Whiplash is defined by the Quebec Task Force as “an acceleration-deceleration mechanism of energy transfer to the neck”. It is commonly the result of a rear-end road traffic accident, but can also be caused by side-on crashes, contact or impact sports, falls, and other trauma. Unexpected injuries such as falls and rear-end collisions can be particularly symptomatic as the muscles are likely to be relaxed, thus the deeper ligaments are less protected and bear the brunt of the force.
Taking a rear-end accident as an example, a whiplash injury occurs in two parts. The first part is when the head is thrown back into an extension movement, primarily affecting the structures towards the front of the neck. This may include the anterior longitudinal ligament which attaches to the front of the vertebrae and the intervertebral discs- this ligament can be strained and pull on the disc in this way. There can also be micro-tears to the muscles at the front of the neck as they are overstretched and automatically recoil. This is when the second part of the injury occurs.
As the head moves forwards (flexion) again in a combination of momentum and reflex, stressing the ligaments at the back of the neck and the highest joint in the neck. This flexion-extension movement is best accommodated by the vertebrae in the middle area of the neck, so they are often most affected. If there is any rotation the upper neck will absorb it, potentially causing symptoms higher up.
If symptoms do not resolve adequately, Whiplash Associated Disorders (WAD) can develop, leading to chronic or late Whiplash Syndrome: “the presence of pain, restriction of motion, or other symptoms at six months or more after the injury, sufficient to hinder return to normal activities.”
For more information on whiplash including how best to set up your headrest in the car, see this post in association with APM.