Motion analysis of cervical vertebrae during whiplash loading

Cervical intervertebral disc injury during simulated frontal impact

Cervical disc injury due to frontal impact has been observed in both clinical and biomechanical investigations; however, there is a lack of data that elucidate the mechanisms of disc injury during these collisions. The goals of the current study were to determine the peak dynamic disc annular tissue strain and disc shear strain during simulated frontal impact of the whole human cervical spine model with muscle force replication at 4 g, 6 g, 8 g and 10 g horizontal accelerations of the T1 vertebra. These data were compared with those obtained during physiological loading, and with previously reported rear impact data. Peak disc shear strain and peak annular tissue strain during frontal impact exceeded (p<0.05) corresponding physiological limits at the C2-C3 intervertebral level, beginning at 4 g and 6 g, respectively. These subsequently spread throughout the entire cervical spine at 10 g, with the exception of C4-C5. The C5-C6 intervertebral level was at high risk for injury during both frontal and rear impacts, while during frontal impact, in addition to C5-C6, subfailure injuries were likely at superior intervertebral levels, including C2-C3. The disc injuries occurred at lower impact accelerations during rear impact as compared with frontal impact. The subfailure injuries of the cervical intervertebral disc that occur during frontal impact may lead to the chronic symptoms reported by patients, such as head and neck pain.

Effect of Trunk Flexion on the Occupant Neck Response to Anterolateral Whiplash Impacts

OBJECTIVE

The purpose of this study was to determine the response of the cervical muscles to increasing low-velocity anterolateral impacts with the volunteer's trunk flexed to the right and left.

METHODS

A total of 20 healthy volunteers were subjected to left anterolateral impacts of 4.0, 7.6, 10.7, and 13.4 m/sec and, sequentially, with trunk flexed either left or right. Bilateral electromyograms (EMGs) of the sternocleidomastoids, trapezii, and splenii capitis were recorded.

DESIGN

At an acceleration of 13.4 m/sec, with the trunk flexed left, the left trapezius generated 48% of its maximal voluntary contraction EMG, whereas the right trapezius (contralateral to the left anterolateral impact) generated 38% of this variable. All other muscle generated </=23% of their maximal voluntary contraction EMG, a significant difference from the trapezii (P = 0.005). Similarly, with the trunk flexed to the right under these same conditions, the left trapezius generated 26% and the right trapezius 35% of their maximal voluntary contraction EMG. Again, all other muscles generated significantly less EMG activity, </=22% (P = 0.009). Overall, the EMG responses were of low magnitude compared with known data with the trunk in neutral posture in this direction of impact.

CONCLUSIONS

When the subject sits with trunk flexed out of neutral posture at the time of an anterolateral impact, the cervical muscle response is reduced compared with anterolateral impacts with the trunk in neutral posture.

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.

Looking away from whiplash: effect of head rotation in rear impacts

STUDY DESIGN

Twenty healthy volunteers in a laboratory were subjected to rear-end impacts 4.4, 7.9, 10.9, and 13.1 m/s acceleration, with head rotation to the right and left.

OBJECTIVE

The purpose of this study was to determine the response of the cervical muscles to increasing low-velocity rear impacts when the head is rotated at the time of impact.

SUMMARY OF BACKGROUND DATA

A previous study of rear impacts with head in neutral posture suggests that the burden of impact is borne primarily by the sternocleidomastoid muscles bilaterally. To improve automobile designs to prevent whiplash injury, we need to understand the response of the cervical muscles to whiplash-type perturbations in less-than-ideal conditions, such as when the head is rotated to the right and left at the time of rear-end impact.

METHODS

Triaxial accelerometers recorded the acceleration of the sled, torso at the shoulder level, and head of the participant, while bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis were also recorded.

RESULTS

For participants having a rear-end impact, whether having the head rotated to the left or right at the time of impact, the muscle responses increased with increasing levels of acceleration (P < 0.01). The time to onset and time to peak electromyogram for all muscles progressively decreased with increasing levels of acceleration (P < 0.01). Which muscle responded most to a whiplash-type neck perturbation was determined by the direction of head rotation. With the head rotated to the left, the right sternocleidomastoid generated 88% of the maximal voluntary contraction electromyogram (at least triple the response of other muscles). In comparison, the left sternocleidomastoid, both trapezii, and the splenii capitis generated on average only 10% to 30% of the maximal voluntary contraction electromyogram with head rotated to the left. On the other hand, with the head rotated to the right, the left sternocleidomastoid generated 94% of the maximal voluntary contraction electromyogram (again, at least triple the response of other muscles).

CONCLUSIONS

If the head is rotated out of neutral posture at the time of rear impact, the injury risk tends to be greater for the sternocleidomastoid muscle contralateral to the side of rotation. Measures to prevent whiplash injury may have to account for the asymmetric response because many victims of whiplash are expected to be looking to the left or right at the time of collision.

Effect of head rotation in whiplash-type rear impacts

BACKGROUND CONTEXT

Knowledge is increasing about the electromyographic and kinematic response of the neck muscles to rear impact, and also recent information is available on the effect of a rear impact offset to the left (posterolateral). The effect of head rotation, however, at the time of rear impact is not known.

PURPOSE

The purpose of this study was to examine the effects of head rotation to the left and right on the cervical muscle response to increasing low-velocity posterolateral impacts.

STUDY DESIGN/SETTING

Twenty healthy volunteers were subjected to rear impacts of 4.7, 8.3, 10.9 and 13.7 m/s2 acceleration, offset by 45 degrees to the subject's left, with head rotation to right and left.

METHODS

Bilateral electromyograms of the sternocleidomastoids, trapezii and splenii capitis were recorded. Triaxial accelerometers recorded the acceleration of the sled, torso at the shoulder level, and head of the participant.

RESULTS

With the head rotated to the right, at an acceleration of 13.7 m/s2, the left sternocleidomastoid generated 59% and the right sternocleidomastoid 20% of their maximal voluntary contraction (MVC) electromyogram (EMG). Under these conditions, the remaining muscles (both splenii capitis and trapezius) generated 25% or less of their MVC. With the head rotated to the left, at an acceleration of 13.7 m/s2, the right sternocleidomastoid generated 65% and the left sternocleidomastoid only 11% of the MVC EMG. Under these conditions, again the remaining muscles had low EMG activity (27% or less) with the exception of the left trapezius which generated 47% of its MVC. Electromyographic variables were significantly affected by the levels of acceleration (p<.01). The time to onset and time to peak EMG for all muscles progressively decreased with increasing levels of acceleration, for both head rotation conditions. The kinetic variables and the electromyographic variables regressed significantly on the acceleration (p<.01).

CONCLUSIONS

Direction of impact is a factor in determining the muscle response to whiplash, but head rotation at the time of impact is also important in this regard. More specifically, when a rear impact is left posterolateral, it results in increased EMG generation mainly in the contralateral sternocleidomastoid, as expected, but head rotation at the same time in this type of impact reduces the EMG response of the cervical muscles. Muscle injury seems less likely under these conditions in low-velocity impacts.

Turning away from whiplash. An EMG study of head rotation in whiplash impact

OBJECTIVE

To determine the response of the cervical muscles to whiplash-type perturbations through low-velocity frontal impacts when the head is rotated to the right and left.

METHODS

Twenty healthy volunteers were subjected to increasing acceleration in low-velocity frontal impacts, randomly with head rotated either left or right. Bilateral EMG of the sternocleidomastoids, trapezii, and splenii capitis and acceleration of the sled, torso, and head were recorded.

