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

47 Ankle and Foot 2211 47
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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