Outcome of the L5-S1 Segment after Posterior Instrumented Spinal Surgery in Degenerative Lumbar Diseases

Background: Posterior decompression, instrumentation, and posterolateral fusion are surgicalprocedures for the treatment of degenerative lumbar diseases. Solidfusion usually causes adjacent problems. This study investigated the clinicaloutcome and radiographic fate of the L5-S1 segment in patients who underwentposterior 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 (includingdegenerative spondylolisthesis and degenerative lumbar scoliosis) withspinal stenosis. Modified Brodsky’s criteria and the Oswestry disabilityindex were used to evaluate patients before surgery and at the final followup.Degenerative changes in the L5-S1 intervertebral disc were evaluatedwith the University of California at Los Angeles (UCLA) grading scale.Adjacent L5-S1 segmental instability was defined as the appearance ofretrolisthesis, anterolisthesis, or lateral listhesis in the static or dynamic radiographsat the final follow-up.Results: Only 1 of these 181 patients developed inferior adjacent instability, but therewere no symptoms related to this instability. The mean pre-operative L5-S1disc 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 necessitatingfurther L5-S1 fusion during follow-up. One hundred fifty-six patients (86%)exhibited satisfactory results (good or excellent). The mean Oswestry scorewas 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 symptomaticL5-S1 disc degeneration requiring further L5-S1 fusion at a mean 5.1years follow-up.