Nerve Root Dermatomes, Myotomes, Reflexes, And Paresthetic Areas

Front 1

C1

Back 1

Dermatome: Vertex of skull

Myotome: none

Reflex Affected: none

Paresthesias: none

Front 2

C2

Back 2

Dermatome: temple, forehead, occiput

Myotome: longus colli, SCM, rectus capitis

Reflex Affected: none

Paresthesias: none

Front 3

C3

Back 3

Dermatome: entire neck, posterior cheek, temporal area, prolongation forward under mandible

Myotome: traps, splenius capitis

Reflex Affected: none

Paresthesias:cheek, side of neck

Front 4

C4

Back 4

Dermatome: shoulder area, clavicular area, upper scapular area

Myotome: traps, levator

Reflex Affected: none

Paresthesias:horizontal band along clavicle and upper scap

Front 5

C5

Back 5

Dermatome: deltoid area, anterior aspect of the entire arm to the base of thumb

Myotome: supraspinatus, infraspinatus, deltoid, biceps

Reflex Affected: biceps, brachioradialis

Paresthesias:none

Front 6

C6

Back 6

Dermatome: anterior arm, radial side of and to thumb and index finger

Myotome: biceps, supinator, wrist extensors

Reflex Affected: biceps, brachioradialis

Paresthesias: thumb and index finger

Front 7

C7

Back 7

Dermatome: lateral arm and forearm to index, long and ring fingers

Myotome: triceps, wrist flexors

Reflex Affected: triceps

Paresthesias: index, long, and ring fingers

Front 8

C8

Back 8

Dermatome: medial arm and forearm to index, long and little fingers

Myotome: ulnar deviators, thumb extensors, thumb adductors

Reflex Affected: none

Paresthesias: little finger along or with two adjacent fingers; not ring or long fingers, alone or together (C7)

Front 9

T1

Back 9

Dermatome: medial side of forearm to base of little finger

*** disk lesions at upper two thoracic levels do not appear to give rise to root weakness. Weakness of intrinsic mm of the hand is due to other pathology.

Front 10

T2

Back 10

Dermatome: medial side of upper arm to medial elbow, pectoral and midscapular areas.

***disk lesions at upper two thoracic levels do not appear to give rise to root weakness. Weakness of intrinsic mm of the hand is due to other pathology.

Front 11

T3- T12

Back 11

Dermatome: T3-T6= upper thorax; T5-T7= costal margin; T8-T12= abdomen and lumbar region.

*** articular and dural signs and root pain are common. Root signs (cutaneous analgesia) are rare and have such indefinite area that they have little localizing value. Weakness is not detectable.

Front 12

L1

Back 12

Dermatome: back, over trochanter and groin

Myotome: none

Reflex Affected: none

Paresthesias: groin; after holding posture, which causes pain

Front 13

L2

Back 13

Dermatome: back, front of thigh to knee

Myotome: psoas, hip adductors

Reflex Affected: none

Paresthesias: occasionally anterior thigh

Front 14

L3

Back 14

Dermatome: back, upper buttock, anterior thigh and knee, medial lower leg

Myotome: psoas, quadriceps, thigh atrophy

Reflex Affected: knee jerk sluggish, PKB positive, pain on full SLR

Paresthesias:medial knee, anterior lower leg

Front 15

L4

Back 15

Dermatome: medial buttock, lateral thigh, medial leg, dorsum of foot, big toe

Myotome: tib anterior, extensor hallucis

Reflex Affected: SLR limited, neck flexion pain, weak or absent knee jerk, side flexion limited

Paresthesias:medial aspect of calf and ankle

Front 16

L5

Back 16

Dermatome: buttock, posterior and lateral thigh, lateral aspect of leg, dorsum of foot, medial half of sole, first second and third toes

Myotome: extensor hallucis, peroneals, gluteus medius, dorsiflexors, hamstrings and calf atrophy

Reflex Affected: SLR limited one side, neck flexion painful, ankle decreased, crossed-leg raising pain

Paresthesias: lateral aspect of leg, medial three toes

Front 17

S1

Back 17

Dermatome: lateral and plantar aspect of foot

Myotome: calf and hamstrings, wasting of gluteals, peroneals, plantar flexors

Reflex Affected: SLR limited, Achilles reflex weak or absent

Paresthesias: lateral two toes, lateral foot, lateral leg to knee, plantar aspect of foot

Front 18

S2

Back 18

Dermatome: buttock, thigh, and posterior leg

Myotome: calf and hamstrings, wasting of gluteals, plantar flexors

Reflex Affected: SLR limited, Achilles reflex weak or absent

Paresthesias: lateral leg, knee, and heel

Front 19

S3

Back 19

Dermatome: groin, posteromedial thigh to knee

Myotome: none

Reflex Affected: none

Paresthesias: none

Front 20

S4

Back 20

Dermatome: perineum, genitals, lower sacrum

Myotome: bladder, rectum

Reflex Affected: none

Paresthesias:saddle area, genitals, anus, impotence, massive posterior herniation