Fracture of the S1 vertebral body in a patient with ankylosing spondylitis.

We report an unusual case of spinal fracture in ankylosing spondylitis. The fracture occurred through the S1 vertebral body and resembled a traumatic spondylolisthesis. Treatment consisted of prompt operative intervention after extensive diagnostic evaluation. The case emphasizes the difficulty of diagnosing spinal fractures in those with ankylosing spondylitis, the necessity for being alert to the possibility of fracture in this group, and the value of early surgical intervention for sacral fractures with neural deficit.