j SPECIAL FOCUS j Imaging of Talar Dome Chondral and Osteochondral Lesions James M. Linklater, MB, BS Castlereagh Sports Imaging North Sydney Orthopaedic and Sports Medicine Centre Crows Nest, New South Wales, Australia | ABSTRACT Talar dome chondral and osteochondral lesions are a com- mon cause of ankle pain and subjective instability. The goal of imaging these lesions is primarily their detection, demonstration of their position and extent, including sta- tus of the chondral surface, demonstration of any asso- ciated chondral delamination, assessment of the integrity of the subchondral plate, and assessment of the cancellous subchondral bone for bone marrow edema like signal, sclerosis, cystic change, and for the presence of an un- stable osteochondral fragment. Although plain radiogra- phy, computerized tomography, and bone scan may be helpful in the detection and characterization of these lesions, magnetic resonance imaging is the only imaging modality that will provide a comprehensive assessment of all these issues. Technical aspects of plain radiography, computerized tomography, and magnetic resonance ima- ging are discussed, and imaging findings are presented. Keywords: ankle, talar dome, chondral, osteochondral, MRI, CT, radiography | HISTORICAL PERSPECTIVE Chondral and osteochondral lesions in the ankle are a well-recognized cause of persistent ankle pain and sub- jective instability after ankle injury. 1Y4 Clinically, there may be an overlap between a posttraumatic ankle joint synovitis, posttraumatic chondral and osteochondral in- jury, and extraarticular pathologies. Berndt and Harty 5 introduced a plain radiographic classification of talar dome osteochondral lesions. In the 1970s and 1980s, bone scan became widely used in the workup of sus- pected talar dome lesions. In the late 1980s computerized tomographic assessment of talar dome lesion became widespread 6 and magnetic resonance imaging (MRI) began to be applied to the imaging of the ankle. The goal of imaging chondral and osteochondral le- sions in the ankle is primarily their detection, demonstra- tion of their position and extent, including status of the chondral surface, demonstration of any associated chondral delamination, assessment of the integrity of the subchondral plate, and assessment of the cancellous subchondral bone for bone marrow edema like signal, sclerosis, cystic change and for the presence of an un- stable osteochondral fragment. Although plain radiogra- phy, computerized tomography (CT), and bone scan may be helpful in the detection and characterization of these lesions, MRI is the only imaging modality that will pro- vide a comprehensive assessment of all these issues. | PLAIN RADIOGRAPHY Technical Aspects Radiographs should be performed weight bearing in order to provide a more relevant assessment of alignment. In addition, joint space loss may be more conspicuous or even only be present on weight bearing. A routine ankle series should include antero-posterior (AP), lateral, and mortise views. Computerized radiography (CR) and digi- tal radiography (DR) are gradually replacing film-screen radiography units. Computerized radiography and DR allow wider latitude in radiographic exposure, resulting in less repeat exposures and providing a better assessment of bone and soft tissues. Whereas previously it was com- mon to see overexposed radiographs in which the soft tis- sues are ‘‘blacked out,’’ with CR and DR, this should no longer be the case. Computerized radiography and DR also offer improvements in patient throughput, not achiev- able with film-screen systems. The digital image data from CR and DR is also readily transferred to picture archive and communication system. Diagnostic Features Plain radiography is of limited sensitivity in the dem- onstration of chondral and osteochondral pathology in the ankle. 7 In the setting of acute trauma, plain ra- diographs may demonstrate an acute osteochondral frac- ture (Fig. 1). In the chronic setting, central osteophyte Address correspondence and reprint request to James M. Linklater MB, BS, Castlereagh Sports Imaging, North Sydney Orthopaedic and Sports Medicine Centre, 286 Pacific Hwy, Crows Nest, New South Wales 2065, Australia. E-mail: linklj@bigpond.com. Techniques in Foot & Ankle Surgery 140 Techniques in Foot & Ankle Surgery 7(3):140–151, 2008 Ó 2008 Lippincott Williams & Wilkins, Philadelphia Copyright @ 2008 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.