How to test the patency of cervical nerves?

Testing Cervical Nerve Root Function

Cervical nerve root patency is assessed through a systematic clinical examination evaluating motor strength (myotomes), sensory distribution (dermatomes), and deep tendon reflexes, with electrodiagnostic studies and MRI serving as confirmatory tools when clinical findings are equivocal or surgical planning is needed. 1, 2

Clinical Examination Components

Motor Testing (Myotomes)

• C5: Test shoulder abduction (deltoid) and elbow flexion (biceps) 2, 3
• C6: Test elbow flexion (biceps), wrist extension (extensor carpi radialis) 2, 3
• C7: Test elbow extension (triceps), wrist flexion, finger extension 2, 3
• C8: Test finger flexion, thumb extension, hand intrinsics 2, 3

Sensory Testing (Dermatomes)

• C4: Shoulder region 4
• C5: Lateral arm 4
• C6: Lateral forearm, thumb and index finger 4
• C7: Middle finger 4
• C8: Medial forearm, ring and little finger 4

Important caveat: Symptom distribution from nerve root irritation (dynatomes) frequently extends beyond classic dermatomal maps, so symptoms outside traditional boundaries do not exclude radiculopathy 4

Deep Tendon Reflexes

• C5-C6: Biceps reflex 5
• C6-C7: Brachioradialis reflex 5
• C7-C8: Triceps reflex 5

Reflex testing demonstrates 72% sensitivity and 85% specificity for cervical radiculopathy detection 5

Diagnostic Hierarchy

When Clinical Examination is Sufficient

• Two or more positive clinical signs (abnormal motor, sensory, or reflex findings) strongly support the diagnosis without additional testing 5
• Patients with three clinical signs show 90% correlation with electrodiagnostic abnormalities 5

When Additional Testing is Needed

MRI cervical spine without contrast is the first-line imaging modality when:

• Only one clinical sign is present 5
• Symptoms are atypical or bilateral 2, 3
• Surgical planning is required 2, 3
• MRI correctly predicts 88% of cervical radiculopathy lesions 1, 3

Electrodiagnostic studies (needle electrode examination and specialized segmental reflexes) are indicated for:

• Atypical symptoms where clinical localization is unclear 6
• Potential pain-mediated weakness 6
• Nonfocal imaging findings 6
• Heteronymous H-reflexes show 72% sensitivity and 85% specificity, matching MRI performance 5

Red Flags Requiring Urgent Evaluation

Immediate imaging and possible emergency intervention are needed for:

• Progressive motor weakness 3
• Bilateral symptoms affecting upper AND lower extremities (suggests myelopathy) 2, 3
• New bladder or bowel dysfunction 2, 3
• Loss of perineal sensation 2
• Gait disturbance or difficulty with fine motor tasks 3

These findings indicate possible cervical myelopathy (spinal cord compression) rather than isolated radiculopathy and require more urgent management 2

Specialized Testing Modalities

Intraoperative Monitoring

• Somatosensory evoked potentials (SSEPs) monitor dorsal column function during cervical spine surgery 1
• Motor evoked potentials (MEPs) via transcranial electrical stimulation detect motor pathway compromise 1
• Combined SSEP and MEP monitoring provides comprehensive assessment during surgical decompression 1

Selective Nerve Root Blocks

• Diagnostic cervical selective nerve root blocks can identify the specific symptomatic nerve root for surgical planning 7
• Posterior approach using curved blunt needles minimizes risk of arterial injection compared to transforaminal approaches 7
• Mechanical stimulation during the procedure provokes symptoms in the distribution of the affected nerve root 4, 7

Contact Heat-Evoked Potentials (CHEPs)

• CHEPs assess spinothalamic tract function from cervical dermatomes C4-C8 8
• Demonstrate substantial test-retest reliability for tracking changes in spinal conduction 8
• Useful for objective assessment of small fiber function when large fiber testing (reflexes, vibration) is normal 8