neurosurg

Whiplash injury

The term Whiplash injury is probably one of the most misused terms of all the medical terminology. It is incorrectly used by the layman, some health professionals and the majority of lawyers. This is because whiplash is a specific term that refers to a specific mechanism of injury and has characteristic pathological consequences.

The Mechanism

To fit the definition, a whiplash injury must be an injury where there is a rear shunt motor vehicle accident which pushes the recipient forwards. The head lags behind slightly and the neck therefore may sustain an extension injury. The head is then thrown forwards and a flexion injury occurs. As the body falls back there is a further insult to the neck as the head is flung back again. A better term would be acceleration / deceleration injury as it describes what happens better. Most of the subsequent symptoms occur because of injury to the small joints of the spine (1), (9).

This is a different injury from that sustained by the driver of the vehicle behind, who is predominantly thrown forwards and the extension component to the neck (where the head is thrown back) is minimal by comparison. Flexion injuries particularly if combined with a degree of rotation are far more likely to result in intervertebral disc lesions than a simple whiplash injury. In such injury there is always a degree of twisting strain as the loading on the neck is never perfectly symmetrical in a forwards / backwards direction at the time of impact. There are therefore twisting elements to the injury which act upon the ligaments in the neck to increase the likelihood of disc prolapse.

Clinical Features

The typical clinical picture in whiplash injury is that following the injury there is no obvious immediate pain. In severe cases there may be initial stiffness of the neck. Initially function is not impaired either. The patient may proceed from the accident to continue with daily activities but begins to notice stiffness in the neck. The following night is often uncomfortable and the majority develop significant pain and stiffness by the subsequent morning. This clinical picture varies considerably from patient to patient according to the severity of the original accident and whether the patient has a vulnerable neck by reason of pre-existing degenerative changes which may give rise to symptoms after injury.

The severity of the injury is determined by many things (8). The posture at the time of the accident may be such that there is twisting of the neck if the patient is looking to the side. Whether a seat-belt is worn, whether there is a headrest, the springiness of the seat back, the angle of the seat back, the height of the patient, the force of impact and the muscle tension (13) at the moment of impact may all be implicated in the evolution of the subsequent clinical picture. It follows therefore that the speed of the impact or the damage to the vehicle is not a good guide to the severity of the injury in this type of clinical picture however there is research suggesting minimum speeds at which injuries can occur (3). Whiplash injuries therefore are more complex than one might think at first glance, and it is unwise to group all the patients together, hence many of the studies published on whiplash injury vary considerably in their findings in relation to outcome.

Delay before Symptoms

Whiplash injury most commonly results in stretching of ligaments (which hold the joints together) and muscles. The affected tissues may be torn in a severe injury but most commonly the injury is mild or moderate and serious mechanical damage to the neck is uncommon. This stretching of the tissues leads to bleeding and an acute soft tissue inflammatory reaction. The inflammatory response takes time to appear as it is akin to the tissues’ reaction to infection. When developing an infection (e.g. a common cold) the symptoms tend to evolve rather than happen instantaneously because it takes time for the inflammatory response to occur.

Soft tissue trauma therefore, takes time to produce symptoms. A typical case with a mild to moderate degree of trauma may take up to a few days to appear and initially may be masked by painkilling medication taken to treat other injuries. It is therefore not uncommon for the patient to start to complain of stiffness and discomfort in the neck up to a week later. The delay in the appearance of the symptoms often leads the unwary to suppose that there is no connection between the injury and the development of the symptoms.

As with any soft tissue injury there are acute symptoms giving rise to initial acute pain and stiffness in the neck and this phase may last up to a few months following the trauma. There is then a secondary phase when the symptoms are intermittent and mild. The secondary phase may last up to two years, (although some studies suggest that improvement in symptoms may continue for longer (7)), with exacerbations caused by specific activities which can last for days at a time. Soft tissue injuries of this type however are not likely to give rise to symptoms after two years (at the outside) and the vast majority of whiplash injuries do not give symptoms for more than a few weeks.

Associated injuries

Anterior Neck Symptoms: Although the most common effect of a whiplash injury is to cause injury to the neck, there may be other associated injuries. As the head is thrown back the muscles at the front of the throat and neck are stretched. It is therefore common for the patient to complain of pain at the front of the neck. This is particularly likely if at the moment of impact the patient clenches the jaw. Much of the force of the extension injury will be absorbed by the muscles at the front leading to tearing of muscle fibres and short term pain. I personally have never seen a case in which there were severe symptom at the back of the neck as well as the front, because of the bracing effect of the two opposing muscle groups upon each other.

Significant tearing of muscles at the front of the spine behind the gullet (oesophagus) may also lead to soft tissue swelling and mild difficulty swallowing. This is unusual however without a fracture or dislocation of the bones in the neck.

Head Injury Symptoms: In Neurosurgical circles it is well known from experimental pathology studies involving sudden acceleration of the head, that severe injury to the brain can occur even without an impact. The rationale behind this is that as the head is thrown forwards, the brain shifts inside the skull, and if this is very sudden it can result in shearing of long white matter nerve cell tracts inside the brain. This leads to significant damage in specific areas. The experimental studies required very forceful flexion rotation / acceleration and sudden deceleration of a severity that is not mirrored by the common whiplash injury, however it is well known and described that symptoms akin to post-concussional syndrome may occur linked with whiplash injury even when there is no actual impact of the head.

