Degenerative lumbar spondylolisthesis with an intact neural arch (pseudospondylolisthesis).

Twenty patients treated for degenerative spondylolisthesis with an intact neural arch principally at the L4-5 interspace had neural compression caused by dislocation of the vertebral bodies and intrusions of lamina and enlarged, arthrotic facets into a stenotic spinal canal. The resulting "pincer" effect caused complete or partial block demonstrable on myelography, with nerve root and cauda equina compression. Most of the patients were women aged 45-84 years. Seven had neurogenic claudication. The majority had unrestricted straight-leg raising, and no signs of acute neural entrapment were seen as in patients with a herniated disc. Absent ankle reflexes, and weakness and atrophy of the anterior tibial muscle group were common, while sensation was relatively undisturbed. Treatment consisted of liberal laminar decompression including foraminotomy and medial or total facetectomy. Good-to-excellent results were obtained, and no patient was made worse by the procedure.