Disc Height Reduction in Adjacent Segments and Clinical Outcome 10 Years after Lumbar 360-Degree Fusion

Material and Methods: Forty patients (degenerative disc disease, n = 27; lytic spondylolisthesis, n = 13) underwent lumbar 360 fusion and instrumentation. Preoperative and follow-up lateral radiographs of the lumbar spine were studied. Disc heights of first and second cephalad adjacent segments were measured by Farfan's and Hurxthal's technique modified by Pope. Clinical outcome was studied using Oswestry Disability Index (ODI) and Visual Analogue Scale (VAS). Age, gender, prior surgery, fusion rate and number of fusion levels were investigated as potential factors affecting the outcome.

Results: Mean follow-up was 114 months. Clinical outcome showed an improvement of 44.6% in ODI and of 43.8% in VAS with a tendency towards better clinical results in group 2. Fusion rate was 95%. Disc height of the first cephalad adjacent segment in all patients was significantly reduced by an average of 21% (Farfan) respectively 19% (Pope), that of the second adjacent level by an average of 16% (Farfan) respectively 14% (Pope). A tendency towards a more explicit disc height reduction in the degenerative group was observed. Advanced age significantly correlated with advanced disc height reduction. Multiple level fusion led to a more pronounced disc height reduction than single level fusion. Gender, prior surgery of the fused segment and fusion level did not affect the amount of disc height reduction. There was no correlation between the clinical outcome (VAS; Oswestry) and the amount of disc space narrowing.

Conclusion: Lumbar fusion is associated with disc height reduction of adjacent discs. This may be induced by additional biomechanical stress, ongoing degeneration affecting the lumbar spine and advancing age. Clinical outcome is not correlated with adjacent disc space narrowing.