Validating a Device for Whiplash Motion Simulation in a Porcine Model

Whiplash injury is a common outcome following minor automobile collisions. One theorizedmechanism for whiplash injury is that the rapid head and neck motions induced by a collision caninjure nerve cells in the dorsal root ganglia through pressure gradients developed in the spinalcanal and surrounding tissues. This injury mechanism has previously been studied in humancadaver and porcine models. However, the whiplash motion simulation methods in the latterstudies lacked the control necessary to explore the independent effects of head rotation andretraction on the measured spinal pressures. This project aimed to address the limitations ofprevious porcine whiplash studies by developing and validating a new whiplash motion simulationdevice to enable further study of this injury mechanism. The new proposed device consists of twoservomotors which can be programmed to precisely actuate a headplate through mechanicallinkages. For the current study, an inert surrogate model was used for preliminary testing of thedevice using a whiplash motion profile from previous porcine studies. The time scale of the motionprofile was adjusted to incrementally increase severity. The positional accuracy and repeatabilityof the device was assessed through marker tracking of the headplate and logging of the motorencoder positions. Angular rates and linear accelerations of the plate were also measured. Testingdemonstrated the strengths of the proposed device in accurately and repeatably replicatingprogrammed motion profiles. Some design modifications can potentially enable simulatingwhiplash motion severities commensurate with previous porcine whiplash studies. With futuretesting using this device, our understanding of the pressure-induced whiplash injury mechanismcan be improved, which can inform effective treatments and preventative measures for whiplashinjury

Load-sharing and kinematics of the human cervical spine under multi-axial transverse shear loading: combined experimental and computational investigation

This preprint has not undergone peer review or any post-submission improvements or corrections. The Version of Record of this article is published in Journal of Biomechanical Engineering, and is available online at https://doi.org/10.1115/1.4050030The cervical spine experiences shear forces during everyday activities and injurious events yet there is a paucity of biomechanical data characterizing the cervical spine under shear loading. This study aimed to 1) characterise load transmission paths and kinematics of the subaxial cervical spine under shear loading, and 2) assess a contemporary finite element cervical spine model using this data. Subaxial functional spinal units (FSUs) were subjected to anterior, posterior and lateral shear forces (200 N) applied with and without superimposed axial compression preload (200 N) while monitoring spine kinematics. Load transmission paths were identified using strain gauges on the anterior vertebral body and lateral masses and a disc pressure sensor. Experimental conditions were simulated with cervical spine finite element model FSUs (GHBMC M50 version 5.0). The mean kinematics, vertebral body strains and disc pressures were compared to experimental results. The shear force-displacement response typically demonstrated a toe region followed by a linear response, with higher stiffness in the anterior shear direction relative to lateral and posterior shear. Compressive axial preload decreased posterior and lateral shear stiffness and increased anterior shear stiffness. Load transmission patterns and kinematics suggest the facet joints play a key role in limiting anterior shear while the disc governs motion in posterior shear. The main cervical spine shear responses and trends are faithfully predicted by the GHBMC finite element cervical spine model. These basic cervical spine biomechanics and the computational model can provide insight into mechanisms for facet dislocation in high severity impacts, and tissue distraction in low severity impacts

Subject-specific ex vivo simulations for hip fracture risk assessment in sideways falls

ISSN:8756-328

The Effect of Lateral Eccentricity on Failure Loads, Kinematics, and Canal Occlusions of the Cervical Spine in Axial Loading

Current neck injury criteria do not include limits for lateral bending combined with axial compression and this has been observed as a clinically relevant mechanism, particularly for rollover motor vehicle crashes. The primary objectives of this study were to evaluate the effects of lateral eccentricity (the perpendicular distance from the axial force to the centre of the spine) on peak loads, kinematics, and spinal canal occlusions of subaxial cervical spine specimens tested in dynamic axial compression (0.5 m/s). Twelve 3-vertebra human cadaver cervical spine specimens were tested in two groups: low and high eccentricity with initial eccentricities of 1% and 150% of the lateral diameter of the vertebral body. Six-axis loads inferior to the specimen, kinematics of the superior-most vertebra, and spinal canal occlusions were measured. High speed video was collected and acoustic emission (AE) sensors were used to define the time of injury. The effects of eccentricity on peak loads, kinematics, and canal occlusions were evaluated using unpaired Student t-tests. The high eccentricity group had lower peak axial forces (1544 ±629 vs. 4296 ±1693 N), inferior displacements (0.2 ±1.0 vs. 6.6 ±2.0 mm), and canal occlusions (27 ±5 vs. 53 ±15%) and higher peak ipsilateral bending moments (53 ±17 vs. 3 ±18 Nm), ipsilateral bending rotations (22 ±3 vs. 1 ±2o), and ipsilateral displacements (4.5 ±1.4 vs. -1.0 ±1.3 mm, p<0.05 for all comparisons). These results provide new insights to develop prevention, recognition, and treatment strategies for compressive cervical spine injuries with lateral eccentricities.Applied Science, Faculty ofMedicine, Faculty ofMechanical Engineering, Department ofOrthopaedic Surgery, Department ofUnreviewedFacult

Acoustic Emission Signals Can Discriminate Between Compressive Bone Fractures and Tensile Ligament Injuries in the Spine during Dynamic Loading

Acoustic emission (AE) sensors are a reliable tool in detecting fracture, however they have not been used to differentiate between compressive osseous and tensile ligamentous failures in the spine. This study evaluated the effectiveness of AE data in detecting the time of injury of ligamentum flavum (LF) and vertebral body (VB) specimens tested in tension and compression, respectively, and in differentiating between these failures. AE signals were collected while LF (n=7) and VB (n=7) specimens from human cadavers were tested in tension and compression (0.4 m/s), respectively. Times of injury (time of peak AE amplitude) were compared to those using traditional methods (VB: time of peak force, LF: visual evidence in high speed video). Peak AE signal amplitudes and frequencies (using Fourier and wavelet transformations) for the LF and VB specimens were compared. In each group, six specimens failed (VB, fracture; LF, periosteal stripping or attenuation) and one did not. Time of injury using AE signals for VB and LF specimens produced average absolute differences to traditional methods of 0.7 (SD 0.2) ms and 2.4 (SD 1.5) ms (representing 14% and 20% of the average loading time), respectively. AE signals from VB fractures had higher amplitudes and frequencies than those from LF failures (average peak amplitude 87.7 (SD 6.9) dB vs. 71.8 (SD 9.8) dB for the inferior sensor, p<0.05; median characteristic frequency from the inferior sensor 97 (interquartile range, IQR, 41) kHz vs. 31 (IQR 2) kHz, p<0.05). These findings demonstrate that AE signals could be used to delineate complex failures of the spine.Applied Science, Faculty ofMedicine, Faculty ofMechanical Engineering, Department ofOrthopaedic Surgery, Department ofReviewedFacult