Are syndesmophytes most prevalent in the lumbar or in the cervical spine in patients with ankylosing spondylitis and do they develop in a specific direction?

Objectives. To describe the distribution of prevalent syndesmophytes and bridges, and the occurrence of new ones in a prevalence cohort of patients with AS. Methods. Clinical and radiological data from 132 patients from the Outcome in Ankylosing Spondylitis International Study of which complete sets of radiographs were available at baseline and at 2- and 4-year follow-up were used. Results. At baseline, 81 (61%) patients, of which 17 (45%) were females and 64 (65%) males (P = 0.03), had prevalent (bridging) syndesmophytes. Both syndesmophytes and bridges were found at all vertebral levels. Syndesmophytes were more frequently seen in the cervical spine compared with the lumbar spine (mean per vertebral level 17.5 vs 11.2%, respectively, P = 0.01). Bridges were more frequently seen in the lumbar spine compared with the cervical spine (mean per vertebral level 16.9% vs 12.1%, P = 0.02). With increasing disease duration more (bridging) syndesmophytes were found, occurring similarly at the lumbar and cervical spines. After 2- and 4-years of follow-up, new (bridging) syndesmophytes developed throughout the entire cervical and lumbar spines. Conclusion. In general, syndesmophytes occur more frequently in the cervical spine and bridges more frequently in the lumbar spine, but neither a specific predilection site nor any particular order for occurrence and development of syndesmophytes could be detected.