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The present study investigated the effects of the structural stiffness of the head restraint and its attachment rigidity on the biomechanical responses and related injury measures of the neck in a rear impact vehicular collision. A series of simulated rear impacts were conducted using a mid-sized male test dummy seated in a modified late-model front passenger seat on a deceleration crash sled with a FMVSS 202 pulse. Preliminary results demonstrated that a more rigid head restraint in its design and attachment produced lesser values in most biomechanical injury measures such as neck shear force, neck extension bending moment, tension-extension neck injury criterion (Nij), shear-moment neck injury criterion (Nkm), and head-torso relative extension angular displacement. This is true for a wide range of seatback recliner stiffness. This suggests that a more rigid head restraint may have a protective advantage over a more pliant one for the neck in a rear impact.

A three-dimensional finite element model of a human ligamentous cervical spine was developed to study the mechanics of cervical injuries related to automotive crashes. Patran and LS-DYNA3D were used to create this preliminary model consisting of the cervical vertebrae, intervertebral discs, and biomechanically relevant spinal ligaments. Material properties were obtained from published experimental data. A rigid head was included to provide proper application of non-contact inertial loading. Model development began with the generation of a single cervical motion segment. This model was subjected to a variety of loading conditions to provide a qualitative check of material properties and tissue interface conditions. Based on this motion segment model, a complete cervical model was developed including an attached rigid head. Simulations were run for axial compression and frontal flexion.

Three different measurement methods for angular displacement (rotation) of a dummy head and torso were evaluated in a rear impact crash environment. The data were collected using a Hybrid III 50th percentile male dummy in rear impact sled tests tuned to the FMVSS 202 deceleration pulse. Angular rate sensors yielded rotation data closely matching the results from high-speed digital video images to within 3 degrees with a total displacement range up to 110 degrees. Linear acceleration data generally yield less accurate angular displacement results, in addition to being cumbersome in data processing.

This study explores the dynamics of head and cervical spine impact with the specific goals of determining the effects of head inertia and impact surface on injury risk. Head impact experiments were performed using unembalmed head and neck specimens from 22 cadavers. These included impacts onto compliant and a rigid surfaces with the surface oriented to produce both flexion and extension attitudes. Tests were conducted using a drop track system to produce impact velocities on the order of 3.2 m/s. Multiaxis transduction recorded the head impact forces, head accelerations, and the reactions at T1. The tests were also imaged at 1000 frames/sec. Injuries occurred 2 to 30 msec following head impact and prior to significant head motion. Head motions were not found to correlate with injury classification. Decoupling was observed between the head and T1, resulting in a lag in the force histories.