Validation of a head-neck computer model for whiplash simulation.

A head-neck computer model was comprehensively validated over a range of rear-impact velocities using experiments conducted by the same group of authors in the same laboratory. Validations were based on mean +/- 1 standard deviation response curves, i.e. corridors. Global head-neck angle, segmental angle and local facet joint regional kinematic responses from the model fell within experimental corridors. This was true for all impact velocities (1.3, 1.8 and 2.6 m s(-1)). The non-physiological S-curvature lasted approximately 100 ms. The present, comprehensively validated model can be used to conduct parametric studies and investigate the effects of factors such as active sequential and parallel muscle contractions, thoracic ramping and local tissue strain responses, as a function of cervical level, joint region and impact velocity in whiplash injury assessment.

Development of extension kinematic corridors to validate a head/neck finite element model.

The objective of the current study was the development of experimental response corridors for the purpose of validating a finite element head-neck model in simulated vehicular rear impact. Six intact human head-neck cadaver complexes were used to understand and quantify the kinematics of the cervical spine secondary to low-speed rear impact. The first and second thoracic vertebrae were mounted in a fixative and attached to a minisled/pendulum apparatus. The specimens experienced live different input velocities applied to the first thoracic vertebral, created t),y the pendulum. The response of the specimen was digitally imaged at 1000 Hz from the right lateral side. Relative angles between vertebrae were analyzed in the sagittal plane at 100 ms after impact of the pendulum. Results correlated well with published physiologic range of motion data and dynamic full-body cadaver real impact experiments. Data obtained from this study will be used to validate the macroscopic motions of a finite element model, which will be used to understand the injury mechanisms involved in low-speed vehicular rear impacts.

Head-neck finite element model for motor vehicle inertial impact: material sensitivity analysis.

The aim of this study was to conduct a material sensitivity analysis using a head-neck finite element model (FEM). The model included the skull, C1-T1 vertebrae, intervertebral discs, facet joints, and biomechanically relevant ligaments. Poisson's ratio and elastic modulus of the head-neck components were varied. The loading condition included the impact load applied to the first thoracic vertebra. Commercially available software (LS-DYNA) was used for the analysis. Head angle versus time, head center of gravity trajectory, and head center of gravity angular acceleration responses were computed. In general, the variation of elastic modulus had a higher effect on the response compared to variation of Poisson's ratio. As the elastic modulus was increased, the head angle and angular acceleration increased. The present findings form a first step in the study of computational biomechanics of vehicular-related trauma.

Biomechanics of human occupants in simulated rear crashes: documentation of neck injuries and comparison of injury criteria.

The objective of this study was to subject small female and large male cadavers to simulated rear impact, document soft-tissue injuries to the neck, determine the kinematics, forces and moments at the occipital condyles, and evaluate neck injury risks using peak force, peak tension and normalized tension-extension criteria. Five unembalmed intact human cadavers (four small females and one large male) were prepared using accelerometers and targets at the head, T1, iliac crest, and sacrum. The specimens were placed on a custom-designed seat without head restraint and subjected to rear impact using sled equipment. High-speed cameras were used for kinematic coverage. After the test, x-rays were obtained, computed tomography scans were taken, and anatomical sections were obtained using a cryomicrotome. Two female specimens were tested at 4.3 m/s (mean) and the other two were tested at 6.8 m/s (mean), and one large male specimen was subjected to 6.6 m/s velocity. One female specimen tested at 4.1 m/s did not sustain injury. All others produced injuries to soft tissue and joint-related structures that included tearing of the anterior longitudinal ligament, rupture of the ligamentum flavum, hematoma at the upper facet joint, anterior disc disruption at the lower spine, and facet joint capsule tear. Compressive forces (100 to 254 N) developed within 60 ms after impact. Tensile forces were higher (369 to 904) and developed later (149 to 211 ms). While peak shear forces (268 to 397 at 4.3 m/s and 257 to 525 N at 6.8 m/s) did not depend on velocity, peak tensile forces (369 to 391 N at 4.3 m/s and 672 to 904 N at 6.8 m/s) seemed to correlate with velocity. Peak extension moments ranged from 22.0 to 33.5 Nm at low velocity and 32.7 to 46.6 Nm at high velocity. All these biomechanical data attained their peaks in the extension phase (with very few exceptions), which ranged from 179 to 216 ms. The neck injury criterion, NIC, exceeded the suggested limit of 15 m(2)/s(2) in all specimens. Axial force and bending moment data were used to evaluate various neck injury criteria (N(ij), N(TE), peak tension and peak extension). The risk for AIS >/= 3 injury for the combined tension-extension criteria was 30 percent in one female specimen tested at 6.8 m/s. For the other specimens the risk of AIS >/= 3 injury was less than five percent using all criteria.