Whiplash

Populations and Risk Factors

• Individuals in motor vehicle accidents, particularly rear-end collisions — the most common mechanism; accounts for approximately 85% of whiplash injuries
• Contact sport athletes (football, hockey, rugby) and participants in collision or fall-prone activities
• Females at significantly higher risk (2–3 times) of developing chronic WAD — attributed to smaller cervical muscle mass, greater cervical lordosis, and hormonal differences in pain processing
• Risk factors for chronification (progression to chronic WAD): high initial pain intensity (VAS > 5.5/10), older age (> 40), pre-existing neck pain or headaches, initial widespread pain distribution, high initial disability score, catastrophizing and fear-avoidance beliefs, previous whiplash injury, early reliance on cervical collar
• Seated position at the time of impact — headrest position and seatbelt use modify injury severity but do not prevent it
• Rear-end collisions produce more severe injuries than lateral or frontal impacts because the cervical spine is loaded in its most vulnerable sagittal plane

Causes and Pathophysiology

Cervical Acceleration-Deceleration Mechanism

• Phase 1 — S-curve formation (0–50 ms): The torso is thrust forward by the seat, but the head remains momentarily stationary due to inertia. This creates an abnormal S-shaped curve in the cervical spine: the lower cervical segments (C5–C7) are forced into hyperextension while the upper segments (C0–C2) are simultaneously forced into relative flexion. This S-curve is the primary injury-producing mechanism — it subjects the lower cervical facet joints to compressive shearing forces that exceed their physiological tolerance.
• Phase 2 — Hyperextension (50–100 ms): The entire cervical spine moves into hyperextension as the head whips backward. The anterior longitudinal ligament, anterior disc annulus, and longus colli/longus capitis are stretched or torn. The facet joints are compressed posteriorly, and the capsular ligaments are strained. The vertebral arteries may be compressed or stretched during this phase.
• Phase 3 — Hyperflexion rebound (100–300 ms): The head whips forward as the body decelerates. The posterior ligamentous complex (interspinous, supraspinous, ligamentum flavum), posterior disc annulus, and posterior cervical muscles (semispinalis, splenius, upper trapezius) are stretched or torn. The seatbelt restrains the torso, concentrating flexion forces at the cervical spine.
• The entire sequence occurs within 200–300 milliseconds — faster than voluntary muscle contraction can produce a protective response. The cervical muscles activate after the injury-producing movement has already occurred, which is why "bracing for impact" has limited protective effect.

Tissue-Specific Injuries

• Facet joints (most common source of chronic pain): The lower cervical facet joints (C5/C6, C6/C7) sustain the greatest compressive and shearing forces during the S-curve phase. Facet capsular ligament sprains, intra-articular hemorrhage, and cartilage damage are common. Facet joint injury is identified as the pain generator in approximately 50–60% of chronic WAD cases and is the primary reason for chronification — facet joint nociceptors are richly innervated and capable of producing both local and referred pain.
• Disc injury: Annular tears (particularly posterior and posterolateral) occur during the hyperflexion phase. Disc injury may not produce immediate symptoms but can progress to disc herniation or accelerated degenerative disc disease over months to years. Disc-related radiculopathy (WAD III) changes the clinical picture significantly.
• Ligament injury: Anterior longitudinal ligament (hyperextension), posterior ligamentous complex (hyperflexion), alar ligaments and transverse ligament (upper cervical instability — WAD IV territory). Ligamentous laxity produces segmental instability that perpetuates muscle guarding as the muscles attempt to compensate for lost passive stability.
• Muscular injury: Sternocleidomastoid (SCM), scalenes, longus colli, longus capitis, and the deep cervical extensors (semispinalis cervicis, multifidus) sustain strain injuries. The SCM and scalenes develop acute protective guarding that transitions to chronic hypertonicity and trigger points. The deep cervical flexors (longus colli, longus capitis) become inhibited and atrophied — the loss of deep flexor endurance is a consistent finding in chronic WAD and contributes to ongoing instability.
• Neurovascular structures: Vertebral artery injury (compression, spasm, or intimal tear during hyperextension/rotation) — rare but catastrophic; cervical nerve root compression from facet edema, disc herniation, or foraminal narrowing; spinal cord involvement in severe cases (WAD IV).

