Finite Element Analysis of Cervical Spinal Nerve Tissue Tolerance to Whiplash Injury: A Preliminary Study

Abstract

Research and/or Engineering Questions/Objective Whiplash can occur in frontal, side and rear car collisions but most complaints occur in rear collision by another vehicle. Whiplash can produce acute and chronic neck pain, headache, paresthesia, or even paralysis. The facet capsule, intervertebral discs, cervical ligaments, and cervical spinal nerves can be injured during whiplash. Injury to the nerve can result in more severe clinical symptoms, including motor, sensory, and sphincter disturbance. But the accelerations that can cause nerve injury are unknown. The aim of this study was to assess the threshold chest acceleration that causes cervical spinal nerve injury using finite element (FE) methods. Methodology Multi-slice CT images with 1.2 mm slice distance of a de-identified adult male were used to construct the three-dimensional FE model of cervical spine components using Mimics software. FE components include the head, neck, upper thorax, ligament, intervertebral disks, ligaments, and muscle fascias. The elements in the FE model components were reconstructed for a better quality using ANSA and Hypermesh software. Acceleration curves obtained from volunteer rear impact tests were input into the FE model and run using LS-DYNA. The FE model was validated by comparing the head movement corridor with volunteer data. Strain on the cervical spinal nerve was used to determine the injury probability based on our neurophysiology and biomechanical in vivo experimental data. Results Mimics software provided an effective and rapid approach to build a FE model. An increase of chest acceleration caused an increase of the strain of the spinal nerve. The maximum stretch speed of the spinal nerves was showed to be 199 ± 23 mm/sec from the simulation of rear impact. 7 Gs chest acceleration produced a maximum 24 % strain of the spinal nerve resulting in a 40 % probability of spinal nerve injury. The highest strain was found to be in the 3rd cervical spinal nerve. Increased acceleration in the shoulder more than 7 Gs did not cause further increase of nerve strain in the simulation. Limitations of this study The limitation of this study is that only the cervical spine, head and upper shoulder model was used in the computer simulation. It will be better if the whole vehicle and whole body FE model was constructed for our research. In addition, muscle biofidelities were not simulated in this model. What does the paper offer that is new in the field in comparison to other works of the author Currently, most research uses ANSYS software to construct FE models, which is a tedious procedure. Mimics, ANSA, and HyperMesh software combined applications provided a new and rapid approach to build a human FE model, yet the element quality can be better controlled. This paper first reported a research of spinal nerve tolerance to whiplash injury using FE analysis methods. Conclusion Mimics, ANSA, and HyperMesh software combined applications provided a new and rapid approach to build a human FE model, yet the element quality can be better controlled. Our neck finite element model was the first FE model developed to study the spinal nerve tolerance to whiplash injury. The model validation was performed at the global level by tracking the head kinematics. The simulation results corresponded to clinical scenarios and volunteer testing outcomes. Our simulation demonstrated that 6 Gs chest accelerations with no headrest may cause 25 % probability of cervical spinal nerve injury. Increased chest acceleration to 9, or 10 Gs did not cause further increase of spinal nerve maximum strain, or injury probability. A higher strain was frequently found in the C3 spinal nerve under different chest accelerations.

F2012-F05-006