Although MRI can demonstrate 

abnormal marrow signal in the sesamoids, owing to 

the small size of these bones this may be present on only 

a single slice, and all imaging planes should be carefully 

scrutinized. Short-axis images are particularly helpful in 

comparing the marrow signal from the medial and lateral 

sesamoids side-by-side (Fig. 47-110). The imaging of sesamoiditis 

is one of the few instances when we recommend a 

nuclear medicine bone scan over an MRI. In particular, the 

both-feet-on-the-detector view is extremely effective for 

localizing abnormal radiotracer uptake to one of the sesamoids 

(see Fig. 47-110C). 


9/9/2008 5:36:08 PM

A 

B 

C 


Figure 47-110. Fracture of the medial sesamoid in a 

27-year-old with a several-month history of pain 

localized to the head of the first metatarsal. Short-axis 

T1-weighted (A) and T2-weighted fat-suppressed (B) 

images show normal bone marrow signal in the lateral 

sesamoid (white arrow) and bone marrow edema in 

the medial sesamoid (black arrow). C, Bone scan, bothfeet-on-detector 

view, localizes the increased uptake 

to the medial sesamoid of the left foot. This patient 

failed to respond to conservative therapy and 

ultimately had the medial sesamoid resected. 

Infection 

Osteomyelitis is always a diagnostic dilemma. The term 

osteomyelitis comes from the Greek roots osteon meaning 

“bone,” myelos meaning “marrow,” and itis meaning 

“inflammation.” Thus, osteomyelitis literally means “inflammation 

of bone marrow,” and this is perhaps symbolic of 

the dilemma. MRI is extremely sensitive for the detection 

of marrow inflammation, but it is not specific for the 

inflammation caused by infection. By MRI, the bone 

marrow edema caused by infection looks just like the bone 

marrow edema caused by a stress response as well as the 

edema caused by a nonhealing fracture or even a healing 

fracture. For this reason, an MRI for osteomyelitis should 

not be read in isolation. It is difficult to arrive at the correct 

diagnosis without a thorough clinical workup and 

complete understanding of any prior surgical resections or 

debridements. 

• Imaging Techniques 

• Radiography 

Radiographs are essential in the workup of osteomyelitis, 

and at the UW we insist on having recent radiographs 

before we will perform an MRI for infection. Although it 

is true that radiographs are insensitive to the bone marrow 

and soft tissue edema seen on MRI, they are not without 

value. First, radiographs are crucial to screen for the presence 

of metal, particularly in the feet of diabetic patients 

who may be insensate and thus unknowingly stepped 

on pins, not to mention the presence of orthopedic 

hardware. 

Second, in diabetic feet it is necessary to screen for the 

joint-centered collapse that is typically seen with peripheral 

neuropathy, the Charcot joint. These radiographic 

findings have been described as “the six Ds”: destruction, 

increased density, dislocation, debris, distension, and disorganization. 

The bone marrow and soft tissue edema seen 

with MRI in patients with sterile neuropathic osseous 

changes may be indistinguishable from infection, and for 

this reason at the UW we recommend that patients who 

exhibit radiographic findings of a Charcot joint undergo a 

nuclear medicine bone scan and white blood cell scan, 

rather than MRI, for the workup of osteomyelitis. And 

because neuropathic collapse can occur relatively quickly 

and go unnoticed by a patient with an insensate foot (Fig. 

47-111), we require that the pre-MRI radiographs be recent, 

preferably within the last week. 

Third, radiographs may reveal findings that, in the 

proper clinical setting, are diagnostic for osteomyelitis. 

New cortical erosions (Fig. 47-112) in a bone deep to a 

nonhealing ulcer or unresponsive cellulitis are as diagnostic 

as MRI for active osteomyelitis. Periosteal reactions, 

particularly the aggressive periosteal reaction of acute 

osteomyelitis or the thick involucrum of chronic osteomyelitis 

(Fig. 47-113), can be diagnostic. Gas in the soft 

tissues, such as from a gas-forming organism, is easily 

detected on radiographs yet may be hard to interpret on 

MRI because it can cause susceptibility artifacts similar to 

those caused by metal. 

• Magnetic Resonance Imaging 

Ultimately, it is easier to rule out osteomyelitis by MRI than 

it is to confirm its presence. The absence of increased bone 

marrow signal on a good edema-sensitive MRI effectively 


9/9/2008 5:36:09 PM

Figure 47-111. Rapid onset of severe Charcot 

neuropathic collapse in a diabetic patient. 

