Cervical muscle response during whiplash: evidence of a lengthening muscle contraction

OBJECTIVE: To assess the potential for cervical muscle injury from a rear-end automobile collision. DESIGN: Experimental design in which human subjects were exposed to low-speed rear-end collisions. The influence of independent variable (gender, speed change, muscle group, and motion phase) on dependent variables (kinematic response, muscle onset and muscle activation level) was examined using repeated-measures analysis of variance. BACKGROUND: Injuries to various tissues of the cervical spine have been proposed, yet little attention has been focused on the cervical muscles as a site of injury. METHODS: 42 subjects (21 males, 20-40 yr) were exposed to collisions of 4 and 8 km/h speed change while measuring kinematic response of the head and torso and electromyography of the sternocleidomastoid and cervical paraspinal muscles. RESULTS: Muscle activation occurred earlier in females and in the 8 km/h speed change. Sternocleidomastoid onset preceded paraspinal onset. Muscle activation level varied significantly with speed change, motion phase and muscle group. Initial rearward retraction of the head relative to the torso resulted in lengthening of the activated sternocleidomastoid, consistent with a contraction-induced muscle injury. CONCLUSIONS: The cervical muscles contract rapidly in response to impact and the potential exists for muscle injury due to lengthening contractions. RELEVANCE: The clinician should recognize the role of cervical retraction in the mechanism of whiplash injury and avoid aggressive motion in that plane during diagnosis and treatment. An understanding of whiplash injury mechanisms should improve patient education and preventative measures.     

Kinematics of head movement in simulated low velocity rear-end impacts

Objectives. To evaluate kinematics of head movement related to impact velocity, gender and awareness in simulated low velocity rear-end impacts.

Methods. Thirty individuals were subjected in random order to three rear-end impacts: two unexpected impacts causing chair acceleration of 4.5 m/s² (slow) and 10.0 m/s² (fast) and one 10.0 m/s² expected impact. Rearward head displacement, and linear and angular head accelerations were recorded.

Results. Angular head displacement was almost two times higher for the fast than the slow unexpected-impacts (P = 0.04). Rearward and forward angular head accelerations increased two to three times with increased impact magnitude (P < 0.05). Rearward and forward linear head accelerations were two and a half to three and a half times higher for the fast than for the slow unexpected impacts (P < 0.05). Males presented two times higher upward linear head acceleration than females in the unexpected fast impact. No significant magnitude differences were identified for impact awareness in kinematics of head movement (P > 0.05). Rearward angular head acceleration reached the peak between 62 and 84 ms later than the rearward linear head acceleration (P < 0.05) in all impacts. No significant differences were identified for timing of kinematics of head movement (P > 0.05) with increased impact magnitude; however, statistical powers were low.

Interpretation. Kinematics of head movement increases with increased impact magnitude. Gender differences exist for vertical linear head acceleration only. Temporal and amplitude awareness do not change the magnitude in kinematics of head movement. There are temporal differences between angular and linear head accelerations.     

Lumbar spinal strains associated with whiplash injury: a cadaveric study

OBJECTIVES: To study and quantify the effects of rear-end collision on the lumbar spine. DESIGN: The lumbar spine of a cadaver was instrumented with rosette strain gauges applied on the lateral and anterior surfaces of T12, L2, and L4. Biaxial accelerometers were mounted on L1, L3, and L5. The cadaver was seated, restrained, and subjected to rear impacts of 5g and 8g. RESULTS: The anterior shear strains had a biphasic shape. Spinal strains peaked at the T12 at approximately 120 and 370 msec, whereas in the L4 vertebra, it peaked at 200 and 380 msec. The anterior strain pattern of the L4 and T12 vertebrae were in diametrically opposite directions. In the second set of tests (8g experiment), the acceleration forces and strains pattern were similar to the 5g test but of higher magnitude. The principal anterior strain was 480 microm/m for 5g and 530 microm/m for 8g; the lateral shear strain was 680 microm/m and 1500 microm/m in the 5g and 8g experiments, respectively. CONCLUSIONS: Forces generated during simulated whiplash collision induce biphasic lumbar spinal motions (increased-decreased lordosis) of insufficient magnitude to cause bony injuries, but they may be sufficient to cause soft-tissue injuries.     

