Gooyers Chad E, McMillan Elliott M, Noguchi Mamiko, Quadrilatero Joe, Callaghan Jack P
Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Waterloo, ON, Canada, N2L 3G1.
Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Waterloo, ON, Canada, N2L 3G1.
Clin Biomech (Bristol). 2015 Nov;30(9):953-9. doi: 10.1016/j.clinbiomech.2015.07.003. Epub 2015 Jul 11.
Previous research suggests that when the magnitude of peak compressive force applied during cyclic loading exceeds 30% of a functional spinal unit's estimated ultimate compressive tolerance, fatigue failure of the cartilaginous endplate or vertebra will occur before intervertebral disc herniation.
Three levels of peak compressive force, three cycle rates and two dynamic postural conditions were examined using a full-factorial design. Cyclic compressive force was applied using a modified material testing apparatus, in accordance with a biofidelic time-varying waveform with synchronous flexion/extension rotation for 5000 cycles. Annulus fibrosus tissue from 36 "survivor" FSUs was excised for histological analysis.
80% of specimens survived 5000 cycles of cyclic loading. A marked difference of the magnitude of peak compressive force was noted in the Kaplan-Meier survival function of experimental conditions that induced fatigue injury. Overall, in the 40% ultimate compressive tolerance load condition, the probability of survival was less than 67%. The micro-structural damage detected in excised samples of annulus fibrosus tissue consisted of clefts and fissures within the intra-lamellar matrix, as well as delamination within the inter-lamellar matrix.
Consistent with previous research, our findings support a threshold of peak compressive force of 30% ultimate compressive tolerance, where cyclic loading above this level will likely result in fatigue injury in less than 5000 cycles of in vitro mechanical loading. However, findings from our histological analyses demonstrate that considerable micro-structural damage occurred in specimens that "survived" the cyclic loading exposure.
先前的研究表明，在循环加载过程中施加的峰值压缩力大小超过功能性脊柱单元估计的极限压缩耐受性的30%时，软骨终板或椎体的疲劳失效将在椎间盘突出之前发生。
采用全因子设计，研究了三个峰值压缩力水平、三个循环速率和两种动态姿势条件。使用改良的材料测试设备施加循环压缩力，按照生物逼真的随时间变化的波形并同步进行屈伸旋转，持续5000个循环。从36个“存活”的功能性脊柱单元中切除纤维环组织进行组织学分析。
80%的标本在5000个循环加载中存活。在导致疲劳损伤的实验条件的Kaplan-Meier生存函数中，峰值压缩力大小存在显著差异。总体而言，在40%极限压缩耐受性负荷条件下，存活概率小于67%。在切除的纤维环组织样本中检测到的微观结构损伤包括层内基质中的裂缝和裂隙，以及层间基质中的分层。
与先前的研究一致，我们的研究结果支持峰值压缩力阈值为极限压缩耐受性的30%，在此水平以上的循环加载可能会在体外机械加载少于5000个循环时导致疲劳损伤。然而，我们组织学分析的结果表明，在经历循环加载暴露后“存活”的标本中发生了相当大的微观结构损伤。
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