Introduction / Definition

Degenerative Cervical Myelopathy (DCM) represents the most common cause of non-traumatic spinal cord dysfunction worldwide. It encompasses several degenerative and hypertrophic pathologies including:

• Cervical spondylotic myelopathy (CSM)
• Ossification of the posterior longitudinal ligament (OPLL)
• Hypertrophy or ossification of the ligamentum flavum (OLF)
• Degenerative disc disease and facet arthropathy

The pathophysiological mechanism involves chronic static mechanical compression, dynamic micro-instability during flexion-extension kinematics, and secondary spinal cord ischaemia via compromise of the anterior spinal artery and microvascular pial plexus, culminating in neuronal loss, demyelination, and astrogliosis.

Epidemiology & Natural History

• Demographics: Most prevalent in patients over 55 years; male-to-female ratio roughly 2:1.
• Predisposition: A congenital narrow canal (anteroposterior spinal canal diameter <13 mm on lateral radiographs) markedly accelerates clinical onset.
• Natural History (Clarke & Robinson / Nurick): The course is characteristically a stepwise, unpredictable deterioration with periods of quiescent clinical stability in up to 75% of patients, rather than a steady linear decline. Spontaneous, meaningful neurological recovery is exceedingly rare.

Relevant Anatomy

Spinal Cord Vascularity & Vulnerability

• Arterial Supply: The anterior spinal artery supplies the anterior two-thirds of the spinal cord (including the lateral corticospinal tracts and anterior horns), while paired posterior spinal arteries supply the dorsal columns.
• Vascular Watershed: The central grey matter and lateral corticospinal tracts are vulnerable to chronic mechanical ischemia.
• Dynamic Factors: In flexion, the cord stretches over anterior disc-osteophyte bars, increasing intramedullary pressure. In extension, the spinal canal shortens and narrows while the ligamentum flavum buckles into the dorsal cord, reducing available canal space by up to 2 mm per segment.

Cervical Spine Dimensions

• Normal Sagittal Diameter: 17–18 mm at C3–C7.
• Relative Stenosis: Canal diameter 10–13 mm.
• Absolute Stenosis: Canal diameter <10 mm.
• Pavlov-Torg Ratio: Ratio of sagittal canal diameter to vertebral body diameter on lateral plain radiographs. A ratio <0.82 defines developmental canal stenosis, eliminating magnification errors.

Clinical Presentation & Examination

Symptoms frequently develop insidiously and are often erroneously attributed to normal ageing or peripheral nerve entrapment.

Subjective Symptoms

• Loss of fine motor coordination of the hands (e.g. difficulty buttoning shirts, turning keys, altered handwriting)
• Gait unsteadiness, described as walking on sponges or feeling drunk
• Axial neck and shoulder discomfort (often absent or mild)
• Sphincter disturbance: Urinary frequency, urgency, or retention (usually late)

Physical Examination & Clinical Provocative Signs

• Gait: Broad-based, spastic, scissoring, or tandem gait ataxia; Romberg test positive.
• Upper Motor Neuron (UMN) Signs:
  • Hyperreflexia (biceps, brachioradialis, triceps, patellar, Achilles tendon)
  • Sustained clonus (>3 beats)
  • Babinski sign: Great toe dorsiflexion and fanning of digits upon lateral plantar stimulation
  • Hoffman's sign: Flicking the terminal phalanx of the middle finger produces reflexive flexion/adduction of the thumb and index finger
  • Inverted Brachioradialis Reflex (Babinski-Martini reflex): Brachioradialis percussion yields finger/wrist flexion without forearm supination/elbow flexion (indicates C5/6 root compression with cord compression below)
  • Lhermitte’s phenomenon: Electric shock sensation radiating down the spine and extremities upon neck flexion
• Myelopathy-Specific Hand Function Signs:
  • Finger Escape Sign: Inability to maintain adduction and extension of the fourth and fifth digits when holding fingers extended for 30 seconds
  • Grip and Release Test: Inability to form a tight fist and fully extend digits more than 20 times within 10 seconds
• Combined Radiculopathy: Coexistent lower motor neuron signs (focal wasting, hyporeflexia) at the level of compression with UMN signs below (cervicomedullary tandem syndrome).

