Ab0939 Bend Ease: A Novel App-Based Digital Measurement Tool for Assessing at-Home Morning Stiffness and Spinal Range of Motion in Axial Spondyloarthritis

Background: Morning stiffness with limited spinal range of motion (SRoM) is a hallmark symptom of axial spondyloarthritis (axSpA), playing an important role in diagnosis and management. However, the evaluation of morning stiffness relies on subjective questionnaires that may be affected by recall bias and placebo effects. A readily accessible, objective measurement of morning stiffness and SRoM with digital health technology may aid axSpA diagnosis and monitoring by including patient self-measurements in an at-home setting. Objectives: To evaluate the accuracy, reliability, and usability of Bend Ease, a novel smartphone application, in measuring morning stiffness among patients with axSpA and healthy volunteers (hv) in a phase 1 study, and to use this tool at home to examine SRoM during the expected, early morning peak window of stiffness. Methods: Bend Ease was developed for this study to objectively measure morning stiffness by quantifying forward flexion bend angle based on triaxial accelerometry. In this ongoing phase 1 study, data were analyzed from a one-week period in hv and axSpA patients, with bend angle measured via both video capture and the Bend Ease app in a clinical setting (days 1 and 7) and via Bend Ease in an at-home setting (days 2-6) after wakeup, 30 min after wakeup (wake + 30 min), and 1 hr after wakeup (wake + 1 hr) (Figure 1). The data cutoff for the present analysis is 2 November 2023; the end of study is planned for January 2024. At-home adherence was assessed for days 2-6 based on 3 repeated forward bends (the median of which was used to calculate bend angle at a given timepoint) completed at 3 timepoints per day. Study participants also completed the System Usability Scale (SUS) on days 1 and 7 to evaluate usability. The accuracy of Bend Ease against a video-based bend angle capture method (gold standard) was assessed using Pearson's correlation coefficient (r). Bend angles of hv and axSpA patients were compared using the Mann-Whitney U test. Results: Data were available from 20 hv and 9 axSpA patients. Bend Ease accurately measured the forward flexion bend angle with a strong Pearson's correlation compared to the video-based method (r=.77) (Figure 2). The test-retest reliability calculated at the wake timepoint over all at-home days (days 2-6) was robust (ICC=.84). Overall adherence to the clinical protocol in an at-home setting was 91.5%. Usability was rated highly (median SUS score of 91.2), indicating good user acceptance. Participants were also able to rapidly perform bend measurements, with a median time of 9.5 seconds per bend task (28.6 seconds for triplicate tasks). In an at-home setting, the wake bend angle and wake + 30 min bend angle differed significantly between the hv and axSpA cohorts (P<.01). By wake + 1 hr, the hv and axSpA groups were no longer statistically distinguishable. When the bend angle was measured in the afternoon within a clinical setting, however, there was no significant distinction between the hv and axSpA cohorts, demonstrating that SRoM measures upon waking best distinguish the impaired spinal mobility of axSpA patients relative to hv. Consistently, when evaluating changes at an individual level, axSpA patients showed a numeric increase in bend angle from waking to the first hour thereafter, while the bend angle of hv remained relatively stable. Conclusion: Bend Ease is a first-of-its-kind digital health technology demonstrating accuracy and reliability for measuring SRoM. Its high usability, rapid measurement capability, and adherence rates indicate its potential for regular at-home monitoring in axSpA. The significant differentiation between hv and axSpA populations in bend angle at wake and wake + 30 min underscores the potential of Bend Ease as a measure of morning stiffness and the importance of serial SRoM measurement during this critical time window to complement in-clinic assessments. This digital health technology offers an advancement in the objective assessment of axSpA, potentially improving diagnosis accuracy, patient care management, and drug efficacy measurement. REFERENCES: NIL. Acknowledgements: AbbVie and the authors thank the patients, study sites, and investigators who participated in this clinical trial. AbbVie funded this study, designed the Bend Ease smartphone application, and participated in the study design, research, analysis, data collection, interpretation of data, reviewing, and approval of the publication. All authors had access to relevant data and participated in the drafting, review, and approval of this publication. No honoraria or payments were made for authorship. Medical writing support was provided by Matthew Eckwahl, PhD, of AbbVie. Disclosure of Interests: Angela Crowley AbbVie, GSK, Horizon, and Janssen, AstraZeneca, Novartis, and UCB, AbbVie, Lilly, Labcorp, Set Point Medical, and SunPharma, Lori Siegel AbbVie, Amgen, Boehringer Ingelheim, GSK, Novartis, UCB, and Sanofi-Genzyme, AbbVie, Amgen, Boehringer Ingelheim, GSK, Novartis, UCB, and Sanofi-Genzyme, Heather Jones AbbVie, AbbVie, Dan Webster AbbVie, AbbVie, Elina Moon AbbVie, AbbVie, Tiancheng He AbbVie, AbbVie, Liuqing Yang AbbVie, AbbVie, Jeffrey Curtis AbbVie, Amgen, Bristol Myers Squibb, Janssen, CorEvitas, Lilly, Novartis, Sanofi, Pfizer, and UCB, AbbVie, Amgen, Bristol Myers Squibb, Janssen, CorEvitas, Lilly, Novartis, Sanofi, Pfizer, and UCB.