Kijowski R et al. (2008) Juvenile versus adult osteochondritis dissecans of the knee: appropriate MR imaging criteria for instability. Radiology 248: 571–578

The juvenile and adult forms of osteochondritis dissecans (OCD) of the knee have distinct clinical courses and variable prognoses. The stability of OCD lesions, determined by MRI, is the most important factor for predicting healing after conservative surgery; however, a recent study by Kijowski and colleagues has shown that existing criteria for defining instability have a high specificity for adult, but not juvenile, OCD lesions (100% [95% CI 81–100%] vs 11% [95% CI 1–33%]; P <0.001).

Using arthroscopic findings as the reference standard, radiologists retrospectively analyzed MRI findings in 65 patients who were classified as having juvenile (n = 32) or adult (n = 33) OCD on the basis of skeletal maturity. The existing MRI criteria, namely the presence of a rim of high T2 signal intensity, surrounding cysts, a high T2 signal intensity cartilage fracture line and a fluid-filled osteochondral defect, were useful in distinguishing stable and unstable adult OCD lesions. By contrast, the secondary MRI findings of a rim of fluid signal intensity, multiple breaks in the subchondral bone plate and an outer rim of low T2 signal intensity were highly sensitive and specific for instability in juvenile OCD lesions with a high-intensity T2 signal rim.

The authors argue that controversy over the best method for assessing patients with OCD has arisen from a failure to distinguish between the juvenile and adult forms of the disease, and that revised criteria, selected on the basis of skeletal maturity, could improve the usefulness of MRI for assessing OCD lesions.