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

BACKGROUND: 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. METHODS: We conducted a population-based cohort study using data from the Danish Hip Arthroplasty Register and the Danish National Patient Register. 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 5-year follow-up period. We used 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. RESULTS: 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. CONCLUSIONS: 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.