Neumann P, Nordwall A, Osvalder A L
Department of Orthopaedics, Göteborg University, Sahlgrenska University Hospital, Sweden.
Spine (Phila Pa 1976). 1995 May 15;20(10):1111-21. doi: 10.1097/00007632-199505150-00001.
This in vitro study determined the effect on the lumbar spine of a dynamic flexion-distraction loading simulating a lap seatbelt injury. The proportion by which the forces and the moments contributed to the injury of the lumbar spinal segment in such a situation was analyzed. The remaining stability of the injured lumbar motion segment was determined together with the threshold for lumbar spine instability in such an injury.
Based on the experimental results in this study, radiographic guidelines for instability criteria in lumbar and thoracolumbar dislocations in the sagittal plane without concomitant compression fracture of the middle column were proposed.
A number of check-lists and guidelines were suggested for the diagnosis of spinal instability after trauma, but no conclusive system was established. Those systems were mostly based on experiments performed on spinal segments after sequential ablation of ligaments and facet joints followed by static, unidirectional physiologic loading. We believed that there was a need for more profound knowledge of spinal injury and for instability criteria of lumbar spinal injuries based on more realistic experimental data simulating the clinical situation. In our injury model, we decided to study the biomechanic outcome of a flexion-distraction injury similar to seatbelt type injury seen in frontal motor vehicle collisions.
Twenty lumbar functional spinal units were first loaded statically with a physiologic flexion-shear load to determine angulations and displacements under noninjurous conditions. Dynamic flexion-shear loading to injury with two different load pulses was then applied. Static physiologic load was then again applied to determine any permanent residual deformation.
The viscoelastic effect of loading rate on translatory and angular displacements and the values for translatory and angulation displacements at first sign of injury (yield) and at failure were determined.
Radiographic guidelines for instability criteria in lumbar and thoracolumbar fracture-dislocations without concomitant posterior vertebral body compression are proposed: 1. Instability exists if there is a kyphosis of the lumbar motion segment > or = 12 degrees (impending instability) or > or = 19 degrees (total instability) on lateral radiographs. 2. Relative increase in interspinous process distance > or = 20 mm (impending instability), > or = 33 mm (total instability) on anteroposterior radiographs.
本体外研究确定了模拟安全带损伤的动态屈伸牵张负荷对腰椎的影响。分析了在这种情况下，力和力矩对腰椎节段损伤的贡献率。确定了受伤腰椎运动节段的剩余稳定性以及这种损伤中腰椎不稳定的阈值。
基于本研究的实验结果，提出了矢状面腰椎和胸腰段脱位且无中柱压缩骨折时不稳定标准的影像学指南。
已提出许多用于诊断创伤后脊柱不稳定的检查表和指南，但尚未建立确凿的系统。这些系统大多基于在依次切除韧带和小关节后对脊柱节段进行的实验，然后进行静态、单向生理负荷实验。我们认为，需要更深入地了解脊柱损伤，并基于更逼真模拟临床情况的实验数据来确定腰椎损伤的不稳定标准。在我们的损伤模型中，我们决定研究类似于正面机动车碰撞中所见安全带型损伤的屈伸牵张损伤的生物力学结果。
首先对20个腰椎功能脊柱单元施加静态生理屈伸剪切负荷，以确定非损伤条件下的角度和位移。然后用两种不同的负荷脉冲施加动态屈伸剪切负荷以造成损伤。接着再次施加静态生理负荷以确定任何永久性残余变形。
确定了加载速率对平移和角位移的粘弹性效应以及损伤初始迹象（屈服）和破坏时的平移和角位移值。
提出了无椎体后柱压缩的腰椎和胸腰段骨折脱位不稳定标准的影像学指南：1. 如果腰椎运动节段在侧位X线片上出现后凸≥12度（即将发生不稳定）或≥19度（完全不稳定），则存在不稳定。2. 棘突间距离在前后位X线片上相对增加≥20毫米（即将发生不稳定）、≥33毫米（完全不稳定）。
