INFLUENCE OF DISC HEIGHT ON OUTCOME OF POSTEROLATERAL FUSION

Abstract

Purpose of the study: Experimentally, posterolateral fusion only allows incomplete control of flexion/extension, rotation and lateral inclination. This defect of posterolateral fusion is most marked with there is a wide anterior gap. For certain authors, this situation justifies use of intersomatic arthrodesis. The purpose of this work was to evaluate, within a spinal segment immobilized by posterolateral fusion, the changes observed in disc height and the possible clinical and radiographic impact of a change in disc height.

Material and methods: This was a retrospective analysis of a consecutive series of patients who underwent posterolateral fusion from January 1999 through December 2003 performed in addition to radicular release for degenerative spondylolisthesis were included. Functional symptoms were noted using: VAS, Beaujon function scale, Beaujon self-administered questionnaire, satisfaction scale, GHA28 anxiety/depression scale, and SF36 quality of life questionnaire. Spineview® was applied at the olisthesic level (disc height, listhesis, anglulation), at adjacent levels, for pelvic parameters, sagittal tilt, and vertebral motion on stress views. We searched for a correlation between the consequences of changes in these variables was and the functional outcome as well as the quality of the fusion. The effect of variations in the following preoperative variables was studied with multivariate analysis: disc height, intervetebral angulaion, listhesis, vertebral motion, sagittal balance, use of osteosynthesis or not.

Results: Forty patients were reviewed with a mean follow-up of 38 months (range 15–70 months). Decreased disc height at the olithesic level was associated with local kyphosis. The level above tended towards lordosis while the level below towards kyphosis. These variations had no effect on the final functional outcome.

Discussion: No formal argument could be found in the literature favoring the use of intersomatic arthrodesis to complete posterolateral fusion for the treatment of degenerative spondylisthesis. Disc height is lost after isolated posterolateral fusion with a risk of local kyphosis and persistent intervertebral motion, but these effects do not appear to influence the functional outcome nor the rate of fusion. More than disc height, it would appear that sagittal balance should be preserved to improve functional outcome.

Conclusion: This study enabled us to observe, as is reported in the literature, decreased disc height after posterolateral fusion for degenerative spondylolisthesis. However, there appears to be no correlation between this decreased disc height and the functional outcome. More than disc height, sagittal balance appears to be the determining factor.