Q: I saw a special on TV about whiplash injuries. I was especially interested because I had a car accident three years ago and still have neck pain. What I wonder is how do they get those X-rays showing what happens to the neck during the sudden stop. Is it all just photo-shopped in?

A: Sometimes computer simulated graphics are used to depict what happens during an accident causing injuries such as whiplash. But even those simulations are based on actual biomechanics studies conducted in research laboratories.

Biomechanics studies refer to research done on live humans (adults only). Volunteers willing to experience a low-speed rear impact are videotaped and X-rayed during the injury. This is how we know the sequence of events that occur within the cervical spine at the point of impact and the moments following. Correlating these cineradiography studies with postmortem examination of cadavers known to have a history of whiplash has confirmed some things.

First, compression and strain that exceeds the physiologic limits of the soft tissue structures around the facet joints has been identified. The greater the impact magnitude, the more damage is done. Low impact events seem to affect the C45 disc most often. But as the impact of the injury increases, damage extends to include C34, C56, and C67.

Tears in the anulus fibrosus (thick covering around the intervertebral discs) and tears in the joint capsules have been demonstrated. When the impact and force of injury is great enough, the anterior longitudinal ligament along the front of the cervical spine can be torn, too. Tiny meniscus cartilage in the facet joints called intraarticular meniscoids can become contused (compressed and bruised) and can even rupture.

The result of all the soft tissue damage is that the zygapophysial joints in the neck are left unprotected and can be injured as well. Animal studies added to what we know from biomechanics studies have shown that stretch of the joint capsule from the injury sets off nociceptors. Nociceptors transmit messages of pain. They are located at the joints and in the muscles and tendons near the joints. Once these transmitters get started, they don't turn off and the result can be chronic pain.

There is one other area of study that has helped identify what really happens during a whiplash injury and that is postmortem studies. Postmortem refers to studies of humans after death. By examining all of the structures in the neck in people who had a history of whiplash, scientists have been able to see that tiny fractures and tears of the joint surface (called articular cartilage) and joint capsule are the main reasons for continued neck pain long after the car accident or other injury.

And the key finding here is the fact that these lesions don't show up on X-rays or MRIs. They are only seen when the neck is studied directly in postmortem analysis. The agreement among all these studies called convergence has increased the validity of what were previously just theories about what happens inside the body during a sudden stop or collision and the physical causes of neck pain after whiplash.

Reference: Nikolai Bogduk, MD, PhD. On Cervical Zygapophysial Joint Pain After Whiplash. In Spine. December 1, 2011. Vol. 36. No. 25S. Pp. S194-199.