43.2 Acute Cervical Strain, Whiplash & Axial Neck Pain

Cervical Spine Anatomy, Biomechanics & Nerve Root Exits

The cervical spine comprises seven vertebrae (C1-C7) divided into two distinct functional units:

1. Upper Cervical Spine (Craniocervical Junction):
   • C1 (Atlas): Ring-shaped vertebra without a vertebral body or spinous process; articulates with the occipital condyles at the atlanto-occipital joints, providing 50% of total cervical flexion and extension (the "nodding" motion).
   • C2 (Axis): Features the odontoid process (dens), which projects superiorly to articulate with the anterior arch of C1. The atlantoaxial joint provides 50% of total cervical rotational mobility (approximately 45° of rotation to each side). The transverse atlantal ligament secures the dens against the anterior arch of C1; laxity or rupture (seen in rheumatoid arthritis or Down syndrome) risks catastrophic atlantoaxial subluxation.
2. Subaxial Cervical Spine (C3-C7):
   • Characterized by intervertebral discs, paired zygapophysial (facet) joints, and unique uncovertebral joints (joints of Luschka). Located at the posterolateral margins of the C3-C7 vertebral bodies, uncovertebral joints undergo degenerative hypertrophic osteophytosis in older adults, projecting directly into the neural foramen to cause neuroforaminal stenosis and cervical radiculopathy.

The Cervical Nerve Root Exit Rule: High-Yield Neuroanatomy

Unlike the thoracic and lumbar spine, cervical nerve roots exit ABOVE their correspondingly numbered vertebral body:

• The C1 nerve root exits above the C1 vertebra (between the occiput and C1 atlas).
• The C6 nerve root exits above the C6 vertebra through the C5-C6 intervertebral foramen.
• The C7 nerve root exits above the C7 vertebra through the C6-C7 intervertebral foramen.
• The C8 nerve root exits below the C7 vertebra and above the T1 vertebra through the C7-T1 intervertebral foramen (there are 8 cervical nerve roots but only 7 cervical vertebrae).
• From T1 downward, each spinal nerve exits below its corresponding vertebral body.

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Whiplash-Associated Disorders (WAD) & Cervical Strain

Whiplash describes an acute acceleration-deceleration transfer of energy to the cervical spine, most frequently occurring during rear-end or collision-type motor vehicle accidents.

Pathomechanics of the Acceleration-Deceleration Injury

In a classic rear-end collision, the patient's torso is accelerated forward by the seatback while the unsupported head lags behind due to inertia. This creates a rapid, non-physiologic S-shaped curve in the cervical spine during the initial 100 milliseconds, with hyperextension of the lower cervical segments and flexion of the upper segments. As the head rebounds forward, violent hyperflexion ensues. This bi-phasic excursion causes strain and microtearing of the anterior longitudinal ligament, sternocleidomastoid, scalenes, and trapezius muscles, as well as compressive sprain and hemarthrosis of the posterior facet joint capsules.

Quebec Task Force Classification of WAD

The Quebec Task Force provides the internationally recognized staging system for whiplash-associated disorders:

                  QUEBEC TASK FORCE CLASSIFICATION OF WAD

   Grade    Clinical Features                                  Recommended Management
   ═════════════════════════════════════════════════════════════════════════════════════════
   Grade 0  No neck complaints; no physical signs              Reassurance; full activity

   Grade I  Neck pain, stiffness, or tenderness ONLY;          Reassurance; early active motion;
            No physical/musculoskeletal signs; full ROM        Oral NSAIDs / Acetaminophen

   Grade II Neck symptoms + MUSCULOSKELETAL signs:             Early mobilization; active PT;
            Point tenderness; restricted cervical ROM          Avoid rigid collars; oral NSAIDs

   Grade III Neck symptoms + NEUROLOGICAL signs:               Urgent cervical spine MRI;
            Focal weakness; sensory deficits; diminished DTRs  Neurology / Spine consultation

   Grade IV Neck symptoms + FRACTURE or DISLOCATION:           IMMEDIATE rigid immobilization;
            Bony disruption or spinal malalignment             Emergency CT; Spine surgery
   ═════════════════════════════════════════════════════════════════════════════════════════

