Effect of Oral Direct Factor Xa Inhibitors on the Prevalence of Hip Heterotopic Ossification following Arthroplasty for Acute Femoral Neck Fracture: A Propensity Score-Matched Cohort Study.

Background: Heterotopic ossification (HO) is a common complication following hip arthroplasty that can limit hip range of motion (ROM). Oral direct factor Xa (FXa) inhibitors are commonly used anticoagulants after arthroplasty; however, they have a high risk of local bleeding and hematoma formation, which are significant triggers for HO formation. To our knowledge, there is no evidence regarding whether FXa inhibitors will increase HO incidence following hip arthroplasty.

Methods: This retrospective, observational, propensity-score-matched (PSM) cohort study was conducted from January 1, 2019, to November 30, 2023. A total of 944 patients who underwent hip arthroplasty following an acute femoral neck fracture were included. The present study excluded patients who had a central nervous system injury, spinal cord injury, burns, or destructive injury; those who had multi-part injuries or fractures; those who had postoperative complications such as surgical field infection and dislocation; those who had a history of hip surgery or trauma (including old femoral neck fractures); and those who refused to participate in the study or had been lost to follow-up. Following 1:1 propensity score matching based on sex, age, body mass index (BMI), injury side, nonsteroidal anti-inflammatory drugs (NSAIDs) use, tranexamic acid (TXA) use, surgical duration, and blood loss during surgery, the FXa inhibitors group and the no-FXa inhibitors group each consisted of 367 patients. All patients underwent hip arthroplasty within 48 hours after injury and received low-molecular-weight heparin (LMWH) before arthroplasty, but no other anticoagulants. All patients received a similar rehabilitation protocol postoperatively.

Results: In the PSM population, the incidence of HO was 28.8% in the FXa inhibitors group and 15.5% in the no-FXa inhibitors group (7.6 and 2.4% for clinically important HO, respectively). Logistic regression analyses revealed that FXa inhibitor usage was significantly associated with a higher rate of HO (odds ratio [OR], 2.21; 95% confidence interval [CI], 1.54 to 3.19; P < 0.001) compared to no usage. Additionally, FXa inhibitors were also linked to an increased risk of clinically significant HO (OR, 3.29; 95% CI, 1.59 to 7.48; P = 0.002). None of the baseline covariates demonstrated a significant influence on the association between FXa inhibitor use and HO incidence (P > 0.05 for all). Sensitivity analyses further corroborated these results.

Conclusions: Direct factor Xa inhibitor use may be a new risk factor for HO development following hip arthroplasty for acute femoral neck fracture.