Natural progression of osteochondritis dissecans of the humeral capitelluminitial observations

PURPOSE: To determine the earliest findings, subsequent changes, and natura l course of osteochondritis dissecans of the humeral capitellum. MATERIALS AND METHODS: Among 95 patients with osteochondritis dissecans of the humeral capitellum, 16 (mean age, 12.5 years) were selected for this re trospective study because they seemed to have early osteochondritis disseca ns and had been followed up without any surgical treatment for 6 months or more (mean, 3.5 years). RESULTS: The initial imaging appearances of the 16 patients' lesions were d ivided into two types: localized subchondral bone flattening without fragme nts in seven, and nondisplaced fragments in nine. Patients with lesion flat tening had younger ages and significantly shorter durations of symptoms, an d most had open growth plates. In five of the seven with flattening, new bo ne formed over the flattened bone, and the fragments united after arm motio n reduction. In contrast, patients with nondisplaced fragments at clinical presentation had longer durations of symptoms with continued arm motion, an d their nondisplaced fragments failed to unite. CONCLUSION: The earliest feature of osteochondritis dissecans is subchondra l bone flattening, over which new bone subsequently forms. The new bone the n can unite with the underlying bone. However, if subjected to repetitive f orces over a given time, unstable fragments develop. These fragments, even if not yet displaced, are unable to unite.