Overview
This lecture covers myotome testing of the upper extremity, its clinical significance for diagnosing cervical radiculopathy, and steps for testing each cervical segment from C5 to T1.
Clinical Significance of Myotome Testing
- Myotome testing is vital in neurological exams when radiculopathy is suspected.
- Muscle strength changes in specific myotomes help localize pathological disc levels.
- Common causes of cervical nerve root pathology: herniated discs (20–25%) and degenerative disc disease (70–75%).
- Herniated discs are more frequent in younger patients; degenerative disc disease occurs more in older adults.
- Cervical radiculopathy most often affects C5/6 and C6/7 segments.
- Neurological examination sensitivity is 83%, but specificity is only 28%; thus, diagnostic value is limited.
Myotome Testing Procedure
- Assess each myotome for strength differences side-to-side.
C5 Myotome
- Test the deltoid muscle: have patient abduct arms to ~90° while you apply downward pressure.
C6 Myotome
- Test biceps brachii: flex forearm to 90°, supinate, and resist your extension force.
- Test wrist extensors: pronate forearm on table, close fist in slight extension, resist wrist flexion force.
C7 Myotome
- Test triceps brachii: flex forearm to 90°, resist flexion force.
- Test wrist flexors: supinate forearm on table, close fist in slight flexion, resist wrist extension force.
C8 Myotome
- Test abductor pollicis brevis: support forearm, have patient resist thumb adduction, compare both sides.
T1 Myotome
- Test first dorsal interosseous: fixate last three digits, apply adduction force to index finger, check strength.
Key Terms & Definitions
- Myotome — group of muscles innervated by fibers from a single spinal nerve root.
- Radiculopathy — dysfunction of a spinal nerve root, often causing weakness or sensory change.
- Herniated Disc — displacement of disc material causing nerve compression.
- Degenerative Disc Disease — age-related breakdown of spinal discs, sometimes leading to nerve compression.
Action Items / Next Steps
- Watch the suggested video on dermatomes for sensory assessment of the upper extremity.