Imaging of acute and chronic osteochondral lesions of the talar dome

Acute fractures involving the articular surface of the talus run parallel t o the surface and are confined to the cartilage and/or the immediate subcho ndral cancellous bone. Subchondral microfractures ("bone bruises"), osteoch ondral fractures and solely chondral fractures are different manifestations of impaction injuries that affect the articular surface. This article reviews the radiologic appearance of acute osteochondral lesio ns of the talus and comments on the role of the noninvasive imaging modalit ies. Conventional radiography and MRI provide the most relevant information and are widely discussed. A MRI classification is presented emphasizing th e distinction between lesions with intact and disrupted cartilage. Osteochondrosis dissecans (OCD) is a chronic osteochondral lesion. It is di agnosed in most cases by conventional radiography. MRI has become a decisiv e tool in staging the lesions. Intact cartilage and contrast enhancement of the lesions are findings of MRI stage I. Cartilage defects with or without incomplete separation of the fragment, fluid around an undetached fragment , cysts larger than 5 mm in diameter and a dislodged fragment are MRI findi ngs observed in stage II and operative treatment has to be considered.