Multimorbidity measured with Charlson Comorbidity Index is not associated with clinically relevant risk of revision after primary total hip arthroplasty: a popula-tion-based cohort study on 98,647 patients from the Danish Hip Arthroplasty Register

Background and purpose - Evidence for guiding healthcare professionals on the risks of total hip arthroplasty (THA) in multimorbid patients is sparse. We aimed to examine the association between multimorbidity and the risk of revision due to any cause and specific causes after primary THA due to osteoarthritis. Patients and methods - We identified 98,647 THA patients and subsequent revisions in the Danish Hip Arthroplasty Register from 1995 to 2018. Multimorbidity was measured with the Charlson Comorbidity Index (CCI). Using the CCI (low, medium, high), we calculated the cumulative incidence function (CIF) of first revision up to 10 years after THA. Adjusted cause-specific hazard ratios (aHRs) were estimated using Cox regressions. All estimates are presented with 95% confidence intervals (CI). Results - Overall, the prevalence of patients with low, medium, and high CCI was 70%, 24%, and 6%. The CIF of any revision within 10 years was 6.5% (CI 6.2-6.7) in low and 6.5% (CI 5.8-7.3) in high CCI, with an aHR of 1.4 (CI 1.2-1.6) for patients with high compared with low CCI. The corresponding aHRs for cause-specific revision were 1.3 (CI 1.0-1.6) for aseptic loosening within 10 years, 1.2 (CI 0.9-1.6) for infection, and 1.7 (CI 1.3-2.2) for dislocation, both within 2 years. Conclusion - Multimorbidity is associated with a minor but not clinically relevant increased risk of revision up to 10 years after primary THA.