RESULTS

With either direction of head rotation at the time of impact, the muscle responses increased with increasing levels of acceleration (p < 0.01). The time to onset and peak electromyogram for all muscles progressively decreased with increasing levels of acceleration. With the head rotated to the left, the left trapezius generated 77% of its maximal voluntary contraction (MVC) EMG (more than double the response of other muscles). In comparison, the right trapezius generated only 33% of its MVC. The right sternocleidomastoid (25%) and left splenius muscles (32%), the ones responsible for head rotation to the left, were more active than their counterparts (the left sternocleidomastoid generated only 5% of its MVC EMG and the right splenius 9%). On the other hand, with the head rotated to the right, the right trapezius generated 71% of its MVC EMG, while the left trapezius generated only 30% of this value. Again, the left sternocleidomastoid (27% of its MVC EMG) and right splenius (28% of its MVC EMG), being responsible for head rotation to the right, were more active than their counterparts (the right sternocleidomastoid generated only 4% of its MVC EMG and the left splenius 13%).

CONCLUSIONS

Frontal impacts tend to generate the most muscle activity in the ipsilateral trapezius muscle, increasing the risk of their injury.

Traumatisme cervical et dysfonctionnement de l’appareil manducateur

Attributing dysfunction of the temporomandibular joint (TMJ) to whiplash injury is a difficult problem to solve. TMJ disorders do not seem to be secondary to direct articular trauma but rather caused by a postural disorder of the cervical spine. Occlusal disorders and stress further complicate the picture. Four clinical cases illustrate a new hypothetical approach.

Cervical spine ligament injury during simulated frontal impact

STUDY DESIGN

The supraspinous and interspinous ligaments, ligamentum flavum, and capsular and posterior longitudinal ligament strains were monitored during simulated frontal impact of whole cervical spine specimens with muscle force replication and compared with corresponding physiologic strain limits.

OBJECTIVES

To quantify the strains in the cervical spine ligaments during simulated frontal impact and investigate injury mechanisms.

SUMMARY OF BACKGROUND DATA

Clinical and biomechanical studies have documented injuries to cervical spine ligaments during frontal impact. There are no biomechanical studies investigating subfailure injury mechanisms to these ligaments during simulated frontal impacts of increasing severity.

METHODS

The whole cervical spine with muscle force replication model and a bench-top sled were used to simulate frontal impacts at 4, 6, 8, and 10 g horizontal accelerations of the T1 vertebra. The peak ligament strains during frontal impacts were compared with physiologic strain limits determined during intact flexibility testing.

RESULTS

Significant increases (P < 0.05) in the supraspinous and interspinous ligaments and the ligamentum flavum strains beyond physiologic limits were observed throughout the cervical spine, with the highest strains occurring at C3-C4. Significant increases were observed in the capsular ligament strains only during the 10 g impact, whereas the posterior longitudinal ligament strains did not exceed physiologic limits.

CONCLUSIONS

The supraspinous and interspinous ligaments and the ligamentum flavum may be at risk for injury due to excessive strains during frontal impacts.

In vitro low-speed side collisions cause injury to the lower cervical spine but do not damage alar ligaments

Whether injuries to the alar ligaments could be responsible for complaints of patients having whiplash injury in the upper cervical spine is still controversially discussed. It is known that these ligaments protect the upper cervical spine against excessive lateral bending and axial rotation movements. The objective of the present in vitro study was therefore to examine whether the alar ligaments or any other structures of the cervical spine are damaged in side collisions. In a specially designed acceleration apparatus, six human osteoligamentous cervical spine specimens were subjected to incremental 90 degrees side collisions from the right (1 g, 2 g, 3 g, etc.) until structural failure occurred. A damped pivot table accounted for the passive movements of the trunk during collision, and a dummy head (4.5 kg) ensured almost physiological loading of the specimens. For quantification of functional injuries, the three-dimensional flexibility of the specimens was tested in a spine tester before and after each acceleration. In all six specimens, structural failure always occurred in the lower cervical spine and always affected the facet joint capsules and the intervertebral discs. In four specimens, this damage occurred during the 2 g collision, while in the other two it occurred during the 3 g and 4 g collision, respectively. The flexibility mainly increased in the lower cervical spine (especially in lateral bending to both sides) and, to a minor extent, in axial rotation. In vitro low-speed side collisions caused functional and structural injury to discoligamentous structures of the lower cervical spine, but did not damage the alar ligaments. Since the effects of muscle forces were not taken into account, the present in vitro study reflects a worst-case scenario. Injury thresholds should therefore not be transferred to reality.

Electromyographic and kinematic exploration of whiplash-type rear impacts: effect of left offset impact

BACKGROUND CONTEXT

Although there are some volunteer collision studies reporting the effects of rear impacts on head and neck kinematics, there are few studies detailing the cervical muscle electromyogram response. Moreover, the effect of a rear impact offset to the left on the resultant muscle responses is unknown.

PURPOSE

The purpose of this study was to determine the response of the cervical muscles to increasing low-velocity rear impacts offset by 45 degrees to the subject's left, and to compare the quantitative effects of expected and unexpected impact.

STUDY DESIGN/SETTING

Nine healthy volunteers were subjected to rear impacts, offset by 45 degrees to the subject's left, of 4.6, 8.7, 11.0 and 14.5 m/s2 acceleration, at two levels of expectation: expected and unexpected.

METHODS

Bilateral electromyograms of the sternocleidomastoids, trapezii and splenii capitis were recorded. Triaxial accelerometers recorded the acceleration of the chair, torso at the shoulder level and head of the participant.

RESULTS

At an acceleration of 14.5 m/s2, the left sternocleidomastoid generated 71% and the right sternocleidomastoid 82% of their maximal voluntary contraction electromyogram in the unexpected impact conditions. Under these conditions, the right splenius capitis (contralateral to the left offset rear impact) also generated 71% of its maximal voluntary contraction, whereas the left splenius capitis generated only 20% of this variable. The trapezii generated only 25% of their maximal voluntary contraction. Subjects exhibited lower levels of their maximal voluntary contraction electromyogram when the impact was expected. Electromyographic variables were significantly affected by the levels of acceleration and expectation (p<.001). The time to onset and time to peak electromyogram for all muscles progressively decreased with increasing levels of acceleration, in the unexpected condition. The kinetic variables and the electromyographic variables regressed significantly on the acceleration (p<.001). In response to rear impacts offset to the subject's left, muscle responses were greater with higher levels of acceleration, greater with unexpected impact conditions and greatest for both sternocleidomastoids and for the splenius capitis muscle contralateral to the side of impact.

CONCLUSIONS

Because the muscular component of the head-neck complex plays a role in the abatement of impact at higher acceleration levels, they are likely a primary site of injury in the whiplash phenomenon in rear collisions. More specifically, when a rear impact is offset to the subject's left, it results in not only increased electromyographic generation in both sternocleidomastoids, but the splenius capitis contralateral to the direction of impact offset also bears part of the force of the neck perturbation. Expecting or being aware of imminent impact also plays a role in reducing muscle responses in low-velocity offset rear impacts.

A novel rodent neck pain model of facet-mediated behavioral hypersensitivity: implications for persistent pain and whiplash injury

Clinical, epidemiological, and biomechanical studies suggest involvement of cervical facet joint injuries in neck pain. While bony motions can cause injurious tensile facet joint loading, it remains speculative whether such injuries initiate pain. There is currently a paucity of data explicitly investigating the relationship between facet mechanics and pain physiology. A rodent model of tensile facet joint injury has been developed using a customized loading device to apply two separate tensile deformations (low, high; n = 5 each) across the C6/C7 joint, or sham (n = 6) with device attachment only. Microforceps were rigidly coupled to the vertebrae for distraction and joint motions tracked in vivo. Forepaw mechanical allodynia was measured postoperatively for 7 days as an indicator of behavioral sensitivity. Joint strains for high (33.6 +/- 3.1%) were significantly elevated (P < 0.005) over low (11.1 +/- 2.3%). Digitization errors (0.17 +/- 0.20%) in locating bony markers were small compared to measured strains. Allodynia was significantly elevated for high over low and sham for all postoperative days. However, allodynia for low injury was not different than sham. A greater than three-fold increase in total allodynia resulted for high compared to low, corresponding to the three-fold difference in injury strain. Findings demonstrate tensile facet joint loading produces behavioral sensitivity that varies in magnitude according to injury severity. These results suggest that a facet joint tensile strain threshold may exist above which pain symptoms result. Continued investigation into the relationship between injury mechanics and nociceptive physiology will strengthen insight into painful facet injury mechanisms.

