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

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2222 VII Imaging of the Musculoskeletal System 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 Ch047-A05375.indd 2222 9/9/2008 5:33:47 PM
47 Ankle and Foot 2223 47 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. Ch047-A05375.indd 2223 9/9/2008 5:33:49 PM
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