title: The association between body mass index and the outcomes of total knee arthroplasty.
abstract: BACKGROUND
  In the United Kingdom, organizations involved in health-care commissioning have recently introduced legislation limiting access to total knee arthroplasty through the introduction of arbitrary thresholds unsupported by the literature and based on body mass index. This study aimed to establish the relationship between body mass index and patient-reported specific and general outcomes on total knee arthroplasty.
  
  
  METHODS
  Using national patient-reported outcome measures (PROMs) linked to the National Joint Registry, we identified 13,673 primary total knee arthroplasties performed for the treatment of osteoarthritis. The PROMs project involves the collection of condition-specific and general health outcomes before and at six months following total knee arthroplasty. The relationships between body mass index and the Oxford Knee Score, EuroQol 5D index, and EuroQol 5D Visual Analogue Scale were assessed with use of scatterplots and linear regression. The improvement in these measures was compared for three distinct groups based on body mass index (Group I [15 to 24.9 kg/m(2)], Group II [25 to 39.9 kg/m(2)], and Group III [40 to 60 kg/m(2)]) with use of multiple regression analysis to adjust for differences in age, sex, American Society of Anesthesiologists grade, general health rating, and number of comorbidities.
  
  
  RESULTS
  The preoperative and postoperative patient-reported outcome measures declined to a similar extent with increasing body mass index. The gradient of the linear regression equation relating to the change in scores was positive in all cases, indicating that there was a tendency for scores to improve to a greater extent as body mass index increased. After adjustment, the changes in patient-reported outcome measures in Group I and Group III were equivalent for the Oxford Knee Score (mean difference, 0.5 point [95% confidence interval, -0.5 to 1.5 points]; p = 0.78), the EuroQol 5D index (mean difference, 0.014 point [95% confidence interval, -0.021 to 0.048 point]; p = 1.00), and the EuroQol 5D Visual Analogue Scale (mean difference, 1.9 points [95% confidence interval, -0.4 to 4.1 points]; p = 0.13). Wound complications were significantly higher (p < 0.001) at a rate of 17% (168 of 1018 patients) in Group III compared with 9% (121 of 1292 patients) in Group I.
  
  
  CONCLUSIONS
  The improvements in patient-reported outcome measures experienced by patients were similar, irrespective of body mass index. Health policy should be based on the overall improvements in function and general health gained through surgery. Obese patients should not be excluded from the benefit of total knee arthroplasty, given that their overall improvements were equivalent to those of patients with a lower body mass index.
authors.affiliation: Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, England. drpnbaker@hotmail.com
authors.forename: Paul
authors.initials: P
authors.lastname: Baker
authors.forename: Tim
authors.initials: T
authors.lastname: Petheram
authors.forename: Simon
authors.initials: S
authors.lastname: Jameson
authors.forename: Mike
authors.initials: M
authors.lastname: Reed
authors.forename: Paul
authors.initials: P
authors.lastname: Gregg
authors.forename: David
authors.initials: D
authors.lastname: Deehan
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D015992:Body Mass Index; D015897:Comorbidity; D005260:Female; D006297:Health Services Accessibility; D006305:Health Status Indicators; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology; D020370:Osteoarthritis, Knee / Q000453:epidemiology / Q000601:surgery; D010147:Pain Measurement; D017060:Patient Satisfaction; D011159:Population Surveillance; D011788:Quality of Life; D020127:Recovery of Function; D012042:Registries; D012086:Reoperation; D013222:State Medicine / Q000706:statistics & numerical data*; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D006113:United Kingdom