The T1 myotome is tested by finger abduction, the ISNCSCI key movement for T1, using abductor digiti minimi to spread the little finger. It supplies the small intrinsic muscles of the hand with C8. These muscles control fine finger movements.
| Nerve root | T1 |
|---|---|
| Area | Finger abduction (ISNCSCI key muscle: abductor digiti minimi) |
| How to test | The patient spreads the fingers apart while the examiner pushes the little finger back toward the ring finger. Strength is graded 0-5 on the Medical Research Council scale and compared side to side. |
| Muscles |
|
| Nerve Supply | Ulnar nerve; Median nerve (recurrent branch) |
Spreads and brings together the fingers and controls fine hand movements.
Weak or wasted small hand muscles suggest a T1 root, lower brachial plexus, ulnar nerve or motor neuron disease. A T1 lesion can also interrupt sympathetic fibres to the face, causing Horner syndrome on the same side. 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 of the lower trunk of the brachial plexus causing weakness and wasting of the intrinsic hand muscles, especially on the thumb side.
A lung apex tumour invading T1 causing hand muscle wasting, arm pain and Horner syndrome.
Amyotrophic lateral sclerosis often first appears as wasting of the small hand muscles.
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