Author(s): IWASYK, A., FEDERICO, A., HOLASH, J., WATSON, L., MONUMENT, M., KENDAL, J., Institution: UNIVERSITY OF CALGARY, Country: CANADA, Abstract-ID: 2522

INTRODUCTION:
Physical activity is central to independence and quality of life, particularly in individuals with metastatic bone disease (MBD), where fractures and pain limit mobility. Orthopaedic intervention aims to restore safe weight-bearing and functional capacity; however, postoperative recovery has not been characterized using objective free-living mobility data. Smartphones offer scalable, low-burden monitoring of real-world activity. This pilot study used the ACTIVATION smartphone platform to evaluate longitudinal changes in physical activity and patient-reported function after surgery for MBD.
METHODS:
Twenty-two adults (64 +/- 11 years; 41 percent female; 14 lower extremity, 8 upper extremity; 14 established fractures, 8 impending) were prospectively enrolled. PROMIS Physical Function (PF), Pain Interference (PI), and Upper Extremity (UE) T-scores were collected preoperatively and at Weeks 1 through 6 and 12. In an iPhone subset (n = 5), daily step count and walking distance were extracted from Apple Health and aggregated into weekly means (greater than or equal to 4 valid days per week). Linear mixed-effects models evaluated PROMIS trajectories. Mobility changes were assessed using paired t-tests and Cohen dz. Associations used repeated-measures correlation.
RESULTS:
Fourteen patients contributed PF data (baseline 30.4 +/- 6.9). PF declined to 22.4 at Week 1 (beta = -7.45, p < 0.001), partially recovered by Week 4 (beta = +0.61, p = 0.675), improved at Week 6 (+3.81, p = 0.015), and exceeded baseline by Week 12 (+7.18, p < 0.001). Mean PF increased from 30.4 to 39.3 by Week 12 (+29 percent). Twenty-two patients contributed PI data (baseline 66.8 +/- 8.3). PI decreased from Week 3 onward (Week 3 beta = -4.82, p = 0.003; Week 4 beta = -5.50, p = 0.0008; Week 5 beta = -7.50, p < 0.001; Week 6 beta = -6.72, p < 0.001), reaching 55.1 at Week 12 (beta = -9.71, p < 0.001; -17 percent vs baseline). UE function (n = 8) improved from 23.9 pre-op to 32.9 at Week 6 (+9.05, p < 0.001) and 39.0 at Week 12 (+13.73, p < 0.001). In the mobility subset, step counts declined 38 percent at Week 2 (-453 steps, p = 0.048; dz = -1.26) and rose above baseline by Week 12 (+544 steps, p = 0.009; dz = 0.79). Walking distance decreased 81 percent at Week 1 (dz = -1.43, p = 0.033) with large recovery effects by Week 12 (dz = 1.19). Mobility correlated with PF (steps r = 0.48, p = 0.005; distance r = 0.55, p = 0.001) and inversely with PI (distance r = -0.39, p = 0.029; steps r = -0.32, p = 0.077).
CONCLUSION:
Surgical stabilization for MBD causes acute but reversible reductions in free-living physical activity. Wearable-derived mobility metrics mirror improvements in patient-reported function and pain, supporting clinical validity. These findings demonstrate the feasibility of smartphones in free-living conditions to monitor postoperative recovery trajectories in orthopaedic populations, offering a scalable approach to data-driven patient surveillance.