The actual source of chronic neck pain after whiplash injuries has been a mystery for a long time. It has been difficult to sort out because there are so many possibilities within the neck structures (hemorrhage, fracture, contusion, tears). But over the last 10 years studies have started to consistently point to one area: the cervical zygapophysial joints.
A more common term for these joints is facet joints. Between each pair of vertebrae are two facet joints. These joints connect the vertebrae together in a chain but slide against one another to allow the neck to move in many directions. Except for the very top and bottom of the spinal column, each vertebra has two facet joints on each side. The ones on top connect to the vertebra above; the ones below join with the vertebra below.
Studies of humans after death called postmortem studies have really helped identify the problem areas. Animal studies and biomechanics studies have also added similar information about the possible lesions of whiplash. The agreement among all these studies called convergence has increased the validity of what were previously just theories about the physical causes of neck pain after whiplash.
The results of these studies show 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.
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 (facet) joints are left unprotected and can be injured as well. Animal 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.
Treatment blocking the nerves to the facet joints has also added confirmation that the source of chronic post-whiplash neck pain is coming from those particular joints. Nerve blocks have become both a diagnostic test and a treatment. In other words, if the nerve block eliminates the pain, the problem is coming from the facet joint.
Radiofrequency neurotomy is another treatment that has developed out of the knowledge that blocking nerve signals to the joint can eliminate the pain. This is a neurosurgical procedure. Radiofrequency waves directed at the tiny nerve branches to the joints create enough heat to destroy the nerve endings.
The pain relief is long-lasting and works better than any other surgical or conservative approach for 70 per cent of the patients studied. And if the pain comes back, the neurotomy procedure can be repeated successfully. Ongoing relief with return to work and daily activities is reported for 60 per cent of patients who have a repeat radiofrequency neurotomy.
In summary, the certain knowledge that chronic neck pain following whiplash injuries is coming from the facet joints is helpful. Treatment directed at stopping nerve signaling pathways can provide sustained pain relief never before possible with other treatment approaches. Diagnostic nerve blocks help identify patients who might benefit from neurotomy before actually doing the procedure.
Zygapophysial (facet) joint pain is not the only cause of chronic whiplash pain. But it does account for up to half of all chronic neck pain sufferers. A 70 per cent success rate for that many patients is considered a major breakthrough in this area.
There is one drawback to this information. There aren't specially trained neurosurgeons who can do this procedure in every community. That means the most successful treatment isn't widely available. The answer to this dilemma isn't clear.
It sounds simple that more neurosurgeons should train to become skilled in this technique. But even with more training, there's no guarantee the procedures will be performed properly according to the practice guidelines already identified. And with 50 per cent of patients who have some other source of neck pain, other means of successful treatment must be determined. There is a need for additional study of this problem.
Reference: Nikolai Bogduk, MD, PhD. On Cervical Zygapophysial.