Dermatome Distribution

A dermatome distribution is defined as the area of skin supplied by a single nerve root. The area innervated by a nerve root is larger than that innervated by a peripheral nerve. The examiner must be able to differentiate a dermatome (nerve root) from the sensory distribution of a peripheral nerve.

Nerve roots are made up of anterior (ventral) and posterior (dorsal) portions that unite near or in the intervertebral foramen to form a single nerve root or spinal nerve. They are the most proximal parts of the peripheral nervous system. The sensory distribution of each nerve root is called the dermatome.

The human body has 31 nerve root pairs:

1. 8 cervical,
2. 12 thoracic,
3. 5 lumbar,
4. 5 sacral,
5. 1 coccygeal.

Slight differences and variabilities occur with each patient and dermatomes also exhibit a great deal of overlap. The variability in dermatomes was aptly demonstrated by Keegan and Garrett in 1948. The overlap may be demonstrated by the fact that, in the thoracic spine, the loss of one dermatome often goes unnoticed because of the overlap of the adjacent dermatomes.

See Also: Reflex Testing

Dermatome Distribution

Dermatomes of Upper Limb (Cervical)

Nerve Root	Dermatome
C1 nerve root	Vertex of skull
C2 nerve root	Temple, forehead, occiput
C3 nerve root	Entire neck, posterior cheek, temporal area, prolongation forward under mandible
C4 nerve root	Shoulder area, clavicular area, upper scapular area
C5 nerve root	Deltoid area, anterior aspect of entire arm to base of thumb
C6 nerve root	Anterior arm, radial side of hand to thumb and index finger
C7 nerve root	Lateral arm and forearm to index, long, and ring fingers
C8 nerve root	Medial arm and forearm to long, ring, and little fingers

Trunk Dermatomes

Nerve Root	Dermatome
T1 nerve root	Medial side of forearm to base of little finger
T2 nerve root	Medial side of upper arm to medial elbow, pectoral and midscapular areas
T3–T6 nerve roots	Upper thorax
T5–T7 nerve roots	Costal margin
T8–T12 nerve roots	Abdomen and lumbar region

Dermatomes of Lower Limb

Nerve Root	Dermatome
L1 nerve root	Back, over trochanter and groin
L2 nerve root	Back, front of thigh to knee
L3 nerve root	Back, upper buttock, anterior thigh and knee, medial lower leg
L4 nerve root	Medial buttock, lateral thigh, medial leg, dorsum of foot, big toe
L5 nerve root	Buttock, posterior and lateral thigh, lateral aspect of leg, dorsum of foot, medial half of sole, first, second, and third toes
S1-S2 nerve roots	Buttock, thigh, and leg posterior
S3 nerve root	Groin, medial thigh to knee
S4 nerve root	Perineum, genitals, lower sacrum

See Also: S1 Nerve Root Examination

See Also: Lumbar Spine Nerve Roots

Dermatomes Testing

Dermatome Testing is performed with a pin and cotton wool. Ask the patient to close their eyes and give the feedback regarding the various stimuli. Testing should be done on specific dermatomes and should be compared to bilaterally.

1. Light Touch Test: Light Touch Sensation – Dab a piece of cotton wool on an area of skin.
2. Pinprick Test: Pain Sensation – Gently touches the skin with the pin ask the patient whether it feels sharp or blunt.

References & More

1. Baglien P, Varacallo M. Anatomy, Shoulder and Upper Limb, Cutaneous Innervation. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK545249/
2. Whitman PA, Launico MV, Adigun OO. Anatomy, Skin, Dermatomes. [Updated 2023 Oct 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535401/
3. Orthopedic Physical Assessment by David J. Magee, 7th Edition.
4. Dermatomes – Physiopedia