117 Standardizing Wearable-based Real-life Physical Activity Monitoring in Patients Undergoing Surgery for Degenerative Lumbar Disorders

INTRODUCTION: Assessment of function in patients with degenerative thoracolumbar disorders (DTD) has traditionally relied solely on the patient’s subjective perception of disability. There is a clear need to better understand an objective measure of physical activity impairment in this patient cohort. METHODS: This analysis is part of the Stanford SpineTrak study, a RCT to assess the feasibility of using a commercially available smartwatch (AppleWatch) to monitor outcome in patients with DTD. Mean preoperative physical activity 2 weeks before surgery was expressed as raw step count, as well as in standardized z-scores that wre referenced to age- and sex-specific values of a control population from a large public database. Step counts were assessed for convergent validity with established patient-reported outcome measures (PROMs) and impairment in activity was stratified into performance groups based on z-score cut-off values. RESULTS: Of 67 patients with DTD, 65 patients (62% female) with a mean age (SD) of 63.8 (12.8) years were available for analysis with a mean (SD) daily step count of 5215 (3868). Physical activity showed significant correlation with the ODI (r = 0.28, 95% CI -0.49-0.03), SF36-PCS (r = -0.34, 95% CI 0.11-0.54) and PROMIS-PF (r = -0.48, 95% CI 0.27-0.65). No, Mild, moderate, and severe impairment in activity performance were defined as corresponding z-scores of >0, 0 to -0.99, -1 to -1.99 and = -2, accounting for 20%, 29%, 43% and 8% of the study population. Each 1-step increase in activity impairment resulted in increased subjective disability as measured by the ODI, SF36-PCS and PROMIS-PF (all < 0.05). CONCLUSIONS: This study establishes a new wearable-based objective measure of real-life physical activity as well as corresponding standard scores that allow for a direct comparison of test results between individual patients and different study populations.