Department of Bioengineering, Imperial College London, London, UK.
Department of Bioengineering, Imperial College London, London, UK; Biomechanics Group, Department of Mechanical Engineering, Imperial College London, London, UK.
J Biomech. 2024 Mar;166:111990. doi: 10.1016/j.jbiomech.2024.111990. Epub 2024 Feb 15.
Nucleus replacement devices (NRDs) have potential to treat degenerated or herniated intervertebral discs (IVDs). However, IVD height loss is a post-treatment complication. IVD height recovery involves the nucleus pulposus (NP), but the mechanism of this in response to physiological loads is not fully elucidated. This study aimed to characterise the non-linear recovery behaviour of the IVD in intact, post-nuclectomy, and post-NRD treatment states, under physiological loading. 36 bovine IVDs (12 intact, 12 post-nuclectomy, 12 post-treatment) underwent creep-recovery protocols simulating Sitting, Walking or Running, followed by 12 h of recovery. A rheological model decoupled the fluid-independent (elastic, fast) and fluid-dependent (slow) recovery phases. In post-nuclectomy and post-treatment groups, nuclectomy efficiency (ratio of NP removed to remaining NP) was quantified following post-test sectioning. Relative to intact, post-nuclectomy recovery significantly decreased in Sitting (-0.3 ± 0.4 mm, p < 0.05) and Walking (-0.6 ± 0.3 mm, p < 0.001) coupled with significant decreases to the slow response (p < 0.05). Post-nuclectomy, the fast and slow responses negatively correlated with nuclectomy efficiency (p < 0.05). In all protocols, the post-treatment group performed significantly worse in recovery (-0.5 ± 0.3 mm, p < 0.01) and the slow response (p < 0.05). Results suggest the NP mainly facilitates slow-phase recovery, linearly dependent on the amount of NP present. Failure of this NRD to recover is attributed to poor fluid imbibition. Additionally, unconfined NRD performance cannot be extrapolated to the in vitro response. This knowledge informs NRD design criteria to provide high osmotic pressure, and encourages testing standards to incorporate long-term recovery protocols.
核替换装置 (NRD) 具有治疗退化或突出的椎间盘 (IVD) 的潜力。然而，IVD 高度丢失是一种治疗后的并发症。IVD 高度恢复涉及到髓核，但这种对生理负荷的反应机制尚未完全阐明。本研究旨在描述完整、核切除术后和 NRD 治疗后状态下 IVD 在生理负荷下的非线性恢复行为。36 个牛椎间盘 (12 个完整、12 个核切除术后、12 个治疗后) 进行了蠕变-恢复实验，模拟了坐、走或跑，然后进行了 12 小时的恢复。流变学模型将流体独立（弹性、快速）和流体依赖（缓慢）的恢复阶段解耦。在核切除术后和治疗后组中，在测试后切片后定量测量核切除效率（去除的 NP 与剩余 NP 的比值）。与完整组相比，核切除术后的恢复在坐和走时显著降低（分别为-0.3 ± 0.4 毫米，p < 0.05），同时缓慢响应也显著降低（p < 0.05）。核切除术后，快速和缓慢响应与核切除效率呈负相关（p < 0.05）。在所有方案中，治疗后组的恢复（-0.5 ± 0.3 毫米，p < 0.01）和缓慢响应（p < 0.05）均明显更差。结果表明，NP 主要促进缓慢相恢复，与 NP 的含量呈线性相关。NRD 无法恢复的原因是其较差的流体吸收能力。此外，无约束的 NRD 性能不能外推到体外反应。这些知识为 NRD 设计标准提供了高渗透压的依据，并鼓励测试标准纳入长期恢复协议。
