Older patients with documented preoperative cognitive impairment undergoing elective total knee arthroplasty had substantially higher rates of postoperative delirium and postoperative functional decline compared with matched patients without cognitive impairment, according to a retrospective NSQIP database study. Among 104 matched patient pairs, postoperative delirium occurred in 27% of patients with cognitive impairment vs less than 1% without impairment (OR 40.15), while 83% vs 52% were partially or totally dependent in activities of daily living postoperatively.