Fractures of the thoracolumbar spine in ankylosing spondylitis.

Fractures through the disc or juxta-end plate region of the vertebra as well as the posterior elements have been observed in the thoracic and lumbar spine in ankylosing spondylitis. These are usually associated with increasing pain, usually do not produce neurologic deficit, and may require orthopedic fixation to heal. Irregularity and sclerosis at the margins secondary to pseudarthrosis may develop and should not be confused with a pyogenic or granulomatous infection. Biomechanically these fractures resemble the "seat belt type" or Chance fracture probably because of shifting of the axis of flexion and extension in the ankylosed spine away from its normal location in the center of the nucleus pulposus.