Revision Risk After Unipolar or Bipolar Hemiarthroplasty for Femoral Neck Fractures

Abstract

Background: There remains much international practice variation regarding the choice of a unipolar or bipolar prosthesis design for displaced femoral neck fractures that are treated with hemiarthroplasty. The purpose of the present study was to compare revision rates following primary hemiarthroplasty for femoral neck fracture to determine if the unipolar hemiarthroplasty design increases the risk of revision arthroplasty for all causes. Methods: Instrumental variable analysis was performed with use of data that had been entered into the Australian Orthopaedic Association National Joint Replacement Registry from September 1, 1999, to December 31, 2018. Sixty-two thousand, eight hundred and seventy-five patients with femoral neck fractures that were treated with primary modular unipolar or bipolar hemiarthroplasty procedure were analyzed. Hospital preference for prosthesis design in the 12 months prior to the index procedure was used as an instrument to adjust for unmeasured confounding. The primary outcome was time to first revision for any cause. Secondary analyses were performed on the reason for revision (infection, dislocation, periprosthetic fracture, or acetabular erosion), the use of cement femoral stem fixation, and the type of stem (polished or matte). Results: Modular unipolar hemiarthroplasty was associated with a higher rate of revision at >2.5 years (hazard ratio [HR], 1.86; 95% confidence interval [CI], 1.46 to 2.36; p < 0.001), but there was no difference between the groups before 2.5 years (HR, 0.98; 95% CI, 0.85 to 1.13; p = 0.79). Protective factors for revision included female sex (HR, 0.82; 95% CI, 0.74 to 0.9), use of cemented fixation (HR, 0.69; 95% CI, 0.62 to 0.77), and surgery performed in a public hospital setting (HR 0.79; 95% CI, 0.70 to 0.89). Modular unipolar prostheses had a greater risk of revision for acetabular erosion, particularly in later time periods (HR at ≥5.5 years, 5.10; 95% CI, 2.40 to 10.83; p < 0.001), while being protective against periprosthetic fractures (HR, 0.72; 95% CI, 0.59 to 0.87; p < 0.001) at all time points. There was no difference in terms of the risk of revision for infection, dislocation, or stem type. Conclusions: Bipolar hemiarthroplasty designs resulted in a lower risk of revision than unipolar designs. Unipolar hemiarthroplasties are justified for patients with femoral neck fracture and a shorter life expectancy (≤2.5 years). Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Risk of Aseptic Revision and Periprosthetic Fracture Following Bipolar Versus Unipolar Hemiarthroplasty

“…With regard to revision for periprosthetic fracture, no difference in risk was observed between the 2 devices. The rate of subsequent aseptic revision observed in this study (2.8%) is similar to the rate of 2.6% reported previously by investigators using the AOANJRR 10 . Even among the youngest individuals in this study (age 60 to 69 years at the time of hemiarthroplasty), the rate of aseptic revision was just 4.5% at 5 years postoperatively.…”

Bipolar Hemiarthroplasty Does Not Result in a Higher Risk of Revision Compared with Total Hip Arthroplasty for Displaced Femoral Neck Fractures

“…As the number of studies with adequate allocation concealment and randomization methods has increased, the evidence supporting the use of THA over HA has diminished, indicating an equivalent risk of revision up to 5 years without a higher risk of dislocation or periprosthetic fracture. Of the 16 trials included in the most recent systematic review 11 , only half included bipolar HA as the comparator against THA, the rest instead pooled unipolar and bipolar HA in the comparator despite differences in the rates of revision between these common types of HA 17 . To our knowledge, only 1 systematic review has compared bipolar HA to THA 23 , finding a lower overall risk of reoperation but a higher risk of dislocation for THA compared with bipolar HA.…”

“…However, the majority of these studies have been limited to ≤2 years of follow-up, with only a small cohort of patients from clinical trials receiving follow-up of >5 years with high levels of loss to follow-up 12-16 . Recently, we demonstrated a higher risk of revision for unipolar compared with bipolar HA at 2.5 years postoperatively, as a result of a higher incidence of acetabular erosion 17 . Previous meta-analyses have combined both unipolar and bipolar HA designs, potentially biasing results in favor of THA.…”

Is the Revision Rate for Femoral Neck Fracture Lower for Total Hip Arthroplasty Than for Hemiarthroplasty?

“…Both unipolar and bipolar HA procedures were included since the use of both prosthesis types is common in Australia, and there is controversy as to differences in outcomes 71 . Conducted studies have also not limited inclusion to cemented femoral stems as our study did 72 . Many Australian hospitals also do not allow for a decision option for HA 72 , on the basis of the increased cost of bipolar HA and the short life expectancy of many patients selected for HA 71 .…”