Regional variation in incidence of primary total hip arthroplasties and revisions in Denmark, 1996-2002

Background We examined incidence rates (IR) of total hip arthroplasty (THA) in Denmark according to county and type of hospital, and investigated possible factors associated with any variations. Methods Through the Danish Hip Arthroplasty Registry, we identified all cases of primary THAs (n = 37,144) and revisions (n = 6,446) between 1996 and 2002. Unadjusted and age- and gender-standardized, hospital type- and county-specific IRs were calculated. Using multiple regression analysis, we examined possible factors associated with the variations. Results Over the study period, age- and sex-standardized IRs of primary THAs for university and other hospitals increased by 10% and 40%, respectively. IRs of revisions increased for other hospitals by 33%, but decreased for university hospitals by 30%. Unadjusted IRs varied among counties (n = 15), which remained despite age- and gender-standardization. The IR ratio was 1.4 (95% Cl: 1.3-1.6) when comparing the counties with the highest and lowest IRs. No association was found between IRs of THA and the number of orthopedic surgeons per 100,000 inhabitants, proportion of patients with primary arthrosis, preoperative Harris Hip Score, hospital costs, the counties' Gross Domestic Product, or population density. Interpretation Substantial regional differences in the IRs of THA procedures were found. We found no associations between IRs and a range of patient- and healthcare system-related factors.