Obese patients with osteoarthritis experience greater gains in physical function 7 years after undergoing total knee arthroplasty than do obese controls who did not have the surgery, according to an English study.
Based on data from 688 patients, there is no justification to withhold knee replacements from obese patients on the grounds that obesity is a risk factor for OA. At least one National Health Service trust has been reported to apply such a policy, the investigators wrote (Ann. Rheum. Dis. 2008 July 24 [doi:10.1136/ard.2008.093229]).
In a subgroup of 108 obese patients (body mass index greater than or equal to 30 kg/m
“Improvements in physical function following [TKA] for osteoarthritis are sustained,” wrote Janet Cushnaghan of the University of Southampton, England, and her associates. “These benefits extend to [obese patients] and, provided appropriate selection criteria are applied with regard to fitness for surgery, there seems no justification for withholding TKA.”
The researchers studied patients and controls aged 45 and older who had taken part in an earlier case-control study of knee OA. That study compared patients placed on a waiting list for TKA between 1995 and 1997 with controls in the community. Functional status and BMI were measured as part of data collection.
During 2001–2004, the authors wrote to the original study group with a questionnaire about their surgery and included the functional status sections of the SF-36 form. A total of 325 patients and 363 controls were included in this analysis.
Overall, at a mean follow-up of 7 years, median physical function scores in patients who underwent TKA improved from 20 to 26; scores in controls fell from 89 to 75.
Mental health scores on the SF-36 form improved equally in both groups. Vitality scores declined in both groups, but the decline was greater in patients than in controls (a loss of 10 points vs. a loss of 5 points).
Of 82 patients older than age 75, the median physical function score stayed steady at 17 points; scores declined from 83 to 43 points in 87 controls in that age group.
The researchers said their findings might have been biased by migration, although subjects were as likely to have moved, demonstrating greater function, as to have entered nursing care, demonstrating poorer function.
They also said OA might have been undetected in the controls at baseline, which would have biased their findings in favor of the intervention group.