Long-Term Dislocation Risk Following Primary Total Hip Arthroplasty Due to Osteoarthritis: A Population-Based Cohort Study from the Danish Hip Arthroplasty Register.

Abstract

Population-based data on long-term dislocation risks are currently lacking in literature. Thus, the purpose of this study was to investigate the long-term cumulative incidence of dislocation after total hip arthroplasty (THA) stratified by femoral head size. Furthermore, we investigated the difference in cumulative incidence of dislocation over different time periods. We conducted a population-based cohort study utilizing data from the Danish Hip Arthroplasty Register (DHR) and the Danish National Patient Register (DNPR). The cohort comprised 56,515 THAs. The study included patients who had a primary THA due to primary osteoarthritis, performed in Denmark from 2000 to 2016. Follow-up was extended until death, implant removal, or December 31, 2021, to ensure a potential minimum five-year follow-up period. We utilized a recently validated algorithm to include dislocations that were treated with closed reduction without revision. Cumulative incidence of dislocation was estimated using the Aalen-Johansen estimator with death and implant removal as competing risks. Cumulative incidence of dislocation was stratified by femoral head size and the three time periods: 2000 to 2004, 2005 to 2009, and 2010 to 2016. The 10-year cumulative incidence of dislocation was 8.8% (95% confidence interval (CI), 8.4 to 9.3) for 28-mm femoral heads, 7.4% (95% CI, 7.0 to 7.9) for 32-mm, and 5.7% (95% CI, 5.4 to 6.0) for 36-mm. Changes over time showed an increase in dislocations for 28- and 32-mm femoral heads, whereas no difference was found for the 36-mm group. We found that the cumulative incidence of dislocation continued to increase after surgery. It varied from 5.7 to 8.8% after 10 years. The larger femoral heads were associated with lower dislocation rates. Furthermore, we found that 28- and 32-mm femoral heads were associated with a higher cumulative incidence of dislocation in patients who were operated on in more recent years.