The zygapophyseal joint determines morphology of the enthesophyte

Objective. To determine the contribution of zygapophyseal joint ankylosis o n the morphology of the spinal enthesophyte. Methods. Radiographic analysis of lumbar spine in ankylosing spondylitis (A S) patients with different types of enthesophytes. Computerized axial tomog raphic analysis of the zygapophyseal (ZA) joints of the lumbar spine of AS patients with chunky enthesophytes and bridging syndesmophytes. Results. Four patients with AS were selected for the simultaneous presence of chunky enthesophytes and bridging syndesmophytes. At the levels with bri dging syndesmophytes at least one ZA joint was ankylosed. At the levels wit h chunky enthesophytes alone the ZA joints were not ankylosed. Conclusion. The morphology of the enthesophytes is influenced by the presen ce of ankylosis in the: ZA joint.