Hereditary multiple exostoses (HME) is characterized by growths of multiple exostoses, benign cartilage-capped bone tumors that grow outward from the metaphyses of long bones. Exostoses can be associated with a reduction in skeletal growth, bony deformity, restricted motion of joints, shortened stature, premature osteoarthrosis, and compression of peripheral nerves. The median age of diagnosis is three years; nearly all affected individuals are diagnosed by twelve years of age. The risk for malignant degeneration to osteochondrosarcoma increases with age, although the lifetime risk of malignant degeneration is low (~1%).
The clinical diagnosis of hereditary multiple exostoses is established in individuals with the following: * Multiple exostoses (cartilage-capped bony growths) arising from the area of the growth plate in the juxtaphyseal region of long bones or from the surface of flat bones such as the scapula. The key radiographic and anatomic feature of an exostosis is the uninterrupted flow of cortex and medullary bone from the host bone into the exostosis. Exostoses possess the equivalent of a growth plate that ossifies and closes with the onset of skeletal maturity Note: Approximately 70% of affected individuals have a clinically apparent exostosis about the knee, suggesting that radiographs of the knees to detect non-palpable exotoses may be a sensitive way to detect mildly affected individuals. * Family history consistent with autosomal dominant inheritance
Surgery is performed to address angular deformities; pain caused by irritation of skin, tendons, or nerves; and leg-length inequalities. Painful lesions in the absence of bone deformity are treated with surgical excision that includes the cartilage cap and overlying perichondrium to prevent recurrence; excision of exostoses may slow growth disturbance and improve cosmesis. Surgery for forearm deformity involves excision of the exostoses, corrective osteotomies, and ulnar-lengthening procedures; leg-length inequalities greater than one inch are treated with epiphyseodesis (growth plate arrest) of the longer leg or lengthening of the involved leg. Early treatment of ankle deformity may prevent or decrease later deterioration of function. Sarcomatous degeneration is treated by surgical resection.