Revision rates of one new and two established hemiarthroplasty heads: a comparative cohort study from the Swedish Arthroplasty Register.

Introduction: The anatomical Lubinus SPII-stem is commonly used in hemi-arthroplasty for femoral neck fractures (FNF), combined with either the bipolar Variocup, the Unipolar Head (UH) and a newly introduced unipolar Modular Trauma Head (MTH). Similar constructs like the MTH are reported to have risk of corrosion and wear. This is the first publication evaluating the MTH.

Aim: To describe the revision rate of the SPII-stems/heads which were divided into 3 groups (Variocup, UH, MTH). The head types are compared by their rate of revision at 2 years, due to any cause and to dislocation. Revision and mortality rates up to 10 years are reported.

Methods: This observational cohort study based on prospectively registered data from the Swedish Arthroplasty Register included 33,059 patients with hemiarthroplasty 2005-2021 due to FNF. SPII-stems combined with Variocup (n = 7,281), UH (n = 23,980), MTH (n = 1,798) were included. The follow-up ended at 10 years for Variocup and UH, for MTH at 2 years. Kaplan-Meier survival analyses was used, with a 95% confidence interval (CI). Patients were censored at death or at the end of the study (31 December 2021).

Results: The 2-year revision rate regardless of cause was similar between the groups: after Variocup 3.5% (CI, 3.1-4.0), UH 3.1% (CI, 2.9-3.4), MTH 3.5% (CI, 2.6-4.5).At 10 years, the Variocup and UH had similar revision rates; 4.6% (CI, 4.0-5.2) and 5.0% (CI, 4.4-5.6).For revision due to dislocation at 2 years Variocup 2.3% (CI, 1.9-2.7) had an inferior outcome compared to UH 1.5% (CI, 1.3-1.7). The MTH had an intermediate outcome, 1.7% (CI, 1.0-2.3). Variocup had a higher dislocation related revision rate, until the 10th year.The 2-year-mortality was 36% (CI, 35-37) after Variocup, 43% (CI, 42-43) after UH and 44% (CI, 41-47) after MTH.

Conclusions: The hemi-heads have comparable revision rates within 2 and 10 years. The new MTH performs similar to the standard UH. The bipolar Variocup is associated with more revisions due to dislocation.