Osteochondritis dissecans of the talus and knee: prospective comparison of MR and arthroscopic classifications.

The primary objective of this study was to determine if magnetic resonance (MR) could accurately predict the arthroscopic stage of osteochondritis dissecans lesions of the knee and ankle. Twelve patients, who were indicated for arthroscopy on either clinical or radiographic findings, underwent an MR examination prior to arthroscopy. All scans were performed on a 0.35 T magnet using the same spin echo sequence: repetition time 1,000 ms and echo time 40 ms. Magnetic resonance scans were interpreted prospectively (D.W.N.) and retrospectively (J.S.) by the radiologists without knowledge of the arthroscopic findings. Both radiologists predicted the exact grade in 11 of 12 patients. A single Grade 2 lesion was called Grade 3 by both radiologists. An MR staging classification has been developed that allows accurate preoperative staging of osteochondritis dissecans lesions of the talus and knee.