POS0948 HYPERKYPHOSIS IN AXIAL SPONDYLOARTHRITIS: FACTORS THAT PRODUCE ITS APPEARANCE AND EFFECT ON MOBILITY AND FUNCTION

Background: Hyperkyphosis (HK) is a characteristic sign in patients with a large level of axial spondyloarthritis (axSpA) involvement. Kyphosis is defined as a sagittal deviation in the spinal alignment. Kyphosis can be graded in severity by the Cobb angle. The occiput-wall distance (OWD) is a surrogate measure of kyphosis. When this distance is greater than 0 cm, it is because the patient has an advanced affectation level that produces a reduction of physical function and other comorbidities. It is important that HK does not appear in the patient. Objectives: To analyze contributors and effects of HK in patients with axSpA. Methods: Nonparametric preprocessing for parametric causal inference was used for selection of two matched groups, formed by 42 axSpA patients each one, from the CASTRO cohort with similar covariate distributions (age and sex). Outcomes analyzed, besides OWD, included activity (BASDAI, ASDAS), physical function (BASFI) and mobility (BASMI). An inertial sensor-based system (ViMove) was used to analyze cervical and lumbar mobility and to calculate the UCOASMI index[1]. Structural damage was assesed according the mSASSS and its components (cervical and lumbar). Results: Mean (sd) values of the different variables for each group are shown in table 1. Significant differences according to an independent t-test (p), variation coefficient (V.C.), effect size (E.S.) and correlation with OWD (Pearson r), are also included in this table. There were not significant differences in age, sex as expected. HK group patients started earlier (5.2 years). The percentage of HLAB27+ is similar, so this antigen has not a relationship with HK. BMI is greater in HK group (14%); this can be a factor for HK appearance or a consequence of HK (less physical activity). Activity (according ASDAS) was slightly higher in HK. There were very significant differences in structural damage, and HK appears to be equally affected by damage at cervical and lumbar regions. BASFI also shown a significant reduction in HK. There was great reduction of mobility according to mobility indexes and cervical range of movement (23%-33%). In a multivariate regression analysis using all variables of the table and OWD as dependent variable, only mSASSS and BMI were included in the final model (adj. r2= 0.61). In a ROC analysis, mSASSS shown to and acceptable variable to distinguish between groups (AUC=0.70, cutoff=13). ASDAS obtained lower results (AUC=0.60, cutoff=2.38). Figure 1 shows cumulative probability plots of mSASSS and ASDAS versus OWD, showing cutoff values determined by ROC analysis. Conclusion: Structural damage, in cervical and lumbar spine, are the main contributor to HK appearance in axSpA patients. Inflammation it is not so determinant and acts only in the short term. HK produces a significant reduction of cervical mobility and physical function. New treatments that decrease radiographical progression, and overweight reduction are the most important factor to avoid HK. References: [1]Measuring Spinal Mobility Using an Inertial Measurement Unit System: A Validation Study in Axial Spondyloarthritis. Diagnostics 2020, 10(6), 426. Disclosure of Interests: None declared