Ankylosed posterior spinal structures: the catalyst for syndesmophytes growth and impaired spinal mobility in axial spondyloarthritis.

Abstract

To identify risk factors for spinal structural progression and determine the most significant impact on syndesmophytes growth and impaired spinal mobility in axSpA. Baseline and 2-year follow-up clinical, thoracic and lumbar spine CT data of 94 patients were analysed. A vertebral syndesmophytes unit (VSU) was defined as syndesmophytes anterior to the vertebral body and its intervertebral disc space, with volumes calculated by Mimics software. Bilateral facet/costovertebral/costotransverse joints were assessed. Syndesmophytes growth was assessed with a linear mixed-effects model, and posterior spinal structures progression were evaluated with generalized linear mixed-effects models. Influence of spinal changes on BASMI-change was analysed with a generalized linear model. Conditional R2 values quantified model fit, with coefficient percentage representing each variable's contribution. Syndesmophytes growth occurred in 44.99% of VSUs. Baseline facet joints ankylosis/erosion and costovertebral/costotransverse joints ankylosis were associated with syndesmophytes growth (P < 0.05). Contributing factors included changes of facet joints (56.84%), costotransverse joints (17.65%), costovertebral joints (16.26%) and age (6.08%). Structural progression was found in 8.79% (281/3196) of facet joints, among which 43.77% progressed to ankylosis, with age (6.56%) and baseline ankylosis/erosion (48.02%) driving this change. In addition, 16.31% of costovertebral joints progressed, with age (3.63%) and 2-year costotransverse lesions progression (12.30%) as significant predictors. And 2.07% of costotransverse joints progressed, with costovertebral lesions (25.61%) and age (0.81%) correlating significantly. Ankylosed costovertebral joints (25.10%), facet joints (16.86%), costotransverse joints (12.72%) and syndesmophytes growth (4.45%) significantly contribute to BASMI-change. Ankylosed posterior spinal structures emerged as the paramount driver of syndesmophytes growth and a critical impediment to spinal mobility in axSpA.