Evidence-Based Management of WAD Grades I and II

• Early Mobilization vs. Rigid Immobilization: Rigid cervical collars (e.g., Philadelphia collar) or prolonged soft collar wear are actively harmful and prolong disability. Multiple randomized controlled trials prove that early active mobilization, home range of motion exercises, and rapid resumption of ordinary activities achieve faster symptom resolution and reduce chronic pain development.
• Pharmacotherapy: Scheduled oral NSAIDs (naproxen or ibuprofen) or acetaminophen for 1 to 2 weeks. A short course of a non-sedating or mildly sedating muscle relaxant (e.g., cyclobenzaprine 5 mg at bedtime) may be prescribed for severe sleep-disrupting muscle spasms during the first 3 to 7 days.
• Physical Therapy: Indicated if symptoms fail to resolve after 2 to 3 weeks; multimodal physical therapy emphasizing gentle isometric strengthening, postural retraining, and thoracic spine mobility exercises.

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Cervical Spine Clearance in Trauma: Canadian C-Spine Rule vs. NEXUS

Clearing the cervical spine after blunt trauma without obtaining unnecessary radiographs or CT scans is a vital skill. Two highly validated decision rules exist: the Canadian C-Spine Rule (CCR) and the NEXUS Criteria (National Emergency X-Radiography Utilization Study). Both achieve near 100% sensitivity for detecting clinically significant cervical spine injuries; however, the Canadian C-Spine Rule demonstrates higher specificity, resulting in lower imaging rates.

The Canadian C-Spine Rule (CCR)

Applicable to alert (Glasgow Coma Scale score = 15), hemodynamically stable trauma patients with neck pain or injury. Follows a three-step sequential algorithm:

                   CANADIAN C-SPINE RULE (CCR) ALGORITHM

    [Alert, Stable Trauma Patient with Neck Pain or Potential Cervical Injury]
                                 │
                                 ▼
   STEP 1: ANY HIGH-RISK FACTOR PRESENT?
   • Age >= 65 years
   • Dangerous Mechanism:
     - Fall from elevation >= 3 feet or 5 stairs
     - Axial load to head (e.g., diving into water)
     - High-speed MVC (>100 km/h or 60 mph), rollover, or ejection
     - Motorized recreational vehicle collision (ATV, snowmobile)
     - Bicycle collision with stationary object or motor vehicle
   • Paresthesias in upper or lower extremities
                                 │
                 ┌───────────────┴───────────────┐
                 ▼                               ▼
               [YES]                            [NO]
                 │                               │
                 ▼                               ▼
   [CERVICAL IMAGING MANDATED]     STEP 2: ANY LOW-RISK FACTOR PRESENT
   (Non-Contrast CT Spine)         ALLOWING SAFE ASSESSMENT OF RANGE OF MOTION?
                                   • Simple rear-end MVC (excludes pushed into
                                     oncoming traffic, hit by bus/truck, rollover)
                                   • Sitting position in emergency department
                                   • Ambulatory at ANY time since injury
                                   • Delayed (not immediate) onset of neck pain
                                   • Absence of midline cervical spine tenderness
                                                 │
                                 ┌───────────────┴───────────────┐
                                 ▼                               ▼
                               [NO]                            [YES]
                                 │                               │
                                 ▼                               ▼
                    [CERVICAL IMAGING MANDATED]    STEP 3: PATIENT ABLE TO ACTIVELY
                    (Non-Contrast CT Spine)        ROTATE NECK 45° LEFT AND RIGHT?
                                                                 │
                                                 ┌───────────────┴───────────────┐
                                                 ▼                               ▼
                                               [NO]                            [YES]
                                                 │                               │
                                                 ▼                               ▼
                                    [CERVICAL IMAGING MANDATED]     [NO IMAGING NEEDED]
                                    (Non-Contrast CT Spine)         (C-Spine Cleared Clinically)

The NEXUS Low-Risk Criteria

Cervical spine radiography or CT is required unless the patient meets ALL 5 of the following low-risk criteria:

1. No Posterior Midline Cervical Spine Tenderness: Palpation of the spinous processes from occiput to T1 elicits no tenderness (paraspinal muscle tenderness alone does not violate this rule).
2. No Focal Neurological Deficit: Motor strength and sensation are normal and symmetric in all four extremities.
3. Normal Level of Alertness: GCS score of 15, oriented, able to remember events, and responsive to questioning.
4. No Evidence of Intoxication: No clinical history or examination evidence of alcohol, sedatives, or illicit substance intoxication.
5. No Clinically Distracting Painful Injury: Absence of severe injuries (e.g., long-bone fracture, large visceral injury, extensive burns, severe crush injury) that could distract the patient from perceiving cervical pain.

