Biomechanics and Implants Research Group, Medical Device Research Institute, College of Science & Engineering, Flinders University, Adelaide, Australia.
Department of Spinal Surgery, Royal Adelaide Hospital, Adelaide, Australia.
Spine (Phila Pa 1976). 2020 Mar 15;45(6):357-367. doi: 10.1097/BRS.0000000000003270.
A biomechanical analysis correlating internal disc strains and tissue damage during simulated repetitive lifting.
To understand the failure modes during simulated safe and unsafe repetitive lifting.
Repetitive lifting has been shown to lead to lumbar disc herniation (LDH). In vitro studies have developed a qualitative understanding of the effect of repetitive loading on LDH. However, no studies have measured internal disc strains and subsequently correlated these with disc damage.
Thirty human cadaver lumbar functional spinal units were subjected to an equivalent of 1 year of simulated repetitive lifting under safe and unsafe levels of compression, in combination with flexion (13-15°), and right axial rotation (2°) for 20,000 cycles or until failure. Safe or unsafe lifting were applied as a compressive load to mimic holding a 20 kg weight either close to, or at arm's length, from the body, respectively. Maximum shear strains (MSS) were measured, and disc damage scores were determined in nine regions from axial post-test magnetic resonance imaging (MRI) and macroscopic images.
Twenty percent of specimens in the safe lifting group failed before 20,000 cycles due to endplate failure, compared with 67% in the unsafe group. Over half of the specimens in the safe lifting group failed via either disc protrusion or LDH, compared with only 20% via protrusion in the unsafe group. Significant positive correlations were found between MRI and macroscopic damage scores in all regions (rs > 0.385, P < 0.049). A significant positive correlation was observed in the left lateral region for MSS versus macroscopic damage score (rs = 0.486, P < 0.037) and MSS versus failure mode (rs = 0.724, P = 0.018, only specimens with disc failure). Pfirrmann Grade 3 discs were strongly associated with subsequent LDH (P = 0.003).
Increased shear strains were observed in the contralateral side to the applied rotation as disc injury progressed from protrusion to LDH. Larger compressive loads applied to simulate unsafe lifting led to frequent early failure of the endplate, however, smaller compressive loads at similar flexion angles applied under safe lifting led to more loading cycles before failure, where the site of failure was more likely to be the disc. Our study demonstrated that unsafe lifting leads to greater risk of injury compared with safe lifting, and LDH and disc protrusion were more common in the posterior/posterolateral regions.
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模拟重复提升过程中内部椎间盘应变与组织损伤的生物力学分析。
了解模拟安全和不安全重复提升过程中的失效模式。
重复提升已被证明会导致腰椎间盘突出症（LDH）。体外研究已经对重复加载对 LDH 的影响有了定性的理解。然而，尚无研究测量内部椎间盘应变，并随后将其与椎间盘损伤相关联。
对 30 个人体腰椎功能脊柱单位进行模拟重复提升，在安全和不安全的压缩水平下，结合 13-15°的屈伸和 2°的右侧轴向旋转，共进行 20000 次循环或直至失效。安全或不安全的提升通过模拟握持 20 公斤重物的压缩载荷来施加，分别靠近身体或手臂长度。测量最大剪切应变（MSS），并通过轴向磁共振成像（MRI）和宏观图像测试后的椎间盘损伤评分确定 9 个区域的评分。
20%的安全提升组试件在 20000 次循环之前因终板失效而失效，而不安全组则为 67%。超过一半的安全提升组试件通过椎间盘突出或 LDH 失效，而不安全组仅 20%通过突出失效。所有区域的 MRI 和宏观损伤评分之间均存在显著的正相关（rs＞0.385，P＜0.049）。在左侧外侧区域，MSS 与宏观损伤评分（rs＝0.486，P＜0.037）和 MSS 与失效模式（rs＝0.724，P＝0.018，仅椎间盘失效的试件）之间存在显著正相关。Pfirrmann 3 级椎间盘与随后的 LDH 强烈相关（P＝0.003）。
随着椎间盘损伤从突出发展到 LDH，在施加旋转的对侧观察到较大的剪切应变。更大的压缩载荷模拟不安全的提升会导致终板早期频繁失效，然而，在类似的屈伸角度下应用较小的压缩载荷进行安全提升会导致更多的循环次数，直至失效，而失效部位更可能是椎间盘。我们的研究表明，不安全的提升比安全的提升会导致更大的损伤风险，LDH 和椎间盘突出更常见于后/后外侧区域。
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