Central Sensitization and Chronification

• In 40–60% of WAD II–III cases, symptoms persist beyond three months and evolve into chronic WAD. The transition from acute to chronic is driven by:
• Peripheral sensitization: Persistent nociceptive input from damaged facet joints, discs, and ligaments lowers the activation threshold of peripheral nociceptors. Normal movements begin to produce pain (allodynia at the cervical level).
• Central sensitization: Prolonged peripheral nociceptive bombardment of the dorsal horn produces neuroplastic changes — enhanced synaptic efficiency, reduced inhibitory modulation, and expansion of receptive fields. Clinically: widespread hyperalgesia (pain sensitivity extending beyond the cervical region to areas that were not injured), allodynia (pain from normally non-painful stimuli such as light touch), and temporal summation (pain intensity increasing with repeated stimuli at the same intensity).
• Deep cervical flexor inhibition: The longus colli and longus capitis become inhibited and atrophied, shifting cervical stabilization to the superficial muscles (SCM, scalenes, upper trapezius). This superficial dominance produces abnormal movement patterns, ongoing muscle fatigue, and sustained nociceptive input — perpetuating the sensitization cycle.
• Psychosocial factors: Catastrophizing, fear-avoidance beliefs, anxiety, depression, and litigation stress are independent predictors of chronification. These factors amplify central sensitization through descending facilitation pathways.
• The clinical implication is direct: chronic WAD requires a treatment approach that addresses central sensitization (graded exposure, pain neuroscience education, generalized relaxation) alongside the peripheral tissue damage. Aggressive cervical mobilization in the presence of central sensitization can worsen symptoms.

WAD Classification (Quebec Task Force)

Secondary Injuries

• Concussion: The same acceleration-deceleration mechanism that injures the cervical spine also produces linear and rotational brain acceleration — concussion co-occurs with whiplash in an estimated 10–30% of MVA cases, often undiagnosed. Screen for cognitive symptoms, dizziness, balance disturbance, and headache pattern changes.
• TMJ dysfunction: The mandible's inertia during the whiplash mechanism produces sudden jaw opening and disc displacement — TMD co-occurs in approximately 30% of whiplash injuries.
• Esophageal/laryngeal injury: Rare but possible from hyperextension stretch of the anterior neck structures.

Signs and Symptoms

By WAD Grade

General Symptom Presentation

• Neck pain and stiffness: Often delayed in onset (hours to days) from delayed inflammatory response and progressive edema around damaged structures; multidirectional ROM restriction from protective muscle splinting
• Headache: Present in approximately 80% of cases; cervicogenic pattern (occipital origin radiating frontally) or tension-type (bilateral band-like pressure)
• Dizziness: Cervicogenic dizziness from proprioceptive disruption in the damaged cervical facet capsules and deep cervical muscles
• Paresthesia: Numbness or tingling into the shoulders, arms, or hands (WAD III — radicular compression)
• Psychosocial symptoms: Fatigue, anxiety, depression, irritability, difficulty concentrating, memory problems, sleep disturbance — these are not secondary to the injury; they are part of the WAD syndrome and are independent predictors of chronification
• Delayed symptom escalation: Symptoms often worsen over the first 24–72 hours as edema and inflammatory mediators accumulate around damaged structures

Assessment Profile

Subjective Presentation

• Chief complaint: "I was hit from behind and now my neck is stiff and painful"; "my neck pain started the morning after the accident"; "I can't turn my head"; often accompanied by headache and upper trapezius/shoulder pain
• Pain quality: Deep, aching, diffuse neck pain (facet/muscular); sharp with movement (ligamentous/muscular strain); radiating arm pain with numbness/tingling in WAD III (radicular); headache — occipital to frontal (cervicogenic) or bilateral band-like (tension)
• Onset: History of acceleration-deceleration mechanism (MVA, collision, fall); symptoms may be immediate (severe) or delayed by hours to days (more common in WAD I–II); symptom intensity often peaks at 24–72 hours post-injury
• Aggravating factors: Cervical rotation and extension (loaded facet compression), sustained postures (desk work, driving), overhead reaching, carrying loads, stress and fatigue (central sensitization amplification)
• Easing factors: Rest (acute phase), warm applications (chronic phase), gentle supported movement, NSAIDs (temporary), soft cervical collar in acute phase (short-term only — prolonged use promotes deconditioning)
• Red flags: Bilateral arm numbness or weakness, severe unremitting headache unresponsive to position change, visual disturbances, dysarthria, dysphagia, drop attacks → suspect vertebral artery injury or upper cervical instability; emergency referral; do not treat