Anteroposterior (A) and oblique (B) radiographs show 

anatomic alignment along the Lisfranc joint. 

Anteroposterior (C) and oblique (D) radiographs only 

3 months later reveal complete destruction of the 

Lisfranc joint. 

A 

B 

C 

D 

A 

B 

Figure 47-112. Radiographic evidence of active 

osteomyelitis in a 39-year-old. A, Oblique radiograph 

of the toes reveals subtle erosions in the lateral cortex 

of the fourth middle phalanx (arrow) and the lateral 

head of the fourth proximal phalanx (black 

arrowhead). Incidentally seen is a metallic foreign 

body (white arrowhead), not an uncommon finding in 

patients who are insensate because of peripheral 

neuropathy. B, Same oblique view just 2 months later 

reveals a new erosion in the medial cortex of the 

fourth middle phalanx (white arrow). The rapid onset 

of this erosion is highly suggestive of osteomyelitis. 

Marginal erosions from noninfectious inflammatory 

arthropathies such as rheumatoid arthritis, or 

crystalline arthropathies such as gout, could have a 

similar appearance but would not be expected to 

exhibit such rapid changes. 


9/9/2008 5:36:12 PM


Figure 47-113. Evolution of involucrum in 

chronic osteomyelitis in a patient with diabetes. 

A, Anteroposterior radiograph reveals a somewhat 

lamellated periosteal reaction around the diaphysis of 

the fifth metatarsal. B, Six weeks later, the periosteal 

reaction is thicker and more mature. C, Eleven weeks 

later, the periosteal reaction has developed the thick, 

irregular appearance of an involucrum. The 

underlying metatarsal has become a dead and 

sclerotic sequestrum. 

A B C 

Figure 47-114. Early neuropathic changes in a 66- 

year-old with a long history of diabetes. Oblique axial 

T1-weighted (A) and T2-weighted fat-suppressed (B) 

images show marrow edema throughout the midfoot 

bones. 

A 

B 

rules out the diagnosis of osteomyelitis. However, the 

converse is not true. Although the presence of bone 

marrow edema may be due to infection, the edema may 

represent a sterile stress response owing to the altered 

biomechanics of the patient walking on a neuropathic 

foot that has not yet collapsed. Indeed, marrow edema 

diffusely involving several of the tarsal bones can indicate 

neuropathic precollapse (Fig. 47-114), and such patients 

need to be treated with a prolonged period of non–weight 

bearing. 

The diagnosis of osteomyelitis can be presumed when 

MRI shows not only marrow edema but also abscess in the 

adjacent soft tissues (Fig. 47-115) or a sinus tract communicating 

from the infected bone to the skin. 1 IVGd-based 

contrast is extremely helpful in diagnosing the abscess, 

which exhibits thick, irregular enhancement peripherally 

but not centrally (see Fig. 47-115H and K). 

• Brodie’s Abscess 

Brodie’s* abscess is a chronic intraosseous abscess resulting 

from incomplete resolution of acute osteomyelitis and isolation 

of the infection by surrounding bone. These abscess 

pockets are typically found in the metaphyses of skeletally 

immature children, and the usual pathogen is Staphylococcus 

aureus. However, the organisms tend to be of low virulence, 

*Sir Benjamin Collins Brodie (1783-1862) was an English physiologist and 

surgeon who pioneered research into bone and joint disease. His most important 

work is widely acknowledged to be the 1818 treatise Pathological and Surgical 

Observations on the Diseases of the Joints, in which he attempts to trace the 

beginnings of disease in the different tissues that form a joint and to give an exact 

value to the symptom of pain as evidence of organic disease. This volume led to 

the adoption by surgeons of more conservative measures in the treatment of diseases 

of the joints, with consequent reduction in the number of amputations and 

the saving of many limbs and lives. 


9/9/2008 5:36:14 PM


A 

C 

E 

G 

B 

D 

F 

H 

Figure 47-115. Developing calcaneal osteomyelitis 

in a 63-year-old diabetic patient. A, Lateral radiograph 

of the calcaneus shows intact cortex along the plantar 

surface (white arrowheads). Incidentally seen is mural 

calcification of the posterior tibial artery (gray 

arrowheads). Such arterial calcifications are common 

in diabetic patients. B, Midsagittal T1-weighted image 

shows no bone destruction. C, Corresponding sagittal 

inversion recovery (IR) image shows little, if any, bone 

marrow edema. D, Corresponding sagittal post– 

intravenous (IV) gadolinium contrast T1-weighted fatsuppressed 

image reveals diffuse enhancement of the 

plantar soft tissues, indicative of cellulitis, but no 

nonenhancing abscess pockets. When the patient’s 

symptoms did not respond to antibiotics, repeat 

imaging was obtained 2 weeks later. E, Lateral 

radiograph now demonstrates loss of cortex along the 

plantar surface of the calcaneus (arrowheads). 

