PRIMARY TOTAL KNEE ARTHROPLASTY IN THE SUPER-OBESE POPULATION: LONG-TERM FOLLOW-UP OF 631 PATIENTS

Despite the progress made in addressing obesity and its associated complications, the prevalence of this complex disease continues to rise. This has led to the emergence of a group known as “super-obese” individuals, with body mass index (BMI) exceeding 50 kg/m2. Without clinical practice guidelines, arthroplasty surgeons and anesthesiologists continue to push the limits of patient size and surgical feasibility despite risks of harm. To better inform clinical decision-making and guideline development, we analyzed a large set of follow-up data in knee arthroplasty patients with BMI above 50 kg/m2. In a retrospective database study of patients who had undergone primary total knee arthroplasty (TKA) in our academic centre (N = 11,768), we compared the outcomes of super-obese TKA patients (N = 631) against patients of normal weight (BMI 18-25), overweight (BMI 25-30), Obese Class I (BMI 30-35), Class II (BMI 35-40), and Class III (BMI 40-50). Patient follow-up ended at the earliest of the date of revision, date of death, or date of the end of follow-up (October 17, 2023), average patient follow-up was 8.6 years. We used Cox proportional hazard models to estimate the association between patient BMI and revision risk using overweight patients (N = 2,548) as the reference group, while censoring patients for the other outcomes. Patient-reported outcome measures including overall patient satisfaction and Oxford-12 knee score (OKS) were compared pre-operatively and at five years postoperatively. Compared to our overweight control group, TKA patients with BMI > 50 kg/m2 are at significantly higher risk of a revision with a hazard ratio (HR) of 2.3 (95% confidence interval [CI] = 1.5-3.5). We observed a gradient in increased risk with increasing BMI, the HRs in the BMI 40-50 and BMI 35-40 groups were 1.6 (95% CI 1.1-2.3) and 1.5 (95% 1.0-2.1), respectively. Compared to the overweight group, super obese patients reported worse pre-operative function of their knee, with a mean OKS of 15.4 (standard deviation [SD] 6.8) versus 22.2 (SD 8.1). The gap was smaller after 5 years postoperatively, 35.2 (SD 9.3) versus 39.4 (SD 8.4). The improvement in OKS was slightly higher after 5 years for super obese patients (+19.1; 95% CI 16.9-21.4) than overweight patients (+17.4; 95% CI 16.4-18.4), although this difference was not statistically significant in an underpowered comparison (p = 0.143, power = 0.29, two-sample, two-sided t-test). Our study confirms the significant risk of failure associated with TKA in the super-obese. Despite worse pre-operative and post-operative knee function, this population still derives significant benefits from knee arthroplasty. Treating physicians should engage their patients with BMI > 50 kg/m2 with empathy and transparency regarding the risks and benefits of TKA.