Incremental and single trauma produce equivalent subfailure soft tissue injury of the cervical spine

BACKGROUND

Automotive collision simulations have been performed using either incremental or single trauma. In single trauma, a single impact is performed, while in incremental trauma, a series of impacts of increasing severity are executed. Equivalency of incremental and single trauma for soft tissue injury severity due to the final impact has not been established. Thus, the purpose of the present study was to investigate whether incremental and single trauma produced similar cervical spine subfailure injury severity due to simulated frontal impacts.

METHODS

Porcine cervical spine specimens (C2-T1) of the incremental trauma group were subjected to five frontal impacts (2, 3.5, 5, 6.5, 8 g), while single trauma specimens were subjected to a single impact (8 g). Flexibility tests were performed on specimens while intact and following each impact. Intact and post 8 g flexibility parameters were compared within incremental and single trauma groups and between groups.

FINDINGS

No significant differences (P < 0.05) were found between incremental and single trauma groups when either intact or post 8 g flexibility parameters were compared. Significant increases in flexibility parameters from intact to post 8 g were observed in both groups, indicating soft tissue injury.

INTERPRETATION

Incremental and single trauma produced equivalent subfailure cervical spine injury in simulated impacts, for the experimental conditions studied. This study may facilitate greater use of the incremental trauma protocol in future experimental designs.

Quantification of C2 cervical spine rotatory fixation by X-ray, MRI and CT

Atlanto-axial rotatory displacement is known to be a cause of childhood torticollis and may as well be responsible for chronic neck pain after rear-end automobile collisions. The objective was to determine whether quantification of C2 malrotation is possible by plain radiographs in comparison to CT as the golden standard. MR imaging was evaluated as to whether it was of equal value in the detection of bony landmarks. C2 vertebra of five human cadaveric cervical spine specimens, ligamentously intact, were rotated using a Steinmann pin in steps of 5 degrees up to 15 degrees right and 15 degrees left. Plain radiographs, CT and MRI images were taken in each rotational step. Data were analyzed for quantification of C2 rotation by three independent examiners. A rotation of 5 degrees led to a spinous process deviation (SPD) from the midline of 3 mm as measured on an a.p. plain radiograph. A coefficient of rotation was calculated (1.62 degrees mm(-1)). Data analyzed by three examiners revealed a small coefficient of variation (0.03). MRI and CT measurements showed comparable results for the quantification of rotation; however, in both techniques the 15 degrees rotation was underestimated. Quantification of upper cervical spine malrotation was possible on plain radiographs using the SPD and a rotation coefficient. MRI and CT were equally successful in the assessment of C2 malrotation.

A new acceleration apparatus for the study of whiplash with human cadaveric cervical spine specimens

The biomechanics of whiplash is often studied using cadaveric cervical spine specimens. One of the most important points in this kind of study is to create realistic loading conditions. The aim of the present project therefore was to develop an acceleration apparatus, which allows the study of whiplash with human cadaveric cervical spine specimens under as realistic loading conditions as possible. The new acceleration apparatus mainly consisted of a sled, a pneumatic acceleration unit and a railtrack and offered several unique features to create more realistic loading conditions. Among these features, the possibility to simulate the passive movements of the trunk is of capital importance. In this new apparatus, first, the general feasibility of whiplash experiments was studied, second, the reproducibility of the impacts was quantified and third, the effect of simulated movements of the trunk on accelerations and loads was examined. In the new acceleration apparatus various types of collisions could reproducibly be simulated. Simulated passive movements of the trunk strongly influenced the loading pattern of the neck. Without pivoting a steep increase of all loading parameters could be observed. This increase was less pronounced if pivoting was allowed. In conclusion, biomechanical aspects of whiplash could reproducibly be examined in the new acceleration apparatus. Due to its significant effects on the loading of the neck, pivoting of the trunk should always be taken into account in future experiments on the biomechanics of whiplash in which isolated cervical spine specimens are used.

Management of whiplash-associated disorder addressing thoracic and cervical spine impairments: a case report

STUDY DESIGN

Clinical case report.

OBJECTIVES

To describe a physical therapy program addressing impairments of the upper thoracic and cervical spine region for an individual with a whiplash-associated disorder.

BACKGROUND

A 32-year-old female with complaint of diffuse posterior cervical and upper thoracic region pain was evaluated 2 weeks following a motor vehicle accident. The patient reported that she was unable to sit for longer than 10 minutes or perform household duties for longer than 1 hour. In addition, she was unable to perform her tasks as a postal worker or participate in her customary running and aerobic exercise activities because of pain in the cervical and upper thoracic region.

METHODS AND MEASURES

An examination for physical impairments was performed, including the measurement of cervical range of motion using the CROM device, and the assessment of soft tissue and segmental mobility of the upper thoracic and cervical spine regions. The Northwick Park Neck Pain Questionnaire was used to assess functional limitations and disability. Manual therapy and therapeutic exercises were applied to address the identified impairments. Manual therapy techniques included soft tissue mobilization, joint mobilization, and joint manipulation.

RESULTS

The patient's cervical range of motion was improved and the disability score improved from 25% to 19.5% 3 days after the initial session addressing the thoracic spine. Following a second session also addressing thoracic spine impairments and the use of therapeutic exercises for 7 days, the disability score improved to 11.1%. At the final visit 17 days following the third visit, which focused on addressing the cervical spine impairments, there was complete resolution of signs and symptoms and disability.

CONCLUSIONS

Interventions addressing the impairments of the upper thoracic and cervical spine region were associated with reducing pain, increasing cervical range of motion, and facilitating return to work and physical activities in a patient with a whiplash-associated disorder. There is a need for continued research investigating the efficacy of providing interventions to the thoracic spine for patients with whiplash-related injuries.

Using a finite element model to evaluate human injuries application to the HUMOS model in whiplash situation

STUDY DESIGN

In the field of numerical simulation, the finite element method provides a virtual tool to study human tolerance and postulate on potential trauma under crash situations, particularly in case of whiplash trauma.

OBJECTIVES

To show how medical and biomechanical interpretations of numerical simulation can be used to postulate on human injuries during crash situations. This methodology was applied to whiplash trauma analysis. A detailed analysis of kinematics of joints, stress level in hard tissues, and strain level in soft tissues was used to postulate on chronology and patterns of injury. Data were compared with published biomechanical and clinical studies of whiplash.

SUMMARY OF BACKGROUND DATA

Although many in vitro and in vivo studies have been conducted to investigate whiplash cervical injury, and despite the number of finite element models developed to simulate the biomechanical behavior of the cervical spine, to date, there are only limited finite element models reported in the literature on the biomechanical response of the whole cervical spine in these respects.

METHODS

A complete finite element model of the human body (HUMOS) build in a sitting position in a car environment was created to investigate injury mechanisms and to provide data for automotive safety improvements. It includes approximately 50,000 elements, including descriptions of all bones, ligaments, tendons, skin, muscles, and internal organs. A 15-g whiplash injury was simulated with the HUMOS model. The model predicted cervical motion segment kinematics, deformations of disks and ligaments, and stresses in bone. Model output was then compared with experimental and clinical whiplash literature.

