title: Effect of Surgical Caseload on Revision Rate Following Total and Unicompartmental Knee Replacement.
abstract: BACKGROUND
  High-volume surgeons attain the best results following unicompartmental knee replacement (UKR), but the exact relationship between caseload and outcome is not clear. It is not known whether this effect is due to patient selection or surgical skill nor whether a similar effect is seen in total knee replacement (TKR). The aim of this study was to quantify the effect of surgical caseload on survival of both TKR and UKR.
  
  
  METHODS
  This study was based on 459,280 patient records (422,149 TKRs and 37,131 UKRs) from the National Joint Registry for England and Wales. The caseload-outcome relationship was characterized graphically and quantified using regression techniques. Patient selection was compared among high, medium, and low-volume surgeons. Prosthetic survival was compared between UKRs (performed by high, medium, and low-volume surgeons) and matched TKRs.
  
  
  RESULTS
  Caseload affected survival of TKR and, more strongly, of UKR. The revision rate following UKR dropped steeply until the volume reached ten cases per year, plateauing at thirty cases. For surgeons performing fewer than ten UKRs per year, the mean eight-year rate of survival of the UKRs was 87.9% (95% confidence interval [CI] = 86.9% to 88.8%) compared with 92.4% (95% CI = 90.9% to 93.6%) for those who performed thirty UKRs or more per year. Analysis of the TKRs showed a linear decrease in revision rate as caseload increased (hazard ratio [HR] for revision = 0.99 [95% CI = 0.98 to 0.99] for every five-case increase in caseload). Surgeons who performed a lower volume of UKRs tended to operate on younger and healthier patients and were more likely to perform revisions to treat loosening and pain. After matching of patients who had undergone UKR with those who had undergone TKR, the surgeons who performed a high volume of UKRs were found to have an eight-year revision/revision rate similar to that seen after TKR (HR for revision or reoperation = 1.10 [95% CI = 0.99 to 1.22] favoring TKR).
  
  
  CONCLUSIONS
  This study confirmed the importance of surgical caseload in determining the survival of UKR and, to a lesser extent, TKR. The reasons for this effect are complex and not fully explained by variables recorded in the National Joint Registry; however, the patient selection and revision threshold of lower-volume surgeons may be a factor. Examination of matched patients in this study demonstrated that high-volume surgeons can achieve revision/reoperation rates similar to those observed following TKR.
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology, and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, England. E-mail address for D.W. Murray: david.murray@ndorms.ox.ac.uk.
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Liddle
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology, and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, England. E-mail address for D.W. Murray: david.murray@ndorms.ox.ac.uk.
authors.forename: Hemant
authors.initials: H
authors.lastname: Pandit
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology, and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, England. E-mail address for D.W. Murray: david.murray@ndorms.ox.ac.uk.
authors.forename: Andrew
authors.initials: A
authors.lastname: Judge
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology, and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, England. E-mail address for D.W. Murray: david.murray@ndorms.ox.ac.uk.
authors.forename: David W
authors.initials: DW
authors.lastname: Murray
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000379:methods; D015331:Cohort Studies; D016001:Confidence Intervals; D004739:England; D005260:Female; D005500:Follow-Up Studies; D062785:Hemiarthroplasty / Q000009:adverse effects* / Q000379:methods; D006801:Humans; D015994:Incidence; D053208:Kaplan-Meier Estimate; D016014:Linear Models; D008297:Male; D016347:Medical Records Systems, Computerized; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery; D016016:Proportional Hazards Models; D011474:Prosthesis Design; D011475:Prosthesis Failure / Q000639:trends*; D012042:Registries; D012086:Reoperation / Q000706:statistics & numerical data; D016896:Treatment Outcome; D014852:Wales; D016526:Workload / Q000706:statistics & numerical data*