REASSESSMENT OF THE MR CRITERIA FOR STABILITY OF OSTEOCHONDRITIS-DISSECANS IN THE KNEE AND ANKLE

Objective. T2-weighted MR images has been reported to be an accurate m ethod for assessing osteochondritis dissecans. We reviewed our MR expe rience to confirm the accuracy of the published criteria of instabilit y. We also assessed the value of each of four MR signs of instability. Design. We reviewed the original MR interpretations, arthroscopic rep orts, and MR examinations of 40 patients with osteochondritis dissecan s of the talar dome or femoral condyles. Arthroscopy was used as the g old standard for stability. The MR examinations were reviewed retrospe ctively for a high-signal-intensity line or cystic area beneath the le sion, a high-signal-intensity line through the articular cartilage, or a focal articular defect. Patients. All patients who had undergone MR imaging for osteochondritis dissecans from 1990 to 1993 were reviewed . Forty patients were identified who had arthroscopy after the MR exam ination. There were 30 male and 10 female patients with an average age of 25.7 years. Thirty-one lesions were in a femoral condyle and nine were in the talar dome. Results and conclusions. The original MR inter pretations correctly identified 35 of the 36 unstable lesions and all 4 stable lesions, giving a sensitivity of 0.97 and specificity of 1.0. There was a 98% agreement between the original and retrospective diag noses. A high-signal-intensity line was seen beneath 72% of the 36 uns table lesions. The other three signs were noted in 22-31% of the unsta ble lesions. Fifty-six percent of the unstable lesions showed only one sign of instability MR imaging is a highly sensitive method for detec tion of unstable osteochondritis dissecans. The presence of any one si gn indicates instability, the most frequent sign being an underlying h igh-signal-intensity line. Because we examined only four stable lesion s, our 95% confidence interval of 0.40-1.0 for a specificity of 1.0 gi ves only a limited estimate of the specificity of MR.