There is general consensus that most, but not necessarily all osteochondral lesions of the ankle are a result of acute trauma, or microtrauma from residual instability. Osteochondral lesions of the talar dome are frequently observed in individuals who had prior ankle trauma and have persistent symptoms , and if left untreated can result in chronic disability of the athlete . There is a high association of osteochondral lesions with fracture of the lateral malleolus. In follow-up of 92 distal fibular fractures, 65 cases (70.7%) had osteochondral lesions of the talus at time of surgical repair . In a separate study of supination external rotation injuries, 19 of 50 fractures (38%) were found to have a lateral talar dome lesion .
Acute chondral or osteochondral fractures of the talar dome typically have a transverse oblique orientation, and are frequently associated with adjacent sites of marrow edema best seen in the coronal plane (see Fig. 1). Medial lesions frequently are convex or cup-shaped, whereas lateral lesions are generally smaller and thin. Location of the lesion reflects the mechanism of ankle injury . Regional differences in cartilage thickness and biomechanical properties may also impact the propensity for osteochondral injuries of the ankle to occur in specific sites . In the talus, osteochondral lesions most frequently occur in the anterolateral or posteromedial talar dome, although rare central dome lesions have been reported [132,133]. As with the knee, the pattern of marrow abnormality in subchondral bone of the tibial plafond and talar dome can suggest the mechanism of injury [134,135]. The posterior medial location is most common. During inversion injuries with plantar flexion, the posterior third of the medial talar dome impacts the tibia. Lesions of the anterolateral talar dome occur during inversion injuries with the foot in dorsiflexion, causing the fibula to strike against the anterior to middle third of the lateral talar dome. In evaluating the lateral talar dome on sagittal images, the normal groove of the posterior talofibular ligament must not be mistaken for a chondral defect  (Fig. 11). Fibrous or synovial bands abutting the anteromedial tibial plafond near the notch of Harty and synovial tissue along the posterior edge have been reported as potential mimics of tibial chondral lesions .
In the tibia, acute osteochondral lesions generally occur on the anterior and posterior margins of the tibial plafond. In the tibia, it is more common to identify marrow contusion than it is to find an osteochondral fracture . This is
Fig. 11. Pseudodefect of the talar dome: 52-year-old male with MRI evaluation for tear of the Achilles tendon. Sagittal 3.0 T fat-suppressed, PD-weighted FSE MRI demonstrates an osteochondral notch on the posterior margin of the lateral talar dome. The posterior talofibular ligament seen in cross-section (arrow) should not be mistaken for an osteochondral fracture.
likely a result of greater forces applied to the concave surface of the talus, as well as greater stiffness of tibial cartilage . Osteochondral lesions of the distal fibular have been reported as a source of chronic ankle instability in young athletes who have a history of multiple inversion injuries .
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