Abstract
Introduction
Implementing operative eligibility thresholds based on body mass index (BMI) alone risks restricting access to improved pain, function, and quality-of-life. The purpose of this study was to: 1) investigate the relationship between BMI and improvements in 1-year patient reported outcome measures (PROMs), and 2) determine how many patients would have been denied 1-year improvements with specific BMI cut-offs.
Methods
Data were collected on a prospective cohort of 3,214 TKA patients from 2015–2018. Clinically meaningful 1-year improvements were defined as 15 points for Knee Injury and Osteoarthritis Outcome Scores (KOOS) pain and Physical Function Shortform (PS), and 14 points for Knee-Related Quality-of-Life (KRQOL). For specific BMI cut-offs, the positive predictive value for predicting a failure to improve and number of patients denied surgery to avoid one failed improvement was calculated.
Results
PROMs improvements were greater with increasing BMI. Patients with BMI ≥40 kg/m2 had median (Q1, Q3) KOOS pain improvements of 47.2 points (33.3, 58.3) and those with BMI 18.5–24.9 kg/m2 had median improvements of 41.7 (27.8, 55.6). Similar findings were observed for KOOS PS (28.4 vs. 26.3) and KRQOL (50.0 vs. 43.8). With a BMI cut-off of 30 kg/m2, 9 patients would have been denied improvements from surgery for each failed improvement avoided whereas with a BMI cut-off of 50 kg/m2, 15 patients would have been denied improvements from surgery. Implementing BMI thresholds alone did not influence the rate of improvements in KOOS-PS or KRQOL.
Conclusion
Patients with higher BMI were observed to have greater improvements in PROMs after primary TKA. Enforcing arbitrary BMI cut-offs would deprive pain and functional improvements from patients who would benefit the most. Moreover, there appears to be no increase in the rate of PROMs improvements by enforcing BMI thresholds. This study demonstrates that determining TKA eligibility should involve a holistic approach rather than limiting to BMI measurements alone.
