Whiplash Injury

Definition

Whiplash is an acceleration-deceleration mechanism of energy transfer to the neck, most commonly seen after rear-end or side-impact motor vehicle collisions, but also occurring in falls, sports (diving, rugby) and assaults. The resulting bony or soft-tissue injury and its clinical manifestations are together termed Whiplash-Associated Disorder (WAD) (Quebec Task Force, 1995). The term implies amplification of relatively small applied forces into much larger forces transmitted to the cervical spine (Scott-Brown's Otorhinolaryngology, p. 3771).

Mechanism / Biomechanics

Classically taught as pure cervical hyperextension followed by hyperflexion, but biomechanical and cineradiographic studies show this is oversimplified.
On rear-end impact the torso is thrust forward first, driving the lower cervical spine upward and forward while the head lags behind (inertia) - producing axial compression with an abnormal "S-shaped" curvature: lower segments go into extension while upper segments are still flexed (within the first 50-100 msec).
This occurs around pathological (abnormally high) axes of rotation, so the anterior vertebral margins separate and the tip of the inferior articular process impinges on the superior articular process below - explaining the vulnerability of the cervical facet (zygapophyseal) joints.
Only after this phase does the whole cervical spine undergo the classical extension, followed by rebound flexion (Rheumatology, 2-Vol Set, p. 1594-1621).

Structures Injured

Zygapophyseal (facet) joint capsules and cartilage - most consistently implicated source of chronic pain
Anterior/posterior longitudinal ligaments, intervertebral disc annulus
Cervical paraspinal and strap muscles (sprain/strain)
Dorsal root ganglia (stretch injury) - proposed cause of persistent neuropathic-type symptoms
Rarely: fracture-dislocation at C2-C3/C3-C4 level, vertebral artery injury, disc prolapse (Textbook of Forensic Medicine and Toxicology, p. 899).
Pathological material is limited because whiplash is largely a soft-tissue injury without gross radiological findings in most grades.

Classification - Quebec Task Force Grading of WAD

Grade	Features
0	No neck complaint, no physical signs
I	Neck pain, stiffness, tenderness only; no physical signs
II	Neck complaint + musculoskeletal signs (decreased range of motion, point tenderness)
III	Neck complaint + neurological signs (decreased/absent deep tendon reflexes, weakness, sensory deficit)
IV	Neck complaint + fracture or dislocation

Grades III and IV are increasingly considered true traumatic cervical spine/cord injury rather than "simple" whiplash.

Clinical Features

Neck pain and stiffness, often delayed onset (hours to 1-2 days after injury)
Headache (occipital/suboccipital), shoulder and interscapular pain
Dizziness/vertigo, tinnitus (uncommon and not persistent in Grade I-II), visual disturbance
Paraesthesia of upper limbs, temporomandibular joint pain
Cognitive complaints (memory, concentration) and psychological distress (anxiety, fear of movement) in a subset
Late whiplash syndrome (persistent complaints beyond 3-6 months) develops in roughly 15-20% of cases in large cohort studies.

Investigations

Plain radiographs (AP, lateral, open-mouth odontoid) to exclude fracture/dislocation, especially in Grade III-IV or when red flags (midline tenderness, neurological deficit, high-energy mechanism) are present
CT for suspected bony injury; MRI if neurological signs, suspected disc/ligamentous injury, or symptoms fail to resolve
Flexion-extension views only after acute phase and if instability suspected
Most Grade I-II cases have normal imaging - whiplash remains largely a diagnosis of exclusion.

Management

Acute phase (first 2 weeks):

Early mobilization and reassurance are superior to prolonged rest, soft collar immobilization, and passive modalities alone
Analgesics/NSAIDs, active range-of-motion exercises, early return to normal activity
Avoid prolonged cervical collar use (promotes deconditioning and chronicity)

Subacute phase (2-12 weeks):

Structured exercise/physiotherapy program, mobilization techniques

Chronic phase (> 12 weeks, "late whiplash syndrome"):

Exercise therapy remains the best-evidence option
Percutaneous radiofrequency neurotomy of cervical facet joints is the most promising interventional/palliative option for confirmed facet-mediated pain
Psychological factors (passive coping, depression, fear-avoidance) should be addressed as they predict poor recovery
Multidisciplinary pain management for refractory cases

Prognosis

Most patients improve within the first 3 months; systematic reviews show little further improvement beyond this point if symptoms persist. Predictors of poor outcome include high initial pain/disability, psychological distress, and passive coping style rather than severity of the collision itself.

Medicolegal Importance

Whiplash injury is a common subject of motor vehicle accident litigation and insurance claims; documentation of mechanism, grade (Quebec classification), and objective findings is important for medicolegal reporting (Textbook of Forensic Medicine and Toxicology, p. 899).

Recent evidence check: A quick literature check found ongoing systematic reviews on exercise-based rehabilitation and psychologically-informed physiotherapy for WAD, generally consistent with the management principles above (early activation, exercise therapy, addressing psychosocial factors) - no findings that contradict this note's core teaching points.

Key exam points to remember: definition (Quebec/WAD), biomechanics (S-shaped curve, not pure hyperextension), grading I-IV, facet joint as chief pathological structure, early mobilization over collar/rest, and psychological factors as prognostic determinants.

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