Outcome of the L5-S1 segment after posterior instrumented spinal surgery in degenerative lumbar diseases.

BACKGROUND Posterior decompression, instrumentation, and posterolateral fusion are surgical procedures for the treatment of degenerative lumbar diseases. Solid fusion usually causes adjacent problems. This study investigated the clinical outcome and radiographic fate of the L5-S1 segment in patients who underwent posterior instrumented surgery for degenerative lumbar diseases. METHODS From January 1999 to December 2000, 181 patients (average age 59.4 years, range 45-79 years) underwent posterior decompression, posterior instrumentation, and posterolateral fusion for degenerative lumbar diseases (including degenerative spondylolisthesis and degenerative lumbar scoliosis) with spinal stenosis. Modified Brodsky's criteria and the Oswestry disability index were used to evaluate patients before surgery and at the final followup. Degenerative changes in the L5-S1 intervertebral disc were evaluated with the University of California at Los Angeles (UCLA) grading scale. Adjacent L5-S1 segmental instability was defined as the appearance of retrolisthesis, anterolisthesis, or lateral listhesis in the static or dynamic radiographs at the final follow-up. RESULTS Only 1 of these 181 patients developed inferior adjacent instability, but there were no symptoms related to this instability. The mean pre-operative L5-S1 disc degenerative score was 1.73 -/+ 0.66 and at the last follow-up, 1.87 -/+ 0.72 (p = 0.006). There was no symptomatic disc degeneration necessitating further L5-S1 fusion during follow-up. One hundred fifty-six patients (86%) exhibited satisfactory results (good or excellent). The mean Oswestry score was 21.8 -/+ 6.0 preoperatively, which improved to 9.6 -/+ 7.4 at the last follow-up (p = 0.001). CONCLUSIONS The L5-S1 disc degenerated more after posterolateral lumbar floating fusion. However, there was no symptomatic inferior adjacent instability or symptomatic L5-S1 disc degeneration requiring further L5-S1 fusion at a mean 5.1 years follow-up.