Age-Adjusted Charlson Comorbidity Index Outperforms Other Comorbidity Measures in Predicting 90-Day Readmissions After Simultaneous Bilateral Total Knee Arthroplasty.

Abstract

Simultaneous bilateral total knee arthroplasty (TKA) is associated with increased perioperative risk compared with unilateral procedures, making accurate risk stratification essential. Several comorbidity indices are widely used in arthroplasty; however, their comparative performance in simultaneous bilateral TKA remains unclear. This study aimed to compare the predictive ability of four commonly used indices, the age-adjusted Charlson Comorbidity Index (aCCI), the Elixhauser Comorbidity Index (ECI), the 5-factor modified Frailty Index (mFI-5), and the health-related quality of life comorbidity index (HRQoL-CI), for postoperative outcomes following simultaneous bilateral TKA. This study included 1,785 patients who underwent simultaneous bilateral TKA between 2010 and 2020. The cohort had a mean age of 71 years (range, 51 to 91), 81.0% were women, and the mean body mass index was 28.2 (range, 17.1 to 42.4). The primary outcomes were 90-day readmissions, including medical, surgical, and surgery-related infection complications. The secondary outcomes included 1-year reoperations and prolonged lengths of stay (≥ eight days). Predictive performance of each index was assessed using receiver operating characteristic analyses, with area under the curve (AUC) values compared using DeLong tests. The aCCI demonstrated the highest discriminative ability for overall readmissions (AUC: 0.778), outperforming ECI (AUC: 0.680), mFI-5 (AUC: 0.654), and HRQoL-CI (AUC: 0.698). All indices showed excellent performance for predicting medical readmissions (AUC range, 0.806 to 0.843). For surgical and surgery-related infection readmissions, aCCI consistently demonstrated superior discrimination, with higher AUC values compared with other indices. For 1-year reoperations and prolonged lengths of stay, all indices showed poor to acceptable predictive ability. Among commonly used comorbidity indices, aCCI demonstrated the most clinically predictive performance for 90-day readmissions following simultaneous bilateral TKA, particularly for surgical and surgery-related infection complications. These findings support the use of aCCI as a practical tool for perioperative risk stratification in this population.