Postoperative spondylolisthesis.

The conditions and clinical significance of postlaminectomy spondylolisthesis were investigated in eight cases of lumbar spondylolisthesis, including five with slips not present at the time of decompression and three with progression of previously observed degenerative slips. All were women with an average age of 62 years. The major instability occurred at the L4-L5 level in seven of the eight cases. Either bilateral facetectomy or transection of the pars interarticularis had been part of the laminectomy. The L4-L5 level seems predisposed to spondylolisthesis in women whose facets have been destabilized by either bilateral removal or pars transection. Extra effort should be made to preserve facet stability during decompression, or add fusion after excision of posterior elements of spondylolisthesis.