Dermatomes of the lower limb

Dermatomes of the lower limb are defined as the areas of the skin on the lower leg supplied by a single spinal nerve (afferent nerve fiber). Spinal nerves are a part of the peripheral nervous system (PNS). Your PNS functions to link the rest of your body with your CNS.

Each of your dermatomes is connected with one spinal nerve. These nerves are generally afferent nerves that transmit sensations such as pain, from a particular area of your skin to your CNS. Dermatomes are distributed into segments throughout your body. The exact pattern of dermatome may differ from person to person.

The dermatome pattern is a bit more different along the arms and the legs. As in the lower limb, you can see the anterior leg dermatome pattern is different from the posterior leg dermatome pattern. The dermatomes run longitudinally along with the limbs, and so that each half of the limb has a different dermatome.

Why is the testing of dermatomes necessary?

Testing dermatomes is a part of neurological examinations as it helps in assessing and diagnosing a variety of conditions. Symptoms that occur along a specific dermatome of the lower limb, such as pain, tingling, or a rash, may indicate a problem that involves the related nerve root.

Examples of these problems include –

Radiculopathies 

This describes the state where a nerve root in the spine is compressed or pinched. Symptoms may include fatigue, pain, and tingling sensations. Pain from radiculopathies may accompany one or more dermatomes. One kind of radiculopathy is sciatica. Sciatica generally affects the right side of the body. The most common cause of sciatica is rightward herniation of the disc below the fifth lumbar vertebra (L5), which causes irritation or compression of the sciatic nerve root.

Shingles

Shingle is a viral infection caused by the same virus as chickenpox (varicella-zoster). After encountering chickenpox once in a lifetime, the virus stays dormant in the nerve roots of your body and can be reactivated in the later phase of life as shingles. Anybody who has had chickenpox once in a lifetime can go on to develop shingles.

The virus inflames the spinal nerve along a particular skin dermatome. Symptoms of shingles include pain, redness, rash on the skin that occur along the specific dermatome on one side of the body either left or right.

Distribution of lower limb dermatomes

In lower limb dermatomes are distributed on the thighs, knees, legs, and the foot on both side anteriorly as well as posteriorly.

Here is the diagrammatic representation of the lower limb divided on the basis of the areas.

Your dermatomes are numbered according to what spinal nerves they correspond to. Below, we will outline each dermatome of the lower limb, and also the area of the body that is associated with that particular dermatome. L2 to S5 spinal nerves supply the lower limb.

Bear in mind that the specific area that a dermatome may cover may differ by person. Some overlapping is also possible. Therefore, consider the below table as an outline to be a general guide.

Spinal Nerves	Area Covered
L2	Upper 2/3rd of the thigh (Anterior, Medial and Lateral)
L3	Lower 1/3rd of the Thigh (Anterior, Medial and Lateral) and the whole Knee
L4	Medial side of the Leg anteriorly
L5	Lateral side of the Leg anteriorly and the Medial side of the foot anteriorly and posteriorly
S1	Whole ankle (Anteriorly as well as posteriorly) and the lateral side of foot both anteriorly and posteriorly
S2	Posterior aspect of the Thigh, Knee and the Leg
S3, S4, S5	Concentric rings around the anus and the outermost is S3

As it is clear that dermatomes are numbered according to what spinal nerves they correspond to. So here is the diagrammatic representation of showing dermatomes of the lower limb along with area wise distribution.

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