Whiplash-associated disorders

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Whiplash-associated disorders

Previous accounts used different terms – whiplash injury, hyperextension injury, acceleration injury, soft tissue neck injury, cervical strain, cervical sprain – to describe the lesion that may occur after and the consequences of a typical car accident: a rear-end motor vehicle collision.

When a vehicle is struck from the rear, the occupants rarely have any warning and do not brace the muscles to prevent head movement. As a result, the body is propelled forwards and the neck hyperextends backwards well beyond the normal range of allowable movement (Fig. 10.1). This violent motion is followed by a less rapid forwards recoil into flexion that can often result in a head injury if the head impinges on the windscreen.

Fig 10.1 Whiplash injury: (a) hyperextension on impact, followed by (b) recoil into flexion.

Although rear-end impacts are most common and result in hyperextension–hyperflexion injuries, other types of car accident may also cause whiplash-type injuries and, in any trauma, complex head and neck movements may occur, leading to different lesions that resemble whiplash.

Definition

Medical literature, in an attempt to find a proper definition, has so far described ‘whiplash injury’ in terms of the mechanism of the accident, the type of lesion that is caused or the clinical appearance after the injury. In 1995 ¹ the Quebec Task Force (QTF) proposed the following definition:

Whiplash is an acceleration–deceleration mechanism of energy transfer to the neck. It may result from rear-end or side-impact motor vehicle collisions but can also occur during diving or other mishaps. The impact may result in bony or soft tissue injuries (whiplash injury), which in turn may lead to a variety of clinical manifestations (whiplash-associated disorders).

The term ‘whiplash-associated disorders’ (WAD) indicates the clinical features that result from an accident in which two elements – acceleration, followed by deceleration – are responsible for the traumatic forces that act on the cervical spine and related structures.

Incidence

As the result of increases in availability and use of cars worldwide, motor vehicle accidents have become very frequent with, as a result, an enormous increase in whiplash-type trauma. It is one of the most common mechanisms of injury to the cervical spine.

The incidence is not precisely known. A figure of 1 per 1000 people per year has been suggested.²

The QTF mentions figures on whiplash injuries in Canada. In 1987 in the province of Quebec there were approximately 131 whiplash injuries per 100 000 vehicles per year – 70 injuries per 100 000 inhabitants. This cost the Canadian government CAN $19 000 000, of which 70% was income compensation. The female : male ratio is about 1.5 : 1 and the main age group 20–24 years.

Other studies in Canada mention 5000 whiplash cases a year in the province of Quebec, accounting for 20% of all insurance claims after motor vehicle accidents.3,4

In the United States 11 300 000 car accidents were reported for the year 1991, of which 2 690 000 were rear-end collisions and caused 85% of all whiplash injuries.⁵

Classification

The QTF, persuaded that proper diagnosis is difficult to achieve, has proposed two classifications: one according to the severity of the symptoms and signs (grades) (Box 10.1) and one according to the time elapsed since the accident (stages) (Box 10.2).

Box 10.1 Clinical (Quebec) classification of whiplash-associated disorders

Box 10.2 Classification according to the time elapsed since the accident

Neither classification suggests what lesion is present nor stipulates the type of tissue damage. They reflect only the clinical appearances that occur after acceleration–deceleration injury.

Pathology

Depending on the movement of the head during the accident, several lesions may occur, ranking from severe to moderate to slight. Hyperextension is the most common mechanism, followed by hyperflexion and lateral flexion.⁶

Severe lesions

Hyperextension and distraction of the neck may rupture the anterior longitudinal ligament as well as some discs. A ruptured disc can lead to backward displacement of the vertebra lying above it – the upper facets then slide downwards on the lower – with damage to the spinal cord as a result.⁷ Spinal cord injuries after motor vehicle accidents occur most often in young car users in the 15–24 year age group.^8,9

Pure hyperextension may also cause compression of the spinal cord in those cases in which retrolisthesis or spinal stenosis already existed. In other instances, compression fractures of the posterior elements may occur.

Hyperflexion injury may lead to fractures of the vertebral body – most fractures of the atlas ¹⁰ and of the axis¹¹ are the result of motor vehicle accidents – and/or to disruption of posterior ligaments and occasionally facet joint luxation.

Less frequently, lesions of arteries, veins, neural structures, oesophagus and retropharyngeal tissues may occur.

Other lesions

Less severe lesions are much more frequent and may involve the intervertebral discs, the zygapophyseal joints, and the cervical ligaments and muscles. These lesions may occur in isolation but are more often combined and therefore are sometimes difficult to recognize. The common complaint is neck pain.

Discodural and discoradicular interactions

Recent retrospective studies have shown that the occurrence of disc lesions after whiplash injury is quite high 12,13 and one prospective study indicates the value of clinical diagnosis.¹⁴ Most disc lesions are endplate avulsions and ruptures of the anterior annulus fibrosus.

As the result of the hyperextension element during the trauma the disc may have fissured. The subsequent flexion or hyperflexion element causes displacement of disc material in a posterior direction. Davis et al describe a number of posterolateral disc lesions with radicular symptoms as the result of a hyperextension whiplash trauma.¹² These herniations seemed to develop only after the acute phase and it took a few weeks for the radicular symptoms to appear. In postmortem studies Taylor et al describe the intervertebral disc as the most frequently damaged structure.^15–17 Jónsson et al¹⁸ Also confirmed the large number of disc lesions after whiplash, and during surgery were able to confirm the findings from magnetic resonance imaging (MRI).

Posterocentral protrusions lead to central, bilateral or unilateral pain in a multisegmental distribution: pain in the neck, trapezius and upper scapular area. On examination a symmetrical (mimicking a full articular pattern) or asymmetrical pattern of limitation is found. In acute cases the picture may be torticollis-like. For a detailed description of disc pathology, see page 145.

Facet joint problems

Whiplash may also lead to problems at the level of the zygapophyseal joint capsules.¹⁹ Lord et al undertook a placebo-controlled prevalence study after whiplash and found that chronic cervical facet joint pain was common.²⁰

Pain is felt unilaterally and is usually quite localized. A convergent or divergent motion pattern may occur, although any asymmetrical pattern is compatible. (Facet joint pathology is discussed on p. 163).

Ligaments can become overstretched, leading to minor lesions,¹² or may become adherent as the result of post-traumatic immobilization. They present with vague stretching pain felt at the end of range of those movements that stretch the ligament (see p. 168).

Muscular lesions

Muscular lesions, mostly anteriorly, are described in clinical studies,21,22 on echography,²³ in experiments in animals^24,25 and in postmortem studies.²⁶ Muscles, particularly their occipital insertions, can be strained during injury. The subsequent pain will be quite localized and can be elicited during either contraction or stretching – the contractile tissue pattern (see p. 169).