Patients who undergo total knee replacement are at substantial risk for weight gain during the 5 years after the surgery, a large retrospective study showed.

On an adjusted multivariable analysis, recipients of knee arthroplasty were 60% more likely to gain 5% or more of their baseline body weight than matched controls who did not have the procedure (OR 1.6, 95% CI 1.2 to 2.2, P=0.003), according to Daniel L. Riddle, PhD, of Virginia Commonwealth University in Richmond, and colleagues.

And the chance of that "clinically important" weight gain doubled for individuals who had a second arthroplasty during the subsequent 5 years (OR 2.1, 95% CI 1.4 to 3.1, P<0.001), the researchers reported in the May Arthritis Care & Research.

"The logical assumption may be that persons who are overweight or obese prior to surgery are more likely to lose weight following surgery. Because there is less pain and improved mobility, the impediments to increased activity and exercise are eased following surgery, and weight loss would logically follow," they observed.

However, that hasn't been the case consistently in previous studies, which have been hampered by short follow-up times and a lack of controls.

To provide a more accurate picture of the weight effects of knee replacement over the long term, Riddle and colleagues analyzed outcome data for 917 patients in the Mayo Clinic arthroplasty registry, matching them with 237 controls from the population-based Rochester Epidemiology Project.

A total of 205 of the 917 Mayo patients had a second lower-limb or hip arthroplasty procedure.

Baseline weight was 89.1 kg (196 lbs) in the arthroplasty group and 76.3 kg (168 lbs) in the control group. Two-thirds were women.

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