The six degrees of freedom motion of the human head, spine, and pelvis in a frontal impact.

OBJECTIVE: The goal of this study is to characterize the in situ 6-degree-of-freedom kinematics of the head, 3 vertebrae (T1, T8, and L2), and the pelvis in a 40 km/h frontal impact. METHODS: Three postmortem human surrogates (PMHS) were exposed to a deceleration of 15 g over 125 ms and the motion of selected anatomical structures (head, T1, T8, L2, and pelvis) was tracked at 1000 Hz using an optoelectric stereophotogrammetric system. Displacements of the analyzed structures are reported in the sagittal and the transverse planes. Rotations of the structures are described using the finite helical axis of the motion. RESULTS: Anterior displacements were 530.5 ± 39.4 mm (head), 434.7 ± 20.0 mm (T1), 353.3 ± 29.6 mm (T8), 219.9 ± 19.3 mm (L2), and 78.9 ± 22.1 mm (pelvis). The ratio between peak anterior and lateral displacement was up to 19 percent (T1) and 26 percent (head). Magnitudes of the rotation of the head (69.9 ± 1.5°), lumbar (66.5 ± 9.1°), and pelvis (63.8 ± 11.8°) were greater than that of the thoracic vertebrae (T1: 49.1 ± 7.8°; T8: 47.7 ± 6.3°). Thoracic vertebrae exhibited a complex rotation behavior caused by the asymmetric loading of the shoulder belt. Rotation of the lumbar vertebra and pelvis occurred primarily within the sagittal plane (flexion). CONCLUSION: Despite the predominance of the sagittal motion of the occupant in a pure (12 o'clock) frontal impact, the asymmetry of belt loading induced other relevant displacements and rotations of the head and thoracic spine. Attempts to model occupant kinematics in a frontal impact should consider these results to biofidelically describe the interaction of the torso with the belt.

Thoracic response to shoulder belt loading: comparison of tabletop and frontal sled tests with PMHS.

OBJECTIVE: The recent refinement of high-rate optical tracking allows dramatically detailed thoracic deformation measurements to be taken during postmortem human subject (PMHS) sled tests. These data allow analysis of restraint belt geometry and the 3-dimensional thoracic deformations generated by belt impingement. One consequence of this new capability is a better understanding of complementary thoracic characterization experiments such as tabletop tests and how the thoracic response can be interpreted for applications involving more complex loading mechanisms. METHODS: This article reports a detailed evaluation of the timing, magnitude, and direction of the applied belt forces and the resulting thoracic deformations in 2 previously performed tests series involving frontal sled tests and tabletop belt-loading tests. RESULTS: In the sled tests, the posteriorly directed component (SAE x) of the belt tension (F(B)) was F(Bx) = 0.70 F(B) at the shoulder but only F(Bx) = 0.14 F(B) where the belt engaged the anterolateral torso inferiorly. The corresponding components on the tabletop were F(Bx) = 0.60 F(B) (shoulder) and F(Bx) = 0.48 F(B) (lower). CONCLUSIONS: When these components are cross-plotted with chest deflection, pronounced consequences of thoracic anterior wall deformation patterns due to flexion of the thoracic spine and the internal viscera's inertia can be seen in the effective thoracic stiffness. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Kinematics of the unrestrained vehicle occupants in side-impact crashes.

A test series involving direct right-side impact of a moving wall on unsupported, unrestrained cadavers with no arms was undertaken to better understand human kinematics and injury mechanisms during side impact at realistic speeds. The tests conducted provided a unique opportunity for a detailed analysis of the kinematics resulting from side impact. Specifically, this study evaluated the 3-dimensional (3D) kinematics of 3 unrestrained male cadavers subjected to lateral impact by a multi-element load wall carried by a pneumatically propelled rail-mounted sled reproducing a conceptual side crash impact. Three translations and 3 rotations characterize the movement of a solid body in the space, the 6 degrees of freedom (6DoF) kinematics of 15 bone segments were obtained from the 3D marker motions and computed tomography (CT)-defined relationships between the maker array mounts and the bones. The moving wall initially made contact with the lateral aspect of the pelvis, which initiated lateral motion of the spinal segments beginning with the pelvis and moving sequentially up through the lumbar spine to the thorax. Analyzing the 6DoF motions kinematics of the ribs and sternum followed right shoulder contact with the wall. Overall thoracic motion was assessed by combining the thoracic bone segments as a single rigid body. The kinematic data presented in this research provides quantified subject responses and boundary condition interactions that are currently unavailable for lateral impact.

Pressure waves in the aorta during isolated abdominal belt loading: the magnitude, phasing, and attenuation.

While rupture of the aorta is a leading cause of sudden death following motor vehicle crashes, the specific mechanism that causes this injury is not currently well understood. Aortic ruptures occurring in the field are likely due to a complex combination of contributing factors such as acceleration, compression of the chest, and increased pressure within the aorta. The objective of the current study was to investigate one of these factors in more detail than has been done previously; specifically, to investigate the in situ intra-aortic pressure generated during isolated belt loading to the abdomen. Ten juvenile swine were subjected to dynamic belt loads applied to the abdomen. Intraaortic pressure was measured at multiple locations to assess the magnitude and propagation of the resulting blood pressure wave. The greatest average peak pressure (113.6 +/- 43.5 kPa) was measured in the abdominal aorta. Pressures measured in the thoracic aorta and aortic arch were 70 per cent and 50 per cent, respectively, that measured in the abdominal aorta. No macroscopic aortic trauma was observed. To the authors' knowledge the present study is the first one to document the presence, propagation, and attenuation of a transient pressure wave in the aorta generated by abdominal belt loading. The superiorly moving wave is sufficient to generate hydrostatic and intimal shear stress in the aorta, possibly contributing to the hypothesized mechanisms of traumatic aortic rupture.

Viscoelastic response of the thorax under dynamic belt loading.

OBJECTIVE: Three postmortem human surrogates (PMHS) were positioned and rigidly mounted through the spine to a tabletop test fixture for the purpose of characterizing thoracic response to diagonal belt loading with well-defined boundary conditions. METHODS: These PMHS were mounted to a stationary apparatus that supported the spine and shoulders in a configuration comparable to that seen in a 48 km/h automobile sled test at the time of maximum chest deformation. A belt restraint was positioned across the anterior torso with attachments at D-ring and buckle locations based on the geometry of a mid-sized sedan. The belt was attached to a trolley driven by a hydraulic ram linked to a universal test machine. Ramp and hold experiments were conducted at rates of 0.5, 0.9, and 1.2 m/s and hold times of 60 s. Ramp-hold displacement waveforms of up to 20 percent of the chest depth were applied to the chest while the resulting belt loads and spinal reaction loads were recorded. These data were used to identify parameters in a seven-parameter thoracic structural model mathematically analogous to a viscoelastic material model. A final test with 40 percent deflection was performed at the completion of the loading sequence. RESULTS: Model fits to ramps of different magnitudes indicated that the assumption of temporal linearity was reasonable over the range of inputs in this study. In agreement with previous studies, the spatial (force-deflection) response was only slightly nonlinear, indicating that a fully linear model would be reasonable up to the deflection levels used here. CONCLUSIONS: Pronounced variability in the instantaneous elastic behavior was observed among the three test subjects, whereas the relaxation behavior exhibited less variability.