Konz R J, Goel V K, Grobler L J, Grosland N M, Spratt K F, Scifert J L, Sairyo K
Department of Biomedical Engineering, Department of Mechanical Engineering, Iowa Spine Research Center, University of Iowa, Iowa City, Iowa, USA.
Spine (Phila Pa 1976). 2001 Feb 15;26(4):E38-49. doi: 10.1097/00007632-200102150-00003.
Immature Chacma baboon (Papio ursinus) spine specimens were used to determine load-displacement behavior as related to disc injury. This was accomplished through the application of A-P shear force until failure of FSUs with pars defects. Several finite element models (FEMs) of the FSU were developed to study the mechanism of slippage in immature baboon lumbar spines.
The purpose was to show that spondylolisthesis (olisthesis) always occurs through the growth plate using a model similar to immature human lumbar spines. Using FEMs, the roles of facet orientation, pars interarticularis thickness, and a weak growth-plate in producing slippage were examined.
Progression from spondylolysis (lysis) to olisthesis occurs, most often, during the adolescent growth spurt. The biomechanical literature dealing with the slippage mechanism in the immature lumbar spine does not provide a clear understanding and is sparse.
Several groups of FSUs were subjected to A-P shear force until failure. The results provided displacement at failure as a function of disc injury and flexion-extension fatigue. A bilateral pars defect was created in each specimen prior to application of A-P shear force using an MTS machine. Failure sites were assessed radiographically and histologically. A nonlinear 3-D FEM of the intact L4-L5 was created from CT scans. The model was modified to predict the effects of a pars fracture, a thin pars, a weak growth plate, and facet orientation on the shear load through the growth plate and stresses in the pars.
Experimentally, failures always occurred through the growth-plate in the disc intact and disc-incised groups. In the intact FEM, the growth plate carried21% of the applied A-P shear force. The load increased when the facets were more sagittally oriented. The effect of thin pars and/or weaker growth plate was an increase in stresses in the pars. Changes in the load through the growth plate were minimal.
The weakest link in immature baboon lumbar functional spinal units (FSUs) with lysis during an A-P shear load was the growth plate, between the cartilaginous and osseous end plates. Surgeons may assess this lesion on MRI views, thereby predicting the possible development and preventing progression of olisthesis. Finite element model results predict that more sagittally orientated facets and/or a pars fracture are prerequisites for olisthesis to occur.
使用未成熟的查卡马狒狒（山魈）脊柱标本，以确定与椎间盘损伤相关的载荷 - 位移行为。这是通过施加前后剪切力直至具有椎弓峡部缺损的功能性脊柱单元（FSU）失效来实现的。开发了几个FSU的有限元模型（FEM），以研究未成熟狒狒腰椎滑脱的机制。
目的是使用类似于未成熟人类腰椎的模型，证明椎体滑脱总是通过生长板发生。使用有限元模型，研究了小关节方向、椎弓峡部厚度和薄弱生长板在产生滑脱中的作用。
从椎弓根峡部裂（峡部裂）发展到椎体滑脱，最常发生在青少年生长突增期。处理未成熟腰椎滑脱机制的生物力学文献并不清晰且稀少。
几组FSU承受前后剪切力直至失效。结果给出了失效时的位移，作为椎间盘损伤和屈伸疲劳的函数。在使用MTS机器施加前后剪切力之前，在每个标本中制造双侧椎弓峡部缺损。通过放射学和组织学评估失效部位。根据CT扫描创建完整L4 - L5的非线性三维有限元模型。对模型进行修改，以预测椎弓根骨折、薄椎弓根、薄弱生长板和小关节方向对通过生长板的剪切载荷和椎弓根应力的影响。
在实验中，在椎间盘完整组和椎间盘切开组中，失效总是通过生长板发生。在完整的有限元模型中，生长板承受21%的施加的前后剪切力。当小关节更矢状位时，载荷增加。薄椎弓根和/或较弱生长板的影响是椎弓根应力增加。通过生长板的载荷变化最小。
在前后剪切载荷下，具有峡部裂的未成熟狒狒腰椎功能性脊柱单元（FSU）中最薄弱的环节是软骨终板和骨终板之间的生长板。外科医生可以在MRI图像上评估这种病变，从而预测椎体滑脱的可能发展并防止其进展。有限元模型结果预测，更矢状位的小关节和/或椎弓根骨折是椎体滑脱发生的先决条件。
