Multiple exostosis: a short study of abnormalities near the growth plate.

The pathogenesis of multiple exostosis has been controversial with many theories put forward including the structural/mechanical theory, which emphasizes that the osteochondroma arises in the displaced growth plate cartilage penetrating a defective periosteum. Recently, molecular genetics has offered the neoplastic model with tumor suppressor genes implicated in the development and pathogenesis of exostosis. In this study, we demonstrated the spectrum of histological abnormalities in the developing exostosis present on the surface of the bone at the physis. Seven skeletally immature patients with multiple exostoses were used in this study. The patients' families were advised of and consented to the proposed study. Coincident with removal of symptomatic exostoses that was adjacent to the physis, a thin strip of bone with overlying periosteum was removed to include the edge of the physis. This was followed by formalin fixation and routine paraffin embedding. We demonstrated the earliest lesion as a microchondroma within the periosteum adjacent to the normal physis (also called the 'groove of Ranvier'). More mature progressively larger lesions showing enchondral ossification were seen distally. The periosteum and the perichondrium were intact with normal physis. Our observations give support to the fact that precursor cells in the periosteum adjacent to the physis (also called the 'groove of Ranvier') gives rise to the chondrocytes that clonally expands and develops into exostosis.