Exploring the influence of sagittal imbalance on spinal mobility, function and quality of life in axial spondyloarthritis: a novel comprehensive compensatory mechanism of adaptation

Objectives To investigate whether sagittal imbalance, defined by sagittal vertical axis (SVA) using EOS ® imaging, is associated with spinal mobility, function, and quality of life in patients with axial spondyloarthritis (axSpA). Methods Patients with axSpA were cross-sectionally assessed for sagittal imbalance (SVA ≥ 50 mm). Spinal mobility (BASMI), function (BASFI) and quality of life (ASQoL) were compared between patients with and without sagittal imbalance. Multivariable analyses examined the associations between SVA and the above-mentioned disease outcomes, adjusted for confounders. Mediation analysis explored whether sagittal alignment mediated the relationship between spinal mobility and structural damage. Results Among 117 patients (mean age 51 (SD 11) years, 68% males), 44 (38%) had sagittal imbalance. SVA was only independently and significantly associated with BASMI but not with BASFI or ASQoL. SVA minimally mediated the relationship between mSASSS and BASMI. The optimal BASMI cutoff to identify patients with sagittal imbalance was 5.2 with 80% of correct classification. Conclusions Sagittal imbalance is associated with impaired spinal mobility but not with impaired function or quality of life. These findings may reflect compensatory mechanisms for sagittal balance in long-term axSpA patients. Impaired spinal mobility can be used to identify patients with sagittal imbalance who may benefit from physiotherapy or rehabilitation. Clinical trial number Not applicable.