The Influence of Spondylolisthesis Reduction on the Adjacent Lumbar Segment

Objective Mild to moderate stenosis at the adjacent level sometimes co-occurs with lumbar spondylolisthesis, but whether to include the adjacent level during surgery for the index level is a matter of debate. Spondylolisthesis causes anterior slipping of the vertebra and reduces the segmental angle at the index level, and the adjacent level may compensate for this change through hyperextension to maintain spinal balance. This study investigated the radiological changes and clinical outcomes of adjacent segment stenosis in patients with lumbar spondylolisthesis. Methods Forty consecutive patients (12 men and 28 women, age 66.6±10.4 years) underwent single-level oblique lumbar interbody fusion for L4-5 or L5-S1 spondylolisthesis. Lumbar central stenosis at the cranial adjacent segment was present in 16 patients (stenosis group) and absent in 24 patients (no-stenosis group). Clinical and radiological parameters were longitudinally compared between the stenosis and no-stenosis groups. Results Both groups showed similar and significant clinical improvement. The segmental angle at the index level significantly improved in both groups (p<0.05), but the segmental angle at the cranial adjacent segment significantly decreased only in the stenosis group (p<0.05). The spinal canal area at the adjacent level significantly improved only in the stenosis group (p<0.05). Conclusion Realigned spondylolisthesis may reduce hyperextension of the adjacent segment. If mild lumbar spinal stenosis is present at an adjacent level to spondylolisthesis, it may not be essential to include it in surgery. Key words: Lumbar vertebrae; Spinal fusion; Spinal stenosis; Spondylolisthesis