BACKGROUND The role of the axial pre-strain on the torsional response of the intervertebral disc remains largely undefined. Moreover, the chemo-mechanical interactions in disc tissues are still unclear and corresponding data are rare in the literature. The paper deals with an in-vitro study of the pre-strain effect on the chemical sensitivity of the disc torsional response. METHODS Fifteen non-frozen 'motion segments' (two vertebrae and the intervening soft tissues) were extracted from the cervical spines of mature sheep. The motion segments were loaded in torsion at various saline concentrations and axial pre-strain levels in order to modulate the intradiscal pressure. After preconditioning with successive low-strain compressions at a magnitude of 0.1 mm (10 cycles at 0.05 mm/s), the motion segment was subjected to a cyclic torsion until a twisting level of 2 deg. at 0.05 deg./s while a constant axial pre-strain (in compression or in tension) is maintained, the saline concentration of the surrounding fluid bath being changed from hypo-osmotic condition to hyper-osmotic condition. FINDINGS Analysis of variance shows that the saline concentration influences the torsional response only when the motion segments are pre-compressed (p < .001) with significant differences between hypo-osmotic condition and hyper-osmotic condition. INTERPRETATION The combination of a compressive pre-strain with twisting amplifies the nucleus hydrostatic pressure on the annulus and the annulus collagen fibers tensions. The proteoglycans density increases with the compressive pre-strain and leads to higher chemical imbalances, which would explain the increase in chemical sensitivity of the disc torsional response.

中文翻译：

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预应变如何影响椎间盘的化学扭转反应。

背景技术轴向预应变在椎间盘扭转响应中的作用仍未明确。此外，椎间盘组织中的化学机械相互作用仍然不清楚，相应的数据在文献中也很少。本文涉及预应变对椎间盘扭转反应的化学敏感性的体外研究。方法从成熟绵羊的颈棘中提取出十五个非冻结的“运动节”（两个椎骨和中间的软组织）。运动节段在各种盐浓度和轴向预应变水平下承受扭转载荷，以调节椎间盘内压力。在连续进行0.1毫米的低应变压缩预处理（0.05毫米/秒的10个循环）后，运动段经受周期性扭转，直到扭转水平为2度。当以0.05度/秒的速度保持恒定的轴向预应变（压缩或拉伸）时，周围液浴的盐水浓度从低渗状态变为高渗状态。结果方差分析表明，仅当运动段被预压缩（p <.001）时，盐水浓度才会影响扭转响应，低渗和高渗条件之间存在显着差异。解释压缩预应变与扭曲的结合会放大环上的细胞核静水压力和环的胶原纤维张力。蛋白多糖的密度随预应变的增加而增加，并导致更高的化学失衡，