Age-stratified risk of major systemic complications following unicompartmental versus total knee arthroplasty: a nationwide cohort study
The optimal surgical approach for knee arthroplasty remains under debate regarding reducing systemic complications. Although unicompartmental knee arthroplasty (UKA) is generally considered less invasive than total knee arthroplasty (TKA), it remains unclear whether this advantage persists across age groups. This study aimed to compare the risk of major systemic complications between UKA and TKA across age categories using a large-scale nationwide database. Patients who underwent UKA or TKA between July 2010 and March 2022 were identified from the Diagnosis Procedure Combination database in Japan. The primary outcome was a composite of postoperative in-hospital death and major systemic complications requiring additional interventions. Rates of postoperative red blood cell (RBC) transfusion were also evaluated as a secondary outcome. Stabilized inverse probability of treatment weighting (IPTW) using propensity scores was applied to compare outcomes between the groups. The cohort included 36,235 UKA and 322,424 TKA cases. After stabilized IPTW adjustment, the composite outcome occurred less frequently after UKA than after TKA (risk ratio [RR] 0.65; 95% confidence interval [CI] 0.50–0.85; p = 0.001). The RBC transfusion rate was also reduced in the UKA group (RR, 0.09; 95% CI 0.08–0.11; p < 0.001). In subgroup analyses stratified by age (≤ 79 and ≥ 80 years), UKA was associated with a lower incidence of the composite outcome compared with TKA in patients aged ≤ 79 years (RR 0.48; 95% CI 0.34–0.68; p < 0.001), whereas no significant difference between UKA and TKA was observed among patients aged ≥ 80 years (RR 0.92; 95% CI 0.62–1.35; p = 0.670). The rate of RBC transfusion was lower in the UKA group across age groups (for ≤ 79 years, RR 0.07; 95% CI 0.05–0.09; p < 0.001; for ≥ 80 years, RR 0.12; 95% CI 0.10–0.14; p < 0.001). RBC transfusion rates were consistently lower following UKA across age groups. While UKA was associated with fewer major systemic complications than TKA in patients aged ≤ 79 years, no such difference was observed in patients aged ≥ 80 years. In very elderly patients, careful perioperative risk assessment remains essential when considering UKA, similar to that for TKA.