RESULTS

In term of kinematics during the chronology of whiplash, two injury phases were identified: the first was hyperextension of the lower cervical spine (C6-C7 and C5-C6) and mild flexion of the upper cervical spine(C0-C4). The amount of upper cervical flexion was 15 degrees from C0 to C4. The second phase was hyperextension of the entire cervical spine. Potential patterns of ligamentous injuries were observed; the anterior longitudinal ligament experienced the most strain (30%) at the lower cervical spine at the time of lower cervical extension and the interspinous ligament experienced the most strain (60%) at the time of upper cervical flexion. Von Mises stresses in bone do not exceed 15 Mpa, which is largely under injury levels reported in the literature. CONCLUSIONS.: This study reports a methodology to describe and postulate on human injuries based on finite element model analysis. The output of the HUMOS model in the context of whiplash shows a strong correlation with clinical and experimental reported data. HUMOS shows promise for the modeling of other types of trauma as well.

Injury mechanisms of the cervical intervertebral disc during simulated whiplash

STUDY DESIGN

A kinematic analysis of cervical intervertebral disc deformation during simulated whiplash using the whole cervical spine with muscle force replication model was performed.

OBJECTIVES

To quantify anulus fibrosus fiber strain, disc shear strain, and axial disc deformation in the cervical spine during simulated whiplash.

SUMMARY OF BACKGROUND DATA

Clinical studies have documented acute intervertebral disc injury and accelerated disc degeneration in whiplash patients, although there has been no biomechanical investigation of the disc injury mechanisms.

METHODS

A bench-top sled was used to simulate whiplash at 3.5, 5, 6.5, and 8 g using six specimens. The 30 degrees and 150 degrees fiber strains, disc shear strains, and axial disc deformations during whiplash were compared with the sagittal physiologic levels.

RESULTS

Increases over sagittal physiologic levels (P < 0.05) were first observed during the 3.5 g simulation. Peak fiber strain was greatest in the posterior 150 degrees fibers (running posterosuperiorly), reaching a maximum of 51.4% at C5-C6 during the 8 g simulation. Peak disc shear strain was also greatest at the posterior region of C5-C6, reaching a maximum of 1.0 radian due to posterior translation during the 8 g simulation. Axial deformation at the anterior disc region exceeded physiologic levels at 3.5 g and above, while axial deformation at the posterior region exceeded physiologic limits only at C5-C6 at 6.5 g and 8 g.

CONCLUSIONS

The cervical intervertebral discs may be at risk for injury during whiplash because of excessive 150 degrees fiber strain, disc shear strain, and anterior axial deformation.

Soft tissue injury threshold during simulated whiplash: a biomechanical investigation

STUDY DESIGN

A newly developed biofidelic whole cervical spine (WCS) model with muscle force replication (MFR) was subjected to whiplash simulations of varying intensity, and the resulting injuries were evaluated through changes in the intervertebral flexibility.

OBJECTIVES

To identify the soft tissue injury threshold based on the peak T1 horizontal acceleration and the association between acceleration magnitude and injury severity resulting from simulated whiplash using the WCS + MFR model.

SUMMARY OF BACKGROUND DATA

Whiplash has been simulated using mathematical models, whole cadavers, volunteers, and WCSs. The measurement of injury (difference between prewhiplash and postwhiplash flexibilities) is possible only using the WCS model.

METHODS

Six WCS + MFR specimens (C0-T1) were incrementally rear-impacted at nominal T1 horizontal maximum accelerations of 3.5, 5, 6.5, and 8 g, and the changes in the intervertebral flexibility parameters of neutral zone and range of motion were determined. The injury threshold acceleration was the lowest T1 horizontal peak acceleration that caused a significant increase in the intervertebral flexibility.

RESULTS

The first significant increase (P <0.01) of 39.8% occurred in the C5-C6 extension neutral zone following the 5 g acceleration. At higher accelerations, the injuries spread among the surrounding levels (C4-C5 to C7-T1).

CONCLUSIONS

A rear-end collision is most likely to injure the lower cervical spine by intervertebral hyperextension at a peak T1 horizontal acceleration of 5 g and above. These results may aid in the design of injury prevention systems and more precise diagnoses of whiplash injuries.

Facet joint kinematics and injury mechanisms during simulated whiplash

STUDY DESIGN

Facet joint kinematics and capsular ligament strains were evaluated during simulated whiplash of whole cervical spine specimens with muscle force replication.

OBJECTIVES

To describe facet joint kinematics, including facet joint compression and facet joint sliding, and quantify peak capsular ligament strain during simulated whiplash.

SUMMARY OF BACKGROUND DATA

Clinical studies have implicated the facet joint as a source of chronic neck pain in whiplash patients. Prior in vivo and in vitro biomechanical studies have evaluated facet joint compression and excessive capsular ligament strain as potential injury mechanisms. No study has comprehensively evaluated facet joint compression, facet joint sliding, and capsular ligament strain at all cervical levels during multiple whiplash simulation accelerations.

METHODS

The whole cervical spine specimens with muscle force replication model and a bench-top trauma sled were used in an incremental trauma protocol to simulate whiplash of increasing severity. Peak facet joint compression (displacement of the upper facet surface towards the lower facet surface), facet joint sliding (displacement of the upper facet surface along the lower facet surface), and capsular ligament strains were calculated and compared to the physiologic limits determined during intact flexibility testing.

RESULTS

Peak facet joint compression was greatest at C4-C5, reaching a maximum of 2.6 mm during the 5 g simulation. Increases over physiologic limits (P < 0.05) were initially observed during the 3.5 g simulation. In general, peak facet joint sliding and capsular ligament strains were largest in the lower cervical spine and increased with impact acceleration. Capsular ligament strain reached a maximum of 39.9% at C6-C7 during the 8 g simulation.

CONCLUSIONS

Facet joint components may be at risk for injury due to facet joint compression during rear-impact accelerations of 3.5 g and above. Capsular ligaments are at risk for injury at higher accelerations.

Injury of the anterior longitudinal ligament during whiplash simulation

Anterior longitudinal ligament (ALL) injuries following whiplash have been documented both in vivo and in vitro; however, ALL strains during the whiplash trauma remain unknown. A new in vitro whiplash model and a bench-top trauma sled were used in an incremental trauma protocol to simulate whiplash at 3.5, 5, 6.5 and 8 g accelerations, and peak ALL strains were determined for each trauma. Following the final trauma, the ALLs were inspected and classified as uninjured, partially injured or completely injured. Peak strain, peak intervertebral extension and increases in flexibility parameters were compared among the three injury classification groups. Peak ALL strains were largest in the lower cervical spine, and increased with impact acceleration, reaching a maximum of 29.3% at C6-C7 at 8 g. Significant increases ( P<0.05) over the physiological strain limits first occurred at C4-C5 during the 3.5 g trauma and spread to lower intervertebral levels as impact severity increased. The complete ligament injuries were associated with greater increases in ALL strain, intervertebral extension, and flexibility parameters than were observed at uninjured intervertebral levels ( P<0.05).

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.

Anatomic study of the morphology of human cervical facet joint

STUDY DESIGN

Geometrical properties of the facet joint including cartilage thickness and gap were obtained using human cadaver cervical spinal columns and cryomicrotomy techniques.

OBJECTIVES

To determine the existence of level or gender dependency on facet joint morphology in the human cervical spine.

BACKGROUND DATA

Although measurements of the human cervical spine have been reported in literature, to the best of knowledge of the authors, geometrical data on the facet joint structures such as the cartilage are not available. These data are important to understand the anatomy of the cervical spine and the role of the cartilage in sharing the external load during physiologic and traumatic situations. Furthermore, the data will assist mathematical modelers to accurately simulate this component of the cervical facet joint in finite element analysis of the spine.

