Elective hip and knee joint replacement for osteoarthritis are cost-effective surgical procedures requiring specific rehabilitation programs. Actigraphy is widely used in both research and clinical practice to study activity patterns with great accuracy and validity but it has never been utilized in orthopedic patients. Therefore, the aim of this study was to objectively assess, through actigraphy, physical activity (PA) levels and rest-activity daily rhythm (RAR) in patients undergoing hip or knee joint replacement and hospitalized for ten days after surgery. Twenty subjects (11 males and 9 females; age: 62.68 ± 10.39 years old; BMI: 29.03 ± 3.92 kg/m²) wore the Actiwatch 2 actigraph (Philips Respironics, Portland, OR) to record both PA levels and RAR for 11 consecutive days and data on subjective scores of pain, by a visual analog scale (VAS), and functional and clinical scores were collected. The following time-points were considered for the statistical analysis: pre-surgery (PRE), the first (POST1), the fourth (POST4) and the tenth (POST10) day after surgery. RAR were processed with the population mean cosinor to describe the rhythm's characteristics (acrophase, amplitude and MESOR) while data on actigraphy-based PA, VAS, and functional clinical scores were compared among PRE, POST1, POST4 and POST 10 with the RM-ANOVA or the non-parametric Friedman test. The day after surgery the subjects had a flattened RAR compared to the other conditions: lower values were detected in POST1 compared to both PRE, POST4 and POST10 for MESOR (p < .0001; η²_p = .71, large) and amplitude (p < .0001; η²_p = .63, large) while RAR's acrophase (p < .0001; η²_p = .61, large) was delayed in PRE (16:45) compared to POST1 (12:42), POST4 (14:38), and POST10 (14:38). PA levels were significantly lower at POST 1 (76.7 ± 33.4) compared to PRE (192.3 ± 91.5; p < .0001 and ES: 1.68, large), POST4 (137.9 ± 45.9; p < .0001 and ES: 1.54, large), and POST10 (131.2 ± 54.3; p < .0001 and ES: 1.21, large) whereas VAS and functional clinical values significantly improved at POST10. Hip and knee joint replacement negatively influenced RAR and PA the first day after surgery but a progressive improvement in the circadian pattern of rest-activity cycle, PA levels, VAS and functional ability was recorded from POST4 to POST10. Actigraphy has the ability to collect real-life data without interfering with clinical practice and give clinicians a new measure of performance that is currently not available. This tool could allow to identify patients with disrupted circadian rhythm and reduced PA in the peri-operative period in orthopedic surgery, and timely intervene on these subjects with personalized rehabilitative intervention.

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