A 2011 study published in Spine found that there is evidence supporting a lesion-based model in Whiplash Associated Disorders (WAD).[1] The study concluded that the best evidence on correlating soft tissue damage and WAD is to look at zygapophysial (facet) joint pain since there was scientific evidence supporting a lesion-based model in WAD. The researchers also felt that further research and clinical study was needed for ligaments, nerve roots and muscles.
Tissue Damage and Biomechanics
Bioengineers have been studying automobile collisions for years to predict the presence, timing and severity of tissue damage and how well injury prevention systems responded. Based on these studies, it is known that during rear-end collisions the cervical spine initially undergoes a horizontal shear or retraction. With continued retraction, the cervical spine accelerates into extension, followed by acceleration into flexion. There are areas in the cervical spine that can exceed the physiological limits, particularly when the occupant’s head is turned to the left or right resulting in an increased risk of cervical injury.
Pushing the Phsyiologic Limit: Lesions
The study notes that a broad spectrum of tissue damage occurs in extension/flexion injuries to the zygapophysial joint capsules and annuli fibrosi, as well as partial or complete ruptures of capsules, ligaments and even intra-articular fractures and transarticular synovial joint fractures. This damage can lead to modifications in tissue properties, nociceptor activation, immediate and sustained dysfunction in afferents and spinal neurons, neuroplastic changes and pain.
The Facet Joint and Capsules
The researchers in this study further note that various animal studies have focused on a variety of tissues, but that the greatest body of literature is on the zygapophysial (facet) joint. The researchers further note that in these studies, when maximum principal strains are applied to the facet capsular ligament, afferents become saturated and persistent pain occurs. This loading of the joint is associated with production of collagen fiber disorganization, axonal swelling and altered morphology in the ligament, as well as permanent modification in the neuronal signaling in the spinal cord. The researchers conclude that these observations provide pivotal scientific evidence that cervical facet joints can become damaged by a whiplash injury and can become sources of pain.
Ligament and Disc Damage
When the spine is pushed into abnormal movements in a whiplash injury, tearing of the anterior longitudinal ligament and rim lesions of the anterior annulus fibrosus can occur. This process has been studied using cadavers, but the researchers note this process has not been tested elsewhere. Nor has discogenic pain after whiplash injury been explored clinically. The researchers seem to suggest that this is an area where further research is needed.
Nerve Root Damage
The authors note that while there is the potential for trauma to the nerve roots and dorsal ganglion in the neck, neural impingement is challenging to investigate experimentally. However, the cervical nerve roots and dorsal root ganglia are at risk for injury due to rapid changes in the canal pressure during rapid extension/flexion movement. This pressure has been shown to induce plasma membrane breakdown of spinal ganglia nerve cells.
Vertebral Artery Disection
A recent study of 500 whiplash patients indicated that there was a higher rate of cervical arterial dissections when compared to the general population. (1.6 vs. 0.0041%). In addition, the onset of arterial dissection may occur 4-12 months after a motor vehicle collision and altered blood flow rates have been associated with chronic pain. The researchers believe that this type of injury occurs when the cervical spine is pushed past its physiological limit, causing a pinching of the vessel or a tear in the intimal layer due to overstretching. The researchers noted further study is needed in this area since the only research on this issue has been cadaver studies.
Muscle Injury and WAD
It is clear that direct injury can occur to neck muscles caused by reflex muscle activation in response to a motor vehicle collision. This occurs most often in the sternocleidomastoid muscle and the semispinalis muscle. In addition, elevated levels of serum creatine kinase, a marker for muscle injury, have been recorded in whiplash patients 24 hours after the collision. When pain lasts more than three months, the data suggests that lesions to the muscles following whiplash may be related to the acute rather than the chronic phase of whiplash injury. The researchers note that no research has produced clinical evidence for a role of the muscles in determining the symptoms associated with WAD, but it is largely recognized that muscles can be a referred area of pain, with the primary nociceptive focus being in another structure of the neck.
Key Points From the Study
- There is evidence supporting a lesion-based model in whiplash associated disorders (WAD).
- Zygapophysial joint pain is the one entity predicted by biomechanical studies, validated through animal studies, and for which there is both a valid diagnostic test and a proven treatment.
- Other types of lesions to ligaments, discs, nerve roots, and muscle likely undergo similar changes related to WAD, but additional study is needed to better understand these structures.
This study confirms that damage to the facet joint can be directly correlated to WAD and could be useful in providing a basis for understanding that not all patients recover fully from whiplash associated disorders. Though studies are useful to provide a basis for establishing that musculoskeletal injuries result in chronic residuals, explaining why it occurs is of critical importance in a traumatic injury case both for the healthcare professional who is establishing the basis of ongoing treatment needs and for the patient who can be potentially left with long term residuals.
The attorneys at Adler Giersch, PS are committed to helping those patients struggling with long term residuals from a traumatic injury. We know that injuries can have a profound short term and long term impact to one’s daily activities at work, home and recreational pursuits – and we can prove it.