MATERIALS AND METHODS

Six unembalmed human cadaver cervical spinal columns were used. A heavy-duty cryomicrotome was used to obtain the geometrical characteristics. The specimens were sectioned in the sagittal plane at 20- to 40-microm intervals. Geometric properties of the facet joint width, cartilage thickness, and cartilage gap (defined as the distance from the ventral-most or dorsal-most region of the facet joint to the location where the cartilage began to appear) were extracted from the anatomic sections that were midsagittal with respect to the facet joints from occiput to T1 levels. Multiple factorial analysis of variance techniques were used to determine the statistical significance of various geometrical parameters obtained from the anatomic sections.

RESULTS

The cartilage gap in the upper cervical spine (UCS) (C1-C2, i.e., UCS, 5.4% +/- 0.8) was lower (P < 0.0001) than the gap in the lower cervical spine (LCS) (C3-C7, i.e., LCS, 16.4% +/- 0.8). The gap at the ventral and dorsal regions was lower in the UCS (ventral 3.8% +/- 0.6, dorsal 7.0% +/- 1.4) than in the LCS (ventral 18.5% +/- 0.9, dorsal 14.2% +/- 1.1) with p values of less than 0.0001 and equal to 0.0004, respectively. Further, the gap in the dorsal region for females (14.7% +/- 1.8) was greater (P = 0.0523) than the gap for males (10.8% +/- 1.1). The overall mean facet cartilage thickness was lower (P = 0.0111) in females (0.6 mm +/- 0.1) than males (0.9 mm +/- 0.2) in the UCS. It was also lower (P = 0.0077) in females (0.4 mm +/- 0.02) than males (0.5 mm +/- 0.03) in the LCS. The facet joint width demonstrated differences only between the UCS and LCS (P < 0.0001), with higher magnitudes in the upper (17.4 mm +/- 0.4) than in the lower (11.3 mm +/- 0.3) region.

CONCLUSIONS

Facet joint morphology varies with the regions of the cervical spine (upper vs. lower), gender (male vs. female), and location (dorsal vs. ventral). Because of the lack of intervertebral discs in the UCS region, variations in these geometrical characteristics affect the biomechanical behaviors of the human spine secondary to external loads. Furthermore, the lack of adequate cartilage in females may expose the underlying adjacent subchondral bone to direct stresses during normal physiologic and traumatic loads.

Increased sagittal plane segmental motion in the lower cervical spine in women with chronic whiplash-associated disorders, grades I-II: a case-control study using a new measurement protocol

STUDY DESIGN

Case-control study comparing sagittal plane segmental motion in women (n = 34) with chronic whiplash-associated disorders, Grades I-II, with women (n = 35) with chronic insidious onset neck pain and with a normal database of sagittal plane rotational and translational motion.

OBJECTIVE

To reveal whether women with chronic whiplash-associated disorders, Grades I-II, demonstrate evidence of abnormal segmental motions in the cervical spine.

SUMMARY OF BACKGROUND DATA

It is hypothesized that unphysiological spinal motion experienced during an automobile accident may result in a persistent disturbance of segmental motion. It is not known whether patients with chronic whiplash-associated disorders differ from patients with chronic insidious onset neck pain with respect to segmental mobility.

METHODS

Lateral radiographic views were taken in assisted maximal flexion and extension. A new measurement protocol determined rotational and translational motions of segments C3-C4 and C5-C6 with high precision. Segmental motion was compared with normal data as well as among groups.

RESULTS

In the whiplash-associated disorders group, the C3-C4 and C4-C5 segments showed significantly increased rotational motions. Translational motions within each segment revealed a significant deviation from normal at the C3-C4 segment in the whiplash-associated disorders and insidious onset neck pain groups and at the C5-C6 segment in the whiplash-associated disorders group. Significantly more women in the whiplash-associated disorders group (35.3%) had abnormal increased segmental motions compared to the insidious onset neck pain group (8.6%) when both the rotational and the translational parameters were analyzed. When the translational parameter was analyzed separately, no significant difference was found between groups, or 17.6% (whiplash-associated disorders group) and 8.6% (insidious onset neck pain group), respectively.

CONCLUSION

Hypermobility in the lower cervical spine segments in 12 out of 34 patients with chronic whiplash-associated disorders in this study point to injury caused by the accident. This subgroup, identified by the new radiographic protocol, might need a specific therapeutic intervention.

Gender dependent cervical spine segmental kinematics during whiplash

Clinical and epidemiological studies have frequently reported that female occupants sustain whiplash injuries more often than males. The current study was based on the hypothesis that segmental level-by-level cervical intervertebral motions in females are greater than in males during rear impact. The hypothesis was tested by subjecting 10 intact human cadaver head-neck complexes (five males, five females) to rear impact loading. Intervertebral kinematics were analyzed as a function of spinal level at the time of maximum cervical S-curve, which occurred during the loading phase. Segmental angles were significantly greater (p<0.05) in female specimens at C2-C3, C4-C5, C5-C6, and C6-C7 levels. Because greater angulations are associated with stretch in the innervated components of the cervical spinal column, these findings may offer a biomechanical explanation for the higher incidence of whiplash-related complaints in female patients secondary to rear impact acceleration.

Classification of spinal injuries based on the essential traumatic spinal mechanisms

STUDY DESIGN

A biomechanical unitary classification of spinal injuries is proposed.

OBJECTIVE

To present an evaluation of spinal injuries based on the essential traumatic spinal mechanisms: axial deformation, torsion, translation and combined mechanisms in connection with the concept of the stabilizing axial spinal pillar.

SETTING

Hospital 'Sf. Treime', Iasi, Romania.

METHODS

The essential mechanisms of spinal injuries are considered: (1) axial deformation with (a) compression (centric or eccentric), most often eccentric, including compression in flexion or extension; (b) spinal elongation with distraction as centric elongation, but frequently axial eccentric elongation and a flexion or extension injury; (2) torsion or axial spinal rotation, (3) segmental translation, with a shearing version for the double translation and (4) combined mechanisms - the most frequent situation. Over 300 patients with spinal injuries were analysed and the spinal instability was determined using the criteria of clinical instability. The cases of spinal instability were studied in connection with the types of lesion of the central axial spinal pillar.

RESULTS

All cases with lesions of the central axial spinal pillar had traumatic spinal instability. The spinal instability was absent in cases of isolated lesions of the anterior or posterior secondary pillar. The X-ray and spinal CT analysis of the traumatic spinal lesions showed the types of lesions and specified the mechanisms of spinal injuries. The combined mechanisms were responsible for the majority of the spinal injuries.

CONCLUSIONS

Spinal instability occurs because of the lesion of the central axial spinal pillar The types of lesions of the central spinal pillar and of the secondary spinal pillars are determined by the essential traumatic spinal mechanisms: axial deformation (with compression or elongation), axial rotation, translation and most frequently the above combined mechanisms.

Surgical anatomy of the nerves and muscles in the posterior cervical spine: a guide for avoiding inadvertent nerve injuries during the posterior approach

STUDY DESIGN

An anatomic study investigated the cervical dorsal rami and major cervical paravertebral muscles.

OBJECTIVE

To provide a detailed description of the cervical dorsal rami and important paravertebral muscles as a way of avoiding inadvertent injuries during the posterior approach.

SUMMARY OF BACKGROUND DATA

No detailed anatomic studies of the nerves and the muscles in the posterior neck useful for the posterior approach have been reported previously.

METHODS

Running courses of the cervical dorsal rami of spinal nerves and the morphology of cervical major paravertebral muscles were studied using 14 cadavers. In four posterior approaches of cervical laminoplasty, subcutaneous facial exits of cutaneous nerves and the running course of the right C3 medial branches around facet joint were exposed for observation of living anatomy.

