The relative value of spinal and thoracic mobility measurements in ankylosing spondylitis.

The relative value of nine spinal and thoracic mobility measurements was investigated in 73 male patients with ankylosing spondylitis (AS). The value of a test was obtained by the relative ranks of validity, reliability and sensitivity to change. Validity was determined as age-adjusted correlation of the test result with AS-specific radiological changes in the lumbar spine. Reliability was determined as inter-observer error. Sensitivity to change was determined as change in test result during an intensive rehabilitation course. The five most valuable tests were rotation of the thoracolumbar spine (TR), finger-to-floor distance (FFD), the Schober test, thoracolumbar flexion and occiput-to-wall distance. Of these, FFD had high reliability and sensitivity ranks, but poor correlation with AS-specific spinal changes. TR had high validity and sensitivity ranks, and improvement of the measurement technology would probably result in a superior test for the follow-up of AS. Chest expansion and vital capacity had low ranks in all comparisons.