Classification & Grading Scales

1. Nurick Scale

Focuses primarily on ambulatory status and walking disability:

• Grade 0: Signs/symptoms of root involvement; no cord involvement
• Grade 1: Signs of cord involvement; normal gait
• Grade 2: Mild gait impairment; employment unaffected
• Grade 3: Moderate gait impairment; prevents working, walks independently without cane
• Grade 4: Severe gait impairment; requires assistance or cane/walker to ambulate
• Grade 5: Chair-bound or bedridden

2. Modified Japanese Orthopaedic Association (mJOA) Scale

Total of 18 points spanning upper limb motor (5), lower limb motor (5), sensation (3), and bladder function (3):

• Mild DCM: 15–17 points
• Moderate DCM: 12–14 points
• Severe DCM: 0–11 points

3. Ranawat Classification

Useful in rheumatoid and inflammatory cervical disease (Class I: no deficit; Class II: subjective weakness/hyperreflexia; Class IIIA: objective weakness, ambulatory; Class IIIB: objective weakness, non-ambulatory).

Investigations

1. Magnetic Resonance Imaging (MRI)

• Gold Standard: Defines the level, direction, and magnitude of cord compression.
• T2-weighted sequences: Highlights CSF effacement, ligamentum flavum infolding, and intramedullary signal hyperintensity (oedema, gliosis).
• T1-weighted hypointensity combined with T2 hyperintensity: Signifies cord myelomalacia and cystic necrosis, predicting poorer neurological recovery.

2. Computed Tomography (CT) and CT Myelography

• Non-contrast CT assesses bony architecture, facet morphology, and uncovers OPLL.
• CT Myelography is the choice investigation when MRI is contraindicated (e.g. non-MRI-compatible implants) or obscured by metallic artefact.

3. Plain Cervical Radiographs

• Anteroposterior, neutral lateral, and flexion-extension views evaluate sagittal alignment, spondylolisthesis, dynamic instability, and Torg-Pavlov ratios.

4. Neurophysiology

• Somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) confirm central conduction delay and assist in differentiating cervical pathology from peripheral neuropathies or motor neurone disease.

Management

                          Cervical Myelopathy
                                  │
                    Assess Severity & Progression
                                  │
         ┌────────────────────────┴────────────────────────┐
         ▼                                                 ▼
    Mild (mJOA ≥15)                            Moderate to Severe (mJOA <15)
    Stable, Elderly, Frail                     OR Rapid Progression
         │                                                 │
Non-Operative Care with                              Surgical Decompression
Strict Serial Clinical & MRI Review                        │
         │                                  Assess Sagittal Profile &
         │ Any Deterioration                Number of Involved Levels
         └────────────────────────┐                        │
                                  ▼                        ▼
                          ┌───────────────┬────────────────┴───────────────┐
                          ▼                                                ▼
            Anterior Approach                                Posterior Approach
        (ACDF / Anterior Corpectomy)                     (Laminoplasty / PSF)
        - Kyphosis >10°                                  - Maintained Cervical Lordosis
        - 1 to 2 Levels                                  - ≥3 Levels Involved
        - Ventral Compression/OPLL                       - Dorsal Compression

Non-Operative Management

Reserved exclusively for patients with mild, stable DCM (mJOA ≥15), high anaesthetic risk, or severe comorbidities.

• Immobilisation in a soft collar (short-term only), physiotherapy, lifestyle modification, and close serial follow-up.
• Patients must be warned to present urgently if gait instability or hand clumsiness deteriorates.

Operative Decompression: Indications

• Moderate-to-severe myelopathy (mJOA ≤14)
• Documented progressive neurological deterioration
• Bowel/bladder dysfunction secondary to myelopathy

Anterior Approaches

Typically performed via the standard anterior Smith-Robinson approach (inter-nervous plane between medial visceral cylinder/tracheoesophageal sheath and lateral carotid sheath).

