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Posterior Neck Muscles Take Burden of Rear-End Impact Resulting in Whiplash

Posted on: 11/30/1999
Researchers have been investigating ways to determine how neck muscles are affected when someone is injured in a rear-end motor vehicle crash, resulting in whiplash. Using human subjects and cadaveric necks have given some clues, but a biomechanical neck was needed for more in-depth study.

The researchers in this study used human subject data gleaned from subjects who were exposed to low-impact rear-end motor vehicle collision and then integrated the data into a biomechanical neck model. Using electromyographic data from the sternocleidomastoid (SCM) and the posterior cervical muscles, the researchers determined which muscles were being contracted in an unnatural fashion during and after the impact. This allowed the researchers to quantify the magnitude and rate of muscles strain resulting from the forced neck action.

The results showed that the SCM muscle lengthened at impact and then shortened in the rebounding motion. The posterior muscles, the spelius capitis (SPL), semispinalis capitis and the trapezius, did the opposite, shortening upon impact and forward motion, and lengthening on rebound.

Electromyography data showed that the muscle strains on both anterior and posterior muscles were most active during imposed muscle lengthening. The researchers noted that the peak lengthening fascicle strains were significantly greater in the posterior muscles, specifically the SPL. The findings suggest that this is the point when there is most activity in the posterior muscles, during the imposed lengthening, when there is the greatest potential for muscle injury.

Although these tests were done at low velocity impact (less than 8 km/hr), itís likely that a higher velocity impact would result in a more severe muscle reaction and injury. This type of study is important in order for researchers to understand the factors that are important in the development of whiplash.

The authors concluded that the rate of strain in the neck muscles, following a rear-end collision, is highest among the posterior muscles and that this indicates that they are more likely to be injured.

Anita N. Vasavada, PhD, et al. Musculotendon and Fascicle Strains in Anterior and Posterior Neck Muscles During Whiplash Injury. In Spine. April 2007. Vol. 32. No. 7. Pp. 756-765.

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