Background

Damage to the spinal cord is one of the most debilitating pathologies with considerable health, economic and social impact. Improved prevention, treatment and rehabilitation after spinal cord injury (SCI) requires the complex biomechanics of the spinal cord with all its structural elements and the injury mechanism to be understood. This comprehensive understanding will also allow development of models and tools enabling better diagnosis, surgical treatment with increased safety and efficacy and possible development of regenerative therapies. The denticulate ligaments play an important role in stabilising spinal cord within the spinal canal. They participate in spinal cord movements and play a role in determining the stress distribution during physiological but also traumatic loading. We present detailed tensile characterisation of the denticulate ligaments and a Finite Element micro-scale model of the ligament relating its structure with the distribution of stress under physiological loading.

Method

Denticulate ligaments were dissected from cervical spinal levels from 6 porcine cervical specimens with fragments of the pia and dura mater and characterised in terms of their geometry and response to uniaxial tensile loading. The stress-strain characteristics were recorded until rupture of the ligament, ultimate parameters and Young's moduli were determined. The parametric micro-structural Finite Element model was constructed based on literature microscope and histological images of a denticulate ligament as a phenomenological representation of the complex microstructure of a soft tissue. The model was validated against the experimental data.

Results

Stress-strain characteristics obtained in tensile test were typical for a soft tissue behaviour. No statistically relevant differences in ultimate strength, strain and Young's moduli were observed between the ligaments harvested from different vertebral levels. Average ultimate tensile stress was 1.26 ± 0.20 MPa at strain 0.51 ± 0.00, rupturing force (1.01 ± 0.21 N) was in agreement with results obtained previously. The Finite Element model accurately predicted the extension-load behaviour of the denticulate ligament in elastic regime. The micro-scale structural representation enabled capturing deformation modes representative of the experimentally observed behaviour.

Conclusions

The presented stress-strain characteristics of the denticulate ligaments add valuable data to the understanding of the biomechanics of the spinal cord and enable development of more accurate models. The developed micro-scale model was capable of capturing biomechanical response of collagenous tissue under tensile loading, it can be applied for the prediction of other soft tissues behaviours. The denticulate ligament model should be included into future spinal cord models to fully represent the complex system's biomechanics and enable development of surgical aid tools to improve patient outcomes and future regenerative therapies.

中文翻译：

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细小韧​​带-稳定脊髓结构的拉伸特性和有限元微观模型。

背景

脊髓损伤是最令人衰弱的病理之一，对健康，经济和社会产生重大影响。改善脊髓损伤（SCI）后的预防，治疗和康复，需要了解具有其所有结构要素和损伤机制的复杂的脊髓生物力学。这种全面的理解还将允许开发模型和工具，以实现更好的诊断，具有更高安全性和功效的外科治疗以及可能开发再生疗法。细小韧​​带在稳定椎管内的脊髓中起重要作用。它们参与脊髓运动，并在确定生理负荷和创伤负荷期间的应力分布中发挥作用。

方法

从6个猪的颈椎标本中分离出带有颈椎和硬脑膜碎片的细小齿状韧带，并对其几何形状和对单轴拉伸载荷的响应进行了表征。记录应力-应变特性，直到韧带破裂，确定最终参数和杨氏模量。基于文献显微镜和细齿韧带的组织学图像，作为软组织复杂微观结构的现象学表示，构建了参数化微结构有限元模型。该模型已针对实验数据进行了验证。

结果

在拉伸试验中获得的应力应变特性是软组织行为的典型特征。从不同椎骨水平收获的韧带之间在极限强度，应变和杨氏模量上均没有统计学上的显着差异。在0.51±0.00应变下的平均极限拉伸应力为1.26±0.20 MPa，断裂力（1.01±0.21 N）与先前获得的结果一致。有限元模型可以准确地预测细小韧带在弹性状态下的拉伸载荷行为。微观结构表示能够捕获代表实验观察到的行为的变形模式。

结论

所呈现的小齿韧带的应力-应变特性为了解脊髓的生物力学提供了宝贵的数据，并能开发出更准确的模型。建立的微尺度模型能够在拉伸载荷下捕获胶原组织的生物力学响应，可用于预测其他软组织的行为。未来的脊髓模型中应包含细小韧带模型，以充分代表复杂系统的生物力学，并能够开发外科手术辅助工具以改善患者预后和未来的再生疗法。