Modality of Choice: When imaging is mandated by CCR or NEXUS in modern acute care settings, non-contrast cervical spine CT is the preferred modality due to significantly higher sensitivity (>98% to 100%) for detecting occult fractures compared to plain radiography.

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Cervical Radiculopathy: Localization & Provocative Maneuvers

Cervical radiculopathy results from mechanical compression or chemical inflammation of an exiting cervical nerve root. In younger individuals (<45 years), posterolateral disc herniation is the primary etiology; in older adults (>50 years), neuroforaminal encroachment secondary to cervical spondylosis and uncovertebral (Luschka) osteophytosis accounts for >70% of cases.

Root-by-Root Neurological Localization

More than 80% to 90% of cervical radiculopathies involve either the C7 or C6 nerve root.

                  CERVICAL RADICULOPATHY NEUROLOGICAL LOCALIZATION

   Nerve Root     Disc Level      Motor Deficit &               Sensory Distribution Deep Tendon
   Involved       (Foraminal)     Muscle Group                  Affected             Reflex
   ═════════════════════════════════════════════════════════════════════════════════════════════
   C5             C4-C5           Deltoid; Biceps brachii;      Lateral upper arm;   Biceps reflex
                                  Weak shoulder abduction &     Shoulder "epaulet"   [Diminished]
                                  elbow flexion                 region

   C6             C5-C6           Biceps brachii;               Radial forearm;      Brachioradialis
   (~25% cases)                   Brachioradialis; ECRL/ECRB;   Thumb and index      & Biceps reflex
                                  Weak elbow flexion &          finger               [Diminished]
                                  wrist extension

   C7             C6-C7           Triceps brachii;              Middle finger;       Triceps reflex
   (~60% cases;                   Wrist flexors;                Palmar aspect of     [Diminished/Absent]
    most common)                  Weak elbow extension &        hand
                                  finger extension

   C8             C7-T1           Flexor digitorum profundus;   Medial forearm;      No reliable
   (~10% cases)                   Intrinsic hand muscles;       Ring and small       tendon reflex
                                  Weak hand grip &              fingers (4th & 5th)  (Finger flexor)
                                  finger abduction/adduction
   ═════════════════════════════════════════════════════════════════════════════════════════════

Provocative Physical Examination Tests

1. Spurling Test (Neck Compression Test):
   • Maneuver: The patient sits upright. The clinician instructs the patient to slightly extend the neck and rotate/side-bend the head toward the symptomatic side. The clinician then applies a gentle downward axial compressive force onto the crown of the head.
   • Biomechanical Mechanism: Extension and lateral rotation significantly narrow the neuroforamen on the ipsilateral side, mechanically compressing the exiting nerve root.
   • Positive Finding: Sharp, lancinating radicular pain shooting down the ipsilateral arm in the specific dermatomal distribution. Local neck soreness does not constitute a positive test.
   • Diagnostic Value: High Specificity (>92% to 95%), with modest sensitivity (30% to 50%). A positive Spurling test strongly confirms cervical radiculopathy.
2. Shoulder Abduction Test (Bakody Sign):
   • Maneuver: The patient actively or passively raises the symptomatic arm and rests the hand on top of the head (shoulder abducted and elbow flexed).
   • Biomechanical Mechanism: Shoulder abduction elevates the suprascapular nerve and slackens the lower trunks of the brachial plexus, reducing tension on the C5, C6, and C7 nerve roots.
   • Positive Finding: Substantial relief or complete abolishment of radiating arm pain.
   • Diagnostic Value: High specificity (~90%). Crucially, this maneuver differentiates cervical radiculopathy from primary shoulder pathology (in subacromial impingement or rotator cuff disease, shoulder abduction exacerbates pain; in cervical radiculopathy, it relieves pain!).
3. Neck Distraction Test:
   • Maneuver: The examiner places one hand under the patient's chin and the other under the occiput, applying gentle axial upward traction (approximately 10 to 15 lbs of force).
   • Interpretation: Relief of radicular arm symptoms indicates foraminal decompression and confirms radiculopathy.

