Postoperative spondylolisthesis at L4-5. The role of facet joint morphology.

Thirty-three patients underwent decompression without fusion at the L4-5 level for spinal stenosis or degenerative spondylolisthesis. Using preoperative and 1-year postoperative lateral lumbar spine radiographs, the incidence of postoperative spondylolisthesis of greater than 5% was found to be 58%. Computed tomographic scans were used to analyze the presurgical facet joint morphology and facet joint-pedicle spatial relationship. This allowed calculation of the facet joint orientation for each side; the coronal dimension of each facet joint; the amount of the facet joint coronal dimension removed if a decompression was performed up to the medial border of the L5 pedicle (facet joint reduction); and the residual coronal dimension of facet joint after such a decompression (residual facet joint). The lateral radiographs were analyzed for presurgical disc height and the presence of traction spurs or spondylophytes. A well-maintained disc height was associated with an increase slip (7.47%) compared with those cases with a narrow or complete loss of disc space before surgery (4.84% P < 0.1 trend). Presence of spondylophytes was associated with a reduced tendency to slip. When spondylophytes were controlled for there was a significant relationship between slip of greater than 10% and sagittal facet joint orientation. Although there was a lesser residual facet joint after decompression in the group that slipped these values were not statistically significant. This study suggests that the development of postoperative spondylolisthesis is related to facet joint orientation and dimensions, rather than the absolute amount of joint removed. The stabilizing effects of reduced disc height and spondylophytes were confirmed.