The patient's age and activity in high-performance sports point to the possibility of an osteochondral defect (OCD). The plain x-ray shows a narrow, well-calcified lesion off the femoral condyle, which could support this diagnosis (Figure 1). The intraoperative photo confirms the diagnosis (Figure 2).
OCD is characterized by the separation of an area of subchondral bone. This may result in the formation of cracks in the overlying articular cartilage; the damaged cartilage may then separate from the surrounding cartilage, followed by separation of the osteochondral fragment from the epiphysis. Although "osteochondritis" implies inflammation, the lack of inflammatory cells in histological examination suggests a noninflammatory cause. The pathophysiology of OCD is not yet clear, as both trauma and ischemia have been thought to be involved. If separation of an osteochondral fragment from the articular surface occurs, this fragment can be present in situ, partially detached, or entirely detached. A completely detached fragment becomes a loose body. Injury to the articular cartilage allows an influx of synovial fluid into the epiphysis, creating a subchondral cyst.
In humans, OCD is a rare disease, occurring in 15-30 per 100,000 persons in the general population each year. OCD tends to affect young patients, with an average age at presentation of 10-20 years (but it may occur in persons of any age). It is more common in the male population, with a male-to-female ratio of 2:1.[2,3,4] Other studies quote a male-to-female ratio of 5:3. The number of reported cases has increased along with an increasing level of participation in competitive sports among both boys and girls. Two forms are recognized: a juvenile form, which appears before closure of the physes, and an adult form.
High-impact sports, such as gymnastics, soccer, basketball, lacrosse, football, tennis, and baseball, have been associated with a higher risk for OCD in stressed joints.[5,6] Other factors, such as rapid growth during puberty, deficiencies and imbalances in the ratio of calcium to phosphorus, and anomalies of bone formation, have been suggested to have a role in the development of OCD, but clear evidence is lacking.[7,8,9] Some case reports have suggested a genetic predisposition.[8,10,11]
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