Observation

• Local inspection: Cervical muscle guarding visible (prominent SCM and upper trapezius contraction); cervical collar if recently prescribed; no visible swelling or bruising typically (deep tissue injury), though anterior neck bruising may be present from seatbelt in frontal collisions
• Posture: Loss of normal cervical lordosis (flattened or reversed curve from protective guarding); forward head posture (chin protraction from deep flexor inhibition and superficial flexor dominance); upper crossed syndrome pattern (elevated, protracted shoulders); guarded lateral head tilt toward the less symptomatic side; "military posture" (rigid, splinted cervical spine)
• Gait: Generally normal; may show guarded, stiff-necked movement pattern — the patient turns the entire trunk rather than rotating the cervical spine

Palpation

• Tone: Marked bilateral hypertonicity in SCM, upper trapezius, levator scapulae, and cervical paraspinals (splenius capitis, splenius cervicis, semispinalis) — typically bilateral but may be more pronounced on one side; scalene hypertonicity and trigger points (may produce thoracic outlet symptoms); suboccipital muscle guarding (rectus capitis posterior major/minor, obliquus capitis superior/inferior) contributing to cervicogenic headache; deep cervical flexors (longus colli, longus capitis) may feel inhibited and atrophic on anterior palpation rather than hypertonic — this deep flexor inhibition is a hallmark of chronic WAD
• Tenderness: Segmental tenderness at the facet joints (C5/C6, C6/C7 most commonly — correlates with the S-curve mechanism producing maximal shear at the lower cervical spine); SCM tenderness with trigger points referring into the face, ear, and temporal region; upper trapezius trigger points referring into the temporal and occipital region; suboccipital tenderness (cervicogenic headache generator); spinous process tenderness (interspinous ligament sprain); anterior neck tenderness if longus colli is strained; TMJ tenderness if concurrent jaw injury
• Temperature: Mild warmth over the cervical paraspinals may be present in the acute phase (first 72 hours) from inflammatory response; usually normalizes within the first week
• Tissue quality: Acute: taut, guarded, boardlike paraspinal tone (protective splinting); chronic: fibrotic, ropy texture in upper trapezius and levator scapulae; active trigger points throughout the cervical musculature; fascial restrictions in the cervicothoracic junction; the cervical paraspinals may develop ropy, nodular changes with palpable trigger points that reproduce the patient's headache or referred pain pattern

Motion Assessment

• AROM: Significant multidirectional restriction — all planes are typically affected but rotation and extension are usually most limited (facet joint loading in these directions provokes maximal pain). The pattern of restriction is non-capsular (all directions restricted, not in a predictable capsular ratio) — this distinguishes WAD from cervical OA (which follows a capsular pattern). ROM improves with warm-up in the chronic phase but remains guarded in the acute phase. Document baseline measurements for progress tracking.
• PROM / end-feel: Guarded, protective end-feel in all directions (acute phase) — the muscles resist passive motion before the anatomical end-range is reached. This protective end-feel is distinct from the bony end-feel of cervical spondylosis and the capsular end-feel of OA. In chronic WAD, end-feel may transition to muscular (tissue stretch) with greater range than the acute phase but still short of normal. PROM typically exceeds AROM (muscle guarding limits active motion more than passive).
• Resisted testing: Pain with resisted cervical flexion (SCM, longus colli strain), extension (cervical extensors), and rotation (SCM, scalenes, splenius). In WAD III, myotomal weakness is present: C5 (deltoid/biceps), C6 (wrist extensors), C7 (triceps), C8 (grip) — the weakness follows a nerve root pattern, not a generalized pattern. Resisted testing in WAD II should show pain but no weakness; weakness = WAD III.

Special Test Cluster

Safety-first cluster: VBI screen, Sharp-Purser, and alar ligament tests must be performed before any cervical treatment in post-whiplash patients. These are non-negotiable safety screens. If any is positive, do not proceed with cervical treatment.

Differential Assessment