F, Midsagittal T1-weighted image reveals infiltration of 

the fatty heel pad (arrows). G, Corresponding sagittal 

inversion recovery image reveals fluid bright signal 

(arrows) in the soft tissues adjacent to the calcaneus, 

as well as bone marrow edema in calcaneus 

(arrowheads). H, Corresponding sagittal post-IV 

gadolinium contrast T1-weighted fat-suppressed 

image reveals a nonenhancing abscess pocket 

(arrows) as well as enhancing bone marrow 

(arrowheads). Coronal T1-weighted (I), inversion 

recovery (J), and post-IV gadolinium contrast T1- 

weighted fat-suppressed (K) images through the 

abscess pocket confirm the findings seen in the 

sagittal plane: an abscess pocket (gray, white, and 

black arrows) adjacent to the osteomyelitis (white 

arrowhead) of the planter surface of the calcaneus. 

I J K 


9/9/2008 5:36:17 PM

A 

B 

C D E 

T1 

T2fs 

T1fs 

IVGd 

F G H 

Figure 47-116. Brodie’s abscess in a young child. A, Anteroposterior radiograph of the asymptomatic right leg. B, Anteroposterior radiograph of 

the swollen left leg reveals a lucency in the distal fibula metaphysis (arrow in the magnified dashed box). This lucency has a well-defined and 

sclerotic margin, indicating chronicity. There are also thick, chronic periosteal reactions (arrowheads) extending up the diaphysis. C, Coronal 

T1-weighted image through the distal fibula confirms the radiographic findings of a thick chronic periosteal reaction (white arrowheads), as well as 

the well-circumscribed dark line (open arrowheads) around the lesion corresponding to the sclerotic margin. D, The corresponding coronal 

T2-weighted fat-suppressed image shows that the well-circumscribed lesion (arrow) is as bright as fluid and thus probably cystic. E, The 

corresponding coronal T1-weighted fat-suppressed post–intravenous (IV) gadolinium contrast image not only confirms that the lesion (arrow) is 

mostly nonenhancing and thus mostly cystic, but demonstrates peripheral enhancement, in some places thick (black arrowhead), characteristic of 

an abscess, in this case an intraosseous or Brodie’s abscess. (There is inadequate fat suppression of the heel pad [large white arrowhead] on both 

of the fat-suppressed sequences, D and E.) F to H, Axial images through the fibular abscess reveal it to be isointense to muscle on T1-weighted 

image (F, arrow) and fluid bright on T2-weighted fat-suppressed image (G, arrow), with peripheral but not central enhancement on fat-suppressed 

T1-weighted image after IV gadolinium (H, arrow). There are edema and enhancement of the soft tissues surrounding the fibula, indicating an 

active inflammatory component to this chronic Brodie’s abscess. 


9/9/2008 5:36:20 PM


A B C 

Figure 47-117. Plantar fibroma in a 44-year-old. 

Coronal T1-weighted (A), proton-density–weighted 

(B), and T2-weighted (C) images reveal that the lesion 

(arrows) is relatively dark on all sequences and 

confined to the fat of the plantar heel pad. 

and it is not uncommon for cultures of such aspirates to 

yield no growth. Clinical symptoms are often mild, generally 

presenting with persistent local pain. 

Radiographs show an intramedullary lucency with surrounding 

sclerosis, the density of which depends on the 

chronicity of the abscess. A thick chronic periosteal reaction 

may also be present (Fig. 47-116B). MRI after the 

administration of IV contrast reveals an intraosseous 

abscess with peripheral but not central enhancement 

(Fig. 47-116E). 29 

Tumors 

• Soft Tissue Masses 

Soft tissue tumors of the feet and ankle are common, and 

MRI is useful in determining the tissue type as well as 

demonstrating the relationship of the mass to the adjacent 

anatomic structures. Synovial cysts or ganglia are among 

the most common soft tissue “masses” found around the 

foot and ankle. These are uniformly bright on fluidsensitive 

images and exhibit minimal if any peripheral 

enhancement after the administration of IVGd-based contrast 

(see Fig. 47-57). In comparison, nerve sheath tumors 

such are schwannomas are heterogeneously bright on T2- 

weighted and inversion recovery images, and they demonstrate 

heterogeneous contrast enhancement (see Fig. 


