Sairyo K, Goel V K, Grobler L J, Ikata T, Katoh S
Department of Biomedical, University of Iowa, Iowa City.
Spine (Phila Pa 1976). 1998 Jul 1;23(13):1442-6. doi: 10.1097/00007632-199807010-00002.
Anterior shearing force was applied to immature calf lumbar functional spinal units until failure.
To clarify the mechanism of slippage in immature calf lumbar spines with pars defects as a first step to understand the mechanism of spondylolisthesis in pediatric human lumbar spines.
Progression from lysis to olisthesis occurs during the adolescent growth spurt. However, the mechanism of slippage in the immature lumbar spine has not yet been understood clearly.
Bilateral pars defects were created at the rostral vertebra. The specimens then were assigned to one of the two groups: functional spinal units with intact disc (n = 5) and with disc dissected (n = 5). In the former group, the disc was left intact, whereas in the disc dissected group, the anterior longitudinal ligament and 75% of the anterior-to-posterior depth of the disc were incised along the mid-disc plane. Using a uniaxial MTS machine (MTS System, Minneapolis, MN), anteroposterior shearing force was applied to each specimen. Failure load and displacement at failure were calculated from the load--displacement curve. Failure sites also were assessed radiographically and histologically.
The five functional spinal units in the intact disc group failed at 973.8 +/- 78.1 N, whereas specimens in the disc dissected group failed at 986.4 +/- 124.2 N. The data showed no significant differences between the two groups. All the specimens showed displacement through the growth plates on radiographs. Histologically, failure was observed to occur between the superior growth plate and osseous endplate of caudal vertebra, indicating that this site is the weakest link.
The results suggest that in the pediatric immature lumbar spine with pars defects, slippage may occur between the growth plate and osseous endplate.
对未成熟小牛的腰椎功能脊柱单元施加前向剪切力直至失效。
阐明未成熟小牛腰椎伴有椎弓根峡部裂时滑脱的机制，作为理解小儿腰椎椎体滑脱机制的第一步。
在青少年生长突增期会发生从椎弓根峡部裂到椎体滑脱的进展。然而，未成熟腰椎滑脱的机制尚未完全清楚。
在头侧椎体制造双侧椎弓根峡部裂。然后将标本分为两组之一：椎间盘完整的功能脊柱单元（n = 5）和椎间盘被切开的（n = 5）。在前一组中，椎间盘保持完整，而在椎间盘切开组中，沿椎间盘中间平面切开前纵韧带和椎间盘前后深度的75%。使用单轴MTS机器（MTS系统，明尼阿波利斯，明尼苏达州），对每个标本施加前后剪切力。根据载荷-位移曲线计算失效载荷和失效时的位移。还通过影像学和组织学评估失效部位。
椎间盘完整组的5个功能脊柱单元在973.8±78.1 N时失效，而椎间盘切开组的标本在986.4±124.2 N时失效。数据显示两组之间无显著差异。所有标本在X线片上均显示通过生长板的位移。组织学上，观察到失效发生在尾侧椎体的上生长板和骨终板之间，表明该部位是最薄弱的环节。
结果表明，在伴有椎弓根峡部裂的小儿未成熟腰椎中，滑脱可能发生在生长板和骨终板之间。
