MYOTOMES & DERMATOMES Myotomes Each muscle in the body is supplied by a particular level or segment of the spinal cord and by its corresponding spinal nerve. Dermatomes ~Greek for"skin cutting" ~An area of the skin supplied by specific nerve fibers. Sensory
Neurologic Level C5 The muscles found within this myotomal pattern are the deltoid and the biceps brachii. Because the latter is also innervated by C6, the deltoid is the most "pure" C5 muscle. One of the most commonly used tests for shoulder abduction is to instruct the patient to flex the elbow at 90 degrees, then offer gradual resistance to abduction
Neurologic Level C6 the biceps brachii is innervated by C5 and C6. C6 also innervates the most powerful wrist extensors, carpi radialis longus and brevis, which do radial extension. To test for wrist extension, stabilize the patient’s forearm and wrist extension
Neurologic Level C7 The muscles found within this myotomal pattern are the triceps, wrist flexors. The triceps muscle primarily does elbow extension. A common test for this action is to ask the patient to fully flex the arm, offer firm, constant resistance until discerning the maximum resistance h/she can overcome.
Neurologic Level C8: The muscles found within this myotomal pattern are finger flexors—flexor digitorum superficialis, flexor digitorum profundis, and the lumbricals. To test for finger flexion, the patient fully flexes h/her fingers at all joints while you curl your fingers into them. Ask the patient to resist your attempt to pull h/her fingers out of flexion.
Neurologic level T1: The muscles found within this myotomal pattern are those involved in finger abduction—dorsal interossei and abductor digiti minimi, and adduction—palmar interossei. To test for finger adduction, ask the patient to extend h/her fingers and hold a piece of paper (or a dollar bill) between two of h/her fingers. Then you pull it out
Neurologic Levels T12 to L3: The muscles found within this myotomal pattern are the iliopsoas, quadriceps, and the adductors Because this myotomal pattern includes multiple muscle groups an injury to this nerve root level can be more easily evaluated by sensory testing of the dermatomal patterns.
Neurologic Level L4: The muscle predominantly innervated at this root nerve level is the tibialis anterior, which does dorsiflexion. Instruct the patient to dorsiflex and invert h/her foot. With your free hand, hold the patient’s foot and ask h/her to resist your attempt to move the foot into plantarflexion
Neurologic Level L5: The muscles found within this myotome are the extensor hallucis longus (big toe extensor) & extensor digitorum (heel walk)
Neurologic Level S1: The muscles found within this myotome are the peroneus longus (eversion) & peroneus brevis (eversion)