Stenosis of the lumbar spinal canal in vertebral ankylosing hyperostosis.

Certain morphologic features frequently observed in radiography or computed tomography (CT) scan in patients with hyperostosis led us to study the association between a narrowed spinal canal and vertebral hyperostosis. Twenty-eight items were selected and studied by three different investigators (two rheumatologists and one radiologist) in radiographs and CT scans of 100 patients with acquired stenosis of the lumbar canal, with or without hyperostosis (46 and 54 cases, respectively). The most distinctive points that we suggest can be used as diagnostic criteria of the hyperostotic narrowed lumbar canal are anterior or posterior lateral marginal somatic osseous proliferations, proliferations of the nonarticular aspects of the posterior apophyses, and ossifications of the posterior articular capsule and of the ligaments (yellow ligament, posterior longitudinal ligament, and the supraspinal ligament). Four of these six criteria should be present to establish the diagnosis of hyperostotic lumbar stenosis. The appearance of lumbar hyperostosis on X-ray or CT scans differs from that of simple degenerative changes due to arthrosis, and the hyperostosis can be held responsible for dural compression.