The association of cervical and lumbar mobility with functional ability in axial spondyloarthritis: Insights from the CASTRO registry using Inertial Measurement Unit system.

Objective: This study aimed to evaluate the association of cervical and lumbar mobility with functional ability in patients with axial spondyloarthritis (axSpA) using an inertial measurement unit (IMU) sensor system, as well as the influence of disease duration on this association.

Methods: This cross-sectional study included 156 patients with axSpA from the Córdoba axSpA Task Force Registry and Outcomes (CASTRO) registry. Spinal mobility was assessed with the IMU system and functional ability was measured using the Bath Ankylosing Spondylitis Functional Index (BASFI). Patients were categorized into non-longstanding (≤23 years) and longstanding (>23 years) groups based on the median disease duration. Univariable and multivariable linear regressions were conducted to evaluate the variability of BASFI explained by each spinal movement (coefficient of determination [R²]).

Results: Multivariable linear regression analysis showed that cervical movements collectively explained 19.9 % (R = 0.199) of BASFI variability, while lumbar mobility accounted for 11.3 %. Among longstanding axSpA patients, cervical rotation (unstandardized regression coefficient [B] = -0.68, 95 % CI1.13 to -0.24) and lumbar flexion (B = 0.65, 95 % CI 0.05 to 1.24), were independently associated with the BASFI scores. In non-longstanding patients, lumbar mobility, particularly lumbar rotation (B = -0.51, 95 % CI0.97 to -0.05), showed a stronger association with functional ability.

Conclusions: This study suggests that cervical mobility is more strongly associated with functional ability than lumbar mobility in axSpA patients. However, the impact of cervical and lumbar mobility on functional ability varies with disease duration.