Bipolar Hemiarthroplasty Does Not Result in a Higher Risk of Revision Compared with Total Hip Arthroplasty for Displaced Femoral Neck Fractures An Instrumental Variable Analysis of 36,118 Procedures from the Australian Orthopaedic Association National Joint Replacement Registry

Background: Previous randomized studies have suggested that there is no short-term difference between the risk of revision following total hip arthroplasty (THA) and hemiarthroplasty (HA) for hip fracture in elderly patients. The aim of the present study was to compare the long-term revision rates of primary THA and HA for femoral neck fracture in order to determine whether unipolar or bipolar HA increases the all-cause risk of revision in patients 50 to 79 years old. Methods: Data for 36,188 patients who underwent primary arthroplasty, including 13,035 unipolar and 8,220 bipolar HAs and 14,863 THAs, from September 1, 1999, to December 31, 2019, were obtained from the Australian Orthopaedic Association National Joint Replacement Registry. Unadjusted analyses were performed, as well as analyses adjusted for age, sex, femoral cement, and procedure year. The primary outcome was time to first revision for any cause. Secondary analyses were performed for the reason for revision (i.e., infection, dislocation, and periprosthetic fracture). Instrumental variable analysis of hospital preference (for either HA or THA) was performed in order to mitigate the effect of any unmeasured confounding. All analyses were restricted to hospitals performing at least 10 procedures in the prior year. Results: A total of 18,955 procedures were available for the comparison of modular unipolar HA to THA. Both the adjusted analysis performed with use of Cox proportional hazards (hazard ratio [HR], 1.94; 95% confidence interval [CI], 1.64 to 2.31; p < 0.001) and the instrumental variable analysis (HR, 2.82; 95% CI, 1.89 to 4.22; p < 0.001) demonstrated a higher risk of revision following modular unipolar HA compared with THA from 3 months postoperatively. A total of 13,168 procedures were available for the comparison of bipolar HA to THA. The adjusted analysis performed with use of Cox proportional hazards showed a significantly higher risk of revision for bipolar HA (HR, 1.29; 95% CI, 1.08 to 1.54; p = 0.01). The instrumental variable analysis showed a similar effect size that was not significant (HR, 1.27; 95% CI, 0.91 to 1.78; p = 0.16). Conclusions: Bipolar HA and THA demonstrated no significant difference in revision risk at long-term follow-up. Unipolar HA demonstrated higher risk of revision from 3 months postoperatively compared to THA. The higher risk of revision for dislocation observed following THA may be offset by the higher risk of revision for acetabular erosion or pain following bipolar HA, resulting in more equivalent revision risk.