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The Association Between Body Mass Index and the Outcomes of Total Knee Arthroplasty
Paul Baker, MBBS, MSc, FRCS(Tr&Orth)1; Tim Petheram, MBBS, MSc, MRCS2; Simon Jameson, MBBS, MRCS3; Mike Reed, MD, FRCS(Tr&Orth)2; Paul Gregg, MD, FRCS(Ed), FRCS(Tr&Orth)3; David Deehan, MD, BSc, FRCS(Tr&Orth)4
1 Institute of Cellular Medicine, Newcastle University, Framlington Place, Newcastle upon Tyne NE1 7RU, England. E-mail address: drpnbaker@hotmail.com
2 Wansbeck General Hospital, Woodhorn Lane, Ashington, Northumberland NE63 9JJ, England. E-mail address for T. Petheram: tim.petheram@hotmail.com. E-mail address for M. Reed: mike.reed@nhs.net
3 James Cook University Hospital, Marton Road, Middlesbrough TS4 3BW, England. E-mail address for S. Jameson: simon.jameson@doctors.org.uk. E-mail address for P. Gregg: prof.gregg@btinterent.com
4 Royal Victoria Infirmary, Queen Victoria Road, Newcastle upon Tyne NE1 4LP, England. E-mail address: deehan1@hotmail.com
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  • Disclosure statement for author(s): PDF

Investigation performed at the Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, England

Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Copyright © 2012 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2012 Aug 15;94(16):1501-1508. doi: 10.2106/JBJS.K.01180
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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.


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.


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.


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.

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    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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