Whiplash-Associated Disorders: Occupant Kinematics and Neck Morphology

Abstract

FIGURE 1.Initial phases of head-neck response to automotive rear impacts. The rear impact initiates with the occupant in a neutral upright position. As the thorax is accelerated anteriorly, the head remains stationary during the retraction phase, producing an S-shaped cervical spine curvature. Eventually, loads from the thorax are transferred up the cervical spine and the head-neck complex transitions into extension, with the cervical spine in an overall C-shaped extension curvature. The head eventually rebounds forward (not shown), and the cervical spine then transitions into flexion. Used with permission from Stemper et al. 93 Copyright ©2011 Wiley-Liss, Inc. foam/springs and rearward deflection, which absorb energy and decrease impact severity for the occupant. The magnitude of seatback deformation and deflection is dependent on the occupant's torso mass and center of gravity. Greater mass and higher center of gravity contribute to greater deflection and decreased overall impact severity. Average female body mass is 20% lighter and torso height is 8% shorter. 30,31 Therefore, the ability to deflect the seatback is decreased in females, who would experience more severe loading on the head-neck complex during a given rear impact.This section highlighted the role of body size on cervical spine injury risk during automotive rear impacts, advancing the theory that size-based mismatches between the vehicle seat and occupant anthropometrics contribute to greater injury risk for smaller occupants. This concept would hold true for either males or females, but may help explain the preponderance of whiplash injuries in females due to their generally smaller body size. Shorter sitting height can result in head interaction with the bottom of the head restraint, which increases injury risk. However, taller occupants with incorrectly adjusted head restraints also experience increased injury risk due to the head rotating over the head restraint and increasing extension moments on the cervical spine. Decreased body mass and shorter center-of-torso mass in smaller occupants also contribute to decreased dynamic energy absorption of the seatback. While these differences illustrate mechanisms of increased injury risk for smaller occupants, other morphological differences may also contribute. Differences in Head and Neck MorphologyGiven that a majority of injuries resulting from automotive rear impacts affect the cervical spine, 9 differences in headneck morphology can influence injury risk. Once again, sex-based differences will be used to demonstrate this concept. Neck slenderness, a mechanical term body sizes farther from those standards may not be protected as well.Research studies report that head-tohead restraint backset is lower in females than in males due to rearward incline of automotive seats and decreased sitting height for average females compared to males.12 Sitting height for average females is approximately 6 cm shorter than that for average males. 30,31 This means that the posterior aspect of the head for the comp...

Sex Differences in Ultrasound-Based Muscle Size and Mechanical Properties of the Cervical-Flexor and -Extensor Muscles

“…4 Another common neck-related injury in young individuals was whiplash injury from a motor vehicle accident and, again, females were at a higher risk of developing chronic NP. 5 Potential explanations for a higher prevalence of NP, neck injuries, and concussions in females are multifactorial and complex. Yet, deficits in neck muscle mass or girth and neck strength are 2 of the most commonly reported sex differences in the literature.…”

“…Yet, deficits in neck muscle mass or girth and neck strength are 2 of the most commonly reported sex differences in the literature. 5 Although these physical characteristics can easily be measured with a tape and handheld dynamometer, respectively, clinicians and researchers recently began using ultrasound (US)-based imaging of the neck muscles to quantify the muscle size (cross-sectional area and thickness) of specific cervical-flexor and -extensor muscles.…”

“…Neck stiffness is also a common symptom after concussions and whiplash injuries. 4,5 However, researchers do not yet know which regions or muscles are involved and how much stiffness is present in individuals with concussions or whiplash injuries. Similarly, possible sex differences in USbased SWE stiffness of the cervical-flexor and -extensor muscles in young and athletic individuals have been largely unexamined.…”

Study of the Emergency Braking Test with an Autonomous Bus and the sEMG Neck Response by Means of a Low-Cost System

“…In literature, we can find numerous biomechanical studies [ 3 , 4 , 5 , 6 , 7 ] focused on the assessment of cervical behaviour. Many of these studies were performed using animals [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], crash dummies [ 17 , 18 , 19 , 20 , 21 , 22 , 23 ], full-body cadavers [ 12 , 19 , 20 , 24 , 25 , 26 , 27 ], isolated cervical [ 12 , 24 , 28 , 29 , 30 ], head–neck complexes and computational models [ 31 , 32 , 33 , 34 , 35 , 36 , 37 ].…”

Whiplash Continues Its Challenge

“…Importantly, and in light of the unsatisfactory clinical path of many people who sustain a whiplash injury, work is presented with an aim toward prevention or minimization of injury. 24 Public health campaigns focusing on stopping distracted driving for prevention of car crashes hold great merit. 3 Insight is also provided into the research on mechanisms of injury and morphological and kinematic characteristics of at-risk individuals to inform car design to lessen the consequences of a crash.…”