RESULTS

Every medial branch from the dorsal rami of the C3-C8 spinal nerves passed through an anatomic tunnel dorsolateral to the facet joint. The base of the tunnel was a bony gutter between neighboring facet joint capsules, and the roof was the tendon of the semispinalis capitis. In this tunnel, the medial branch had a little laxity in moving, and was assumed to be the most susceptible to iatrogenic injury during the operation. The semispinalis cervicis was composed with long muscle bundles. Each of these had only one or two innervating nerves from the dorsal rami of cervical spinal nerves. Cutaneous branches from the dorsal rami were found adjacent to every spinous process below the C2 spinous process in cadaveric studies. However, only two or three larger cutaneous nerves were discernible below the C5 or C6 spinous process in surgical approaches.

CONCLUSIONS

With the posterior approach to the cervical spine, a precise knowledge of the cervical dorsal rami anatomy and the innervating patterns of the paravertebral muscles is necessary for avoidance of inadvertent injuries to the nerves.

[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.

Awareness affects the response of human subjects exposed to a single whiplash-like perturbation

STUDY DESIGN

Human subjects were exposed experimentally to a single whiplash-like perturbation.

OBJECTIVE

To determine how awareness of the presence and timing of a whiplash-like perturbation affects the onset and amplitude of the neck muscle response and the peak magnitude of head and neck kinematics.

SUMMARY OF BACKGROUND DATA

Although most whiplash injuries are sustained in rear-end collisions, which occur without warning, most studies of whiplash injury have used subjects aware of the imminent perturbation.

METHODS

Seated subjects (35 women and 31 men) underwent a single forward horizontal perturbation (peak acceleration, 1.5 g). Surface electromyography measured the sternocleidomastoid and cervical paraspinal muscle activity. Three awareness conditions were tested: a countdown for subjects alerted to their perturbation, a perturbation without an alert for subjects who expected it within 60 seconds, and an unexpected perturbation for surprised subjects who were deceived.

RESULTS

The muscle and kinematic responses of aware (alerted and unalerted) subjects were not significantly different. Sternocleidomastoid activation occurred 7 ms later in surprised subjects than in aware subjects (P < 0.0002). Cervical paraspinal amplitudes were 260% larger and angular head accelerations in flexion were 180% larger in surprised male subjects than in alerted male subjects. Surprised female subjects exhibited a 25% larger head retraction and a 30% lower forward acceleration of the mastoid process than aware female subjects.

CONCLUSIONS

The larger retractions observed in surprised females likely produce larger tissue strains and may increase injury potential. Aware human subjects may not replicate the muscle response, kinematic response, or whiplash injury potential of unprepared occupants in real collisions.

Rapid neck muscle adaptation alters the head kinematics of aware and unaware subjects undergoing multiple whiplash-like perturbations

To examine whether habituation confounds the study of whiplash injury using human subjects, we quantified changes in the magnitude and temporal development of the neck muscle electromyogram and peak linear and angular head/torso kinematics of subjects exposed to sequential whiplash-like perturbations. Forty-four seated subjects (23F, 21M) underwent 11 consecutive forward horizontal perturbations (peak sled acceleration=1.5 g). Electromyographic (EMG) activity was recorded over the sternocleidomastoid (SCM) and cervical paraspinal (PARA) muscles with surface electrodes, and head and torso kinematics were measured using linear and angular accelerometers and a 3D motion analysis system. EMG onset occurred at reflex latencies (67-75 ms in SCM) and did not vary with repeated perturbations. EMG amplitude was significantly attenuated by the second perturbation in PARA muscles and by the third perturbation in SCM muscles. The mean decrement in EMG amplitude between the first trial and the mean of the last five trials was between 41% and 64%. Related kinematic changes ranged from a 21% increase in head extension angle to a 29% decrease in forward acceleration at the forehead, and were also significantly different by the second exposure in some variables. Although a wider range of perturbation intensities and inter-perturbation intervals need to be studied, the significant changes observed in both muscle and kinematic variables by the second perturbation indicated that habituation was a potential confounder of whiplash injury studies using repeated perturbations of human subjects.

A biomechanical evaluation of whiplash using a multi-body dynamic model

This paper presents a biomechanical evaluation of whiplash injury potential during the initial extension motion of the head in a rear-end collision. A four-segment dynamic model is developed in the sagittal plane for the analysis. The model response is validated using the existing experimental data and is shown to simulate the "S-shape" kinematics of the cervical spine and the resulting dynamics observed in human and cadaver experiments. The model is then used to evaluate the effects of parameters such as collision severity, head/headrest separation, and the initial head orientation in the sagittal plane on the "S-shape" kinematics of the cervical spine and the resulting neck loads. It is shown, for example, that the cervical spine forms an "S-shape" for a range of change in speeds and that at lower and higher speeds changes the spine does not form the "S-shape." Furthermore, it is shown that the "S-shape" formation also depends on the head to headrest separation distance.

Whiplash associated disorders: a review of the literature to guide patient information and advice

OBJECTIVES

To review the literature and provide an evidence based framework for patient centred information and advice on whiplash associated disorders.

METHODS

A systematic literature search was conducted, which included both clinical and non-clinical articles to encompass the wide range of patients' informational needs. From the studies and previous reviews retrieved, 163 were selected for detailed review. The review process considered the quantity, consistency, and relevance of all selected articles. These were categorised under a grading system to reflect the quality of the evidence, and then linked to derived evidence statements.

RESULTS

The main messages that emerged were: physical serious injury is rare; reassurance about good prognosis is important; over-medicalisation is detrimental; recovery is improved by early return to normal pre-accident activities, self exercise, and manual therapy; positive attitudes and beliefs are helpful in regaining activity levels; collars, rest, and negative attitudes and beliefs delay recovery and contribute to chronicity. These findings were synthesised into patient centred messages with the potential to reduce the risk of chronicity.

CONCLUSIONS

The scientific evidence on whiplash associated disorders is of variable quality, but sufficiently robust and consistent for the purpose of guiding patient information and advice. While the delivery of appropriate messages can be both oral and written, consistency is imperative, so an innovative patient educational booklet, The Whiplash Book, has been developed and published.

The response of human volunteers to rear-end impacts: the effect of head restraint properties

STUDY DESIGN

Human volunteers were subjected to a rear-end impact while sitting on a standard automobile seat, and sagittal plane kinematic responses were quantified. The effect of changing head restraint properties was determined by use of a repeated measures design.

OBJECTIVE

To determine the forces acting, and relative motions resulting, on volunteers in a rear-end impact and the effect of head restraint properties.

SUMMARY OF BACKGROUND DATA

In several recent studies of the kinematics of the cervical spine during rear-end impact, a forward thrust to the lower cervical spine was produced, and a transient S shape of the spine resulted while the head remained upright during the initial phase of the impact. This may result in nonphysiologic intervertebral motions and tissue strains.

METHODS

Nineteen automobile seats were first tested, and a modified head restraint was designed. Each volunteer sitting on a standard vehicle seat was subjected to an impact pulse of 3g with a 4-kph speed change. Testing was performed first with the modified head restraint, then again after replacement by the head restraint that came with the seat. Kinematic responses were compared for both head restraints by use of a repeated measures analysis of variance.

RESULTS

There was a measurable time difference between peak chest and peak head accelerations, which resulted in the chest being thrust forward by the seat back before the head was thrust forward by the head restraint. The modified head restraint significantly reduced the contact time difference and therefore decreased the relative chest-to-head forward motion.

CONCLUSIONS

Volunteers seated on a standard automobile seat demonstrated differential sagittal plane motion between the chest and head. It is possible to significantly decrease the relative chest-to-head motion by altering the characteristics of the head restraint.

The effectiveness of active head restraint in preventing whiplash

BACKGROUND

Whiplash injury claims have increased for two decades and manual head restraints are often incorrectly adjusted. A Self-Aligning Head Restraint (SAHR) was designed to move upward and forward by occupant motion in a rear crash providing earlier neck support, even when the head restraint is positioned low. This study determines its field effectiveness.