1. Anterior Cervical Discectomy and Fusion (ACDF):
   • Indications: 1–2 level disease; ventral disc-osteophyte pathology; kyphotic deformity >10°.
   • Technique: Total discectomy, decompression of the posterior longitudinal ligament, bilateral uncovertebral foraminotomies, structural interbody cage (PEEK or 3D titanium) with autograft/allograft, and anterior cervical plating.
2. Anterior Cervical Corpectomy and Fusion (ACCF):
   • Indications: Extensive retrovertebral pathology, extruded disc fragments behind the vertebral body, or focal OPLL.
   • Consideration: High graft dislodgement rate with >2 corpectomy levels; typically supplemented with posterior instrumentation (360° construct).

Posterior Approaches

Indicated in multilevel compression (≥3 levels) in a lordotic spine (loss of lordosis/kyphosis >10° is a contraindication as the cord cannot drift posterior away from anterior compressive bars).

1. Cervical Laminoplasty (Open-Door / French-Door):
   • Indications: Multilevel stenosis, preserved cervical lordosis (>10°), non-smoking candidates desiring motion preservation without severe pre-existing axial neck pain.
   • Technique: Unilateral hinge with contralateral through-cut (Hirabayashi open-door) stabilized with microplates, or midline spinous splitting (Kurokawa French-door).
2. Laminectomy and Posterior Instrumented Fusion:
   • Indications: Multilevel stenosis with dynamic instability, significant axial mechanical neck pain, or mild sagittal malalignment amenable to realignment.
   • Technique: Lateral mass screw fixation (Magerl or Roy-Camille trajectory at C3–C6; pedicle screws at C2 and C7/T1), total dome laminectomy, and posterolateral autologous bone grafting.
   • Contraindication to Stand-Alone Laminectomy: Stand-alone laminectomy without fusion is largely abandoned due to high risks of post-laminectomy kyphosis (swan-neck deformity) and late neurological decline.

Complications

• C5 Nerve Root Palsy: Occurs in 5–10% of cases, typically 2–5 days postoperatively, causing deltoid and biceps weakness. Predominantly a traction neuropraxia due to rapid posterior cord shift after wide posterior decompression. The vast majority recover spontaneously within 6 to 12 months.
• Dysphagia & Recurrent Laryngeal Nerve (RLN) Injury: Associated with anterior retractors and pressure on the oesophagus; up to 10% transient, <1% permanent. Higher risk with right-sided approach due to variable RLN anatomy.
• Vertebral Artery Injury: Rare (<0.5%) but catastrophic; risk heightened during lateral uncovertebral resection or lateral mass/pedicle screw placement.
• Dural Tear & CSF Leak: Particularly elevated in OPLL where the dura mater is ossified or adherent.
• Adjacent Segment Pathology: Long-term complication of rigid fusion constructs (up to 2.9% per year requiring intervention).
• Prevertebral Haematoma: Early life-threatening post-op emergency leading to acute airway obstruction; requires immediate bedside stitch/clip removal and haematoma evacuation.

Exam Pearls for FRCS (Orth) & Boards

• Kyphosis Contraindication: Posterior decompression alone is strictly contraindicated if cervical kyphosis exceeds 10° because the cord "bowstrings" across anterior compressive structures, preventing neural decompression.
• The C5 Phenomenon: The C5 nerve root has the shortest, most horizontal course, making it uniquely vulnerable to stretch injury when the spinal cord drifts dorsally following posterior laminectomy or laminoplasty.
• Inverted Brachioradialis Sign: Signifies a combined lesion—a lower motor neuron reflex arc deficit at C5/C6 (absent brachioradialis jerk) combined with upper motor neuron hyperreflexia to lower cord levels (finger flexion).
• Two-Level Corpectomy Rule: Reconstruction after two or more anterior cervical corpectomies carries high hardware failure and non-union rates with anterior plating alone; strongly consider supplemental posterior instrumented fusion (360° stabilization).