Plantar Nerve Supply

Introduction

Introduction to the Plantar Nerve Supply

The nerve supply of the sole of the foot is derived entirely from the tibial nerve, the larger terminal branch of the sciatic nerve. After traversing the popliteal fossa and the posterior compartment of the leg, the tibial nerve enters the foot through the tarsal tunnel, passing behind the medial malleolus deep to the flexor retinaculum. Within the tunnel, it divides into its two terminal branches: the medial plantar nerve and the lateral plantar nerve. These nerves provide motor innervation to all the intrinsic muscles of the sole and sensory innervation to the skin of the plantar surface, including the toes. The medial calcaneal branches, which arise proximal to the division, supply the skin of the heel. The distribution of these nerves is analogous to that of the median and ulnar nerves in the hand, with the medial plantar nerve supplying the majority of the intrinsic muscles and the lateral plantar nerve supplying the remainder and most of the deep muscles. Knowledge of the plantar nerve anatomy is essential for understanding entrapment neuropathies, such as tarsal tunnel syndrome and Baxter’s neuropathy, as well as sensory loss patterns in peripheral neuropathies and after surgical procedures.

Study

1. Tibial Nerve in the Tarsal Tunnel

The tibial nerve (L4–S3) descends in the posterior compartment of the leg and enters the foot by passing behind the medial malleolus through the tarsal tunnel. The tunnel is roofed by the flexor retinaculum and contains from anterior to posterior: the tibialis posterior tendon, flexor digitorum longus tendon, posterior tibial artery and vein, tibial nerve, and flexor hallucis longus tendon. Within the tunnel or just distal to it, the tibial nerve divides into the medial and lateral plantar nerves. Proximal to this division, it gives off the medial calcaneal branches (usually one to three) that pierce the flexor retinaculum to supply the skin of the heel and the medial aspect of the sole. These branches are variable and are at risk during surgical approaches to the tarsal tunnel.

2. Medial Plantar Nerve

The medial plantar nerve is the larger of the two terminal branches of the tibial nerve. It arises deep to the abductor hallucis muscle and runs forward in the sole between the abductor hallucis and flexor digitorum brevis (first layer), accompanied by the medial plantar artery. It is analogous to the median nerve in the hand. The medial plantar nerve gives off muscular, cutaneous, and articular branches.

Muscular branches: It supplies four intrinsic muscles: abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and the first (most medial) lumbrical. The branch to the flexor hallucis brevis may be given off in common with the branch to the first lumbrical.

Cutaneous branches: The nerve gives off a medial proper digital nerve to the medial side of the great toe, and then divides into three common plantar digital nerves. These run between the first and second, second and third, and third and fourth metatarsal spaces, respectively. Each common digital nerve splits into two proper plantar digital nerves that supply the adjacent sides of the toes. Thus, the medial plantar nerve supplies the skin of the medial three and a half toes (great toe, second, third, and medial half of the fourth toe), mirroring the median nerve distribution in the hand.

Articular branches: Small twigs supply the tarsal and tarsometatarsal joints on the medial side.

3. Lateral Plantar Nerve

The lateral plantar nerve is the smaller terminal branch. It runs laterally and forward between the flexor digitorum brevis and quadratus plantae (first and second layers), accompanied by the lateral plantar artery. At the base of the fifth metatarsal, it divides into superficial and deep branches. It is analogous to the ulnar nerve in the hand.

Superficial branch: This branch supplies the flexor digiti minimi brevis and the abductor digiti minimi (muscles of the lateral compartment). It then gives off two cutaneous branches: a proper digital nerve to the lateral side of the little toe, and a common plantar digital nerve that splits to supply the adjacent sides of the fourth and fifth toes. Thus, the superficial branch supplies the skin of the lateral one and a half toes (lateral half of the fourth toe and the entire little toe).

