A three-dimensional finite element model of a human neck has been developed in an effort to study the mechanics of cervical spine while subjected to impacts. The neck geometry was obtained from MRI scans of a 50th percentile male volunteer. This model, consisting of the vertebrae from C1 through T1 including the intervertebral discs and posterior elements, was constructed primarily of 8-node brick elements. The vertebrae were modeled using linear elastic-plastic materials, while the intervertebral discs were modeled using linear viscoelastic materials. Sliding interfaces were defined to simulate the motion of synovial facet joints. Anterior and posterior longitudinal ligaments, facet joint capsular ligaments, alar ligaments, transverse ligaments, and anterior and posterior atlanto-occipital membranes were modeled as nonlinear bar elements or as tension-only membrane elements. A previously developed head and brain model was also incorporated. Only the passive effects of the head and neck muscles were considered.
Data from head drop tests performed at Duke University and data from three 24 km/hr (15 mile/hr) cadaver rearend impact sled tests were used to validate the model. In the drop test simulation, head and neck loads, as well as head acceleration, were chosen to gauge the accuracy of the model predictions against test results. In the rearend impact simulation, head acceleration and the global kinematics of the head and neck correlate well with experimental data. The characteristic “head lag” is clearly demonstrated along with shear and rotation of the vertebral bodies.
The validated model was integrated into a skeleton torso model. This model was previously developed in order to simulate a 50th percentile male driver in a 48 km/hr (30 mile/hr) impact with a pre-deployed airbag. This simulation, which uses a crash pulse with a peak sled deceleration of 36.5 g, is similar to that reported by Cheng et al. In this application, the kinematics and airbag pressure predicted by the model compared favorably with experimental data. It should be noted that both the airbag used in these simulations and those used in the experiments do not represent any airbags that are currently in production. Further research is still needed in order to fully validate the neck model before it can be used to study neck loads during head-airbag interaction or during other types of injurious interactions.