Jaw pain (temporo-mandibular dysfunction): As the muscles at the front of the neck contract they can pull on the lower jaw. The joints between the jaw bone (mandible) and the lower side of he skull can therefore be pulled upon forcibly. This can lead to local pain in the jaw joint, which can lead to uneven movement of the jaw when opening the mouth or chewing. The patient may get into the habit of opening the mouth in an uneven fashion and this leads to a variety of symptoms including pain on eating and clicking of the jaw when opening the mouth.

Outcome

The vast majority of patients experience a few weeks of significant discomfort in the neck which may be accompanied by tingling in the fingers and radiation of the pain to the back of the head. There is then a phase when the symptoms become intermittent. If there is background degenerative disease in the neck however, there may be associated symptoms with significant radiation to the upper limb due to nerve root irritation, neurological symptoms in the arms such as numbness and weakness, and significant headache (radiating upwards from the neck to the back of the head and sometimes over the vertex of the head to behind the eyes). These patients do not do well, and in a small percentage there may be chronic pain that never settles. The number of patients with symptomatic complaints varies considerably in different studies, ranging from 35% (11)to 70% at 15 years from injury (2) and 58% at 5 years in another study.

The whole clinical picture may be altered by psychological effects of the injury. The sudden and unexpected nature of the injury may produce a degree of mental shock or post-traumatic stress and there may be anxiety and depression associated. It has been shown in a research study that certain groups of people have a higher resistance to the psychological effects than others (12). It is of interest that this study showed doctors to be more resistant to long term symptoms than non-doctors, suggesting that if the subject is not as worried about the ill effects of the symptoms then they have less effect.

There is usually an indication of a psychological effect from the expert’s examination however, as such patients often exhibit signs of functional overlay. This may take the form of pain with vertical pressure on the head or non-anatomical patterns of numbness or observing the patient moving the head normally in conversation but having very restricted movement on examination. There is no particular reason to expect these signs to indicate purposeful simulation which in my experience is rare.

The vast majority of patients experience a few weeks to months of acute pain that becomes intermittent then fades gradually into insignificance unless there are associated features on clinical evaluation to suggest either more severe injury or degenerative disease symptomatology.

Chronic Whiplash symptoms

A small proportion of patients continue with significant neck symptoms and whiplash associated disorders on a permanent basis. This has been the subject of much study but the causal evidence is conflicting. On the one hand there are studies that suggest that psychological factors play a large part in the continuation of symptoms (6). On the other hand there are studies to suggest that prolongation of the litigation is related to the chronicity of the clinical picture. It is therefore difficult to know how to assess such studies particularly as the definition of the type of injury is variable and the exact mechanism of injury varies somewhat from case to case, It may be better to assess each individual case for additional factors such as the occurrence of degenerative disease which will influence the time scale of symptoms. It seems likely that the this is the main separating factor between those who have a short tome course and those with permanent symptoms.

The early manage management may also influence the outcome, as the use of collars to immobilize the neck early on after injury will produce stiffness in the joints and may have a negative effect upon the eventual outcome. Early mobilization and gentle exercise and massage are probably the best treatments rather than keeping the neck still.

There is evidence to suggest that up to 7% of patients suffering whiplash injuries do not return to their previous employment (5), although one must consider that is is especially likely in heavy manual workers.

Another factor that may influence the severity of the effects of whiplash injury is the time it takes for the court case to be settled. Those in whom the case is settled quickly have less pain for a shorter duration. This suggests that anxiety or other psychological factors, common in litigation, may have a negative effect upon the severity of the symptoms (4).


References:

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(2) Borchgrevink GE. Lereim I. Royneland L. Bjorndal A. Haraldseth O. National health insurance consumption and chronic symptoms following mild neck sprain injuries in car collisions. Scandinavian Journal of Social Medicine. Vol 24(4) (pp 264-271), 1996.

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(4) Cote P. Hogg-Johnson S. Cassidy JD. Carroll L. Frank JW. The association between neck pain intensity, physical functioning, depressive symptomatology and time-to-claim-closure after whiplash. Journal of Clinical Epidemiology. 54(3):275-86, 2001 Mar.

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(6) Obelieniene D. Schrader H. Bovim G. Miseviciene I. Sand T. Pain after whiplash: a prospective controlled inception cohort study. Journal of Neurology, Neurosurgery & Psychiatry. 66(3):279-83, 1999 Mar.

(7) Olivegren H. Jerkvall N. Hagstrom Y. Carlsson J. The long-term prognosis of whiplash-associated disorders (WAD). European Spine Journal. 8(5):366-70, 1999.

(8) Ono K. Kanno M. Influences of the physical parameters on the risk to neck injuries in low impact speed rear-end collisions. Accident Analysis & Prevention. 28(4):493-9, 1996 Jul.

(9) Siegmund GP. Myers BS. Davis MB. Bohnet HF. Winkelstein BA.
Mechanical evidence of cervical facet capsule injury during whiplash: a cadaveric study using combined shear, compression, and extension loading. Spine. 26(19):2095-101, 2001 Oct 1.

(10) Squires B. Gargan MF. Bannister GC. Soft-tissue injuries of the cervical spine. 15-year follow-up. Journal of Bone & Joint Surgery – British Volume. Vol 78(6) (pp 955-957), 1996.

(11) Soderlund A. Lindberg P Long-term functional and psychological problems in whiplash associated disorders. International Journal of Rehabilitation Research. Vol 22(2) (pp 77-84), 1999

(1) Virani SN. Ferrari R. Russell AS.Physician resistance to the late whiplash syndrome.Journal of Rheumatology. 28(9):2096-9, 2001 Sep.

(12) Winkelstein BA. Nightingale RW. Richardson WJ. Myers BS.The cervical facet capsule and its role in whiplash injury: a biomechanical investigation. Spine. 25(10):1238-46, 2000 May 15.