Deep branch: This is a motor nerve. It curves medially with the deep plantar arch (between the third and fourth layers) and supplies all the remaining intrinsic muscles: the second, third, and fourth lumbricals, the adductor hallucis (both heads), and all dorsal and plantar interossei. It also sends a branch to the flexor hallucis brevis (sometimes this is from the medial plantar nerve, but the deep branch usually contributes to the lateral head). The deep branch is at risk during surgical approaches to the deep plantar structures.

4. Sensory Innervation of the Sole

The skin of the sole is supplied by three sources: (1) Medial calcaneal branches (from the tibial nerve or sometimes the lateral plantar nerve) supply the heel area. (2) Medial plantar nerve supplies the medial two-thirds of the sole and the plantar aspect of the medial three and a half toes. (3) Lateral plantar nerve (superficial branch) supplies the lateral one-third of the sole and the plantar aspect of the lateral one and a half toes. The dorsal surface of the toes is supplied by the superficial and deep fibular nerves, except the nail beds and tips of the toes which are supplied by the plantar digital nerves curving dorsally. This dual innervation of the toe tips is important for digital nerve blocks. The saphenous nerve (from the femoral nerve) supplies the medial side of the foot up to the ball of the great toe, overlapping with the medial plantar nerve. The sural nerve supplies the lateral border of the foot.

5. Clinical Relevance

Tarsal tunnel syndrome: Compression of the tibial nerve or its branches within the tarsal tunnel causes burning pain, paraesthesia, and numbness in the sole and toes, often sparing the heel (if the calcaneal branch arises proximal to the compression). Tinel’s sign is positive behind the medial malleolus. Causes include ganglion cysts, varicosities, tenosynovitis, and post-traumatic fibrosis. Electrodiagnostic studies and MRI can confirm the diagnosis. Treatment ranges from conservative management to surgical decompression.

Baxter’s neuropathy (inferior calcaneal nerve entrapment): The first branch of the lateral plantar nerve (Baxter’s nerve) innervates the abductor digiti minimi and the flexor digitorum brevis. Entrapment occurs at the medial edge of the quadratus plantae or under the deep fascia of the abductor hallucis. It presents with chronic lateral heel pain, often misdiagnosed as plantar fasciitis, and may show isolated atrophy of the abductor digiti minimi. Surgical release may be required.

Medial plantar nerve entrapment (jogger’s foot): Repetitive trauma in runners can compress the medial plantar nerve as it passes under the navicular tuberosity or at the knot of Henry, causing medial arch pain radiating to the toes. This condition is also seen in pes planus.

Morton’s neuroma: A perineural fibrosis of an interdigital nerve, most commonly the third common plantar digital nerve (between the third and fourth metatarsals). It causes sharp, burning pain in the web space and toes, often relieved by removing shoes and massaging the foot. It is thought to result from compression of the nerve between the metatarsal heads and the deep transverse metatarsal ligament. Surgical excision or neurolysis may be performed.

Diabetic neuropathy: The plantar nerves are commonly affected in length-dependent diabetic polyneuropathy, leading to loss of protective sensation in the sole. This predisposes to neuropathic ulcers, especially over the metatarsal heads and heel. Regular monofilament testing is essential for prevention.

Local anaesthetic blocks: The posterior tibial nerve can be blocked at the ankle for procedures on the sole. Toe digital blocks must be performed from the dorsal aspect, but the plantar digital nerves must be anesthetized as well, often requiring a ring block due to the dual innervation of the toe tips.

Summary

Summary of Plantar Nerve Supply

The sole is innervated by the tibial nerve via its terminal branches: the medial and lateral plantar nerves. The medial plantar nerve supplies four intrinsic muscles (abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, first lumbrical) and the skin of the medial three and a half toes. The lateral plantar nerve divides into a superficial branch (supplying abductor digiti minimi, flexor digiti minimi brevis, and the lateral one and a half toes) and a deep branch (supplying the remaining lumbricals, adductor hallucis, and all interossei). The heel is supplied by medial calcaneal branches. Key clinical entities include tarsal tunnel syndrome, Baxter’s neuropathy, jogger’s foot, and Morton’s neuroma.