Teaching Case

Knee pain in a 12-year old girl.

Pain rapidly increasing in a 12 year old girl. Knee MRI performed after plain radiographs of the knee proved unremarkable.

Osteochondritis dissecans is a condition of the joints that appears to affect subchondral bone primarily, with secondary effects on articular cartilage (1). With progression, this pathology may present clinically with symptoms related to the integrity of the articular cartilage.   It is being seen with increased frequency in pediatric and young adult athletes and is thought to be, in part, owing to earlier and increasingly competitive sports participation.   The cause of both juvenile and adult osteochondritis dissecans remains unclear. This pathology may present clinically with symptoms related to the integrity of the articular cartilage. Early signs, associated with intact cartilage, may be related to a softening phenomenon and alteration in the mechanical properties of cartilage. Later stages, because of the lack of underlying support of the cartilage, can present with signs of articular cartilage separation, cartilage flaps, loose bodies, inflammatory synovitis, persistent or intermittent joint effusion, and, in severe cases, secondary joint degeneration.   Juvenile osteochondritis dissecans lesions are typically stable, and those with an intact articular surface have a potential to heal with nonoperative treatment through cessation of repetitive impact loading.   Magnetic resonance imaging may allow early prediction of lesion healing potential. The treatment of osteochondritis dissecans (OCD) in children and adolescents is determined by the stability of the lesion and the state of the overlying cartilage.   Selecting and recommending a surgical intervention require balancing application of nonsurgical interventions with assessment of the degree of articular cartilage stability and the potential for spontaneous recovery.   Some authors have suggested that a high signal line behind a fragment on the T2-weighted image indicates the presence of synovial fluid and is a sign of an unstable lesion (2,3), while more recent reports have suggested that this high signal line is due to the presence of vascular granulation tissue and may represent a healing reaction (4, 5). Others (6) have interpreted the high signal T2 line as a predictor of instability only when it was accompanied by a breach in the cartilage on the T1-weighted image, thus a high signal line behind the OCD fragment does not always indicate instability.