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

ABSTRACT

Objective: To 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. Methods: A 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 C(2) to C(7) 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 mm(2)) 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. Results: The 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%. Conclusion: The 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.