METHODS

Insurance records were analyzed for consecutive Saab rear crashes in Sweden over 18 months. The Saab 9000/900 had standard head restraints and Saab 9-5/9-3 had SAHR. A questionnaire was mailed to the occupants, insurance and medical records were reviewed, and phone interviews were conducted.

RESULTS

SAHR reduced whiplash injury risks by 75 +/- 11% from an 18 +/- 5% incidence in 85 occupants with standard head restraints to 4 +/- 3% in 92 occupants with SAHR. No SAHR seat required repair or replacement after the crashes.

CONCLUSION

SAHR is effective in reducing whiplash injury in rear crashes and is a passive public-health approach that works irrespective of manual head-restraint adjustment.

Immunohistochemical demonstration of nerve fibers in the synovial fold of the human cervical facet joint

The role of the intra-articular synovial fold as a source of facet joint pain is unclear, because the nature of nociceptive innervation in lumbar synovial folds is controversial, and there have been no such studies in cervical synovial folds. The present study aimed to demonstrate the presence of nerve fibers including nociceptive fibers in synovial folds of human cervical facet joints using immunohistochemistry. Synovial folds of cervical facet joints removed from patients undergoing cervical spine laminoplasty were analyzed immunohistochemically using antibodies to protein gene product 9.5, beta III-tubulin, substance P and calcitonin gene-related peptide. Many nerve fibers immunoreactive for protein gene product 9.5 and beta III-tubulin were demonstrated both around blood vessels and as free fibers in the stroma of the synovial fold. Also. immunostaining showed the presence of free nerve fibers immunoreactive for substance P and calcitonin gene-related peptide in the stroma. The presence of putative nociceptive fibers in cervical synovial folds supports a possible role for these structures as a source of cervical facet joint pain.

Radiofrequency medial branch neurotomy in litigant and nonlitigant patients with cervical whiplash: a prospective study

STUDY DESIGN

The efficacy of radiofrequency medial branch neurotomy to treat cervical zygapophysial joint pain from whiplash was compared prospectively in litigants and nonlitigants.

OBJECTIVES

1) To assess the effect of monetary gain on treatment of zygapophysial joint pain in cervical whiplash. 2) To determine whether radiofrequency medial branch neurotomy is effective treatment for whiplash.

SUMMARY OF BACKGROUND DATA

The influence of litigation on treatment outcome is a subject of controversy in both the medical and legal professions. This is the first study to examine this issue in a prospective manner using a previously proven diagnostic and therapeutic method.

METHODS

Sixty patients with cervical whiplash who remained symptomatic after 20 weeks of conservative management were referred for radiofrequency cervical medial neurotomy. The patients were classified as litigant or nonlitigant based on whether the potential for monetary gain via litigation existed. Each group underwent identical evaluation and treatment. Patients were observed for 1 year. Visual analogue scores and self-reported improvement were obtained before, immediately after, and 1 year after radiofrequency cervical medial neurotomy.

RESULTS

Forty-six patients completed the study. The overall reduction in cervical whiplash symptoms and visual analogue pain scores were significant immediately after treatment (nonlitigants vs. litigants: 2.0 vs. 2.5, P = 0.36) and at 1 year (nonlitigants vs. litigants: 2.9 vs. 4.0, P = 0.05). One-year follow-up scores were higher than immediate post-treatment scores (nonlitigants vs. litigants: 2.5 vs. 3.6). The difference between litigants and nonlitigants in the degree of symptomatology or response to treatment did not reach significance.

CONCLUSIONS

These results demonstrate that the potential for secondary gain in patients who have cervical facet arthropathy as a result of a whiplash injury does not influence response to treatment. These data contradict the common notion that litigation promotes malingering. This study also confirms the efficacy of radiofrequency medial branch neurotomy in the treatment of traumatic cervical facet arthropathy.

Whiplash: a review of a commonly misunderstood injury

Whiplash injury is a relatively common occurrence, but its mechanism and optimal treatment remain poorly understood. It is estimated that the incidence of whiplash injury is approximately 4 per 1,000 persons. The most common radiographic findings include either preexisting degenerative changes or a slight flattening of the normal lordotic curvature of the cervical spine. Computed tomography and magnetic resonance imaging are generally reserved for cases of neurologic deficit, suspected disc or spinal cord damage, fracture, or ligamentous damage. Biomechanics studies have determined that after rear impact C6 is rotated back into extension before movement of the upper cervical vertebrae. Thus, the lower cervical vertebrae were in extension while the upper vertebrae were in a position of relative flexion, producing an S shape in the cervical spine. It is believed that this abnormal motion pattern might play a role in the development of whiplash injuries. Historically, a soft cervical collar has been used early after the injury in an attempt to restrict cervical range of motion and limit the chances of further injury. More recent studies report rest and restriction of motion to be detrimental and to slow the healing process.

Variability in the control of head movements in seated humans: a link with whiplash injuries?

The aim of this study was to determine how context and on-line sensory information are combined to control posture in seated subjects submitted to high-jerk, passive linear accelerations. Subjects were seated with eyes closed on a servo-controlled linear sled. They were asked to relax and received brief accelerations either sideways or in the fore-aft direction. The stimuli had an abrupt onset, comparable to the jerk experienced during a minor car collision. Rotation and translation of the head and body were measured using an Optotrak system. In some of the subjects, surface electromyographic (EMG) responses of selected neck and/or back muscles were recorded simultaneously. For each subject, responses were highly stereotyped from the first trial, and showed little sign of habituation or sensitisation. Comparable results were obtained with sideways and fore-aft accelerations. During each impulse, the head lagged behind the trunk for several tens of milliseconds. The subjects' head movement responses were distributed as a continuum in between two extreme categories. The 'stiff' subjects showed little rotation or translation of the head relative to the trunk for the whole duration of the impulse. In contrast, the 'floppy' subjects showed a large roll or pitch of the head relative to the trunk in the direction opposite to the sled movement. This response appeared as an exaggerated 'inertial' response to the impulse. Surface EMG recordings showed that most of the stiff subjects were not contracting their superficial neck or back muscles. We think they relied on bilateral contractions of their deep, axial musculature to keep the head-neck ensemble in line with the trunk during the movement. About half of the floppy subjects displayed reflex activation of the neck muscles on the side opposite to the direction of acceleration, which occurred before or during the head movement and tended to exaggerate it. The other floppy subjects seemed to rely on only the passive biomechanical properties of their head-neck ensemble to compensate for the perturbation. In our study, proprioception was the sole source of sensory information as long as the head did not move. We therefore presume that the EMG responses and head movements we observed were mainly triggered by the activation of stretch receptors in the hips, trunk and/or neck. The visualisation of an imaginary reference in space during sideways impulses significantly reduced the head roll exhibited by floppy subjects. This suggests that the adoption by the central nervous system of an extrinsic, 'allocentric' frame of reference instead of an intrinsic, 'egocentric' one may be instrumental for the selection of the stiff strategy. The response of floppy subjects appeared to be maladaptive and likely to increase the risk of whiplash injury during motor vehicle accidents. Evolution of postural control may not have taken into account the implications of passive, high-acceleration perturbations affecting seated subjects.

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.

Types of synovial fold in the cervical facet joint

Few detailed studies of synovial folds of cervical facet joints exist at the moment. This study was performed to provide anatomical data for each synovial fold in the cervical facet joints, using 20 cervical spines from C2 to C7 for dissection. Anatomic evaluation of the synovial folds included the gross morphology, in three dimensions, and the histology. Also, degenerative changes of the lower facet surface on which synovial folds occurred were evaluated. On the basis of gross morphology and histological composition, three types of synovial folds were identified. Type-1 synovial folds, shaped like a crescent, consisted principally of adipose tissue. Type-2 synovial folds had an apical region made up of dense fibrous tissue, with the base and middle region consisting of adipose tissue. In type-2 folds, the size and shape varied, including some elliptic-shaped synovial folds projecting well into the joint cavity. Type-3 synovial folds were thin with ragged free borders, and were formed exclusively of fibrous tissue. This study shows the variable appearance of synovial folds. Speculation was raised that the articular facet impingement of a large synovial fold and the subluxation of a smaller structure may play a possible role in the pathology of some disorders of the neck.

