Abstract
Study Design. Microstructural investigation of compression-induced disruption of the flexedlumbar disc.Objective. To provide a microstructural analysis of the mechanisms of annular wall failure in healthy discs subjected to flexion and an elevated rate of compression.Summary of Background Data. At the level of the motion segment failure of thedisc in compression has been extensively studied. However, at the microstructural level the exact mechanisms of disc failure are still poorly understood, especially in relation to loading posture and rate.Methods. 72 healthy mature ovine lumbar motion segments were compressed to failure in either a neutral posture or in high physiological flexion (10º) at a displacement rate of either 2mm/min (low) or 40mm/min (high). Testing at the high rate was terminated at stages ranging from initial wall tearing through to facet fracture so as to capture the evolution of failure up to full herniation. The damaged discs were then analysed microstructurally.Results. ∼50% of the motion segments compressed in flexion at the high rate suffered annulus or annulus-endplate junction failure, the remainder failed via endplate fracture with no detectable wall damage. The average load to induce disc failure in flexion was 18% lower (p < 0.05) than that required to induce endplate fracture. Microstructural analysis indicated that wall rupture occurred first in the posterior mid-then-outer annulus.Conclusion. Disc wall failure in healthy motion segments requires both flexion and an elevated rate of compression. Damage is initiated in the mid-then-outer annular fibres, this a likely consequence of the higher strain burden in these same fibres arising from endplate curvature. Given the similarity in geometry between ovine and human endplates it is proposed that comparable mechanisms of damage initiation and herniation occur in humanlumbar discs.
- PMID:
- 24503692
- [PubMed - as supplied by publisher]
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