Mean Body Mass Index Does Not Increase or Decrease at 10 Years after Primary Total Hip or Knee Arthroplasty.

BACKGROUND:Although patients often aim to lose weight after total hip arthroplasty (THA) or total knee arthroplasty (TKA), long-term changes in body mass index (BMI) are unknown. We analyzed BMI at 2, 5, and 10 years after primary THA and TKA and determined predictors of BMI change. METHODS:We identified patients who underwent primary THA or TKA for osteoarthritis between 2001 and 2011 and had a BMI at surgery and at 2, 5, and 10 years postoperatively. This resulted in 763 patients (310 who underwent THA and 453 who underwent TKA). The mean patient age was 66 years, and 60% of patients were female. BMI changes were analyzed with repeated-measures analysis of variance. Multinomial logistic regression determined predictors of BMI change. RESULTS:Following THA, the mean BMI increased from 30.3 kg/m 2 at surgery to 30.9 kg/m 2 at both 2 years (p = 0.003) and 5 years (p = 0.002). Following TKA, the mean BMI increased from 32.7 kg/m 2 at surgery to 33.1 kg/m 2 at both 2 years (p = 0.053) and 5 years (p = 0.040). By 10 years, the mean BMI was 30.6 kg/m 2 (p = 0.453) for patients undergoing THA and 32.6 kg/m 2 (p = 0.947) for patients undergoing TKA, similar to the BMIs at surgery. At 10 years, 27% of patients who underwent THA and 30% of patients who underwent TKA had a BMI decrease of >5%, whereas 30% of patients who underwent THA and 32% of patients who underwent TKA had a BMI increase of >5%. Female sex among patients who underwent THA increased the odds of a >5% BMI increase at 10 years (odds ratio [OR], 2.1; p = 0.006). Older age among patients who underwent TKA decreased the odds of a >5% BMI increase at 10 years (OR per year, 0.95; p < 0.001). CONCLUSIONS:Although most patients experienced a BMI change of >5% at 10 years, the mean BMI did not meaningfully change 2, 5, or 10 years after THA or TKA. Arthroplasty should not be viewed as a gateway to BMI improvement for patients overall, but female sex and older age may predict clinically important weight changes 10 years after arthroplasty. LEVEL OF EVIDENCE:Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.