Department of Orthopaedics, Warren Alpert Medical School of Brown University and Rhode Island Hospital, Providence, Rhode Island, United States of America.
PLoS One. 2013;8(2):e57412. doi: 10.1371/journal.pone.0057412. Epub 2013 Feb 25.
Biomechanical investigations of spinal motion preserving implants help in the understanding of their in vivo behavior. In this study, we hypothesized that the lumbar spine with implanted total spinal segment replacement (TSSR) would exhibit decreased dynamic stiffness and more rapid energy absorption compared to native functional spinal units under simulated physiologic motion when tested with the pendulum system.
Five unembalmed, frozen human lumbar functional spinal units were tested on the pendulum system with axial compressive loads of 181 N, 282 N, 385 N, and 488 N before and after Flexuspine total spinal segment replacement implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5°; resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and bending stiffness (N-m/°) was calculated and compared for each testing mode.
The total spinal segment replacement reached equilibrium with significantly fewer cycles to equilibrium compared to the intact functional spinal unit at all loads in flexion (p<0.011), and at loads of 385 N and 488 N in lateral bending (p<0.020). Mean bending stiffness in flexion, extension, and lateral bending increased with increasing load for both the intact functional spinal unit and total spinal segment replacement constructs (p<0.001), with no significant differences in stiffness between the intact functional spinal unit and total spinal segment replacement in any of the test modes (p>0.18).
Lumbar functional spinal units with implanted total spinal segment replacement were found to have similar dynamic bending stiffness, but absorbed energy at a more rapid rate than intact functional spinal units during cyclic loading with an unconstrained pendulum system. Although the effects on clinical performance of motion preserving devices is not fully known, these results provide further insight into the biomechanical behavior of this device under approximated physiologic loading conditions.
对脊柱运动保留植入物的生物力学研究有助于理解其体内行为。在这项研究中，我们假设在模拟生理运动下，用摆锤系统测试时，植入全脊柱节段置换（TSSR）的腰椎会表现出比天然功能脊柱单元更低的动态刚度和更快的能量吸收。
在 Flexuspine 全脊柱节段置换植入前后，将 5 个未防腐、冷冻的人腰椎功能脊柱单元在摆锤系统上用 181 N、282 N、385 N 和 488 N 的轴向压缩载荷进行测试。在屈伸和侧屈测试中，首先将摆锤旋转到 5°，从而产生无约束的摆动运动。记录达到平衡所需的旋转次数，并计算和比较每种测试模式的弯曲刚度（N-m/°）。
在所有负荷下，全脊柱节段置换达到平衡所需的周期数明显少于完整功能脊柱单元（p<0.011），在 385 N 和 488 N 的侧屈负荷下（p<0.020）也是如此。在屈伸、侧屈和侧屈测试中，无论是完整功能脊柱单元还是全脊柱节段置换结构，弯曲刚度随载荷的增加而增加（p<0.001），在任何测试模式下，完整功能脊柱单元和全脊柱节段置换之间的刚度均无显著差异（p>0.18）。
在无约束摆锤系统周期性加载下，植入全脊柱节段置换的腰椎功能脊柱单元的动态弯曲刚度相似，但能量吸收速度快于完整功能脊柱单元。尽管运动保留装置对临床性能的影响尚不完全清楚，但这些结果为该装置在近似生理负荷条件下的生物力学行为提供了进一步的见解。
