Spinal position sense and disease progression in ankylosing spondylitis - A longitudinal study

Study Design. A longitudinal study of spinal position sense in 27 patients with mild ankylosing spondylitis (AS). Objectives. To test the hypothesis that disease progression in AS is associated with deficits in spinal position sense. Summary of Background Data. AS is a progressive disease that frequently leads to deterioration in spinal posture. The cause of postural change is unknown. However, pathologic involvement of spinal entheses that contain proprioceptive afferents suggests that impaired proprioception may play a role. This study investigates whether longitudinal changes in posture and other measures of disease progression are associated with deficits in spinal position sense in patients with mild AS. Methods. Position sense was assessed using an electromagnetic movement analysis system, the 3-Space Fastrak, to determine the absolute error in reproducing flexed and upright spinal postures. Measurements were taken from sensors at T1, T7, L1, and S2 and repeated following a mean time interval of 13.7 months. Assessments of posture, disease activity, and function were also made on both occasions. Results. Patients showed a significant increase in disease activity, and losses in spinal mobility, over time. However, no significant changes in spinal posture or position sense were found. Repositioning errors in flexed postures were less than or equal to 3.50degrees at the first testing session and less than or equal to 3.77degrees at follow-up. Corresponding values for upright postures were less than or equal to 2.71degrees and less than or equal to 2.25degrees, respectively. Conclusions. Spinal position sense appears unaffected by disease progression in patients with mild AS. Longer follow-ups may help determine any association between disease-related postural change and spinal position sense in AS.