Frontal-Plane Postural Angle Changes Between Double-Leg and Single-Leg Stance in Axial Spondyloarthritis: Associations with Spinal Mobility and Core Endurance

Purpose: To investigate frontal-plane shoulder and pelvic angle changes between double-leg and single-leg stance in axial spondyloarthritis (axSpA) and to examine their associations with core endurance and clinical parameters.Material and Methods: In this cross-sectional study, 55 patients with axSpA (categorized as non-radiographic axSpA, radiographic axSpA without spinal structural involvement, or radiographic axSpA with spinal structural involvement) and 19 healthy controls were evaluated. Core endurance was assessed using flexor, extensor, and bilateral side bridge tests. Angle changes were evaluated using a two-dimensional mobile posture analysis system. Results: Extensor endurance was significantly lower in patients with radiographic axSpA with spinal structural involvement group than in controls (adjusted p=0.010). Frontal-plane shoulder and pelvic angle changes did not differ between groups (p>0.05) and were not associated with core endurance or clinical parameters. Weak correlations were observed between right-stance shoulder angle change and selected spinal mobility measures.Conclusion: Endpoint frontal-plane shoulder and pelvic angle changes were not detectably altered in axSpA. These findings reflect endpoint alignment rather than continuous compensatory movement strategies.