Analysis of high load injury of thoracolumbar spine in pilots during ejection process
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摘要:
针对战斗机飞行员在弹射过程中高负荷引起的胸腰段损伤率较高，且根据临床CT数据建立的有限元模型存在无法反映细微几何特征和骨骼非匀质属性，造成高负荷力学分析不准确等问题。采用非线性有限元方法建立表达特定对象皮质骨、松质骨厚度与密度的胸腰段（T12～L2）有限元模型，对弹射过程中战斗机飞行员胸腰段进行生物力学分析。基于胸腰段CT数据，将皮质骨测量（CBM）得到的皮质骨厚度和密度值纳入基于CT的胸腰段有限元建模过程中，并根据Hounsfield单位（HU）值计算各元素的弹性模量实现材质非均匀赋值，完成特定对象有限元模型的构建。通过添加边界条件和载荷对模型进行有效性验证，并模拟计算直立、前屈、后仰3种生理运动条件下弹射胸腰段脊柱的生物力学响应。结果表明：3种不同生理运动条件下弹射过程中椎骨对负荷的传递特性显著不同，直立生理运动条件下弹射，高负荷产生的椎骨直接急性损伤最小。
Abstract:In an attempt to accurately analyze high load, the finite element model established by clinical CT data was unable to capture the fine geometric features and heterogeneous properties of vertebrae, leading to an inaccurate analysis of the high rate of thoracolumbar spine injuries on fighter pilots during ejection. A finite element model of the thoracolumbar spine (T12-L2) was constructed based on nonlinear finite element, which represents the cortical thickness, cortical density, and cancellous bone density of specific-objects, to analyze the biomechanics of high load on the thoracolumbar spines of pilots during ejection. The object-specific finite element model was constructed based on the CT data of the thoracolumbar spine, and the cortical bone thickness and density values obtained from cortical bone mapping (CBM) were incorporated into the CT-based finite element modeling process of the thoracolumbar spine, and the elastic modulus of each element was calculated according to the Hounsfield units (HU) value to realize the heterogeneous assignment of material. By using the same loads and boundary conditions as those found in published in vitro studies, the model's correctness was confirmed. A Additionally, a simulation and computation were made of the biomechanical reaction of the thoracolumbar spine brought on by the ejection load in the upright, flexion, and extension physiological motion situations. The results showed that the vertebral load transfer characteristics were significantly different among the three different physiological motion conditions subjected to ejection loading, with the upright physiological motion conditions resulting in the least amount of direct acute injury to the vertebrae from the high load.
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Key words:
- biomechanics /
- finite element analysis /
- high load damage /
- thoracolumbar spine /
- ejection
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图 1 皮质骨厚度测量与有限元模型构建流程
Figure 1. Flow of cortical bone mapping and finite element model construction
图 3 空气、脂肪、肌肉ROIs区域HU值频数分布
Figure 3. Frequency histogram of HU of air, fat and muscle within the ROIs
图 4 T12～L2有限元模型和验证边界载荷条件
Figure 4. T12～L2 finite element modeling and verification of boundary load conditions
图 6 本文模型关节活动范围验证结果
Figure 6. The proposed model joint range of motion validation results
图 8 弹射座椅/人椅系统简化结构与受力分析
Figure 8. Seat/occupant system simplified structure and force analysis
表 1 椎间盘髓核、纤维环基质及关节软骨材料属性
Table 1. Nucleus pulposus, annulus fibrosus matrix and articular cartilage material properties of intervertebral discs
材质种类 应变率 ${C_{10}}/{\text{MPa}}$ ${C_{01}}/{\mathrm{MPa}}$ 密度/(g·cm−3) 泊松比 杨氏模量/MPa 髓核 高 31.8 8.0 1 0.495 低 0.12 0.03 1 0.495 纤维环基质 高 11.8 2.9 1.2 0.45 低 0.18 0.045 1.2 0.45 关节软骨 1 0.4 10.4 肌肉等效体 1 650 3 350 1.1 0.492 下部骨骼等效体 1.1 0.3 10 000 
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