Construct validity of clinical spinal mobility tests in ankylosing spondylitis: a systematic review and meta-analysis

The study aimed to determine, using systematic review and meta-analysis, the level of evidence supporting the construct validity of spinal mobility tests for assessing patients with ankylosing spondylitis. Following the guidelines proposed in the Preferred Reporting Items for Systematic reviews and Meta-Analyses, three sets of keywords were used for data searching: (i) ankylosing spondylitis, spondyloarthritis, spondyloarthropathy, spondylarthritis; (ii) accuracy, association, construct, correlation, Outcome Measures in Rheumatoid Arthritis Clinical Trials, OMERACT, truth, validity; (iii) mobility, Bath Ankylosing Spondylitis Metrology Index-BASMI, radiography, spinal measures, cervical rotation, Schober (a further 19 keywords were used). Initially, 2558 records were identified, and from these, 21 studies were retained. Fourteen of these studies were considered high level of evidence. Compound indexes of spinal mobility showed mostly substantial to excellent levels of agreement with global structural damage. Individual mobility tests for the cervico-thoracic spine showed only moderate agreements with cervical structural damage, and considering structural damage at the lumbar spine, the original Schober was the only test that presented consistently substantial levels of agreement. Three studies assessed the construct validity of mobility measures for inflammation and low to fair levels of agreement were observed. Two meta-analyses were conducted, with assessment of agreement between BASMI and two radiological indexes of global structural damage. The spinal mobility indexes and the original Schober test show acceptable construct validity for inferring the extent of structural damage when assessing patients with ankylosing spondylitis. Spinal mobility measures do not reflect levels of inflammation at either the sacroiliac joints and/or the spine.