2007 Award Winners

Paper #66
Hibbs Award Nominee for Best Basic Science Presentation

The Effect Of Two Clinically Relevant Fusionless Scoliosis Implant Strategies On The Health of the Intervertebral Disc

Kenneth J. Hunt, MD; John T. Braun, MD; Bryt A. Christensen, BS

Introduction: Fusionless scoliosis surgery is thought to be more physiologic than fusion and, thus, less likely to cause disc degeneration, particularly at adjacent segments. However, there are no data supporting this belief. This study evaluates the effect of clinically relevant fusionless scoliosis surgery implants on the health of instrumented and sub-adjacent discs. We hypothesize that flexible implants will result in less damage to the discs than rigid implants.

Methods: Scoliosis was created in twelve 8-week-old female goats using two fusionless scoliosis implant strategies from T7-T12. Three groups were studied: 2 SMA staples per level, submaximally tensioned bone anchor/ligament tether (BALT) and untreated controls (n=6 per group). At six months, instrumented and sub-adjacent discs were harvested. Qualitative and quantitative analyses were performed using H & E sections on the discs (cell density and fibrosis), endplates (concave endplate and trabecular thickening, tidemark flattening, bone drift) and surrounding vascularity.

Results: Scoliosis was created in both treatment groups but not controls. All instrumented discs demonstrated a trend toward decreased cell density compared to sub-adjacent discs and controls but no difference between sub-adjacent discs and controls. Endplate/trabecular thickening and bone drift were present in all instrumented discs, but not in sub-adjacent discs or controls. Decreased blood vessel density was present in all instrumented endplates compared to sub-adjacent and control specimens (p=0.012). There was no difference in vascularity between sub-adjacent and control endplates or between convex and concave endplates.

Conclusion: The data in this study demonstrate that both rigid and flexible fusionless scoliosis implants induce some degenerative change at the instrumented disc (reduced cell density) and endplate (thickening, loss of vascularity) but spare the sub-adjacent segment. There were no differences between flexible and rigid implants. Further analysis is necessary to define conditions that optimize scoliosis correction with minimal detrimental effects.
 
Significance: This study improves our understanding of clinically relevant fusionless scoliosis implant strategies and their effect on the intervertebral discs.

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