颈椎爆裂骨折骨碎片撞击速度对颈髓损伤的有限元生物力学研究

Biomechanical behaviors of cervical spinal cord injury related to various bone fragment impact velocities：a finite element study

目的建立带有脑脊液的颈脊髓三维有限元模型，利用生物力学有限元方法研究爆裂骨折时骨碎片不同撞击速度对脊髓造成损伤的机制。方法根据人体颈椎各节段的脊髓的形态学特点，利用Spaceclaim 18.0、Hypermesh 13.0及ABAQUS 6.14软件，重建包括硬膜、脑脊液、灰质及白质的C2～C7节段颈髓三维六面体网格有限元模型，并进行有效性验证。在已验证的颈脊髓模型上，分别用3个横截面积分别为314、157和78.5 mm2但质量均为7 g的打击器模拟椎体爆裂骨折骨碎片，分别以1.5、2.5～6.0 m/s的速度撞击脊髓，记录和比较脊髓横截面积减少量及脊髓内部受到的最大应力，研究脊髓损伤机制。结果建立的颈脊髓有限元模型几何相似性好，颈脊髓模型在3个打击器分别以4.5 m/s撞击时，全脊髓压缩量为37.1%～51.3%，单纯脊髓压缩量为36.3%～40.5%，到达最大压缩量所需时间为2.3～3.0 ms，与文献结果类似，证明脊髓模型有效。无论作用面积大小，脊髓横截面积减少及脊髓内部应力随着撞击速度的增加而增加。当三个打击器以1.5 m/s撞击颈髓时，其内部应力为5～7 kPa，脊髓横截面积减少9.3%～12.3%；3.5 m/s时应力为42～54 kPa，脊髓横截面积减少均超过30%；撞击速度〉3.5 m/s时，脊髓内部应力明显增加，4.5 m/s时增加速度最快。速度为6.0 m/s时脊髓应力为250～320 kPa，脊髓横截面积减少超过50%。结论颈脊髓有限元生物力学研究可对爆裂骨折骨碎片不同撞击速度造成脊髓损伤的力学机制进行分析，当骨折块撞击速度超过3.5 m/s时，其颈脊髓内部应力开始明显升高，横截面积减少超过30%，可能造成脊髓损伤。

ObjectiveTo establish a three-dimensional （3D） finite element （FE） model of the whole cervical spinal cord （WSCS） and explore the biomechanical behaviors of cervical spinal cord injury related to different bone fragment impact velocities by FE analysis.MethodsA 3D FE model of WCSC was established based on the morphologic data of each segment of the human cervical cord. The reconstruction structures, which included the dura mater, the cerebrospinal fluid, the gray and white matter in the C2 to C7 cervical vertebrae, were validated.On the validated WCSC model, three kinds of pellets with same mass （7 g） but different impact areas （314, 157 and 78.5 mm2） were created to represent the bone fragments.These were positioned in the middle of the spinal cord to impact at various initial velocities.The maximum of von Mises stress and the reduction of the cross-sectional area （CSA） of the spinal cord were measured from each impact.ResultsThe compression of WCSC （percentage） and the time to reach maximum compression were similar with the results reported in literatures, indicating the validity of the model.Regardless of the impact areas of the pellet, the maximum of von Mises stress and the reduction of CSA of the spinal cord increased with the increased velocity.The maximum of von Mises stress was 5.0-7.0 kPa at a pellet velocity of 1.5 m/s, and the reduction of CSA was 9.3%-12.3%.At a velocity of 3.5 m/s, the maximum of von Mises stress was 42-54 kPa and the reduction of CSA was over 30%.The stress of the spinal cord significantly increased when pellet velocity exceeded 3.5 m/s, and the fastest increase was recorded at 4.5 m/s.The von Mises stress of the spinal cord ranged between 240 and 320 kPa at a velocity of 6.0 m/s, and CSA decreased by more than 50%.ConclusionThe 3D FE model of WSCS could provide more insights on the biomechanical mechanisms of spinal cord injury through various bone fragment impacts in burst fracture.When the impact velocity of the bone fragment exceeds 3.5 m/s, the maximum stress significantly increases and the reduction of CSA of the spinal cord is over 30%, and this could possibly lead to the contusion injury of the spinal cord.