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

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2210 VII Imaging of the Musculoskeletal System 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). Ch047-A05375.indd 2210 9/9/2008 5:33:19 PM
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 Ch047-A05375.indd 2211 9/9/2008 5:33:23 PM
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