Idiopathic protrusio acetabuli in juveniles.

Eight children, aged 9 to 15, referred to a juvenile rheumatology service on account of undiagnosed hip pain, were ultimately found to have idiopathic protrusio acetabuli (IPA). Clinical and radiographic findings were generally asymmetrical on presentation. Subsequent radiographs tended to lag behind a rapid deterioration in six patients, four of whom required bilateral total hip replacement during adolescence. Pain on full flexion and moderate adductor spasm in the contra-lateral hip proved a useful early sign for predicting bilateral disease. Six of eight patients were hypermobile. In three of five families investigated, symptom-free IPA was revealed in one or more first degree relatives. Histology early in the course in two cases showed a non-diagnostic inflammatory reaction in the sub-synovium.