Objective: To explore the relation between hospital orthopaedic specialisation and postoperative outcomes after total hip or knee replacement surgery. Design: Retrospective analysis of US Medicare data, 2001-5. Setting: 3818 US hospitals carrying out total joint replacement. Population: 1 273 081 Medicare beneficiaries age 65 and older who underwent primary or revision hip or knee replacement. Main outcome measures: Hospitals were stratified into fifths on the basis of their degree of orthopaedic specialisation (lowest fifth, least specialised; highest fifth, most specialised). The primary outcome was defined as a composite representing the occurrence of one or more of pulmonary embolism, deep vein thrombosis, haemorrhage, infection, myocardial infarction, or death within 90 days of the index surgery. Results: As hospital orthopaedic specialisation increased from the lowest fifth to highest fifth, the proportion of people admitted who were women or black, or who had diabetes or heart failure progressively decreased (P<0.001), whereas procedural volume increased. Compared with the most specialised hospitals (highest fifth), after adjustment for patient characteristics and hospital volume, the odds of adverse outcomes increased progressively with decreased hospital specialisation: lowest fifth (odds ratio 1.59, 95% confidence interval 1.53 to 1.65), second fifth (1.32, 1.28 to 1.36), third fifth (1.24, 1.21 to 1.28), and fourth fifth (1.10, 1.07 to 1.13). Conclusions: Increased hospital orthopaedic specialisation is associated with improved patient outcomes after adjusting for both patient characteristics and hospital procedural volume. These results should be interpreted with caution because the possibility that other unmeasured confounders related to socioeconomic status or different factors are responsible for the improved patient outcomes rather than hospital specialisation can not be excluded. The findings suggest that hospital specialisation may capture different components of hospital quality than the components captured by hospital volume.
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