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The Association Between Body Mass Index and the Outcomes of Total Knee Arthroplasty

Baker, Paul MBBS, MSc, FRCS(Tr&Orth); Petheram, Tim MBBS, MSc, MRCS; Jameson, Simon MBBS, MRCS; Reed, Mike MD, FRCS(Tr&Orth); Gregg, Paul MD, FRCS(Ed), FRCS(Tr&Orth); Deehan, David MD, BSc, FRCS(Tr&Orth)

Journal of Bone & Joint Surgery - American Volume: 15 August 2012 - Volume 94 - Issue 16 - p 1501–1508
doi: 10.2106/JBJS.K.01180
Scientific Articles
Supplementary Content

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/m2], Group II [25 to 39.9 kg/m2], and Group III [40 to 60 kg/m2]) with use of multiple regession 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.

Level of Evidence: Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

1Institute of Cellular Medicine, Newcastle University, Framlington Place, Newcastle upon Tyne NE1 7RU, England. E-mail address:

2Wansbeck General Hospital, Woodhorn Lane, Ashington, Northumberland NE63 9JJ, England. E-mail address for T. Petheram: E-mail address for M. Reed:

3James Cook University Hospital, Marton Road, Middlesbrough TS4 3BW, England. E-mail address for S. Jameson: E-mail address for P. Gregg:

4Royal Victoria Infirmary, Queen Victoria Road, Newcastle upon Tyne NE1 4LP, England. E-mail address:

Copyright 2012 by The Journal of Bone and Joint Surgery, Incorporated
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