Elevated Body Mass Index Is a Risk Factor for Failure to Achieve the Knee Disability and Osteoarthritis Outcome Score-Physical Function Short Form Minimal Clinically Important Difference Following Total Knee Arthroplasty

The aims of this study are (1) to assess the association between body mass index (BMI) and failure to achieve the 1-year Knee Disability and Osteoarthritis Outcome Score-Physical Function Short Form (KOOS-PS) minimal clinically important difference (MCID) for total knee arthroplasty (TKA) patients and (2) to determine if there is a BMI threshold beyond which the risk of failing to achieve the MCID is significantly increased.

A regional arthroplasty registry was queried for TKA patients from 2016 to 2019 with completion of preoperative and 1-year postoperative KOOS-PS. The MCID threshold was derived using a distribution-based approach. Demographic and patient-reported outcome measure variables were collected. BMI was analyzed continuously and categorically using cutoffs defined by the Centers for Disease Control and Prevention. The association between failure to achieve 1-year MCID and BMI was analyzed using multiple logistic regression. A BMI threshold was determined using the Youden index and receiver operating characteristic curve.

In total, 1059 TKAs were analyzed. BMI assessed continuously was significantly associated with failure to achieve the KOOS-PS MCID (odds ratio 1.03, 95% confidence interval 1.00-1.05, P = .025). Analysis of BMI categorically revealed that “overweight” (25-30 kg/m²), “obese class I” (30-35 kg/m²), “obese class II” (35-40 kg/m²), and “obese class III” (>40 kg/m²) patients faced 77%, 76%, 83%, and 106% greater risk, respectively, of failing to achieve the KOOS-PS MCID compared to “normal BMI” (<25 kg/m²) patients.

Elevated BMI was associated with an increased risk of failure to achieve the 1-year KOOS-PS MCID following TKA.