Unipolar hemiarthroplasty versus bipolar hemiarthroplasty in patients with displaced femoral neck fractures. A four-year follow-up of a randomised controlled trial

Purpose The treatment of choice for a displaced femoral neck fracture in the most elderly patients is a cemented hemiarthroplasty (HA). The optimal design, unipolar or bipolar head, remains unclear. The possible advantages of a bipolar HA are a better range of motion and less acetabular wear. The aim of this study was to evaluate hip function, health related quality of life (HRQoL), surgical outcome and acetabular erosion in a medium-term follow-up. Methods One hundred and twenty patients aged 80 or more with a displaced fracture of the femoral neck (Garden III and IV) were randomised to treatment with a cemented Exeter HA using a unipolar or a bipolar head. All patients were able to walk independently, with or without aids, before surgery. Follow-ups were performed at four, 12, 24 and 48 months postoperatively. Assessments included HRQoL (EQ-5D index score), hip function (Harris hip score [HHS]) and radiological acetabular erosion. Results The mean EQ-5D index score was generally higher among the patients with bipolar hemiarthroplasties at the follow-ups with a significant difference at 48 months: unipolar HAs 0.59 and bipolar HAs 0.70 (p = 0.04). There was an increased rate of acetabular erosion among the patients with unipolar hemiarthroplasties at the early follow-ups with a significant difference at 12 months (unipolar HAs 20 % and bipolar HAs 5 %, p = 0.03). At the later follow-ups the incidence of acetabular erosion accelerated in the bipolar group, and there were no significant differences between the groups at the 24- and 48-month follow-ups. There was no difference in HHS or reoperation rate between the groups at any of the follow-ups. Conclusions The bipolar HAs seem to result in better HRQoL beyond the first two years after surgery compared to unipolar HAs. Bipolar HAs displayed a later onset of acetabular erosion compared to unipolar HAs.