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Designing for Head and Neck Anatomy
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
The cervical vertebrae, with intervertebral discs between, move in relationship to each other and to the skull positioned at the top of the spine. Bogduk and Mercer (2000) detail cervical spine mobility, section by section. They divide the complex movement of the neck into four functional units, starting at the top. (1) C1, the atlas, cradles the occipital condyles of the skull. (2) The head and atlas rotate as a unit on the dens, the bony structure that projects upward from C2. (3) The C2 vertebra anchors onto the lower cervical vertebral section by a unique orientation of the articulating joints between C2 above and C3 below. (4) Each segment, C2-C3, C3-C4, etc. of the remaining five segments (C3-C7) move forward-backward and side-to-side. The vertebral bodies in this middle and lower region are saddle-shaped to facilitate the motions.
The Neck
Published in Melanie Franklyn, Peter Vee Sin Lee, Military Injury Biomechanics, 2017
Kwong Ming Tse, Jianfei Liu, Victor P.W. Shim, Ee Chong Teo, Peter Vee Sin Lee
The facet articulations of the upper cervical spine are extremely complex due to the convexity and concavity of the vertebral body; with the kidney-shaped facets and their higher internal margins compared to the medial margins (Middleditch and Oliver 2005). The atlanto-occipital joints are formed by the articulation of the concave articular facets on the lateral masses of the atlas with the convex facets on the occipital condyles (Oliver and Middleditch 1991). The lower cervical vertebrae (C3–C7) have similar or typical convexity and concavity, with their superior surface concave transversely and convex anteroposteriorly (Middleditch and Oliver 2005). The articular facets on the inferior surface of the vertebral body articulate with the uncinated processes of the subjacent vertebra (Middleditch and Oliver 2005). The functional joint biomechanics in the cervical spine are determined by the size and orientation of the articular facets (Pal et al. 2001). These allow much of the flexion and extension that occurs in the head–neck junction and at least one half of the axial rotation of the cervical spine which is inevitably coupled with lateral flexion (Bogduk and Mercer 2000). The superior articular surface of the facet joint undergoing an axial rotation slides up the inferior surface, causing a lateral bending motion between the vertebrae. Conversely, when undergoing a lateral bend, the superior articular surface of the compressed facet joint will slide downwards and posteriorly, causing a rotation between the vertebrae
Evaluation of Hybrid III and THOR-M neck kinetics and injury risk under various restraint conditions during full-scale frontal sled tests
Published in Traffic Injury Prevention, 2018
Devon L. Albert, Stephanie M. Beeman, Andrew R. Kemper
In order to quantify neck forces and moments, the ATDs were instrumented with neck load cells and head accelerometers, and the PMHSs were instrumented with head accelerometers. The ATDs were instrumented with 6-axis load cells in the upper and lower neck (see Table A3, online supplement, for further information). ATD upper neck bending moments were transformed to the occipital condyles (OCs). All surrogates were instrumented with 6-degree-of-freedom sensor blocks (Table A3) at the head to record linear accelerations and angular rates for use in inverse dynamics calculations. PMHS sensor blocks were mounted to the posterior aspect of the head so that the sensing axes were approximately aligned with the coordinate axes designated in SAE J211 (Society of Automotive Engineers [SAE] 1995), and the forward-pointing (x) axis was approximately in line with the Frankfort plane. The THOR-M was also instrumented with front and rear neck spring load cells (10386JI4, Humanetics, Plymouth, MI) and a rotary potentiometer (ECO-50-ESC-102, Vishay Intertechnology, Malvern, PA) at the OC to quantify the angle between the neck and the head (OC joint angle). There is not currently a standard method for incorporating the neck spring loads into the calculation of the moment about the y-axis at the OC. Additionally, some distances and angles needed to perform these calculations are not currently available in the published drawings. Therefore, the loads measured in the neck spring load cells were not accounted for when calculating the THOR-M upper neck moment about the y-axis. All data were collected at 20 kHz (TDAS Pro & G5, DTS, Seal Beach, CA) and filtered using channel frequency classes from SAE J211 (SAE 1995; Table A4, see online supplement). Neck force and moment polarities conformed to the SAE J211 sign convention (Table A5, see online supplement; SAE 1995).