Friday, March 30, 2012

Whiplash Injuries: It's Complicated

This excerpt from the December, 2011, issue of Spine is somewhat technical, but may give you an idea of the complexity of whiplash injuries.

"Nikolai Bogduk, MD, PhD, in a recent narrative review published in Spine, summarized evidence which demonstrates that injuries to the cervical zygapophysial (also known as facet) joints are the primary source of pain following hyperflexion-hyperextension injuries following motor vehicle collisions.

Postmortem Studies

Examination of cervical spines of persons killed in motor vehicle collisions identified a number of non-lethal injuries including a variety of injuries to the cervical facet joints, such as intra-articular hemorrhages and lesions, as well as fractures to the subchondral bone, articular cartilage, and articular process. According to the studies,
virtually none of the lesions to the facet joints were present on postmortem radiography.

Biomechanical Studies

In vivo studies of the biomechanical causes of post-whiplash neck pain demonstrate the cervical spine is compressed from below as the trunk rises toward the head. This causes sigmoid deformation when the lower cervical spine is subjected to an abnormally high posterior sagittal rotation. The upper vertebrae rotate in a sagittal direction with practically no posterior translation. The anterior vertebral margins are widely separated, while the posterior inferior articular processes carve into the superior articular surface of the adjacent lower vertebral body. These abnormal movements produce posterior facet joint lesions and rim lesions of the intervertebral disc due to avulsion of the annular fibrosis from the vertebral endplate.

During hyperflexion-hyperextension injuries, the facet joints are initially compressed beyond normal physiological limits, followed by excessive straining to the capsule and annulus fibrosis. The amount of stress increases with the level of impact during trauma. Studies show the C4-5 disc is particularly susceptible to injury in a relatively low speed impact, while C3-4,C5-6 and C6-7 are at increased risk as impact acceleration increases.

A study of post-whiplash lesions in 21 cadavers found intervertebral disc injuries in 90% of the subjects, anterior longitudinal ligament tears in 80% of the cadavers, and a 40% incidence rate of facet capsule joint tears. Other injuries included tears of the annulus fibrosis, anterior longitudinal ligament, and facet joints."

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