Overweight preoperatively impairs clinical outcome after knee arthroplasty

BACKGROUND Obesity contributes much to the development of knee osteoarthritis. However, the association between obesity and outcome after knee replacement is controversial. We investigated whether there was an association between the preoperative body mass index (BMI) of patients who underwent total knee arthroplasty (TKA) and their quality of life (QoL) and physical function 3-5 years after surgery. METHODS 197 patients who had undergone primary TKA participated in a 3-5 year follow-up study. The outcome measures were the patient-reported Short Form 36 (SF-36) and the American Knee Society score (KSS). RESULTS Ordinal logistic regression analysis (adjusted for age, sex, disease, and surgical approach) revealed a statistically significant correlation between BMI and 9 of the 14 outcome measures. For all outcome measures, we found an odds ratio (OR) of < 1. A difference in BMI of 1 kg/m(2) increased the risk of a lower score from a minimum of 2% (OR = 0.98 (0.93-1.03); p = 0.5) (Mental Component score) to a maximum of 13% (OR = 0.87 (0.82-0.93); p < 0.001) (KSS function score). INTERPRETATION Our findings indicate that TKA patients' preoperative BMI is a predictor of the clinical effect and patients' quality of life 3-5 years postoperatively. A high BMI increases the risk of poor QoL (SF-36) and physical function (KSS).