Osteochondritis dissecans (OCD) is an acquired, potentially reversible idiopathic lesion of subchondral bone resulting in delamination and sequestration with or without articular cartilage involvement and instability. While there is a typical location (medial femoral condyle) and thickness, these do not appear to be predictive of healing. A fluid signal on MRI behind the lesion indicates that the fragment is unstable and is less likely to heal according to DeSmet et al. The correct answer comes from a 12-patient study where Paletta et al reviewed quantitative bone scans to find that 100% of patients with open femoral physes that had activity behind the lesions went on to heal but none of in adolescents with closing physes.
Paletta GA Jr, Bednarz PA, Stanitski CL, Sandman GA, Stanitski DF, Kottamasu S. The prognostic value of quantitative bone scan in knee osteochondritis dissecans: a preliminary experience. Am J Sports Med. 1998;26:7–14.
PMID:9474395 (Link to Abstract)
De Smet AA, Ilahi OA, Graf BK. Untreated osteochondritis dissecans of the femoral condyles: prediction of patient outcome using radiographic and MR findings. Skeletal Radiol. 1997;26:463–467.
PMID:9297750 (Link to Abstract)
Flynn JM, Kocher MS, Ganley TJ. Osteochondritis dissecans of the knee. J Pediatr Orthop 2004 24:434-443.
PMID:15205627 (Link to Abstract)