Multiple Hereditary Exostosis: New Orientations

Multiple Hereditary Exostosis (MHE) is an automosal dominant skeletal disorder that begins in childhood. Birth prevalence is estimated at 1/50,000. Three distinct genetic loci are known to cause MHE: one on chromosome 8, and two others on chromosomes 19 and 11. Mutations of the germ line in the EXT tumour suppressor gene family have been identified in MHE. The loci on chromosomes 8 and 11 have been associated with malignant transformation. Bony exostoses are benign osteocartilaginous growths that start close to growth plates, inducing metaphyseal remodeling, bony deformities, and asymmetric long bone growth. Frequent orthopaedic manifestations include short stature, limb-length discrepancy, femoroacetabular impingement, coxa valga with hip dysplasia, genu valgum, ankle valgus, and forearm deformities. The authors focused this study on points which do not make the unanimity in the literature: do surgical procedures alter or not the natural history of exostoses especially for forearm and ankle deformities, frequency and preventive attitude for spinal stenosis, risk of malignant change?Forearm deformities: Characteristic forearm deformities are present in 30-60% of patients with hereditary multiple exostoses. Characteristic forearm deformities include a shortened forearm bowing, an ulnar club hand, and sometimes a radial heas subluxation or dislocation. Patients often suffer for aesthetic reasons. There is no consensus regarding optimal therapy. Some authors recommend « aggressive » early operative surgery to prevent or reduce progression of deformity and functional impairment (or both). Correction of deformity and improvement of function are not necessarily associated. However, it emerges from recent studies that these surgical procedures, judged in a subjective and objective way, do not produce any predictable functional improvement. These studies showed that the gain obtained by surgery did not reach improvement especially for pronosupination but provide only cosmetic satisfaction. Deformations, from natural evolution of the MHE or from residual defects of surgical correction, are well tolerated in the adulthood. Ulna lengthening is currently very contrversial. Ankle deformities: They occur in about 50% of affected individuals. Relative shorthening of the fibula and obliquity of the distal tibial epiphysis result in valgus deformities of the ankle. Surgical procedures for correction include excision of exostosis, lengthening of the fibula, tibial osteotomy, and hemiepiphyseal stapling of the distal tibial physis. Prophylactic surgical procedures in children that are designed to improve alignment in the ankle may be justified because of the high rate of osteoarthritis in individuals with MHE. Spinal stenosis: Recent reports noted a high rate of intracanal exostoses in MHE patients (68%) with medullary compression in 27%. So, systematic spinal screening with clinical examination, magnetic resonance imaging or computed tomography is warranted in these children at the age of 10 to avoid a possible neurological complication. If surgeon decides not to remove an intracanal lesion, he must very regularly control the child with MRI. However, it seems logical to remove any exostose in contact with nervous elements, as the neurological recovery is always favorable and the risk of recurrence very low.Malignant changes: Information and education are essential. Malignant change in children is exceptional. Any modification of size or the appearance of a pain in the adulthood on a known exostose has to bring the patient to consult. Percentage of malignant change is probably about 2%. 80% of tumors develop on the axial skeleton. If some exostoses are clinically easy to detect, others as axial skeleton and pelvis are more difficult to detect. Bone scan and MRI can help in this supervision. Strong uptake at Technetium bone scan is highly suspect of malignant change. It does not seem possible to identify a risk group. The annual risk of malignant transformation being 0,1% between 30 and 50 years, it will be logical to propose a screnning for patients with MHE. Surgical prophylactic resection of the exostoses is not recommended. The rate of complications after exostose resection is about 13%.