An anatomical investigation of the human cervical facet capsule, quantifying muscle insertion area

Facet capsule injury has been hypothesised as a mechanism for neck pain. While qualitative studies have demonstrated the proximity of neck muscles to the cervical facet capsule, the magnitude of their forces remains unknown owing to a lack of quantitative muscle geometry. In this study, histological techniques were employed to quantify muscle insertions on the human cervical facet capsule. Computerised image analysis of slides stained with Masson's trichrome was performed to characterise the geometry of the cervical facet capsule and determine the total insertion area of muscle fibres into the facet capsule for the C4-C5 and C5-C6 joints. Muscle insertions were found to cover 22.4+/-9.6% of the capsule area for these cervical levels, corresponding to a mean muscle insertion area of 47.6+/-21.8 mm2. The magnitude of loading to the cervical facet capsule due to eccentric muscle contraction is estimated to be as high as 51 N. When taken in conjunction with the forces acting on the capsular ligament due to vertebral motions, these forces can be as high as 66 N. In that regard, these anatomical data provide quantitative evidence of substantial muscle insertions into the cervical facet capsular ligament and provide a possible mechanism for injury to this ligament and the facet joint as a whole.

Chronic pain/dysfunction in whiplash-associated disorders

OBJECTIVE

The purposes of this article are (1) to review current knowledge of and recent concepts pertaining to the causes of chronic pain and/or dysfunction following whiplash-type injuries and (2) to acquaint those who treat these types of injuries with possible mechanisms of continued pain and or dysfunction following whiplash.

DATA COLLECTION

A review of the literature on mechanisms of injury and neurologic considerations was undertaken. A hand search of relevant medical, neuroscience, chiropractic, and online Index Medicus sources and other sources involving mechanisms of nociception, neurotransmitters, and receptors that might evolve from whiplash-type soft tissue injuries was conducted.

RESULTS

Pain is a complex phenomenon that has great variability. Chronic pain appears to involve a deficient descending inhibitory process and/or ongoing excitatory input.

CONCLUSIONS

There is a wide variety of reactions by individuals to any given type of stimulus. Injury may lead to increases in neuronal activity and prolonged changes in the nervous system. Chronic pain may be seen as part of a central disturbance accompanied by disinhibition or sensitization of central pain modulation, mirrored in the immune and endocrine systems. Patients with chronic whiplash syndrome may have a generalized central hyperexcitability from a loss of tonic inhibitory input (disinhibition) and/or ongoing excitatory input contributing to dorsal horn hyperexcitability. Dysfunction of the motor system may also occur, with or without pain. The purpose of treatment should be not only to relieve pain but also to allow for proper proprioception.

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.

Whiplash Injuries

The term "whiplash" is not a medical diagnosis, but is the result of soft-tissue trauma to the neck. A whiplash injury occurs as a result of a sudden acceleration or deceleration of the head and neck with respect to the body. This article recommends that patient treatment be individualized.

Injury threshold: whiplash-associated disorders

OBJECTIVES

To review current knowledge and recent concepts of the causes of injuries after minor impact automobile collisions and to acquaint those who treat these types of injuries with possible injury thresholds and mechanisms that may contribute to symptoms.

DATA SOURCES

A review of literature involving mechanisms of injury, tissue tensile threshold, and neurologic considerations was undertaken. A hand-search of relevant engineering, medical/chiropractic, and computer Index Medicus sources in disciplines that cover the variety of symptoms was gathered.

RESULTS

Soft-tissue injuries are difficult to diagnose or quantify. There is not one specific injury mechanism or threshold of injury. With physical variations of tissue tensile strength, anatomic differences, and neurophysiologic considerations, such threshold designation is not possible.

CONCLUSIONS

To make a competent assessment of injury, it is important to evaluate each patient individually. The same collision may cause injury to some individuals and leave others unaffected. With the variability of human postures, tensile strength of the ligaments between individuals, body positions in the vehicle, collagen fibers in the same specimen segment, the amount of muscle activation and inhibition of muscles, the size of the spinal canals, and the excitability of the nervous system, one specific threshold is not possible. How individuals react to a stimulus varies widely, and it is evident peripheral stimulation has effects on the central nervous system. It is also clear that the somatosensory system of the neck, in addition to signaling nociception, may influence the control of neck, eyes, limbs, respiratory muscles, and some preganglionic sympathetic nerves.

Cervical coupling during lateral head translations creates an S-configuration

OBJECTIVE

To determine cervical coupling during the posture of lateral head translation relative to a fixed thoracic cage.

DESIGN

Digitized measurements from anteroposterior cervical radiographs of 20 volunteers were obtained in neutral, left, and right lateral translation posture of the head compared to a fixed thorax.

BACKGROUND DATA

Clinically, lateral translation of the head is a common posture. Ranges of motion and spinal coupling have not been reported for this movement.

METHODS

Vertebral body corners, mid-lateral articular pillars and the superior spinous-lamina junction of C3-T4 were digitized on 60 radiographs. Using the orthogonal axis of positive x-direction to the left, vertical as positive y and anterior as positive z, digitized points were used to measure projected segmental z-axis rotation, y-axis rotation, and segmental lateral translations of each vertebra.

RESULTS

Subjects translated their heads laterally a mean of 51 mm. The major coupled motion was lateral bending (z-axis rotation), which changed direction at the C4-C5 disc space creating an S-shape. Upper cervical (C3-C4) lateral bending was contralateral to the main motion of head translation direction. Lower cervical and upper thoracic lateral bending were ipsilateral. Other segmental motions averaged less than 1 mm and 1 degrees.

CONCLUSIONS

Lateral head translations (x-axis) compared to a fixed thoracic cage can be large with a mean of 51 mm to one side. The major spinal coupling was lateral bending which changed direction at C4-C5 resulting in an S-configuration. This might have application in side impacts. All other segmental movements were small, less than 1 mm and 1 degrees.

RELEVANCE

The clinically common posture of lateral head translation results in an S-shaped cervical spine and may occur in side impact trauma. This posture has not been studied for cervical coupling patterns or range of motion (ROM).

The cervical facet capsule and its role in whiplash injury: a biomechanical investigation

STUDY DESIGN

Cervical facet capsular strains were determined during bending and at failure in the human cadaver.

OBJECTIVE

To determine the effect of an axial pretorque on facet capsular strains and estimate the risk for subcatastrophic capsular injury during normal bending motions.

SUMMARY OF BACKGROUND DATA

Epidemiologic and clinical studies have identified the facet capsule as a potential site of injury and prerotation as a risk factor for whiplash injury. Unfortunately, biomechanical data on the cervical facet capsule and its role in whiplash injury are not available.

METHODS

Cervical spine motion segments were tested in a pure-moment test frame and the full-field strains determined throughout the facet capsule. Motion segments were tested with and without a pretorque in pure bending. The isolated facet was then elongated to failure. Maximum principal strains during bending were compared with failure strains, by paired t test.

RESULTS

Statistically significant increases in principal capsular strains during flexion-extension loading were observed when a pretorque was applied. All measured strains during bending were significantly less than strains at catastrophic joint failure. The same was true for subcatastrophic ligament failure strains, except in the presence of a pretorque.

CONCLUSIONS

Pretorque of the head and neck increases facet capsular strains, supporting its role in the whiplash mechanism. Although the facet capsule does not appear to be at risk for gross injury during normal bending motions, a small portion of the population may be at risk for subcatastrophic injury.