The primary region of the human body to be injured in a whiplash accident is the neck. The whiplash injury is an inertial injury to the neck. This means that there is no direct impact, blow, or contact to the neck. Rather, the injury is indirect, and there is no contact. Another well-known example of a neck inertial injury is “shaken baby syndrome.” The injury to the baby’s neck is indirect, or inertial.
During the whiplash mechanism, two large pieces of inertial mass, the head and the trunk, tend to move in opposite directions. As an example, in a rear end collision, the trunk moves forward with the struck vehicle, while the inertial mass of the head leaves the head behind. The neck, existing between these two large inertial masses, is subjected to mechanical stresses, and may become injured. The injury occurs because there are mechanical stresses to the structures of the neck that occur as a consequence of inertial loading.
The cranial-cervical junction and the upper cervical spine are a mechanically unique region of the spinal column. Their mechanically unique characteristics increase the vulnerability of the upper cervical spine tissues to inertial injury. Four relevant unique mechanical characteristics to this discussion include:
1) The center of mass of the head exists at the location of the sella turcica, the bony location of the pituitary gland. A mechanical lever arm exists between the sella turcica and the joints of the upper cervical spine, especially the occiput, first cervical vertebrae (C1, or atlas), and the second cervical vertebrae (C2 or axis).
When the head becomes inertially involved in the mechanism of a trauma, this unique lever arm increases the inertial injury to the cranial-upper cervical spine region.
2) A general biomechanical principle includes the understanding that there is a trade-off between mobility and stability. Joints that have greater mobility have reduced stability. Joints that have great stability have reduced mobility. Joints that have great mobility have increased vulnerability to injury (including inertial injury).
Although it is not commonly understood, 55% of cervical spine (neck) rotation (turning to the left or right) occurs at a single joint. This joint possesses great mobility, but at a price of reduced stability and increased vulnerability to inertial injury. The joint is the atlas-axis joint (C1-C2).
3) Very little motion occurs between the skull (occiput bone, CO) and the atlas vertebrae (C1). Consequently, during inertial loading, the occiput bone and the atlas vertebrae often function together. This increases the mechanical stresses between the atlas (C1) and the axis (C2). Once again, the atlas-axis joint (C1-C2) has increased vulnerability to inertial injury.
4) A main stabilizing ligament of the cranial-cervical region is called the alar ligament. The alar ligaments exist between the odontoid process of the axis (C2) and the lateral masses of the occiput bone.
The alar ligaments connect the odontoid process (dens) of the axis vertebrae (C2) to the occipital condyles of the occiput bone of the skull.
There is no doubt that a percentage of whiplash injured patients will develop chronic pain that does not improve or go away after all possible monetary compensation has been obtained. Representative examples include:
• A 1990 study reviewed the long-term status of whiplash-injured patients. They reviewed 43 patients who had sustained soft-tissue injuries of the neck after a mean 10.8 years. Of these, only 12% had recovered completely and 88% suffered from residual symptoms. Of these residual symptoms, 28% were intrusive and 12% were severe. After two years, symptoms did not alter with further passage of time, remaining chronic. This indicates that 40% of whiplash-injured patients continued to suffer from significant residual symptoms more than a decade after being injured.
(Gargan, Journal of Bone and Joint Surgery (British), 1990)
• A 1996 study reviewed the long-term status of whiplash-injured patients 15.5 years after injury. The authors documented that 70% of the patients continued to complain of symptoms referable to the original accident. In addition, 33% complained of intrusive symptoms and 10% were unable to work and relied heavily on analgesics or alternative therapy. This means that 43% had significant problems caused by whiplash injury more than 15 years after being injured. Surprisingly, these authors also documented that 60% of symptomatic patients had not seen a doctor in the previous five years because the doctors were unable to help them, and that 18% of these patients had taken early retirement due to their health problems, which they related to the whiplash injury. They also documented that whiplash symptoms do not improve after settlement of litigation.
• A 2002 study looked at the health status of whiplash-injured patients 17 years after injury. At the time, this was the longest follow-up study on whiplash-injured patients published. The authors documented that 55% of the patients still suffered from pain caused by the original trauma 17 years later.
(Bunketorp, European Spine Journal, 2002)
• A 2007 review article documents that between 15-40% of those who are injured in a motor vehicle collision will suffer from ongoing chronic pain.
(Schofferman, Journal of the American Academy of Orthopedic Surgeons, 2007)
• A 2005, 7.5-year prospective study on whiplash-injured patients found that 21% had intrusive symptoms that interfered with work and leisure, and required continued treatment and drugs. In addition, 2% of these whiplash-injured patients had severe pain and problems that required ongoing medical investigations and drugs. This means that 23% of whiplash-injured patients had significant problems more than 7 years after being injured.
(Tomlinson, Injury, 2005)
• A 2009 review article pertaining to whiplash injury and including 100 citations, thoroughly reviewed 15 studies pertaining to whiplash-injury outcomes. The authors document that fewer than 50% of all patients made a full recovery and that 4.5% are permanently disabled. In addition, they document that whiplash-injured patients are 5 times more likely to suffer from chronic neck pain than control populations. The view that a whiplash-injured patient’s symptoms will improve once litigation has finished “is unsupported by the literature.”