Kinematic and electromyographic response to whiplash loading in low-velocity whiplash impacts--a review

Whiplash injury is a common injury, with a substantial health and economic burden. For five decades, researchers have been striving to discover the mechanisms of acute whiplash injury to develop methods of prevention through automobile design, and to develop treatment approaches. While earlier experiments with animals, cadavers, and military volunteers have provided some useful insights, it is only in recent years that research has progressed to reveal how neck muscles respond to collisions, particularly how they bear the burden of the forces of collision and how impact direction affects the neck muscle response which may determine the mechanism of injury. Initial volunteer experiments tended to focus on impact velocities (specifically differences in target and bullet vehicle velocities) and head acceleration, but gradually the focus has shifted to understanding the pattern of spinal segment motion and muscle contraction in response to the perturbation. An approach has been devised using sled impacts with healthy volunteers to elucidate in more detail various head kinematics and cervical muscle responses in low-velocity whiplash-type impacts. This approach involves the use of four levels of very-low to low velocity impacts to describe the kinematics of the head and the EMG response of cervical muscles in response to acceleration, but avoids any discernible risk of injury. This allows researchers to determine the cervical muscle response under many different scenarios, including varying direction of impact, awareness of impending impact, and others, without subjecting volunteers to any discernible risk. An initial series of results of impacts from eight directions is presented here, and these reveal that the cervical response to whiplash-type impacts is modified by impact awareness, muscles studied, and direction of impact. This will hopefully improve the understanding of the human response to low-velocity whiplash impacts.     

Qualitative analysis of neck kinematics during low-speed rear-end impact

OBJECTIVE: To analyze neck kinematics and loading patterns during rear-end impacts. DESIGN: The motion of each cervical vertebra was captured using a 250 frame/s X-ray system during a whole body rear-end impact. These data were analyzed in order to understand different phases of neck loading during rear-end impact. BACKGROUND: The mechanism of whiplash injury remains largely unknown. An understanding of the underlying kinematics of whiplash is crucial to the identification of possible injury mechanisms before countermeasures can be designed. METHODS: Metallic markers were inserted into the vertebral bodies and spinous processes of each of the seven cervical vertebrae. Relative displacement-time traces between each pair of adjacent cervical vertebrae were calculated from X-ray data. Qualitative analyses of the kinematics of the neck at different phase of impact were performed. RESULTS: The neck experiences compression, tension, shear, flexion and extension at different cervical levels and/or during different stages of the whiplash event. CONCLUSIONS: Neck kinematics during whiplash is rather complicated and greatly influenced by the rotation of the thoracic spine, which occurs as a result of the straightening of the kyphotic thoracic curvature. RELEVANCE: Understanding the complicated kinematics of a rear-end impact may help clinicians and researchers shed some light on potential mechanisms of whiplash neck injury.     

Movement coordination and differential kinematics of the cervical and thoracic spines in people with chronic neck pain

Background

Research on the kinematics and inter-regional coordination of movements between the cervical and thoracic spines in motion adds to our understanding of the performance and interplay of these spinal regions. The purpose of this study was to examine the effects of chronic neck pain on the three-dimensional kinematics and coordination of the cervical and thoracic spines during active movements of the neck.

Methods

Three-dimensional spinal kinematics and movement coordination between the cervical, upper thoracic, and lower thoracic spines were examined by electromagnetic motion sensors in thirty-four individuals with chronic neck pain and thirty-four age- and gender-matched asymptomatic subjects. All subjects performed a set of free active neck movements in three anatomical planes in sitting position and at their own pace. Spinal kinematic variables (angular displacement, velocity, and acceleration) of the three defined regions, and movement coordination between regions were determined and compared between the two groups.

Findings

Subjects with chronic neck pain exhibited significantly decreased cervical angular velocity and acceleration of neck movement. Cross-correlation analysis revealed consistently lower degrees of coordination between the cervical and upper thoracic spines in the neck pain group. The loss of coordination was most apparent in angular velocity and acceleration of the spine.

