Failure of bipolar hemiarthroplasty: a retrospective review of 31 consecutive bipolar prostheses converted to total hip arthroplasty.

Bipolar hemiarthroplasty has been widely used for the treatment of femoral neck fractures in elderly patients. Outcome studies show excellent results with near preoperative ambulation and lasting, painless hip function. However, what has only recently been considered is that, in some cases, failure of bipolar hemiarthroplasty may be due to wear of the thin, ultra-high-molecular weight polyethylene (UHMWPE) insert between the inner and outer bearings of the prosthesis with subsequent generation of particulate debris, periprosthetic osteolysis, and stem loos ening. We reviewed 31 consecutive bipolar hemiarthroplasties converted to total hip arthroplasties by a single surgeon between 1986 and 1994. The average time to failure was 38 months. Fifty-six percent of the cases showed radiographic evidence of osteolysis around the stem. Radiographic migration of the bipolar head of more than 1 mm into the pelvis, suggestive of cartilage wear, occurred in 67% of the cases. Among the patients with radiographic osteolysis and a loose stem at the time of revision, 92% showed a characteristic histiocytic and giant cell reaction to polyethylene particles in tissue obtained during surgery. The UHMWPE liners from the retrieved outer shells showed an average wear rate of 0.7 mm per year. Recent studies comparing bipolar to unipolar hemiarthroplasty show little difference between the two with regard to morbidity, mortality, or functional outcome. In light of our findings, it might be prudent to reconsider the design and indications for bipolar hemiarthroplasty.