Preoperative Decline and Postoperative Recovery of Wearable-Derived Physical Activity over a Four-Year Perioperative Period in Total Knee and Hip Arthroplasty.
Zhang Y, Folarin A, et al. • Sensors (Basel, Switzerland) • 2026
Both TKA and THA showed progressive preoperative physical activity decline and staged postoperative recovery over a four-year perioperative period, with higher preoperative activity associated with greater likelihood of recovery to habitual baseline levels.
Key Findings
Results
Both TKA and THA procedures showed progressive preoperative decline in wearable-derived physical activity, with accelerated decline beginning earlier in TKA than in THA.
Study used piecewise linear mixed-effects models to characterize preoperative and postoperative trajectories
Data spanned two years before and two years after surgery
238 participants total: 147 TKA and 91 THA
Mean age was 64.9 years (SD 8.3 years)
The accelerated phase of preoperative decline was temporally earlier for TKA compared to THA
Results
Postoperative physical activity recovery followed a staged pattern with rapid early improvement, slower intermediate gains, and later stabilization.
The staged recovery pattern was observed in both TKA and THA groups
Recovery was characterized relative to two distinct preoperative baselines
The first baseline was activity measured immediately before surgery
The second baseline was a more remote measure approximating longer-term habitual activity
Recovery to the immediate preoperative baseline occurred earlier than recovery to the remote baseline
Results
Higher physical activity during the four weeks before surgery was associated with a greater likelihood of recovery to the remote (habitual) baseline.
This association was examined using Cox proportional hazards models
The preoperative activity level in the 4 weeks immediately before surgery was the key predictor
Recovery was defined relative to the remote baseline approximating longer-term habitual activity
This finding suggests preoperative functional status is relevant to postoperative outcomes
Methods
The study used Fitbit step count data linked to electronic health records from the All of Us Research Program to objectively measure physical activity trajectories.
This was an observational study within the All of Us Research Program
Fitbit-derived step counts were used as the measure of physical activity
Electronic health records were linked to wearable data
The observation window spanned four years total: two years preoperative and two years postoperative
238 participants had sufficient data to be included in analyses
Conclusions
The authors concluded that long-term wearable monitoring supports use as a complementary measure of physical activity recovery after arthroplasty.
Wearable monitoring captured objective, continuous physical activity data across the full perioperative period
Two recovery definitions (immediate vs. remote preoperative baseline) yielded different recovery timing estimates
The study supports integration of wearable-derived data alongside traditional clinical outcome measures
The four-year observation window revealed patterns not detectable in shorter follow-up studies
What This Means
This research suggests that people who undergo total knee or hip replacement surgery experience a gradual decline in their daily physical activity — measured by Fitbit step counts — in the years leading up to surgery, and then recover in a phased pattern afterward. The study tracked 238 patients over four years (two years before and two years after surgery) and found that the decline before knee replacement surgery tended to start earlier than before hip replacement surgery. After surgery, patients initially improved quickly, then more slowly, and eventually leveled off. Notably, recovery back to a patient's longer-term habitual activity level took longer than recovery back to the low level of activity recorded just before surgery, highlighting that 'feeling better than right before surgery' and 'returning to normal long-term function' are meaningfully different benchmarks.
One important practical finding is that patients who were more physically active in the four weeks before surgery were more likely to recover to their long-term habitual activity levels. This suggests that maintaining or improving physical activity in the period leading up to joint replacement may positively influence recovery outcomes. The research also demonstrates that consumer-grade wearable devices like Fitbits, when linked with health records, can provide rich, long-term objective data about how patients function before and after surgery — information that routine clinical visits alone may not capture.
This research matters because it provides a more complete picture of what the physical activity journey looks like for joint replacement patients over multiple years, rather than just the months immediately surrounding surgery. The findings could help clinicians set more realistic expectations with patients about recovery timelines and could support targeted interventions — such as preoperative exercise programs — to help patients arrive at surgery in better physical condition and recover more fully afterward.
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Zhang Y, Folarin A, Zhong R, Kim H, Stewart C, Sun S, et al.. (2026). Preoperative Decline and Postoperative Recovery of Wearable-Derived Physical Activity over a Four-Year Perioperative Period in Total Knee and Hip Arthroplasty.. Sensors (Basel, Switzerland). https://doi.org/10.3390/s26113319