Individualized assessment of post-arthroplasty recovery by actigraphy: a methodology study.

Previous studies using actigraphy to monitor recovery after total knee arthroplasty (TKA) have reported activity as maximum and average count/min, but not utilized the full potential of the data by stratifying activity into various intensities or analysed the individual development in activity over time. The aim of this study was to describe a novel methodology using actigraphy data to describe specific activity-intensities potentially affected by surgery and patients with poor rehabilitation trajectories. Actigraphy data from 10 patients scheduled for primary unilateral TKA were recorded preoperatively and for 3 weeks postoperatively. Data were individualized by comparing pre- and post-operative values, and activity intensities stratified by division into 5 percentiles (10th, 25th, 50th, 75th and 90th). Changes in activity were assessed visually and by non-parametric testing. Individualized recovery trajectories were described by the gradient of the regression line of post- versus pre-operative physical activity over the study period. TKA had a negative impact on all activity intensities with gradual improvement towards preoperative values during the study period. The inter-individual variation increased with intensified activity. Identification of individual patients with positive, neutral or negative activity trajectories was possible. The methodology should be considered in future interventional studies to improve rehabilitation strategies.