Myotomes and Nerves of the Hand

Upper Limb Nerves

• Median Nerve

  • Motor: Wrist and hand flexors (excluding flexor carpi ulnaris and flexor digitorum profundus to 4th and 5th digits), thenar muscles (abductor pollicis brevis, opponens pollicis)

  • Sensory: Lateral 3½ digits on the palmar side and nail beds dorsally

  • Special Test: OK sign for anterior interosseous branch (flexor pollicis longus and FDP to index finger)

• Ulnar Nerve

  • Motor: Finger abduction and adduction (interossei), flexor carpi ulnaris, flexor digitorum profundus to 4th and 5th digits, adductor pollicis

  • Sensory: Medial 1½ digits on palmar and dorsal aspects

  • Special Test: Paper grip test (interossei strength)

• Radial Nerve

  • Motor: Wrist and finger extensors, brachioradialis

  • Sensory: Posterior arm/forearm, dorsal hand (radial side), dorsal thumb web space

  • Special Test: “Shoot a gun” sign (thumb and finger extension)

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Myotomes (Upper Limb)

• C1–C2

  • Neck flexion and extension

  • Clinically tested by “nodding” the head

• C3

  • Neck lateral flexion

  • Important for maintaining head posture

• C4

  • Shoulder elevation

  • Assessed by shrugging the shoulders against resistance

• C5

  • Shoulder abduction or flexion

  • Key muscle group includes deltoid

• C5–C6

  • Elbow flexion and forearm supination

  • Tested with the biceps reflex and “pick up sticks” action

• C6–C7

  • Wrist extension and flexion

  • Vital for grip stability and hand positioning

• C7

  • Elbow extension and finger extension

  • Triceps reflex and “paper” sign for finger extension

• C8

  • Finger flexion

  • Grip strength testing (e.g. “rock” sign)

• T1

  • Finger abduction and adduction

  • Interossei function (“scissors” test)

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Myotomes (Lower Limb)

• L2–L3

  • Hip flexion (“lift my knee”)

  • Iliopsoas strength assessment

• L3–L4

  • Knee extension (“kick the door”)

  • Quadriceps power and patellar reflex

• L4–L5

  • Dorsiflexion of the foot and hip extension

  • Gluteus maximus and tibialis anterior strength

• L5–S1

  • Knee flexion (“kick my bum”)

  • Hamstring function

• S1–S2

  • Plantarflexion (“stand on my shoes”)

  • Gastrocnemius and soleus power, Achilles reflex

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Dermatomes (Upper Limb)

• C1–C2

  • Scalp and upper posterior neck

  • Rarely isolated in clinical testing

• C3

  • Lateral neck region

  • Over the trapezius

• C4

  • Shoulder cap area

  • Meets T2 dermatome around the axilla

• C5

  • Lateral upper arm

  • Over the deltoid region

• C6

  • Lateral forearm, thumb

  • “Six-shooter” thumb area

• C7

  • Middle finger

  • Centre of the hand dorsally and ventrally

• C8

  • Ring and little finger medial side

  • Medial forearm can also be tested

• T1

  • Medial forearm near elbow

  • May overlap with T2 at the axilla

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Dermatomes (Lower Limb)

• L2–L3

  • Anterior thigh

  • Below inguinal ligament and above the knee

• L4

  • Medial side of the leg and medial malleolus

  • Overlaps with saphenous nerve distribution

• L5

  • Dorsum of the foot to the big toe

  • Lateral leg transitioning to foot dorsum

• S1

  • Lateral foot and heel region

  • Includes the little toe

• S2

  • Posterior thigh and calf

  • Extends up to the popliteal fossa

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Additional Notes

• Median nerve compression commonly presents as carpal tunnel syndrome with numbness in the lateral 3½ digits

• Ulnar nerve pathology may lead to claw hand deformity and prominent wasting of interossei

• Radial nerve palsy often causes wrist drop due to loss of extensors

• C5–C6 lesions can compromise biceps strength and sensation over lateral forearm

• L4 pathology may reduce patellar reflex and cause difficulty in heel walking

• Early recognition of myotome or nerve deficits can prompt imaging and nerve conduction studies to detect root or plexus lesions