Evaluating the Accuracy and Reliability of Real-World Digital Mobility Outcomes in Older Adults After Hip Fracture: Cross-Sectional Observational Study

Background
Algorithms estimating real-world digital mobility outcomes (DMOs) are increasingly validated, but their accuracy and reliability in older adults after hip fracture—who often walk slowly and in short bouts—remain insufficiently studied.

Objective
To assess DMO accuracy and reliability in a hip fracture cohort, considering walking bout (WB) duration, physical function, time since surgery, and walking aid use.

Methods
Nineteen community-dwelling older adults were monitored for 2.5 hours using a lower-back wearable and a multimodal reference system. Six DMOs from 164 WBs of 11 participants (aged 71–90 years; 32–390 days post-surgery; SPPB 3–12) were evaluated at WB and participant levels. Analyses were stratified by WB duration and physical function.

Results
Walking speed and distance ranged from 0.25–1.29 m/s and 1.7–436.5 m. Walking speed, cadence, stride duration, step count, and distance showed moderate to excellent reliability (ICC 0.50–0.99; MRE –6.9% to 12.8%). Stride length showed poor reliability. Higher physical function was associated with better accuracy, while time since surgery and walking aid use had no clear effect.

Conclusions
Five DMOs were accurate and reliable in older adults after hip fracture. Accuracy improved when excluding WBs <10 seconds and with longer WBs, but at the cost of data loss, as most WBs were short. These findings support the clinical validity of DMOs for assessing real-world gait after hip fracture.

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