DECOMPRESSION FOR DEGENERATIVE SPONDYLOLISTHESIS AND SPINAL STENOSIS AT L4-5 - THE EFFECTS ON FACET JOINT MORPHOLOGY

Anatomic variations exist in the facet joint orientation, shape, and s ize at L4-5. This morphology is further modified by degenerative chang es in spinal stenosis and degenerative spondylolisthesis. This study e xplored the morphologic alteration of ''pedicle-to-pedicle'' decompres sion on the facet joints in normal patients, spinal stenosis patients, and degenerative spondylolisthesis patients. Using computerized digit ization, computed tomographic scan images of the facet joint at L4-5 a nd the medial border of the pedicle at L5 were superimposed. The facet joint orientation, coronal dimension, percentage, and absolute reduct ion in coronal dimension after pedicle-to-pedicle decompression, and r esidual coronal dimension after decompression at L4-5 were measured fo r the three groups. There is a significantly reduced coronal dimension of the facet joint in degenerative spondylolisthesis patients compare d with spinal stenosis and normal patients (P < 0.01). The average red uction of the facet joint coronal dimension is 34% (SD 30%) in degener ative spondylolisthesis, and 36% (SD 25%) in spinal stenosis. The smal ler preoperative coronal dimension in degenerative spondylolisthesis l eads to a significantly reduced residual coronal dimension in degenera tive spondylolisthesis compared with normal patients (5.9 mm [SD 4.3 m m] vs. 9.3 mm [SD 3.5 mm]), respectively. Wide variations in facet joi nt reduction and residual facet joint coronal dimension exist. The sig nificantly reduced coronal dimension after decompression in degenerati ve spondylolisthesis may be correlated to a trend to further anterior displacement if it is treated with decompression alone. Case-specific assessment of residual facet joint morphology after decompression in b oth spinal stenosis and degenerative spondylolisthesis patients should be integrated into decisions about fusion for stability at the L4-5 l evel.