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Cervical Spondylotic Myelopathy (CSM): The Silent Neurosurgical Danger

Cervical spondylotic myelopathy is the most common cause of spinal cord dysfunction in adults aged >55 years worldwide. It arises from chronic, degenerative narrowing of the cervical spinal canal (<10 to 13 mm anteroposterior canal diameter; normal is 17 to 18 mm), causing direct mechanical spinal cord compression and microvascular ischemia.

Pathophysiology & Etiologic Factors

CSM results from an amalgamation of degenerative changes:

• Posterior osteophytic ridges along vertebral endplates;
• Degenerative disc height loss and posterior bulging;
• Hypertrophy and infolding of the ligamentum flavum during cervical extension;
• Ossification of the posterior longitudinal ligament (OPLL).

Repeated dynamic microtrauma during ordinary cervical flexion and extension compresses the already narrowed cord against osteophytes anteriorly and the buckled ligamentum flavum posteriorly.

Clinical Presentation: The Myelopathic Triad

CSM onset is characteristically insidious, subtle, and painless, frequently misdiagnosed as "normal aging" or carpal tunnel syndrome:

1. Lower Extremity Upper Motor Neuron (UMN) Signs:
   • Spastic, Ataxic Gait: Stiff-legged, wide-based, uncoordinated gait with impaired tandem walking; patients report feeling like their legs are "heavy", "wooden", or "walking on clouds".
   • Hyperreflexia & Clonus: Exaggerated 3+ to 4+ patellar and Achilles tendon reflexes, accompanied by sustained ankle clonus (>3 to 5 beats).
   • Extensor Plantar Response: Positive Babinski sign (great toe dorsiflexion with fanning of lateral toes on plantar scraping).
2. Upper Extremity Lower Motor Neuron (LMN) Signs:
   • Loss of Fine Motor Dexterity: Clumsiness of the hands, difficulty buttoning shirts, tying shoelaces, handling coins, or turning keys; handwriting becomes progressively erratic and enlarged (scrawl sign).
   • Dropped Objects: Spontaneous dropping of coffee mugs or utensils without realizing it.
   • Intrinsic Hand Muscle Wasting: Atrophy of the first dorsal interosseous, thenar, and hypothenar musculature.
   • Finger Escape Sign: The patient holds both hands extended with fingers adducted for 30 seconds. A positive test occurs when the 4th and 5th digits spontaneously abduct and flex away from the middle finger due to intrinsic muscle weakness.
3. Pathognomonic Provocative Myelopathic Signs:
   • Hoffmann Sign: The examiner stabilizes the patient's extended middle finger proximal to the DIP joint and sharply flicks or snaps the nail/distal phalanx downward. A positive sign consists of involuntary reflex flexion and adduction of the ipsilateral thumb and/or index finger. Indicates hyperreflexia of the corticospinal tract above C7.
   • Lhermitte Sign (Barber-Chair Phenomenon): Sudden electric shock-like sensation shooting down the spine and into the extremities triggered by active cervical flexion.
   • Inverted Brachioradialis Reflex: Tapping the distal radius over the brachioradialis tendon elicits no wrist extension/elbow flexion, but instead triggers paradoxical reflex finger flexion.

Diagnostic Confirmation & Urgent Management

• Imaging Modality of Choice: Urgent non-contrast MRI of the cervical spine. MRI demonstrates spinal canal stenosis, cord flattening, and hyperintense intramedullary cord signal changes on T2-weighted sequences (representing edema, gliosis, or permanent myelomalacia).
• Mandatory Surgical Referral: Conservative management (physical therapy, collar immobilization, or injections) is ineffective in reversing mechanical cord compression. Once objective myelopathic signs (spastic gait, Hoffmann sign, intrinsic wasting) are present, urgent referral to spine surgery (neurosurgery or orthopedic spine surgery) for surgical decompression (anterior cervical discectomy and fusion [ACDF], cervical laminoplasty, or posterior laminectomy with fusion) is required to arrest neurologic progression.