AB0734B BONY BRIDGE ON FACET JOINT OR LATERAL SIDE OF LUMBAR VERTEBRA IS MORE FREQUENT AND CORRELATED WITH LUMBAR FLEXION FUNCTION THAN THAT ON ANTERIOR SIDE OF LUMBAR VERTEBRA IN ANKYLOSING SPONDYLITIS; ANALYSIS OF ANKYLOSIS REGISTRY OF AXIAL SPONDYLOARTHRITIS (ANKAS)
Background Ankylosing spondylitis (AS) is a form of chronic inflammatory arthritis characterized by sacroiliitis and a marked propensity for sacroiliac joint and spinal fusion. The modified Stoke ankylosing Spondylitis Spinal Score (mSASSS) has been used when measuring radiographic progression in aS, which only measures bony changes of anterior side in vertebral body (AV). Variation of this score is too small to assess radiographic progression in aS. Some patients have syndesmophytes on lateral side in vertebral body (LV) or ankylosis in facet joints (FJ). Objectives We planned this study to know which side of lumbar vertebra ankylosis more frequently develops in and is more correlated with lumbar flexion function. Methods We analyzed aNKylosis registry of axial Spondyloarthritis (ANKAS). In this cohort, the patients with aS are examined by anteroposterior and lateral view of X-ray every 2 years and low dose whole spine computed tomography (CT) every 5 years to determine radiographic progression. We analyzed the location of near total or total bone bridge at each level of lumbar spine by X-ray and CT in 518 patients with aS. Results Male was 78% and mean age was 38.8 ± 2.8. Ankylosis or bony bridge in sacroiliac joint (SIJ), FJ, LV and aV was respectively 55.2%, 22.8%, 21.6% and 13.1%. T12L1 was the most frequent level of ankylosis in FJ (31.7%) and LV (30.3%). For FJ and LV, there was a tendency that upper levels of spine have more ankylosis, but not in aV. The patients who didn’t have SIJ ankylosis also have a tendency of not having any bony bridge in lumbar spine (negative predictive value: 92.24%, OR 28.1, 95% CI:16.3-48.4, p=0.000). We analyzed the correlation between the flexion score of Bath aS Metrology index (BASMI) 10 and the site of ankylosis. FJ ankylosis showed the strongest correlation with lumbar flexion range (R2=0.456, p=0.000), but bony bridge of LV and aV showed weak correlation with that (respectively, R2=0.288, R2=0.155, p=0.000). We analyzed the correlation between ankylosis of FJ and bony bridge of aV or LV respectively. Ankylosis of FJ and bony bridge of LV showed a stronger correlation (R2=0.712, p=0.000) than that of aV (R2=0.515, p=0.000) Conclusion Bony bridge in LV is not only more developed and correlated with ankylosis in FJ, but also more correlated with limitation of anterior lumbar flexion than that in aV. We suggest bony changes of LV should be also included in radiographic score system for more sensitive detection of radiographic progression in aS. Disclosure of interests None declared