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 t he 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 o f the facet joint coronal dimension removed if a decompression was per formed up to the medial border of the L5 pedicle (facet joint reductio n); and the residual coronal dimension of facet joint after such a dec ompression (residual facet joint). The lateral radiographs were analyz ed for presurgical disc height and the presence of traction spurs or s pondylophytes. A well-maintained disc height was associated with an in crease slip (7.47%) compared with those cases with a narrow or complet e loss of disc space before surgery (4.84% P < 0.1 trend). Presence of spondylophytes was associated with a reduced tendency to slip, When s pondylophytes 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 signifi cant. This study suggests that the development of postoperative spondy lolisthesis is related to facet joint orientation and dimensions, rath er than the absolute amount of joint removed. The stabilizing effects of reduced disc height and spondylophytes were confirmed.