Dermatomes of the Lower Limb

by Imran Hadi

1. About the dermatomes:
(a) it is a specific both-sided group of muscle supplied by motor fibre of single pair of spinal nerve.
(b) each pair of spinal nerve serves its own dermatomes and does not overlap.
(c) injury or infection of spinal nerve or dorsal root ganglion will cause loss of sensation only.
(d) all limb dermatomes are supplied by the anterior ramus of spinal nerve.

2. About the cephalic border:
(a) in lower limb, it is formed by the little toe and fibular border of leg.
(b) due to medial rotation during development of foetus, the cephalic border faced medially.
(c) it is supplied by L2, L5 and S1.

3. Regarding the principal dermatomes of the lower limb:
(a) medial side of great toe is supplied by L5.
(b) anterior surface of lower limb is supplied by L1, L2, L3 and L4.
(c) S1 supplies all surface of foot and posterior surface of lower limb.
(d) L5 only supplies the posterior surface of the lower limb.

4.  Regarding lumbago-sciatica:
(a) patient will feel burning pain and numbness on medial side of the lower limb.
(b) it is due to compression of lumbosacral junction.
(c) it motor S1 root is affected, action of plantarflexion will be weakened.

5. About the myotome of the lower limb:
(a) Flexion at knee joint is caused by L2, L3.
(b) Dorsiflexion at ankle joint is produced by S1, S2.
(c) S2 causes plantar flexion and flexion of the leg.
(d) L2 only flexes of the thigh.