Body Mass Index and Revision Total Knee Arthroplasty: Does Cause for Revision Vary by Underweight or Obese Status?

Background: Body mass index (BMI) impacts risk for revision total knee arthroplasty (rTKA), but the relationship between BMI and cause for revision remains unclear. We hypothesized that patients in different BMI classes would have disparate risk for causes of rTKA.

Methods: There were 171,856 patients who underwent rTKA from 2006 to 2020 from a national database. Patients were classified as underweight (BMI < 19), normal-weight, overweight/obese (BMI 25 to 39.9), or morbidly obese (BMI > 40). Multivariable logistic regressions adjusted for age, sex, race/ethnicity, socioeconomic status, payer status, hospital geographic setting, and comorbidities were used to examine the effect of BMI on risk for different rTKA causes.

Results: Compared to normal-weight controls, underweight patients were 62% less likely to undergo revision due to aseptic loosening, 40% less likely due to mechanical complications, 187% more likely due to periprosthetic fracture, 135% more likely due to periprosthetic joint infection (PJI). Overweight/obese patients were 25% more likely to undergo revision due to aseptic loosening, 9% more likely due to mechanical complications, 17% less likely due to periprosthetic fracture, and 24% less likely due to PJI. Morbidly obese patients were 20% more likely to undergo revision due to aseptic loosening, 5% more likely due to mechanical complications, and 6% less likely due to PJI.

Conclusion: Mechanical reasons were more likely to be the cause of rTKA in overweight/obese and morbidly obese patients, compared to underweight patients, for whom revision was more likely to be infection or fracture related. Increased awareness of these differences may promote patient-specific management to reduce complications.

Level Of Evidence: III.