Myotomes detail description

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Myotomes
By Dr. Himanshu Patel

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Myotome
 The anatomical term myotome refers to the muscles served by
a spinal nerve root. A myotome is, therefore, a set of muscles
innervated by a specific, single spinal nerve. The term is also
used in embryology to describe that part of the somite which
develops into the muscles.

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 There are 31 spinal nerves.Each vertebrae has a spinal nerve.
The nerves are categorized by the vertebra which house them.
There are:
 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.

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 Most muscles in the limbs receive innervation from more than
one spinal nerve root, and are hence comprised of multiple
myotomes. For example, the biceps brachii muscle flexes
the elbow. It is innervated by the musculocutaneous nerve,
which is innervated by C5, C6 and C7 nerve roots. All three of
these spinal nerve roots can be said to be associated with elbow
flexion.

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 The list below details which movement(s) has the strongest association with each
myotome:
 C5- shoulder abduction
 C6– Elbow flexion Wrist extension
 C7 – Elbow extension
 C8 – Finger flexion
 T1 – Finger abduction
 L2 – Hip flexion
 L3 – Knee extension
 L4 – Ankle dorsiflexion
 L5 – Great toe extension
 S1 – Ankle plantarflexion

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Purpose
 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. During
myotome testing, you are looking for muscle weakness of a
particular group of muscles. Results may indicate lesion to the
spinal cord nerve root, or intervertebral disc herniation pressing
on the spinal nerve roots.

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Technique
 Begin by asking the client to perform a movement as per
instructions and hold an isometric contraction against therapist
resistance for a count of 5.
 C5- Shoulder abduction Ask the patient to raise both their arms
to the side of them simultaneously as strongly as then can while
the examiner provides resistance to this movement. Compare
the strength of each arm.

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 C6- Elbow flexion Test the strength of lower arm flexion by holding
the patient's wrist from above and instructing them to "flex their
hand up to their shoulder". Provide resistance at the wrist. Repeat
and compare to the opposite arm. This tests the biceps muscle.
Test the strength of wrist extension by asking the patient to extend
their wrist while the examiner resists the movement. This tests the
forearm extensors. Repeat with the other arm.
 C7- Elbow extension Ask the patient to extend their forearm against
the examiner's resistance. Begin their extension from a fully flexed
position because this part of the movement is most sensitive to a
loss in strength. This tests the triceps. Note any asymmetry in the
other arm.

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 C8- Finger Flexion Examine the patient's hands. Look for
intrinsic hand, thenar and hypothenar muscle wasting. Test the
patient's grip by having the patient hold the examiner's fingers in
their fist tightly and instructing them not to let go while the
examiner attempts to remove them. Normally the examiner
cannot remove their fingers. This tests the forearm flexors and
the intrinsic hand muscles. Compare the hands for strength
asymmetry. Finger flexion is innervated by the C8 nerve root via
the median nerve.

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 C8- Finger abduction & adduction Test the intrinsic hand muscles
once again by having the patient abduct or "fan out" all of their
fingers. Instruct the patient to not allow the examiner to compress
them back in. Normally, one can resist the examiner from replacing
the fingers. Finger abduction or "fanning" is innervated by the T1
nerve root via the ulnar nerve.
 C8 & T1- Thumb Opposition To complete the motor examination of
the upper extremities, test the strength of the thumb opposition by
telling the patient to touch the tip of their thumb to the tip of their
pinky finger. Apply resistance to the thumb with your index finger.
Repeat with the other thumb and compare. Thumb opposition is
innervated by the C8 and T1 nerve roots via the median nerve.

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 L1 & L2 : Hip Flexion Proceeding to the lower extremities, first
test the flexion of the hip by asking the patient to lie down and
raise each leg separately while the examiner resists. Repeat and
compare with the other leg. This tests the iliopsoas muscles.
 L3 Test extension at the knee by placing one hand under the
knee and the other on top of the lower leg to provide resistance.
Ask the patient to "kick out" or extend the lower leg at the knee.
Repeat and compare to the other leg. This tests the quadriceps
muscle.

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 L4: Ankle Dorsiflexion Test dorsiflexion of the ankle by holding
the top of the ankle and have the patient pull their foot up
towards their face as hard as possible. Repeat with the other
foot. This tests the muscles in the anterior compartment of the
lower leg.
 L5: Great toe extension Ask the patient to move the large toe
against the examiner's resistance "up towards the patient's
face". This tests the extensor halucis longus muscle.

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 S1: Ankle plantar flexion and eversion/knee flexion Holding the
bottom of the foot, ask the patient to press down as hard as
possible. Or in standing rise up onto the ball of their foot. Repeat
with the other foot and compare. This tests
the gastrocnemius and soleus muscles in the posterior
compartment of the lower leg.
 S2: Test flexion at the knee by holding the knee from the side
and applying resistance under the ankle and instructing the
patient to pull the lower leg towards their buttock as hard as
possible. Repeat with the other leg. This tests the hamstrings.