Despite Greater Improvement in Pain and Function Among Obese Patients Shortly After Total Knee Arthroplasty, There is No Difference in Patient-Reported Outcomes and Satisfaction Between Body Mass Index Classes at 1 Year Postoperatively.

Background: Although obesity may be associated with an increased risk of perioperative and postoperative complications after total knee arthroplasty (TKA), body mass index (BMI) cutoffs for TKA patient selection remain a controversial topic. This study aimed to investigate patient-reported outcomes, satisfaction, and pain among BMI classes at 3 months and 1 year following TKA.

Methods: A total of 2,365 patients were categorized into Centers for Disease Control BMI classes according to preoperative values. The BMI distribution over the cohort demonstrated 7 underweight, 340 healthy weight, 731 overweight, 666 Class I, 391 Class II, and 230 Class III obesity. Preoperative and postoperative Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR), satisfaction, and pain scores were compared by BMI class by Analysis of Variance with pairwise comparisons.

Results: Preoperative KOOS JR scores and satisfaction scores were both significantly greater for healthy weight patients compared to Class III patients (P < .0001). However, KOOS JR, satisfaction, and pain did not vary by BMI class postoperatively. Changes in scores from baseline suggest larger improvements with increasing BMI class, where Class III patients reported the greatest improvements in KOOS JR (23.24 ± 15.67, P < .0001) and pain scores (-3.56 ± 2.65, P < .0001) at 90 days. Significantly greater improvement with increasing BMI was also present at 1-year postoperatively for KOOS JR scores. A total of 85.8% of Class III patients reached the Minimal Clinically Important Difference for KOOS JR at 90 days compared to 76.8% of the healthy weight group (P = .03). Differences between BMI groups in the proportion reaching Minimal Clinically Important Difference at 1 year were not significant.

Conclusions: Patients of higher BMI reported greater and earlier improvements in satisfaction, knee function, and pain following TKA. Shared decision-making remains paramount to preoperative surgical evaluation. However, rationing of this surgical intervention based on BMI alone may not be warranted.