Patient Mechanisms of Injury in Whiplash-Associated Disorders

Influence of morphological variations on cervical spine segmental responses from inertial loading

OBJECTIVES

The objective of this study was to investigate the influence of morphological variations in osteoligamentous lower cervical spinal segment responses under postero-anterior inertial loading.

METHODS

A parametric finite element model of the C5-C6 spinal segment was used to generate models. Variations in the vertebral body and facet depth (anteroposterior), posterior process length, intervertebral disc height, facet articular process height and slope, segment orientation ranging from lordotic to straight, and segment size were parameterized. These variations included male-female differences. A Latin hypercube sampling method was used to select parameter values for model generation. Forces and moments associated with the inertial loading were applied to the generated model segments. The 7 parameters were grouped as local or global depending on the number of spinal components involved in the shape variation. Four output responses representing overall segmental and soft tissue responses were analyzed for each model variation: response angle of the segment, anterior longitudinal ligament stretch, anterior capsular ligament stretch, and facet joint compression in the posterior region. Pearson's correlation coefficient was used to compute the correlations of these output responses with morphological variations.

RESULTS

Fifty models were generated from the parameterized model using a Latin hypercube sampling technique. Variation in response angle among the models was 4° and was most influenced by change in the combined dimension of vertebral body and facet depth, followed by size of the segment. The maximum anterior longitudinal ligament stretch varied between 0.1 and 0.3 and was strongly influenced by the change in the segment orientation. The anterior facet joint region sustained tension, whereas the posterior region sustained compression. For the anterior capsular ligament stretch, the most influential global variation was segment orientation, whereas the most influential local variations were the facet height and facet angle parameters. In the case of posterior facet joint compression, segment orientation was again most influential, whereas among the local variations, the facet angle had the most influence.

CONCLUSION

Shape variations in the intervertebral disc influenced segmental rotation and ligament responses; however, the influence of shape variations in the facet joint was confined to capsular ligament responses. Response angle was most influenced by the vertebral body depth variations, explaining greater segmental rotations in female spines. Straighter spine segments sustained greater posterior facet joint compression, which may offer an explanation for the higher incidence of whiplash-associated disorders among females, who exhibit a straighter cervical spine. The anterior longitudinal ligament stretch was also greater in straighter segments. These findings indicate that the morphological features specific to the anatomy of the female cervical spine may predispose it to injury under inertial loading.

Impact characteristics of a vehicle population in low speed front to rear collisions

Rear impact collisions are mostly low severity, but carry a very high societal cost due to reported symptoms of whiplash and related soft tissue injuries. Given the difficulty in physiological measurement of damage in whiplash patients, there is a significant need to assess rear impact severity on the basis of vehicle damage. This paper presents fundamental impact equations on the basis of an equivalent single vehicle to rigid barrier collision in order to predict relationships between impact speed, maximum dynamic crush, mean and peak acceleration, time to common velocity and vehicle stiffness. These are then applied in regression analysis of published staged low speed rear impact tests. The equivalent mean and peak accelerations are linear functions of the collision closing speed, while the time to common velocity is independent of the collision closing speed. Furthermore, the time to common velocity can be used as a surrogate measure of the normalized vehicle stiffness, which provides opportunity for future accident reconstruction.

Sex Differences in Patients with Chronic Pain Following Whiplash Injury: The Role of Depression, Fear, Somatization, Social Support, and Personality Traits

BACKGROUND

Chronic whiplash-associated disorders (chronic WAD) cover a large variety of clinical manifestations that can occur after a whiplash injury. Women have an increased risk of developing chronic WAD, and it is suggested that psychosocial factors are related to long-term pain and functioning following whiplash injury and persistence of chronic pain. This leads to the question whether there are sex differences in psychosocial factors in chronic WAD.

METHODS

This study included 117 subjects who had experienced a whiplash injury at least 3 months before the start of the study (mean duration of pain: 67.29 ± 63.86 months, range: 297 months). They were selected as chronically symptomatic, by excluding those who had recovered from their whiplash injury. Psychosocial aspects (including depression, fear, somatization, social support, and personality traits) were assessed by validated questionnaires, and sex differences were tested using a univariate analysis of variance (ANCOVA), with age and time from whiplash injury as covariates.

RESULTS

No differences in depression, fear, somatization, discrepancy in social support personality trait, Neck Disability Index scores, physical functioning, bodily pain, or general health were present between women and men with chronic WAD. Women with chronic WAD reported higher levels of emotional support in problem situations and social companionship.

CONCLUSION

Except for emotional support in problem situations and social companionship, psychosocial factors do not differ between men and women with chronic WAD. These findings imply little to no risk for sex bias in studies investigating psychosocial issues in patients with chronic WAD.