Satisfactory results have been reported from long-term studies on bipolar hemiarthroplasty for femoral neck fracture. However, long-term results of this procedure for osteoarthritis of the hip (OA) and idiopathic necrosis of the femoral head (ION) have given rise to pessimism. These poor results have often reported migration of the bipolar head, but few had described the direction of this migration. The purpose of the present study was to conduct a long-term follow-up analysis of bipolar hemiarthroplasty for OA and ION, including the direction of migration.
We retrospectively reviewed a consecutive series of 64 patients (76 hips) who underwent primary bipolar hemiarthroplasty for symptomatic OA and ION with a cementless femoral component between 1976 and 1995. Of these 64 patients, 35 patients (40 hips) were available for clinical and radiographic review at a minimum follow-up duration of 10 years.
The Japanese Orthopaedic Association score significantly improved and pain relief was high following surgery; however, preservation of acetabular bone stock could not be achieved because of migration. The survival rate declined 10 years after surgery. Superomedial migration was found to be a risk factor for revision, and one factor affecting superomedial migration was the postoperative center edge angle.
The long-term results of bipolar hemiarthroplasty for OA and ION are not favorable. If a sufficient centripetal position is obtained with reaming, the bipolar head tends to migrate superomedially, subsequently requiring revision.