Abstract / Summary
Abstract Background Although the ability to walk longer distances is critical to regaining independence after hip fracture surgery, walking capacity is typically measured in controlled clinical settings and it remains unclear what walking distance people actually cover in their daily lives. Wearable devices can measure daily-life walking behaviour, but methods to quantify real-world walking distance remain limited and comprehensive validation is yet to be done. As a first step, this study assessed the construct and longitudinal validity of real-world walking distance metrics derived from both single walking bouts (WBs) and a novel method for clustering nearby WBs, using a single wearable device during recovery after hip fracture surgery. Methods This multicentre prospective cohort study recruited participants from inpatient and outpatient lists, with real-world mobility and clinical- and patient-reported outcomes collected at first visit, 6- and 12 months follow-up. Four metrics (Mean, SD, Median, and 95th percentile/ P95) were computed for both Single WBs > 30s and Clustered WBs, resulting in 8 digital mobility outcomes (DMOs) to describe walking distance. Each DMO was examined for construct validity (convergent, divergent, and known-groups). Known-groups validity was assessed across four predefined recovery phases (acute, post-acute, extended, and long-term). In addition, the two P95 DMOs were examined for longitudinal validity (ability to detect change and predicted trajectories). Analyses were performed comparing Spearman correlations and effect sizes with a priori expectations and using linear mixed-effects models. Results The total sample ( N = 505) had a median age of 79 years (P25-P75: 72–84), with 66% women, and a 6-minute walk test (6MinWT) distance of 284 ± 126 m. Seven out of eight Distance DMOs demonstrated evidence for construct validity, showing expected correlations with related constructs (clinical outcome assessments, patient-reported outcomes, and daily step count) (|r|=0.51–0.74), and distinguishing between the four hip fracture recovery phase groups. The two P95 Distance DMOs showed longitudinal validity, including ability to detect change, comparable to the 6MinWT distance. Conclusion Real-world Walking Period Distance DMOs, derived from single WBs > 30s and a novel WB clustering method, demonstrated evidence of construct and longitudinal validity in patients after hip fracture. The upper-range Distance DMOs showed correlations, effect sizes, and longitudinal trajectories comparable to 6MinWT distance, with the Cluster Distance consistent with patient-reported unchanged or improved walking ability. These findings support the relevance of upper-range Distance DMOs for characterising real-world walking performance in hip fracture rehabilitation, and pave the way for further clinical validation.