Interpretation

Assessment of the range of motion of the neck is not sufficient to reveal movement dysfunctions in chronic neck pain subjects. Evaluation of angular velocity and acceleration and movement coordination should be included to help develop clinical intervention strategies to promote restoration of differential kinematics and movement coordination.     

Incidence of cervical spine injuries in association with blunt head trauma

To establish an incidence of cervical spine injuries in significant blunt head trauma and to evaluate the necessity of using cervical radiography, all consecutive cases of blunt head trauma admitted to the trauma service over a 7-month period were reviewed. Two hundred twenty-eight charts were reviewed for demographic information, circumstance of injury, complaints and physical findings referable to the cervical spine, presenting level of consciousness, severity of head injury, and cervical spine radiographic findings. Only three patients were found to have cervical spine injuries, for an incidence of 1.7%. Of the 122 alert and asymptomatic patients, none had cervical spine injury. The patient population was defined, yet the very low incidence of cervical spine injuries associated with blunt head trauma in this study precludes any identification of predictors. Nevertheless, the results suggest that alert and asymptomatic patients can be spared cervical spine radiography.     

Biomechanics of the cervical spine. I: Normal kinematics

This review constitutes the first of four reviews that systematically address contemporary knowledge about the mechanical behavior of the cervical vertebrae and the soft-tissues of the cervical spine, under normal conditions and under conditions that result in minor or major injuries. This first review considers the normal kinematics of the cervical spine, which predicates the appreciation of the biomechanics of cervical spine injury. It summarizes the cardinal anatomical features of the cervical spine that determine how the cervical vertebrae and their joints behave. The results are collated of multiple studies that have measured the range of motion of individual joints of the cervical spine. However, modern studies are highlighted that reveal that, even under normal conditions, range of motion is not consistent either in time or according to the direction of motion. As well, detailed studies are summarized that reveal the order of movement of individual vertebrae as the cervical spine flexes or extends. The review concludes with an account of the location of instantaneous centres of rotation and their biological basis. RELEVANCE: The fact and precepts covered in this review underlie many observations that are critical to comprehending how the cervical spine behaves under adverse conditions, and how it might be injured. Forthcoming reviews draw on this information to explain how injuries might occur in situations where hitherto it was believed that no injury was possible, or that no evidence of injury could be detected.     

A study of emergency American football helmet removal techniques

Purpose

The purpose was to compare head kinematics between the Eject Helmet Removal System and manual football helmet removal.

Basic Procedures

This quasi-experimental study was conducted in a controlled laboratory setting. Thirty-two certified athletic trainers (sex, 19 male and 13 female; age, 33 ± 10 years; height, 175 ± 12 cm; mass, 86 ± 20 kg) removed a football helmet from a healthy model under 2 conditions: manual helmet removal and Eject system helmet removal. A 6-camera motion capture system recorded 3-dimensional head position. Our outcome measures consisted of the average angular velocity and acceleration of the head in each movement plane (sagittal, frontal, and transverse), the resultant angular velocity and acceleration, and total motion. Paired-samples t tests compared each variable across the 2 techniques.

Main Findings

Manual helmet removal elicited greater average angular velocity in the sagittal and transverse planes and greater resultant angular velocity compared with the Eject system. No differences were observed in average angular acceleration in any single plane of movement; however, the resultant angular acceleration was greater during manual helmet removal. The Eject Helmet Removal System induced greater total head motion.

Principal Conclusions

Although the Eject system created more motion at the head, removing a helmet manually resulted in more sudden perturbations as identified by resultant velocity and acceleration of the head. The implications of these findings relate to the care of all cervical spine–injured patients in emergency medical settings, particularly in scenarios where helmet removal is necessary.     

