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

Purpose: 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.

Methods: 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.

Results: 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 ≥ 35, a significant increase in revision was noted. Comparing BMI ≥ 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).

Conclusion: All-cause revision rates after primary TKA doubled in patients with a BMI of 35 but were similar in those with a BMI <35.