Impact of cognitive impairment on postoperative delirium and discharge disposition following knee arthroplasty: a Japanese nationwide propensity score–matched study

PURPOSE: As populations age, the number of older patients undergoing knee arthroplasty continues to increase. Cognitive impairment is prevalent among older adults and has been associated with adverse perioperative outcomes; however, its impact on postoperative delirium and discharge disposition following knee arthroplasty remains insufficiently defined, particularly in large Asian populations. METHODS: We conducted a nationwide retrospective cohort study using Japan's Diagnosis Procedure Combination database from April 2016 to March 2023. Older patients who underwent primary total knee arthroplasty (TKA) or unicompartmental knee arthroplasty (UKA) were identified. Cognitive impairment was defined using ICD-10 diagnostic codes at admission. The primary outcome was postoperative delirium, and secondary outcomes included discharge to home, length of hospital stay, and perioperative blood transfusion. Propensity score matching (1:1) was performed to adjust for demographic factors, comorbidities, and surgical characteristics. Multivariable logistic regression and sensitivity analyses were conducted. RESULTS: Among 259,319 eligible patients, 3,934 matched pairs were identified after propensity score matching. Patients with cognitive impairment had a significantly higher risk of postoperative delirium compared with those without cognitive impairment (absolute risk difference, 3.2%; 95% CI, 2.5-3.9). Cognitive impairment was independently associated with postoperative delirium (odds ratio [OR], 4.47; 95% CI, 3.11-6.41) and a reduced likelihood of direct discharge to home (OR, 0.64; 95% CI, 0.57-0.71). Length of hospital stay was modestly longer in patients with cognitive impairment, whereas no clinically meaningful differences were observed in other postoperative complications after adjustment. CONCLUSION: Cognitive impairment is a strong and independent risk factor for postoperative delirium and reduced likelihood of direct discharge to home following knee arthroplasty in older patients. Incorporating cognitive assessment into perioperative risk stratification may help optimize geriatric orthopedic care and postoperative planning.