THE RIDDELLTM RIPKORD SYSTEM FOR SHOULDER PAD REMOVAL IN A CERVICAL SPINE INJURED ATHLETE: A PARADIGM SHIFT

Since the inception of the term Sports Medicine Athletic Trainers, Sports Physical Therapists, Paramedics, and Emergency Room Physicians have faced a number of challenges when it comes to providing care to an equipment laden athlete suspected of having a cervical spine or serious head injury. The same equipment that is designed to protect the player may significantly impede the medical team when it comes to diagnosing and treating cervical spine and head injuries. Incorrectly removing the helmet and shoulder pads from a football player with a cervical spine injury, may lead to unwanted motion of the cervical spine during removal. It is the purpose of this article to review the current concepts relating to equipment removal and to introduce a novel system for quick and easy removal of football shoulder pads called the Riddell™RipKord system.     

Biomechanics of the cervical spine Part 3: minor injuries

Minor injuries of the cervical spine are essentially defined as injuries that do not involve a fracture. Archetypical of minor cervical injury is the whiplash injury. Among other reasons, neck pain after whiplash has been controversial because critics do not credit that an injury to the neck can occur in a whiplash accident. In pursuit of the injury mechanism, bioengineers have used mathematical modelling, cadaver studies, and human volunteers to study the kinematics of the neck under the conditions of whiplash. Particularly illuminating have been cinephotographic and cineradiographic studies of cadavers and of normal volunteers. They demonstrate that externally, the head and neck do not exceed normal physiological limits. However, the cervical spine undergoes a sigmoid deformation very early after impact. During this deformation, lower cervical segments undergo posterior rotation around an abnormally high axis of rotation, resulting in abnormal separation of the anterior elements of the cervical spine, and impaction of the zygapophysial joints. The demonstration of a mechanism for injury of the zygapophysial joints complements postmortem studies that reveal lesions in these joints, and clinical studies that have demonstrated that zygapophysial joint pain is the single most common basis for chronic neck pain after injury.     

Cervical spine injury biomechanics: Applications for under body blast loadings in military environments

Background

While cervical spine injury biomechanics reviews in motor vehicle and sports environments are available, there is a paucity of studies in military loadings. This article presents an analysis on the biomechanics and applications of cervical spine injury research with an emphasis on human tolerance for underbody blast loadings in the military.

Methods

Following a brief review of published military studies on the occurrence and identification of field trauma, postmortem human subject investigations are described using whole body, intact head–neck complex, osteo-ligamentous cervical spine with head, subaxial cervical column, and isolated segments subjected to differing types of dynamic loadings (electrohydraulic and pendulum impact devices, free-fall drops).

Findings

Spine injuries have shown an increasing trend over the years, explosive devices are one of the primary causal agents and trauma is attributed to vertical loads. Injuries, mechanisms and tolerances are discussed under these loads. Probability-based injury risk curves are included based on loading rate, direction and age.

Interpretation

A unique advantage of human cadaver tests is the ability to obtain fundamental data to delineate injury biomechanics and establish human tolerance and injury criteria. Definitions of tolerances of the spine under vertical loads based on injuries have implications in clinical and biomechanical applications. Primary outputs such as forces and moments can be used to derive secondary variables such as the neck injury criterion. Implications are discussed for designing anthropomorphic test devices that may be used to predict injuries in underbody blast environments and improve the safety of military personnel.     

Cervical spine injury in rollover crashes: Anthropometry,excursion, roof deformation,and ATD prediction

While rollover crashes are rare, approximately one third of vehicle occupant fatalities occur in rollover crashes. Most severe-to-fatal injuries resulting from rollover crashes occur in the head or neck region, due to head and neck interaction with the roof during the crash. While many studies have used anthropomorphic test devices (ATDs) to predict head and neck injury, the biofidelity of ATDs in rollover has not been established. This study aims to build on previous research to compare the dynamic response and injuries sustained by four post mortem human surrogates (PMHS) to those predicted by six different ATDs in full-scale rollover crash tests. Additionally, this study evaluates injuries sustained by PMHS relative to possible contributing factors including occupant kinematics, occupant anthropometry, and vehicle roof deformation. While the vehicle kinematics and roof deformation were comparable for all tests, three out of the four PMHS sustained cervical spine injury, but only the tallest specimen sustained cervical spine fracture. Neck flexion at the time of head-to-roof contact appears to have affected cervical spine injury risk in these cases. Despite the injuries sustained in the PMHS, none of the six ATDs measured forces or accelerations that exceeded injury assessment reference values (IARVs), which adds to recent literature illustrating substantial differences between ATDs and PMHS in a rollover-like scenario.     

