Objective To assess changes in activity and movement parameters before and after hip and knee replacement using smartphone-derived data. Methods We invited 952 patients who underwent joint replacement at Sahlgrenska University Hospital in 2023–2024. 166 agreed to share Apple Health data via a mobile app, and 80 submitted usable data. The app collected step count, step length, walking speed, and asymmetry from one year before to two years after surgery. Five time points were analyzed: 3 months preoperatively and 0–3, 3–6, 6–9, and 9–12 months postoperatively. Results Average step count declined from 3,632 steps preoperatively to 2,774 at 0–3 months post-op, peaked at 4,122 at 6–9 months, and decreased to 3,710 at 9–12 months. Step count did not return to preoperative levels during the first postoperative year. Step length and walking speed improved from 0.60 m and 1.03 m/s preoperatively to 0.62 m and 1.08 m/s at 9–12 months. Asymmetry increased immediately postoperatively (0.39%) but improved to 0.15% at 9–12 months, below preoperative levels (0.20%). These trends suggest a gradual recovery in movement quality, with peak improvements occurring between 6 and 12 months postoperatively. Conclusion Smartphone-based movement tracking is a feasible and informative method for monitoring recovery after joint replacement. Improvements in step length, walking speed, and asymmetry indicate enhanced mobility and symptom relief. However, the lack of sustained increase in step count suggests that improved movement quality does not necessarily translate into higher activity levels. This discrepancy highlights the need to better understand behavioral recovery and develop strategies to support long-term engagement in physical activity following surgery.
Tasa et al. (Thu,) studied this question.