The effects of obesity on functional outcomes after total knee arthroplasty: a prospective cohort study.

Background: An increasing number of total knee arthroplasties (TKAs) are performed in people with obesity, but TKAs in this population may come with increased risk of perioperative complications and decreased prosthetic survivorship. Given the lack of conclusive evidence on differences in functional outcomes, we aimed to use the Forgotten Joint Score-12 (FJS-12) to see how body mass index (BMI) affected functional outcomes after TKA.

Methods: We recruited patients who underwent primary unilateral TKA because of osteoarthritic changes from January 2018 to November 2021. We collected the Forgotten Joint Score-12 (FJS-12) measure of functional outcomes and the Western Ontario and McMaster University Osteoarthritis Index (WOMAC) preoperatively and 6- and 12-months postoperatively. We also measured length of stay (LOS), readmission, and emergency department (ED) visits. We compared outcomes by BMI category using linear effects models.

Results: We recruited 351 patients. No differences were found in LOS, readmissions, and ED visits by BMI category. Compared with the preoperative score, we observed significant differences by BMI category for the 6-month FJS-12 (β = -0.66, p = 0.007) and 12-month WOMAC (β = -0.34, p = 0.02) scores. At 6 months, patients with lower BMI showed a greater change in FJS-12 scores than those with higher BMI. However, by 12 months, all patients appeared to return to similar functional levels regardless of BMI.

Conclusion: Despite a slower return to function, patients with elevated BMI were able to return to similar levels of function as those with a lower BMI by 12 months, with no significant differences in readmission, ED visits, or LOS. This similar return to function justifies candidacy for surgery.