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Importance: Little is known about variation in outcomes of surgery, nor about factors that can explain why such variation exists. Objectives: To describe variation in patient outcomes and costs for primary hip and knee replacement across health areas and to identify whether patient, surgical and hospital factors can explain such variation. Design: Retrospective observational cohort study Setting: National Joint Registry, linked to English Hospital Episode Statistics and Patient Reported Outcome Measures datasets Participants: Patients undergoing primary total hip/knee replacement aged ≥18 from 2014 to 2016 Exposures: Patient (age, gender, body mass index, deprivation); surgical (surgeon volume, surgeon grade); hospital organisation (operating theatres, specialist consultants, hospital volume) Main outcome measures: Multilevel regression models were generated for the outcomes: length of stay, bed-day costs, change in Oxford hip/knee scores 6-months after surgery, complications by 6 months. Geographical Information Systems were used to display maps describing adjusted estimates of variation in outcomes across health areas. Results: 173,107 primary total hip replacements and 210,275 total knee replacements were available, nested in 207 health areas. We identified a number of factors that predicted poorer outcomes of surgery: Public hospitals, low volume of surgeries per surgeon and hospital and workforce with a high number of less experienced doctors were associated with poorer outcomes of surgery. Although these factors did not attenuate the magnitude of variation across health areas, they had ecological correlations with the observed geographical variations in outcomes of surgery by health area. Across health areas, predicted mean length of stay ranged from 3 to 7 days and associated bed-day costs from £4727 to £8800, for both total hip and knee replacement. The absolute predicted mean change in Oxford hip score varied from 18.7 to 24.6 points (13.1 to 18.8 for Oxford knee score). Predicted 6-month complications ranged from 3% to 6%, for both total hip and knee replacement. Conclusions and Relevance: Our models indicate that a minimum surgical volume by surgeon and by hospital; and private hospitals are associated with better outcomes of surgery, while a higher proportion of less experienced doctors by hospital might compromise achieving those outcomes. This variation is observed geographically.


Journal article


JAMA Network Open


JAMA Network

Publication Date



Economic Evaluations, Epidemiology, Health services research, Orthopaedic Surgery, Outcomes research