Higher body mass index is associated with larger postoperative improvement in patient-reported outcomes following total knee arthroplasty

BACKGROUND: Total knee arthroplasty is known to successfully alleviate pain and improve function in endstage knee osteoarthritis. However, there is some controversy with regard to the influence of obesity on clinical benefits after TKA. The aim of this study was to investigate the impact of body mass index (BMI) on improvement in pain, function and general health status following total knee arthroplasty (TKA). METHODS: A single-centre retrospective analysis of primary TKAs performed between 2006 and 2016 was performed. Data were collected preoperatively and 12-month postoperatively using WOMAC score and EQ-5D. Longitudinal score change was compared across the BMI categories identified by the World Health Organization. RESULTS: Data from 1565 patients [mean age 69.1, 62.2% women] were accessed. Weight distribution was: 21.2% BMI < 25.0 kg/m(2), 36.9% BMI 25.0–29.9 kg/m(2), 27.0% BMI 30.0–34.9 kg/m(2), 10.2% BMI 35.0–39.9 kg/m(2), and 4.6% BMI ≥ 40.0 kg/m(2). All outcome measures improved between preoperative and 12-month follow-up (p < 0.001). In pairwise comparisons against normal weight patients, patients with class I-II obesity showed larger improvement on the WOMAC function and total score. For WOMAC pain improvements were larger for all three obesity classes. CONCLUSIONS: Post-operative improvement in joint-specific outcomes was larger in obese patients compared to normal weight patients. These findings suggest that obese patients may have the greatest benefits from TKA with regard to function and pain relief one year post-op. Well balanced treatment decisions should fully account for both: Higher benefits in terms of pain relief and function as well as increased potential risks and complications. Trial registration This trial has been registered with the ethics committee of Eastern Switzerland (EKOS; Project-ID: EKOS 2020–00,879)