(Bannister, Journal of Bone and Joint Surgery, British, 2009)
• A very recent study (June 2010), published the assessment of whiplash-injured patients 30 years after injury, making this the longest follow-up of whiplash-injured patients to date. Once again, this study shows that a significant number of those injured in whiplash trauma will suffer with chronic symptoms. Thirty years after being injured, 40% of patients retain nuisance symptoms and 15% have significant symptoms and impairments, requiring ongoing treatment.
(Rooker, Journal of Bone and Joint Surgery, British, 2010)
Again, with there being no doubt to the chronicity of symptoms for some patients following whiplash trauma, numerous clinical investigations have been performed in the assessment of the tissue origin of these symptoms. These investigations have included the careful fluoroscopic insertions of anesthetic needles using gold-standard protocols and techniques. The majority of these studies have focused on the tissues of the lower cervical spine. Since 1993, it has been firmly established the primary tissue source for chronic whiplash injury symptoms are the facet joints of the lower cervical spine, with the annulus of the disc being a close second source.
(Bogduk, Pain, 1993)
However, recently, researchers have turned their attention to the tissues of the upper cervical spine as a source of chronic symptoms following whiplash trauma, especially if the symptom complex includes headaches. Specifically, these researchers have focused on the alar ligaments. As noted above, the alar ligaments are particularly vulnerable to inertial loading injury.
Historically, the most important whiplash injury physician was Ruth Jackson, MD. Ruth Jackson was born in 1902 and graduated from Baylor University College of Medicine in Dallas in 1928. In 1937, she became the first woman to be certified by the American Board of Orthopaedic Surgery. From 1936 to 1941, Dr. Jackson was Chief of Orthopedics at Parkland Hospital in Fairmont, Texas. In 1945, she had her own private clinic built in Dallas, retiring in 1989 at the age of 87.
In her career, Dr. Jackson published more than twenty-five articles, and she lectured extensively in the United States and throughout the world. Dr. Jackson had a special interest in injuries of the cervical spine. Her interest arose after a neck injury she sustained in a motor-vehicle accident. In 1956 she published her acclaimed, authoritative book entitled The Cervical Syndrome. The fourth and final edition of her book was published in 1978. Dr. Jackson personally treated more than 20,000 whiplash-injured patients.
(Jackson, The Cervical Syndrome, 1978)
In her 1978 book, Dr. Jackson discusses the mechanics of the alar ligament injury from whiplash trauma. She also discussed documentation of these injuries using stress radiographs of the upper cervical spine.
After Computed Tomography (CT) scanning became more available, the documentation of alar ligament injury from whiplash trauma became more precise and definitive than the stress radiography methods of Dr. Ruth Jackson. The CT scanning procedure recommended consists of using high-resolution images of the ligaments of the occiput-atlas-axis complex while the patient is in a position of maximum upper cervical spine and head rotation.
(Panjabi, Journal of Spinal Disorders, 1991)
(Panjabi, Journal of Orthopedic Research, 1991)
(Dvorak, Spine, 1987)
Recent advances in MR imaging have further enhanced the assessment of the health of the alar ligaments, and have eliminated the concerns of excessive exposure to ionizing radiation coupled with CT technology. These studies have specifically compared the status of alar ligament health in chronic whiplash patients and compared them to asymptomatic control populations. A pioneering such study appeared in the journal Neurology in 2002, and was titled:
MRI assessment of the alar ligaments in the late stage of whiplash injury:
A study of structural abnormalities and observer agreement
These authors were able to characterize and classify structural changes in the alar ligaments in the late stage of whiplash injuries by using proton density weighted MRI technology, and evaluate the reliability and the validity of their procedures. They studied 92 whiplash-injured and 30 uninjured individuals who underwent proton density-weighted MRI of the cranial-cervical junction in three orthogonal planes. They concluded:
“Whiplash trauma can cause permanent damage to the alar ligaments, which can be shown by high-resolution proton density-weighted MRI.”
The authors of this study made the following important points:
• Alar ligaments consist primarily of collagen proteins with a few elastic fibers. In contrast to elastic fibers, which can tolerate elongation up to 200% before failure, collagen ligaments will fail at only 8% elongation. Consequently, the alar ligaments are particularly vulnerable to traumatic stretching loads.
• The cranial-cervical ligaments are very vulnerable to sudden acceleration and/or deceleration of the head.
• Several studies have documented traumatic alar ligament ruptures or injuries from whiplash trauma mechanisms.
• Plain cervical radiographs are usually normal following whiplash injury.
• The strength of the MRI magnet is important. They suggest that the strength be at least 1.5 tesla.
• The thickness of the section slices is important. They suggest that the slices not be less than 2 mm thick from the foramen magnum to the base of the dens. A slice thickness of 2 mm gives excellent spatial resolution of injured alar ligaments.
• T2-weighted images give inadequate discrimination between ligament, bone and soft tissue due to a low signal-to-noise ratio.
• T1-weighted images give poor contrast resolution and thus less ability to differentiate small variations in signal and therefore to assess injury.
• “A proton-density weighted sequence is the technique of choice for assessment of [alar] ligamentous abnormalities.”
• This study confirms that the alar ligaments are vulnerable to whiplash trauma, “and that the severity of the lesions can be graded using high-resolution MRI.”
• Whiplash trauma can cause permanent damage to the alar ligaments, and this damage can be shown by high-resolution proton density-weighted MRI.
• Alar ligament damage can take up to 2 years for complete healing.