The C6 myotome is tested by wrist extension, the ISNCSCI key movement for C6, using extensor carpi radialis longus and brevis. C6 also helps elbow flexion and forearm supination. The brachioradialis and biceps reflexes test the same root.
| Nerve root | C6 |
|---|---|
| Area | Wrist extension (ISNCSCI key muscles: wrist extensors) |
| How to test | The patient makes a loose fist and extends (cocks back) the wrist while the examiner presses down on the back of the hand. Strength is graded 0-5 on the Medical Research Council scale and compared side to side. |
| Muscles | |
| Nerve Supply | Radial nerve; Musculocutaneous nerve |
Extends the wrist and helps bend the elbow and turn the palm up.
C6 radiculopathy, usually from a C5-C6 disc, weakens wrist extension with thumb numbness and a reduced brachioradialis reflex. In C6 spinal cord injury, preserved wrist extension allows a tenodesis grip, where extending the wrist passively closes the fingers. Myotome charts vary slightly between sources, and most muscles receive more than one root, so a single root lesion usually weakens rather than paralyses.
Compression at C5-C6 causing weak wrist extension, thumb and index finger numbness and reduced biceps and brachioradialis reflexes.
Compression of the radial nerve in the spiral groove (Saturday night palsy) causes wrist drop that can be confused with C6 weakness.
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