OBJECTIVE:To investigate the association of spinal inflammation on MRI in patients with various clinical, functional and radiological outcomes in patients with axial spondyloarthritis (SpA). METHODS:Three hundred and ninety-seven participants with axial SpA and back pain were recruited from 10 rheumatology centres. Clinical, biochemical and radiological parameters were collected and participants underwent MRI of the spine. MRI features including inflammatory lesions of facet joints and costovertebral joints, corner inflammatory lesions, and spondylitis were assessed. BASFI, Bath Ankylosing Spondylitis Disease Activity Index, Bath Ankylosing Spondylitis Global Index, BASMI and modified Stoke Ankylosing Spondylitis Spinal Score were measured. Multivariate linear regression models were used to determine the associations between MRI parameters and various clinical, functional and radiological outcomes. RESULTS:BASMI and BASFI correlated well with inflammatory features in spinal MRI. Multivariate analysis showed that lumbar facet joint inflammation was independently associated with BASMI (regression coefficient (β) = 0.12, P < 0.001), lumbar spinal flexion (β = 0.13, P = 0.00), lateral spinal flexion (β = 0.09, P = 0.04), tragus-to-wall distance (β = 0.16, P < 0.001) and BASFI (β = 0.14, P = 0.01). Costovertebral joint inflammation was also associated with BASMI (β = 0.08, P = 0.05). CONCLUSION:Inflammatory lesions of facet and costovertebral joints in MRI are associated with restriction in spinal mobility and functional impairment. These important yet commonly overlooked lesions should be reviewed in clinical practice in patients with SpA.