Analysis of spinal motion and loads during frontal impacts. Comparison between PMHS and ATD

University of Virginia ECIP- Universidad de Navarra.
Annals of advances in automotive medicine 01/2010; 54:61-78.
Source: PubMed


Quantifying the kinematics of the human spine during a frontal impact is a challenge due to the multi-degree-of-freedom structure of the vertebral column. This papers reports on a series of six frontal impacts sled tests performed on three Post Mortem Human Surrogates (PMHS). Each subject was exposed first to a low-speed, non-injurious frontal impact (9 km/h) and then to a high-speed one (40 km/h). Five additional tests were performed using the Hybrid III 50(th) percentile male ATD for comparison with the PMHS. A 3D motion capture system was used to record the 6-degree-of-freedom motion of body segments (head, T1, T8, L2, L4 and pelvis). The 3D trajectories of individual bony structures in the PMHS were determined using bone-mounted marker arrays, thus avoiding skin-attached markers and their potential measurements artifacts. The PMHS spines showed different behavior between low and high speed. While at low speed the head and upper spinal segments lagged the lower portion of the spine and pelvis in reaching their maximum forward displacement (time for maximum forward head excursion was 254.3±31.9 ms and 140.3±9 ms for the pelvis), these differences were minimal at high speed (127±2.6 ms for the head vs. 116.7±3.5 ms for the pelvis). The ATD did not exhibit this speed-dependant behavior. Furthermore, the ATD's forward displacements were consistently less than those exhibited by the PMHS, regardless of the speed. Neck loads at the atlanto-occipital joint were estimated for the PMHS using inverse dynamics techniques and compared to those measured in the ATD. It was found that the axial and shear forces and the flexion moment at the upper neck of the PMHS were higher than those measured in the ATD.

Download full-text


Available from: Patrick O Riley
  • Source
    • "Recent studies combining full sled tests and computer simulations have found significant differences in the magnitudes of the acceleration at T1 and the neck loads between Anthropomorphic Test Devices (ATD) and cadavers (Shaw et al., 2000, 2001; Lopez-Valdes et al., 2010). Other studies have shown similar findings in pediatric ATD (Sherwood et al., 2003; Ash et al., 2009; Lopez-Valdes et al., 2009). "
    [Show abstract] [Hide abstract]
    ABSTRACT: A growing body of literature points out the relevance of the thoracic spine dynamics in understanding the thorax-restraint interaction as well as in determining the kinematics of the head and cervical spine. This study characterizes the dynamic response in bending of eight human spinal specimens (4 pediatric: ages 7 and 15 years, 4 adult: ages 48 and 52 years) from two sections along the thoracic spine (T2-T4 and T7-T9). Each specimen consisted of three vertebral bodies connected by the corresponding intervertebral discs. All ligaments were preserved in the preparation with the exception of the inter-transverse ligament. Specimens were exposed to a series of five dynamic bending ramp-and-hold tests with varying amplitudes at a nominal rate of 2 rad/s. After this battery of tests, failure experiments were conducted. The 7-year-old specimen showed the lowest tolerance to a moment (T2-T4: 12.1 Nm; T7-T9: 11.6 Nm) with no significant reduction of the relative rotation between the vertebrae. The 15-year-old failure tolerance was comparable to that of the adult specimens. Failure of the adult specimens occurred within a wide range at the T2-T4 thoracic section (23.3 Nm- 53.0 Nm) while it was circumscribed to the interval 48.3 Nm-52.5 Nm for the T7-T9 section. The series of dynamic ramp-and-hold were used to assess two different scaling methods (mass scaling and SAE scaling). Neither method was able to capture the stiffness, peak moment and relaxation characteristics exhibited by the pediatric specimens.
    Full-text · Article · Jan 2011 · Annals of advances in automotive medicine
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Hybrid III 6-year-old ATD has been benchmarked against adult-scaled component level tests but the lack of biomechanical data hinders the effectiveness of the procedures used to scale the adult data to the child. Whole body kinematic validation of the pediatric ATD through limited comparison to post mortem human subjects (PMHS) of similar age and size has revealed key differences attributed to the rigidity of the thoracic spine. As restraint systems continue to advance, they may become more effective at limiting peak loads applied to occupants, leading to lower impact environments for which the biofidelity of the ATD is not well established. Consequently, there is a growing need to further enhance the assessment of the pediatric ATD by evaluating its biofidelity at lower crash speeds. To this end, this study compared the kinematic response of the Hybrid III 6 year old ATD against size-matched male pediatric volunteers (PVs) (6-9 yrs) in low-speed frontal sled tests. A 3-D near-infrared target tracking system quantified the position of markers at seven locations on the ATD and PVs (head top, opisthocranion, nasion, external auditory meatus, C4, T1, and pelvis). Angular velocity of the head, seat belt forces, and reaction forces on the seat pan and foot rest were also measured. The ATD exhibited significantly greater shoulder and lap belt, foot rest, and seat pan normal reaction loads compared to the PVs. Contrarily, PVs exhibited significantly greater seat pan shear. The ATD experienced significantly greater head angular velocity (11.4 ± 1.7 rad/s vs. 8.1 ± 1.4 rad/s), resulting in a quicker time to maximum head rotation (280.4 ± 2.5 ms vs 334.2 ± 21.7 ms). The ATD exhibited significantly less forward excursions of the nasion (171.7 ± 7.8 mm vs. 199.5 ± 12.3 mm), external auditory meatus (194.5 ± 11.8 mm vs. 205.7 ± 10.3 mm), C4 (127.0 ± 5.2 mm vs. 183.3 ± 12.8 mm) and T1 (111.1 ± 6.5 mm vs. 153.8 ± 10.5 mm) compared to the PVs. These analyses provide insight into aspects of ATD biofidelity in low-speed crash environments.
    Full-text · Article · Jan 2010 · Annals of advances in automotive medicine
  • [Show abstract] [Hide abstract]
    ABSTRACT: Previous research has quantified differences in head and spinal kinematics between children and adults restrained in an automotive-like configuration subjected to low speed dynamic loading. The forces and moments that the cervical spine imposes on the head contribute directly to these age-based kinematic variations. To provide further explanation of the kinematic results, this study compared the upper neck kinetics - including the relative contribution of shear and tension as well as flexion moment - between children (n=20, 6-14 yr) and adults (n=10, 18-30 yr) during low-speed (<4 g, 2.5 m/s) frontal sled tests. The subjects were restrained by a lap and shoulder belt and photo-reflective targets were attached to skeletal landmarks on the head, spine, shoulders, sternum, and legs. A 3D infrared tracking system quantified the position of the targets. Shear force (F(x)), axial force (F(z)), bending moment (M(y)), and head angular acceleration (θ(head)) were computed using inverse dynamics. The method was validated against ATD measured loads. Peak F(z) and θ(head) significantly decreased with increasing age while M(y) significantly increased with increasing age. F(x) significantly increased with age when age was considered as a univariate variable; however when variations in head-to-neck girth ratio and change in velocity were accounted for, this difference as a function of age was not significant. These results provide insight into the relationship between age-based differences in head kinematics and the kinetics of the cervical spine. Such information is valuable for pediatric cervical spine models and when scaling adult-based upper cervical spine tolerance and injury metrics to children.
    No preview · Article · Nov 2011 · Journal of Biomechanics
Show more