Gluteus minimus-induced femoral head deformation in dysplasia of the hip

Lateral notching of the femoral head is considered pathognomonic for spasti c subluxation of the hip. Less frequently, flattening is seen with extrusio n of the femoral head in nonspastic hip dysplasia. The aim of this study wa s to throw light on its underlying pathomechanism. On the radiographs of 29 7 hips with developmental dysplasia, lateral flattening of the femoral head was seen in 18 hips (60/0), but notching was present in only 1, Of 7 dyspl asias due to cerebral palsy, 6 showed lateral notching. The gluteus minimus was felt to be responsible for the lateral femoral head changes as the mus cle counteracts lateral migration of the femoral head. Intraoperative disse ction of 3 hips supported this view 1 hip with developmental dysplasia and lateral notching was subjected to a periacetabular osteotomy. At surgery, t he tendon of the gluteus minimus was found to fit tightly into the notch. O f 2 hips with spastic dysplasia, 1 presented with and the other without lat eral notching, In the hip with lateral notching, the gluteus minimus had a normal appearance and it lay in the defect of the femoral head. In the hip without notching, the gluteus minimus was atrophied with signs of fatty deg eneration. We therefore believe that lateral notching is a sign of hyperton icity of the gluteus minimus muscle.