Influence of body mass index on revision rates after primary total knee arthroplasty

Studies demonstrate that revision rates after primary total knee arthroplasty (TKA) tend to be higher in obese patients. However, the existence of a body mass index (BMI) threshold remains unexplored. We conducted a prospective cohort study of 2442 primary TKAs in 2035 patients (69.1 % women; mean age 72 years; mean follow-up 93 months, range 38-203). We evaluated the influence of BMI in five categories on all-cause revision after TKA using incidence rates (IR), hazard ratios (HR), and Kaplan-Meier survival analysis. Adjustment for baseline imbalances was performed using Cox regression analysis. Over the study period, 71 revisions occurred. Revision rates were 3.2 cases/1000 patient-years for patients of normal weight, 3.4/1000 for overweight patients and 3.0/1000 for patients classified as obese class I. At BMI a parts per thousand yenaEuro parts per thousand 35, a significant increase in revision was noted. Comparing BMI a parts per thousand yenaEuro parts per thousand 35 vs. < 35, there were 6.4 vs. 3.2 /1000. Crude HR was 2.0 [95 % confidence interval (CI) 1.2-3.3, p = 0.009], and the adjusted HR was 2.1 (95 % CI 1.2-3.6, p = 0.008). All-cause revision rates after primary TKA doubled in patients with a BMI of 35 but were similar in those with a BMI < 35.