The Association Between Longitudinal Smartphone-Based Mobility Data and PROMs in Spine Surgery

Introduction

Patient-reported outcome measures (PROMs) are the current gold standard for assessing post-operative outcomes in spine surgery. While these validated tools hold great value in assessing patients’ pain and subjective experience of their disease, PROMs are also limited by the inherent subjectivity of self-reported, qualitative data. Recent literature has highlighted the utility of patient mobility data streamed from smartphone accelerometers as an objective measure of functional outcomes after spine surgery that could complement PROMs. Still, for activity-based data to supplement existing PROMs, they must be validated against current metrics. In this study, we assess the relationships between longitudinal smartphone-based mobility data and PROMs and determine the minimum clinically important difference in smartphone-based mobility following spine surgery.

Objectives

The objective of this study is to assess the relationship between patient-reported outcome measures (PROMs) and smartphone-based mobility data and define the Minimum Clinically Important Difference (MCID) in smartphone-based mobility after spine surgery.

Methods

A total of 31 patients receiving laminectomy (21) and fusion (10) patients [AH1] [DC2] between 2017 and 2021 were retrospectively enrolled into the study. Activity data (steps-per-day count) recorded in the Apple Health (Apple Inc., Cupertino, CA) mobile application over a 2-year peri-operative window was extracted using the application Kinesiometrics (Kinesiometrics Inc, Wilmington, DE), and subsequently normalized. The data was normalized to allow for inter-subject comparison since each patient has a unique baseline activity level. PROMS, including PROMIS score, Oswestry Disability Index (ODI) and EQ-5D, were collected at the pre-operative and 6-week post-operative visits were retrospectively extracted from each patient’s electronic medical record. Pearson correlations between PROMs and patient mobility were assessed and compared between patients who did and did not achieve each respective PROM’s minimum clinically important difference (MCID). The mean improvement in patient mobility of the MCID cohorts for respective

Results

VAS and PROMIS pain interference (PROMIS-PI) showed moderate (r = -0.46) and strong (r = -0.74) inverse correlations, respectively, with change in normalized steps-per-day count from pre-op to 6-week post-op. Patients who achieved MCID in pain reduction showed greater improvement in mobility (0.784 SD increase) than non-MCID patients (0.172 SD decrease) [AH3] [DC4]. The MCID cohort experienced an increase in normalized steps-per-day at 6 weeks post-op of 0.442 SD for VAS and 0.784 SD for PROMIS-PI, compared to decrease of 0.270 SD and 0.172 SD for non-MCID, respectively (p < 0.05). An improvement of 0.613 SD from baseline in smartphone-gathered mobility data may be the MCID value.

Conclusions

Our study demonstrates a strong correlation between changes in mobility data extracted from patient smartphones and changes in PROMs following lumbar spine surgery. We also determined the MCID value for improvement in smartphone-gathered physical mobility data. Further exploring the importance of the MCID value through larger studies will allow for more robust supplementation of existing spine outcome measure tools with analyzed objective activity data.