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