Significant spinal injury resulting from low-level accelerations: a case series of roller coaster injuries

OBJECTIVES: To describe a cohort of significantly injured roller coaster riders and the likely levels of acceleration at which the injuries occurred, and to compare these data with contemporary efforts to define a lower limit of acceleration below which no significant spinal injury is likely to occur. DESIGN: A retrospective case series of roller coaster ride-induced significant spinal injuries. SETTING: Injury incident records and emergency medical service records for the Rattler roller coaster in San Antonio, TX, were evaluated for a 19-month period in 1992 and 1993. Medical records for the more significant injuries were also reviewed and the specific injuries were tabulated, along with the demographics of the cohort. PARTICIPANTS: There were 932,000 riders of the Rattler roller coaster, estimated to represent between 300,000 and 600,000 individual riders. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Injury incident reports and medical record review. RESULTS: It is estimated that there were a total of 656 neck and back injuries during the study period, and 39 were considered significant by the study inclusion criteria. Seventy-two percent (28/39) of the injured subjects sustained a cervical disk injury; 71% of these injuries were at C5-6 (15 disk herniations, 5 symptomatic disk bulges) and 54% were at C6-7 (11 disk herniations, 4 symptomatic disk bulges). In the lumbar spine, the most frequent injury was a symptomatic disk bulge (20% of the cohort), followed by vertebral body compression fracture (18%), and L4-5 or L5-S1 disk herniation (13%). Accelerometry testing of passengers and train cars indicated a peak of 4.5 to 5g of vertical or axial acceleration and 1.5g of lateral acceleration over approximately 100ms (0.1s) on both. CONCLUSIONS: The results of this study suggest that there is no established minimum threshold of significant spine injury. The greatest explanation for injury from traumatic loading of the spine is individual susceptibility to injury, an unpredictable variable.     

Head-Neck Motion in Prehospital Trauma Patients under Spinal Motion Restriction: A Pilot Study

Abstract

Background

Spinal precautions are intended to limit motion of potentially unstable spinal segments. The efficacy of various treatment approaches for motion restriction in the cervical spine has been rigorously investigated using healthy volunteers and, to a lesser extent, cadaver samples. No previous studies have objectively measured this motion in trauma patients with potential spine injuries during prehospital care. Objective: The purpose of this study was to characterize head-neck (H-N) kinematics in a sample of trauma patients receiving spinal precautions in the field. Methods: This was a prospective observational study of trauma patients in the prehospital setting. Trauma patients meeting criteria for spinal precautions were eligible for inclusion. Participants received usual care, consisting of either a long backboard, cervical collar, and head blocks (BC) or a cervical collar only (CO), and behavior was categorized as compliant (C) or non-compliant (N). Three inertial measurement units (IMUs), placed on each participant’s forehead, sternum, and stretcher, yielded data on H-N motion. Outcomes were described in terms of H-N displacement and acceleration, including single- and multi-planar values, root mean square (RMS), and bouts of continuous motion above pre-determined thresholds. Data were analyzed to compare H-N motion by phase of prehospital care, as well as treatment type and patient behavior.     

Assessment and management of a child with suspected acute neck injury

Any child presenting at an emergency department after trauma, such as road traffic accidents, falls, sports and head injuries, should be assessed for risk of injury to the cervical spine. The aim of this article is to provide an overview of the assessment and nursing management of a child with a suspected cervical spine injury. Basic anatomy is covered along with neck injury assessment, how to measure a cervical collar correctly, safe immobilisation, and communication.     

