Medial plantar nerve !

The medial plantar nerve is a branch of the tibial nerve; it gives feeling to the inner sole and works some small sole muscles.

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What it is

One of the two end branches of the tibial nerve. It starts in the tarsal tunnel behind the inner ankle and runs along the inner sole.

What it does

Carries feeling from the inner sole and the big toe side, and controls a few small muscles of the big toe and sole.

Key facts

Roots: L4–L5 (larger terminal branch of tibial nerve)
Moves: Abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, 1st lumbrical (some texts: first two lumbricals)
Feeling from: Medial two-thirds of sole; plantar side of medial 3½ toes (like median nerve in hand)

Relations

Course: Arises under the flexor retinaculum in the tarsal tunnel, passes deep to the abductor hallucis, runs forward between the abductor hallucis and flexor digitorum brevis and, near the metatarsal bases, gives a proper digital nerve to the medial big toe and three common plantar digital nerves
Superficial: The abductor hallucis, then the plantar aponeurosis
Deep: The flexor hallucis longus and flexor digitorum longus tendons where they cross (knot of Henry)
Lateral: The flexor digitorum brevis; the lateral plantar nerve diverges laterally from it in the tarsal tunnel
Medial: The medial plantar artery

How to find it

It begins behind and below the medial malleolus. In the foot it lies deep to the abductor hallucis along the medial arch, roughly below the navicular tuberosity, where tenderness and Tinel's sign are sought in jogger's foot.

Examination

Tinel's sign over the medial arch at the abductor hallucis: tingling into the medial toes suggests distal medial plantar entrapment; at the tarsal tunnel it suggests a more proximal lesion
Pinprick on the medial sole and the plantar big toe, plus big-toe flexion and abduction strength (the abductor hallucis often wastes first)

On imaging

Too small for radiographs. High-resolution ultrasound can follow it from the tarsal tunnel deep to abductor hallucis. MRI looks for a compressing cause, such as a ganglion, varicose veins or a tendon sheath mass near the knot of Henry, and for denervation oedema in abductor hallucis and flexor digitorum brevis. Nerve conduction studies remain the main test of function.

Common problems

Tarsal tunnel syndrome: the tibial nerve or its plantar branches are squeezed behind the inner ankle, causing burning, tingling or numbness in the sole.
Jogger's foot: irritation of this nerve in the arch.
Causes include swelling, flatfoot, cysts, enlarged veins or scarring after an injury.

How it is diagnosed

A physical exam (tapping over the nerve, Tinel sign); nerve conduction studies and EMG; MRI or ultrasound to look for a cause.

Treatment

Rest, inserts or a brace, medicines for nerve pain, and sometimes an injection.
Surgery to release the flexor retinaculum and free the nerve, if symptoms continue.

Clinical notes

Runners with flat, valgus feet or orthotics that press on the arch are the classic jogger's foot patients
A tibial nerve block behind the medial malleolus numbs it together with the lateral plantar nerve, covering most of the sole
A tarsal tunnel release has to follow both plantar nerves under the abductor hallucis fascia; leaving these distal tunnels tight is a cause of failure

Anatomical variants

The tibial nerve divides into the plantar nerves under the flexor retinaculum in most feet (about 9 in 10) and above it in the rest, so the medial plantar nerve can already be separate before the tunnel

Test yourself

Think of the answer, then tap the question to see it.

Which muscles does the medial plantar nerve supply?

Abductor hallucis, flexor digitorum brevis, flexor hallucis brevis and the first lumbrical.

What is the sensory territory of the medial plantar nerve, and which hand nerve does it resemble?

The medial two-thirds of the sole and the plantar side of the medial 3½ toes, like the median nerve in the hand.

Between which two muscles does the medial plantar nerve run forward in the sole?

The abductor hallucis and the flexor digitorum brevis, with the medial plantar artery on its medial side.

Where is the medial plantar nerve trapped in «jogger's foot»?

Where it passes under the abductor hallucis near the crossing of the long flexor tendons (knot of Henry).

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): nervus plantaris medialis TA2 6590
Official Spanish (DeCS): Nervio plantar medial
English (TA2): Medial plantar nerve
Also called: nervus plantaris tibialis

Sources: Terminologia Anatomica (TA2); Anatomy, Bony Pelvis and Lower Limb, Foot Nerves.

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Representative model, for educational purposes only.

Medial plantar nerve highlighted on the Durgical 3D model