The C5 myotome is tested by elbow flexion, the ISNCSCI key muscle for C5, and also drives shoulder abduction through the deltoid and supraspinatus. Biceps brachii and brachialis receive both C5 and C6. The biceps reflex shares these roots.
| Nerve root | C5 |
|---|---|
| Area | Elbow flexion (ISNCSCI key muscles: elbow flexors); also shoulder abduction |
| How to test | With the forearm supinated, the patient bends the elbow against the examiner's resistance at the wrist; shoulder abduction can be tested with the arm out to the side. Strength is graded 0-5 on the Medical Research Council scale and compared side to side. |
| Muscles | |
| Nerve Supply | Musculocutaneous nerve; Axillary nerve; Suprascapular nerve |
Bends the elbow and lifts the arm away from the body.
C5 radiculopathy, usually at C4-C5, causes weak shoulder abduction and elbow flexion with a reduced biceps reflex. Selective deltoid and biceps weakness after cervical decompression surgery is called C5 palsy and usually recovers. Myotome charts vary slightly between sources, and most muscles receive more than one root, so a single root lesion usually weakens rather than paralyses.
Root compression at C4-C5 causing shoulder and elbow flexion weakness, lateral arm numbness and a reduced biceps reflex.
Weakness of the deltoid and biceps appearing days after cervical spine surgery, thought to be from root traction, usually recovering over months.
Upper trunk (C5-C6) brachial plexus injury leaving the arm hanging internally rotated with the elbow extended.
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