ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

INTRODUCTION
The cervical spine is frequently injured during motor vehicle accidents (MVAs). In
MVAs, a low-speed 8-mile/hour rear-end collision can produce a 2G acceleration of the
vehicle and a 5G acceleration of the head within a span of 300ms or less [1]. The energy
imparted to spinal tissues in this short span of time may cause acute and chronic pain in
soft tissues (ligaments, muscles, etc.). These injuries may not be instantaneous evident
or demonstrable using general clinical assessment methods (CT, MRI or X-rays) [2].
Profound understanding of the underlying mechanisms of vehicular cervical trauma may
lead to improved methods of prevention, diagnosis, and treatment.
Numerous in vitro and in vivo studies have been devoted to study the mechanism and
tolerance of the cervical spine during whiplash [3-16]. The corresponding kinematic
movements of either each motion segment [6, 8] or the strain values of soft tissues
(especially the capsular ligaments) [4,7,10] were analyzed. Many experimental studies
using human cadavers and FE studies have shown that the cervical spine develops an Sshaped
curvature in the early phase of whiplash, characterized by lower cervical
extension and upper cervical flexion. In the later phase of whiplash, global cervical
hyperextension (C-shape) occurs [8,12]. In most FE studies, the vertebrae of the headneck
complex [14,15] or even the whole body [16] were either geometrically simplified
or modeled as rigid bodies connected by spring elements to predict the motion segment
rotations and internal stress and strains of various components during whiplash.
Although the previous studies provided valuable information on the mechanism of
whiplash, most of them focused solely on one specific (direct or lateral) impact
condition. There are no known experimental and FE studies to determine the head neck
responses under oblique impact conditions.
Accordingly, a detailed 3-D C0-C7 FE model of the whole head-neck complex
developed previously and validated globally under normal physiological loadings, lowspeed
rear impact and near vertex drop tests [17] was modified to include T1 and
accomplish this study. It was shown that the C0-C7 model reasonably reflects the
intervetebral rotation distributions under static moments and basic responses of head
and neck under dynamic situations. In current study, the predicted segmental kinematics
of the modified C0-T1 model would be validated under rear and side impact conditions
firstly. The global and segmental response and strain variations of various ligaments of
the head-neck complex under five impact directions would then be investigated using
the model. We believe this computer model can provide both the primary and
secondary segmental motions in multiple planes, and the variation of ligament strains
over time in different impact directions and lay some insights for future experimental
studies reducing the associated high cost of any cadaveric experiments.
METHODS
The three-dimensional FE models of the skull and C1-T1 vertebrae were developed with
geometrical data based on the actual geometry of a 68 year-old male cadaver specimen.
Adopting the digitizing technique by Teo et al. [18], a flexible digitizer (FaroArm,
Bronze Series, Faro Technologies, Inc., Florida, USA) with accuracy up to 0.1-mm was
used to extract the surface profile of the bony structures (skull, C1-C7). The Surfacer
7.0 (Structural Dynamics Research Corporation, Ohio, USA), to create the sequential
cross section outline of the vertebra at 1-2 mm intervals on the regional geometrical