Vresilovic Edward J, Johannessen Wade, Elliott Dawn M
Department of Orthopaedic Surgery, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
J Biomech Eng. 2006 Dec;128(6):823-9. doi: 10.1115/1.2354210.
Mechanical function of the intervertebral disc is maintained through the interaction between the hydrated nucleus pulposus, the surrounding annulus fibrosus, and the superior and inferior endplates. In disc degeneration the normal transfer of load between disc substructures is compromised. The objective of this study was to explore the mechanical role of the nucleus pulposus in support of axial compressive loads over time. This was achieved by measuring the elastic slow ramp and viscoelastic stress-relaxation mechanical behaviors of cadaveric sheep motion segments before and after partial nucleotomy through the endplate (keeping the annulus fibrosus intact). Mechanics were evaluated at five conditions: Intact, intact after 10,000 cycles of compression, acutely after nucleotomy, following nucleotomy and 10,000 cycles of compression, and following unloaded recovery. Radiographs and magnetic resonance images were obtained to examine structure. Only the short time constant of the stress relaxation was altered due to nucleotomy. In contrast, cyclic loading resulted in significant and large changes to both the stiffness and stress relaxation behaviors. Moreover, the nucleotomy had little to no effect on the disc mechanics after cyclic loading, as there were no significant differences comparing mechanics after cyclic loading with or without the nucleotomy. Following unloaded recovery the mechanical changes that had occurred as a consequence of cyclic loading were restored, leaving only a sustained change in the short time constant due to the trans-endplate nucleotomy. Thus the swelling and redistribution of the remaining nucleus pulposus was not able to fully restore mechanical behaviors. This study reveals insights into the role of the nucleus pulposus in disc function, and provides new information toward the potential role of altered nucleus pulpous function in the degenerative cascade.
椎间盘的机械功能通过水合髓核、周围纤维环以及上下终板之间的相互作用得以维持。在椎间盘退变过程中，椎间盘各亚结构之间正常的负荷传递受到损害。本研究的目的是探讨髓核在长时间支持轴向压缩负荷方面的机械作用。这是通过测量经终板部分髓核摘除术（保持纤维环完整）前后尸体羊运动节段的弹性慢斜坡和粘弹性应力松弛力学行为来实现的。在五种情况下评估力学性能：完整状态、压缩10000次循环后保持完整、髓核摘除术后即刻、髓核摘除术后再进行10000次循环压缩以及卸载恢复后。获取X线片和磁共振图像以检查结构。仅应力松弛的短时间常数因髓核摘除术而改变。相比之下，循环加载导致刚度和应力松弛行为都发生了显著且较大的变化。此外，循环加载后髓核摘除术对椎间盘力学性能几乎没有影响，因为比较有或没有髓核摘除术的循环加载后的力学性能没有显著差异。卸载恢复后，循环加载导致的力学变化得以恢复，仅由于经终板髓核摘除术导致短时间常数持续变化。因此，剩余髓核的肿胀和重新分布无法完全恢复力学行为。本研究揭示了髓核在椎间盘功能中的作用，并为髓核功能改变在退变级联反应中的潜在作用提供了新信息。
