Myotomes

Myotome is defined as ‘a group of muscles innervated by a single spinal nerve root‘. They are clinically useful as they can determine if damage has occurred to the spinal cord, and at which level the damage has occurred.

The anatomical term myotome which describes the muscles served by a spinal nerve root, is also used in embryology to describe that part of the somite which develops into the muscles.

There are 31 spinal nerves.Each vertebrae has a spinal nerve : 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves,1 coccygeal nerve.16 of these 31 nerves has a specific myotome that controls voluntary muscle movement.

Myotomes Clinical significance:

Myotome testing is an essential part of neurological examination when suspecting radiculopathy. Muscle strength in a particular myotome may help in identifying at which level a nerve root compromised. Testing of myotomes, in the form of isometric resisted muscle testing, gives information about the level in the spine where a lesion may be present.

List of myotomes:

The list below details which movement(s) has the strongest association with each myotome:

C1/C2: neck flexion/extension

C3: neck lateral flexion

C4: shoulder elevation

C5: shoulder abduction

C6: elbow flexion

C7: elbow extension/wrist flexion/finger extension

C8: finger flexion

T1: finger abduction

L2: hip flexion

L3: knee extension

L4: ankle dorsi-flexion

L5: great toe extension

S1: ankle plantar-flexion/ankle eversion/hip extension

S2: knee flexion

S3–S4: anal wink

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