Dual mobility cups do not reduce the revision risk for patients with acute femoral neck fracture: A matched cohort study from the Swedish Arthroplasty Register

Introduction: Dual mobility cups (DMC) are gaining in popularity, as a method to reduce the risk of dislocation after fracture-related hip arthroplasty. Our aim was to compare revision rate in general, as well as due to dislocation and infection, after DMC and conventional THA due to femoral neck fracture, for each of the two groups of lateral and posterior approach.

Materials and methods: This observational cohort study based on the Swedish Arthroplasty Register (SAR) compared 2242 patients with dual mobility cups (DMC) and 6726 with conventional total hip arthroplasty (cTHA), all due to acute fracture 2005-2019. This was after propensity score matching of 1:3 (age, gender, ASA). Kaplan-Meier survival analysis was used to investigate the 5-year revision rate after DMC and cTHA in the posterior and lateral approach groups.

Results: The rates of revision in general, and due to dislocation or infection, were similar for DMC and cTHA in the different approach groups during the follow-up. The cumulative revision rate after posterior approach was 4.7% (95% CI 3.1-6.2) for DMC and 4.8% (3.8-5.7) for cTHA at 5 years. For lateral approach, the result was 2.3% (CI 1.3-3.3) for DMC and 3.7% (CI 3.0-4.4) for cTHA. The 5-year results for cumulative revision rate due to dislocation after posterior approach were 1.3% (0.4-2.2) for DMC and 2.2% (1.5-2.8) for cTHA. Corresponding results for lateral approach was 0.4% (0-0.8) for DMC and 0.7% (0.4-1) for cTHA.

Discussion: With implant revision surgery as outcome, we could not detect any differences between DMC and cTHA. Further studies with high external validity are needed regarding total dislocation rate, patient-reported outcome, cost-effectiveness and learning curve, to make a definitive recommendation on the use of DMC for fracture cases.

Conclusions: As treatment of acute femoral neck fractures, total hip arthroplasty with a dual mobility cup have similar outcome in terms of revisions in general, and due to dislocation or infections specifically, as one with conventional bearing. The similar outcome is regardless of surgical approach.