Plantar fibromas can have variable signal characteristics 

but are typically dark on all sequences (Fig. 47-117). 

These are usually found in the plantar fat adjacent to the 

aponeurosis, usually close to the calcaneus. 

Morton’s neuromas usually occur between the heads 

of the second and third or third and fourth metatarsals and 

are also usually dark on noncontrast images, although they 

can exhibit postcontrast enhancement (see Fig. 47-58). 

Giant cell tumor of the tendon sheath is a localized 

form of pigmented villonodular synovitis, the latter being 

a joint-centered synovial proliferative condition. Both diseases 

show areas of decreased signal on T1-images, protondensity–images, 

and T2-weighted images, secondary to 

hemosiderin deposition (Fig. 47-118A to C). The presence 

of hemosiderin can be detected on gradient echo and precontrast 

fat-suppressed T1-weighted images (Fig. 47-118D), 

and the vascularized proliferative synovium should exhibit 

some contrast enhancement (Fig. 47-118E). 

• Bone Tumors 28 

Osseous tumors are much less common than soft tissue 

tumors of the foot and ankle. Like all bone lesions, these 

tumors should be initially evaluated radiographically. MRI, 

however, is useful in localizing tumors and staging their 

extent. Because most tumors have nonspecific signal characteristics, 

MRI is often unable to render a specific preoperative 

diagnosis. 

Primary bone tumors of the feet are rare, accounting 

for only 4% of all bone tumors. 20 Benign bone neoplasms 

are more common than malignant ones, although in the 

foot, most bone neoplasms are primary tumors because 

metastases to the foot are rare. 

• Benign Tumors 

The most common benign tumors of the foot are enchondromas 

and osteoid osteomas. An osteoid osteoma is a relatively 

common cause of bone pain in adolescents and young 

adults, accounting for approximately 10% of all benign 

bone tumors. The classic history is pain at night, relieved by 

aspirin. Osteoid osteomas are one of the few tumors that 

are better imaged by CT than MRI. Thin-slice CT well demonstrates 

the lucent nidus as well as the tiny sclerotic component 

that is characteristically associated with it (Fig. 

47-119A). CT is also used by radiologists for the purpose of 

percutaneously ablating the nidus. On MRI, osteoid osteomas 

are seen as a nonspecific edema pattern emanating 

from a tiny, dark nidus (see Fig. 47-119B to D). 


9/9/2008 5:36:21 PM


A B C 

D 

E 

Figure 47-118. Giant cell tumor of the tendon sheath in a 19-year-old with a palpable medial mass. A, Straight axial T1-weighted image through 

the mass (arrow) demonstrates that it lies within the soft tissues medial to the navicular (N), talus (Ta), and sustentaculum tali (ST) but does not 

invade the bones. B, The corresponding axial proton-density–weighted image shows that the mass has grown through a split tendon sheath 

(arrowheads). The tendons themselves—posterior tibial (T), flexor digitorum longus (D), and flexor hallucis longus (H)—are intact and normal 

in appearance with no evidence of tumor involvement. C, The corresponding axial T2-weighted image shows that the mass (arrow) has 

heterogeneous signal intensity, consistent with the presence of blood products of varying ages. D, Corresponding axial precontrast fat-suppressed 

T1-weighted image reveals that some signal in the mass is brighter than the surrounding suppressed fat, consistent with methemoglobin. 

E, Corresponding axial post–intravenous gadolinium fat-suppressed T1-weighted image demonstrates heterogeneous enhancement, indicative of 

the vascularity of this synovial proliferation. 

Chondroblastomas are rare benign cartilaginous neoplasms, 

and one of the few tumors that arise from the 

epiphysis in a skeletally immature patient. Chondroblastomas 

can expand the cortex but should not cross the unfused 

growth plate (Fig. 47-120A). Radiographically, chondroblastomas 

can have either a lucent or chondroid matrix. By 

MRI, these lesions may exhibit considerable edema in the 

surrounding soft tissues, but the tumor itself should have 

a sharp, non–aggressive-appearing interface with the 

normal bone (see Fig. 47-120B to D). 

Intraosseous lipomas of the calcaneus are rare but have 

a characteristic radiographic appearance in that they are 

well circumscribed and nearly totally lucent except for a 

tiny central sclerotic focus (Fig. 47-121A). By MRI, the 

intraosseous lipoma is uniformly isointense to fat on all 

sequences, except for a signal void corresponding to the 

sclerotic focus (Fig. 47-121C and D). 