Childhood sledding injuries

Sledding is only rarely thought of as a potentially dangerous childhood activity. However, serious injuries and occasional deaths do occur. A review of patients 18 years old and younger admitted to a pediatric trauma center following a sledding accident from 1991 to 1997 was conducted. By design this study was expected to identify the most seriously injured patients. Twenty-five patients were identified, all but four younger than 13. Seventeen were boys. The mechanisms of injury were: collision with stationary object, 15; sled-sled collision, 1; struck by sled, 2; going off jump, 3; foot caught under sled or on ground, 3; fall off sled being towed by snowmobile, 1. The average pediatric trauma score was 10.5, and the average injury severity score 10.6. There were no deaths. The injuries were: head, 11; long bone/extremity, all lower, 10; abdomen, 5; chest, 1; facial, 2; spinal, 1. Five patients sustained multiple injuries. A surprisingly high number, 5, had pre-existing neurological conditions that could have played a contributory role in the accident. Sledding is predominantly an activity of children, and occasional serious injuries occur. Most are preventable. Obeying the simple caveat that sledding should only be done in clear areas away from stationary objects would eliminate the great majority of serious injuries.     

Whiplash injury of the neck from concepts to facts]

OBJECTIVES: To focus on a topic of traumatology and rehabilitation becoming recently a much debated public health problem. METHOD: A references search from Medline database with whiplash as keyword was carried out. Were selected articles with abstracts in french or english and focusing on accidentology, biomechanics, demonstrated lesions, epidemiology and treatments. RESULTS: From 1664 references found, 232 were reviewed. The usual mechanism of crash is a rear-end collision inducing in the occupants of the bumped vehicle a sudden lower cervical spine extension with upper flexion followed by a global flexion. In nearly 50% of the cases, the stress occurring in the collision is comparable to that observed in bumper cars. The velocity changes are seldom up to 15 km/h. A headrest at the level of the center of gravity of the head restrict significantly the extension of the neck. Every structure of the cervical spine could be damaged and mainly the facet joints but the lesions were only demonstrated in severes traumatisms. The discrepancies in incidence among the different countries could be related to their medicolegal system. Although subjectives, the early symptoms are rather similar among patients suggesting true anatomical or functional disorders but the chronicity seems to be mainly related to social and psychological factors. The association of: no posterior midline cervical tenderness, no intoxication, normal alertness, no focal neurological deficit and no painful distracting injuries has a good predictive value of the lack of osteo-articular lesion on X-rays. Except the grade IV of the Quebec task Force (0, no symptom; 1, pain and stiffness; 2, neck complaint and physical signs; 3, neck complaint and neurological signs; 4, fracture or dislocation) the use of a collar should be avoided and the cervical spine should be mobilized. CONCLUSION: In most whiplash injuries, the mildness should be early stated, mobilization encouraged, and procedures of compensation shortened.     

Cervical spine curvature during simulated whiplash

OBJECTIVE: To develop a new method to describe cervical spine curvature and evaluate the potential for injury in the upper and lower cervical spine during simulated whiplash. DESIGN: A method was developed to integrate the upper and lower cervical spine rotations and describe the spine curvature. BACKGROUND: In vivo and in vitro whiplash simulations have documented the development of an S-shape curvature with simultaneous upper cervical spine flexion and lower cervical spine extension immediately following rear-impact. Investigators have hypothesized that the injury potential is highest during the S-shape phase. However, little data exist on the spine curvature during whiplash and its relation to spine injury. METHODS: A biofidelic model and a bench-top whiplash apparatus were used in an incremental rear-impact protocol (maximum 8 g) to simulate whiplash of increasing severity. To describe the spine curvature, the upper and lower cervical spine rotations were normalized to corresponding physiological limits. RESULTS: Average peak lower cervical spine extension first exceeded the physiological limits (P<0.05) at a horizontal T1 acceleration of 5 g. Average peak upper cervical spine extension exceeded the physiological limit at 8 g, while peak upper cervical spine flexion never exceeded the physiological limit. In the S-shape phase, lower cervical spine extension reached 84% of peak extension during whiplash. CONCLUSIONS: Both the upper and lower cervical spine are at risk for extension injury during rear-impact. Flexion injury is unlikely.