Anatomic variations exist in the facet joint orientation, shape, and size at L4-5. This morphology is further modified by degenerative changes in spinal stenosis and degenerative spondylolisthesis. This study explored the morphologic alteration of “pedicle-to-pedicle” decompression on the facet joints in normal patients, spinal stenosis patients, and degenerative spondylolisthesis patients. Using computerized digitization, computed tomographic scan images of the facet joint at L4-5 and the medial border of the pedicle at L5 were superimposed. The facet joint orientation, coronal dimension, percentage, and absolute reduction in coronal dimension after pedicle-to-pedicle decompression, and residual coronal dimension after decompression at L4-5 were measured for the three groups. There is a significantly reduced coronal dimension of the facet joint in degenerative spondylolisthesis patients compared with spinal stenosis and normal patients (P < 0.01). The average reduction of the facet joint coronal dimension is 34% (SD 30%) in degenerative spondylolisthesis, and 36% (SD 25%) in spinal stenosis. The smaller preoperative coronal dimension in degenerative spondylolisthesis leads to a significantly reduced residual coronal dimension in degenerative spondylolisthesis compared with normal patients (5.9 mm [SD 4.3 mm] vs. 9.3 mm [SD 3.5 mm]), respectively. Wide variations in facet joint reduction and residual facet joint coronal dimension exist. The significantly reduced coronal dimension after decompression in degenerative 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 both spinal stenosis and degenerative spondylolisthesis patients should be integrated into decisions about fusion for stability at the L4-5 level.
From the Department of Orthopaedics and Rehabilitation, McClure Musculoskeletal Research Center, Spine Institute of New England, Vermont Rehabilitation Engineering Center, The University of Vermont, Burlington, Vermont. Leon Grobler's current address is Orthopaedic Surgery and Rehabilitation, The Bowman Gray School of Medicine, Wake Forest University, Medical Center Boulevard, Winston-Salem, NC 27157-1070.
Supported by National Institute of Disability and Rehabilitation Research, the McClure Musculoskeletal Research Center, and the Spine Institute of New England research funds.
Accepted for publication February 9, 1993.