Intra-articular osteochondroma of the posterior cavity of the knee.

A patient with a large intra-articular osteochondroma of the posterior cavity of the knee joint is presented. Preoperative imaging included radiographs and magnetic resonance imaging, which revealed a completely intra-articular, locally expanding, mineralised mass in the intercondylar tunnel and posterior joint cavity. Flexion was limited to 70 deg. The osteochondroma was removed from a posterior approach. Gross and histologic pictures are presented, and the origin and pathogenesis of the tumour are discussed. After removal, the clinical course was benign. Full flexion was regained within 2 months. At the 2-year follow-up, no signs of recurrence were evident on radiographs and magnetic resonance imaging.