Feasibility of Smartphone-Derived Short-Interval Walking Tests for Monitoring Functional Recovery After Spine Surgery.

Abstract

Traditional assessments of functional recovery after spine surgery rely on patient-reported outcomes, which are prone to bias. Wearables and smartphone activity tracking offer objective monitoring but may be unreliable if devices are not carried continuously. Capacity-oriented measures, such as the 1-min walk test (1MWT) and 6-min walk test (6MWT), may be more reliable. This study evaluated smartphone-derived interval metrics after lumbar spine surgery retrospectively. iPhone Health exports from 41 patients were analyzed. A sliding-window algorithm parsed daily distances to simulate 1MWT and 6MWT. Step counts and active time were extracted. Activity was compared across four intervals: 6-month baseline, final 2 weeks preoperatively, early postoperative (0-2 weeks), and late postoperative (2-6 weeks). Paired <i>t</i>-tests or Wilcoxon signed-rank tests were used, with Simes-Hochberg adjustment for multiple comparisons. Day-to-day stability was summarized by the coefficient of variation (CV). Pearson correlations were calculated. Median 1MWT fell from 98 m at baseline to 82 m in the final two preoperative weeks (<i>p</i> < 0.05) and increased to 105 m by late recovery (<i>p</i> < 0.05 vs. preoperative). Median 6MWT declined from 403 to 345 m preoperatively, with this decline not reaching significance (<i>p</i> = 0.07), and increased to 407 m by late recovery (<i>p</i> < 0.05 vs. preoperative). Steps declined from 5030 to 3825 preoperatively (<i>p</i> < 0.05) and rose to 5538 at 2-6 weeks (<i>p</i> < 0.05 vs. preoperative). The 1MWT and 6MWT were strongly correlated. CV was lower for 1MWT and 6MWT than for steps. Smartphone-derived 1MWT and 6MWT improved significantly from the immediate preoperative period to late postoperative recovery, showed lower day-to-day variability than longitudinal activity metrics, and were strongly correlated with each other. These findings support smartphone-derived interval metrics as a feasible method to monitor recovery following lumbar spine surgery.