Effect of Potting Technique on the Measurement of Six Degree-of-Freedom Viscoelastic Properties of Human Lumbar Spine Segments
Effect of Potting Technique on the Measurement of Six Degree-of-Freedom Viscoelastic Properties of Human Lumbar Spine Segments
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DOI：
10.1115/1.4029698
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发表时间：
2015-05-01
影响因子：
1.7
通讯作者：
Costi, John J.
中科院分区：
文献类型：
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作者：
Amin, Dhara B.;Lawless, Isaac M.;Costi, John J.
聚甲基丙烯酸甲酯（PMMA）和Wood's Metal是生物力学测试的固定介质;然而，每种灌封介质对人体腰椎间盘测量的六个自由度（DOF）力学性能的影响尚不清楚。本研究的第一个目的是比较嵌入PMMA与重新灌封在Wood's Metal中时测量的椎间盘的6DOF弹性和粘弹性。第二个目的是比较用PMMA和Wood's Metal灌封时圆盘的表面温度。首先将六个人体腰椎功能性脊柱单元（FSU）灌封在PMMA中，并在37 ℃的盐水浴中进行过夜预加载，然后在每个6DOF加载方向（压缩、左/右侧弯、屈曲、伸展、左/右轴向旋转、前/后和横向剪切）上以0.1 Hz进行五次半正矢加载循环。然后将每个样本重新灌封在Wood's Metal中，并进行2小时的再平衡预加载，然后重复相同的6DOF测试。根据每个自由度的最终载荷循环计算刚度和相位角的结果测量值，并表示为相对于PMMA（100%）的归一化百分比。在灌封期间测量椎间盘表面温度（前部、左/右外侧）。进行配对t检验（α针对多个自由度进行调整），以比较PMMA和Wood's Metal之间每个结局参数的差异。PMMA和Wood's Metal之间的刚度或相位角没有显著差异。平均而言，最大的趋势差异出现在刚度（Wood's Metal比PMMA高约35%）和相位角（Wood's Metal高约15%）的剪切自由度中。与PMMA相比，Wood's Metal灌封后前表面的椎间盘温度存在显著差异，不超过26 ℃。Wood's Metal是线性弹性的，比PMMA更硬，可以减少灌封介质的测量伪影，特别是在剪切方向上。此外，它比PMMA更容易去除，可重复使用，并且具有成本效益。
Polymethyl methacrylate (PMMA) and Wood's Metal are fixation media for biomechanical testing; however, the effect of each potting medium on the measured six degree-of-freedom (DOF) mechanical properties of human lumbar intervertebral discs is unknown. The first aim of this study was to compare the measured 6DOF elastic and viscoelastic properties of the disc when embedded in PMMA compared to repotting in Wood's Metal. The second aim was to compare the surface temperature of the disc when potted with PMMA and Wood's Metal. Six human lumbar functional spinal units (FSUs) were first potted in PMMA, and subjected to overnight preload in a saline bath at 37 degrees C followed by five haversine loading cycles at 0.1 Hz in each of 6DOF loading directions (compression, left/right lateral bending, flexion, extension, left/right axial rotation, anterior/posterior, and lateral shear). Each specimen was then repotted in Wood's Metal and subjected to a 2-h re-equilibrating preload followed by repeating the same 6DOF tests. Outcome measures of stiffness and phase angle were calculated from the final loading cycle in each DOF and were expressed as normalized percentages relative to PMMA (100%). Disc surface temperatures (anterior, left/right lateral) were measured during potting. Paired t-tests (with alpha adjusted for multiple DOF) were conducted to compare the differences in each outcome parameter between PMMA and Wood's Metal. No significant differences in stiffness or phase angle were found between PMMA and Wood's Metal. On average, the largest trending differences were found in the shear DOFs for both stiffness (approximately 35% greater for Wood's Metal compared to PMMA) and phase angle (approximately 15% greater for Wood's Metal). A significant difference in disc temperature was found at the anterior surface after potting with Wood's Metal compared to PMMA, which did not exceed 26 degrees C. Wood's Metal is linear elastic, stiffer than PMMA and may reduce measurement artifact of potting medium, particularly in the shear directions. Furthermore, it is easier to remove than PMMA, reuseable, and cost effective.