• Malignant Tumors 

The most common primary malignant tumor of the foot 

is chondrosarcoma, which has a propensity for the calcaneus 

(Fig. 47-122). High-grade chondrosarcomas have a 

calcified matrix that appears radiographically sclerotic (see 

Fig. 47-122A) and dark on T1- and T2-weighted sequences. 

Chondrosarcomas are not highly vascularized tumors and 


9/9/2008 5:36:23 PM


A B C 

T1 

T2fs 

D 

IR 

Figure 47-119. Osteoid osteoma in a 19-year-old with symptoms clinically thought to be due to a tibial stress fracture. A, Axial CT scan through the 

level of the syndesmosis. The nidus is the small lucent lesion (black circle). B, Axial T1-weighted image through same level as A. The low-intensity 

nidus (white circle) is masked by the surrounding marrow edema. C, Corresponding T2-weighted fat-suppressed image. The low-intensity nidus 

(white circle) is unmasked by the bright signal of the surrounding marrow edema. D, Sagittal inversion recovery (IR) image reveals bone marrow 

edema around the small nidus (white circle). 

A 

B 

Figure 47-120. Chondroblastoma in a 16-year-old. 

A, Lateral radiograph demonstrates an expansile mass 

arising from the back of the tibia. B, Midsagittal T1- 

weighted image shows that the mass is purely 

epiphyseal, deforming but not crossing the distal 

physis in this patient who is not yet skeletally mature. 

C, Corresponding sagittal T2-weighted image shows 

heterogeneous bright signal in the mass. There is also 

edema in the adjacent soft tissues (arrows), a common 

finding with chondroblastomas. D, Corresponding 

sagittal cartilage-sensitive sequence (fat-suppressed 

three-dimensional gradient echo) reveals signal 

intensity in this cartilaginous tumor that is nearly as 

bright as the nearby normal articular hyaline cartilage. 

C 

D 


9/9/2008 5:36:24 PM

A 

B 


Figure 47-121. Intraosseous lipoma discovered as 

an incidental finding in a 43-year-old. A, Lateral 

radiograph of the right calcaneus shows the lucent 

lesion in the anterior half with a well-circumscribed 

border (open arrowheads). Centrally, there is a small 

sclerotic focus (black arrowhead), characteristic of an 

intraosseous lipoma. B, Lateral radiograph of the 

contralateral left calcaneus is shown for comparison. 

A lipoma, intraosseous or otherwise, should 

be isointense to fat on all imaging sequences. C, 

Midsagittal T1-weighted image shows the signal 

intensity of the lipoma (open arrowheads) to be 

isointense to that of the surrounding fatty bone 

marrow. The central sclerotic focus (black arrowhead) 

is dark on all imaging sequences. D, On the 

corresponding T2-weighted fat-suppressed image, the 

fat in the lipoma suppresses to a degree similar to that 

of the surrounding fatty bone marrow so that it is 

nearly inconspicuous. 

C 

D 

A 

B 

Figure 47-122. Chondrosarcoma arising from the 

calcaneal tuberosity 30-year-old. A, Lateral 

radiograph. This patient complained of heel pain for 

10 months until the sclerosis in her calcaneus was 

recognized. B, Sagittal T1-weighted image shows 

diffusely decreased signal in the calcaneus 

corresponding to the radiographic sclerosis. C, Sagittal 

fat-suppressed T2-weighted image reveals marrow 

edema only at the periphery of the sclerotic region. 

There is, however, extensive bright signal in the soft 

tissues immediately plantar to the calcaneus, 

indicating that the tumor is extending out of the bone 

and into the soft tissues. D, Sagittal post–gadolinium 

contrast fat-suppressed T1-weighted image 

demonstrates enhancement only at the periphery of 

the osseous and soft tissue masses. This enhancement 

pattern is due to the relative hypovascularity of 

chondrosarcomas. 

C 

D 


9/9/2008 5:36:27 PM


hence demonstrate poor contrast enhancement as well as 

a poor response to chemotherapy. Contrast enhancement 

can be seen at the margins of the tumor where it is aggressively 

invading the bone and in the surrounding soft tissues 

(see Fig. 47-122D). Low-grade chondrosarcomas are difficult 

to distinguish from benign enchondromas for both 

radiologists and pathologists, and the clinical symptom 

of pain is often the deciding factor. Although many 

enchondromas are asymptomatic and may be discovered 

incidentally when imaging the foot for other reasons, all 

chondrosarcomas are painful. 

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