Comparison of Postoperative Outcomes Following Simultaneous versus Staged Bilateral Total Knee Arthroplasty in Obese Patients: A Database Study.

BACKGROUND: Obesity is associated with higher complication risk after total knee arthroplasty (TKA), and evidence comparing simultaneous versus staged bilateral TKA (BTKA) across obesity severity is limited.

METHODS: Adults undergoing BTKA (2014 to 2024) were identified from a global de-identified research network. Patients were classified by surgical timing (simultaneous; short-interval staged [one to less than four months]; longer-interval staged [four to 12 months]) and body mass index (BMI) (non-obese [less than 30]; obesity classes 1 [30 to less than 35]; 2 [35 to less than 40]; 3 [greater than 40]). Both 30-day and two-year outcomes were evaluated using logistic and linear regressions adjusted for age, sex, ethnicity, and Charlson comorbidity score with interaction testing between BMI category and surgical timing.

RESULTS: Among 11,965 patients (5,653 non-obese; 3,096 class 1; 1,870 class 2; 1,346 class 3), BMI category modified surgical timing's association with 30-day composite complications (P < 0.001), readmission (P = 0.017), two-year aseptic loosening (P = 0.011), all-cause revision (P = 0.011) and length of stay (LOS) (P < 0.001). Staged BTKA showed lower odds of composite complications with the largest reductions in class 3 (short-interval [odds ratio (OR) 0.18, 95% confidence interval (CI): 0.09 to 0.35]; comparable for longer-interval). Staged BTKA also showed lower odds of aseptic loosening and revision in classes 2 and 3 with the largest reductions in class 3 (aseptic loosening [OR 0.24, 95% CI: 0.08 to 0.71]; revision [OR 0.13, 95% CI: 0.04 to 0.42]; comparable for longer-interval). In non-obese patients, staged BTKA was conversely associated with higher 30-day readmission ([OR 1.93, 95% CI: 1.17 to 3.17]; comparable for longer interval). The LOS was longer after simultaneous than staged BTKA, decreasing at higher BMI.

CONCLUSION: The BMI category modified surgical timing's association with postoperative outcomes. Staged BTKA showed reductions in 30-day composite complications from class 1 onward and in two-year aseptic loosening and all-cause revision at BMI ≥ 35. The largest reductions for all three outcomes were observed in class 3.