A case of central migration of a prosthetic femoral head following bipolar hemiarthroplasty treated with conversion to total hip arthroplasty using an acetabular reinforcement ring.

INTRODUCTION: Central migration of the prosthetic femoral head occurs in approximately 7% of cases following bipolar hemiarthroplasty (BHA) for femoral neck fractures. If treated promptly, it can be managed by cup placement; however, if left unaddressed, a large acetabular bone defect can develop. Herein, we report a case of central migration with a severe bone defect after BHA, successfully treated with conversion to total hip arthroplasty (THA) using a Burch-Schneider cage. CASE REPORT: An 86-year-old man underwent BHA at a local hospital for a right femoral neck fracture in Year X-8. He experienced right hip pain in Year X-4. An X-ray examination in Year X-3 revealed mild central migration of the prosthesis. However, follow-up was discontinued afterward. In Year X, he visited the hospital with complaints of worsening right hip and abdominal pain. He was subsequently referred to our hospital for further examination and treatment. Based on clinical images, he was diagnosed with central migration of the prosthetic femoral head with a Type 3B acetabular defect in the Paprosky classification. A conversion THA with a reinforcement ring was planned. The surgery was performed using a supine anterolateral approach. A Burch-Schneider cage was placed to bridge the gap, and the defect was filled with bone cement. He commenced full weight bearing the day after surgery without experiencing any pain. He achieved independent ambulation with a cane 8 days after surgery and was discharged home. One year postoperatively, he had a favorable post-operative course without any complications. CONCLUSION: Central migration of the prosthesis inevitably occurs at a certain rate after surgery. In cases involving extensive bone defects, rigid acetabular reconstruction with implants is essential. However, the procedure is technically challenging and could pose a significant surgical burden to patients. Periodic imaging evaluations and timely interventions are essential for patients with BHA to avoid this condition.