The goal of this prospective cohort study is to assess potential differences in sleep biomarkers in older adult patients undergoing major orthopedic surgery. The main questions it aims to answer are: 1. To define sleep/circadian biomarkers of delirium (sleep duration, regularity, stability and timing of rhythm) in a prospective observational study. 2. To determine if plasma Alzheimer's disease (AD) pathology/inflammatory burden interacts with or moderates the relationship between a sleep/circadian biomarker and post-operative delirium (POD) risk. 3. To determine whether sleep/circadian regulation interacts with the genetic risk of AD to influence POD/cognitive decline. Participants will be asked to: 1. Donate several blood samples both intraoperatively and postoperatively 2. Complete baseline and postoperative neurocognitive assessments 3. Wear an actigraphy data collection watch for the two weeks prior to their surgery