Ab0930 Towards Objective Measurement of Spinal Mobility in Axial Spondyloarthritis – Benchmarking an Inertial Measurement Unit System With an Optical Measurement System

Background: Patients with axial spondyloarthritis (axSpA) suffer from progressive spinal stiffness which can significantly restrict the range of movement 1. Quantifying spinal mobility is a cornerstone of clinical assessment 2 and is currently achieved by the Bath Ankylosing Spondylitis Metrology Index (BASMI) 3. This assessment is based on manual distance measurements by a trained physician and is thus very examiner-dependent 4. Objectives: To compare the data quality of an inertial measurement unit (IMU) system with a state-of-the-art optical measurement system (OMS) motion capture technology for spinal mobility assessment in axSpA patients and healthy controls (HC). Methods: AxSpA patients and HC were recruited (Internal Medicine 3 outpatient clinics Erlangen, Germany) for this cross-sectional study. Serum C-reactive protein (CRP) concentration and visual analogue scale (VAS) for global disease activity were retrieved from clinical data. Conventional BASMI scores were obtained by a trained team member. OMS and IMU measurements were conducted on the day of the clinical visit quantifying the following movements: spinal lateral flexion (LF), spinal frontal flexion (FF) and cervical rotation (CR). Fifty-four retro-reflective markers and 16 IMU devices (myoMOTION by Noraxon, Scottsdale, USA) were placed on defined anatomic sites (Figure 1) and marker motion was detected with 11 infrared cameras (Oqus 7+, Qualisys, Göteborg, Sweden). The spinal movements were repeated three times and metric data (distance in cm or degree of rotation) were analyzed from OMS and IMU measurements. The comparison of IMU BASMI with clinical BASMI was performed with BASMI10-normalized values (0-10). Spearman's Rank Correlation Coefficient (ϱ) and Bland-Altman analyses were conducted for all patient data. Intraclass Correlation Coefficients were applied for IMU repeatability analysis 5. Results are stated as mean (standard deviation). Results: 30 axSpA patients (age: 40.9 (12.6) years, 53% female, CRP 5.0 (13.8) mg/l, VAS global 41 (27) mm) and 20 HC (age 28.4 (3.7) years, 55% female) participated in this study. Two patients were excluded due to failed data post-processing, resulting in 28 patients for this analysis. Moderate to strong positive Spearman´s rank correlations were observed for IMU and OMS assessed BASMI data (axSpA: LF ϱ=0.88, FF ϱ=0.57, CR ϱ=0.98, pϱ=0.54 pϱ=0.52 p=0.01, controls: FF ϱ=0.65 p=0.002). The metric results for the patient group are as following: 1) LF: IMU 21.6 (6.7) cm and OMS 19.3 (5.3) cm, 2) FF: IMU 9.6 (2.1) cm and OMS 8.7 (3.9) cm, 3) CR: IMU 65.9 (11.5) and OMS 64.4 (11.5) degrees. The Bland-Altman Plots give a detailed view of measurement agreement in axSpA patients (Figure 2) with mean differences limits of agreement of A) LF 2.3 -3.8-8.4 cm, FF 1.2 -4.9-7.2 cm, CR 1.0 -2.7-4.7 degrees and B) LF 2.35 -0.9-5.6, FF 2.17 -1.6-5.9, CR 0.01 -3.0-3.0 BASMI units, showing consistent best agreement for CR. Repeatability analysis of the IMU measurements resulted in excellent ICC for all exercises in IMU and OMS, that varied from 0.95 – 0.99 ICC(2,1) for axSpA and 0.81 -1.00 ICC(2,1) for controls. Conclusion: The accuracy of the IMU system compared to the gold standard OMS can be considered as good with similar metric results for the three exercises. The BASMI obtained through IMU translates into the clinical BASMI with differences of up to two BASMI units (best agreement for CR and least for FF), which need to be further investigated. IMU measurements show excellent repeatability across all assessed movements, in patients and controls. Overall the results illustrate the potential of IMU to objectively measure spinal mobility in axSpA patients. REFERENCES: 1 Maatallah K. et al., Curr Rheumatol Rev. 2022 2 Castro, M. et al. Clin Rheumatol. 2016 3 Zochling J. et al. Arthritis Care & Research. 2011 4 Calvo-Gutiérrez, J. et al. BMC musculoskeletal disorders. 2016 5 Koo TK. et al. J Chiropr Med. 2016 Acknowledgements: This study war partially funded by Novartis Pharma GmbH, Germany and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – SFB 1483 – Project-ID 442419336, EmpkinS. Disclosure of Interests: None declared.