Lateral Plantar Nerve: Anatomy, Course, Branches, Function, Clinical Significance, MRI & CT Imaging

Topic

Lateral plantar nerve

The lateral plantar nerve is the smaller terminal branch of the tibial nerve, arising beneath the flexor retinaculum in the tarsal tunnel. It provides both motor and sensory innervation to the lateral aspect of the sole and toes, analogous to the ulnar nerve in the hand.

It passes obliquely across the sole between the first and second muscular layers and divides into superficial and deep branches. The lateral plantar nerve supplies most of the intrinsic muscles of the foot, including those responsible for toe abduction and flexion. Clinically, it is significant in entrapment syndromes, trauma, tarsal tunnel compression, and neuropathies associated with diabetes or overuse.

Synonyms

External plantar nerve
Inferior terminal branch of tibial nerve
Plantar branch of tibial nerve (lateral division)

Origin, Course, and Branches

Origin: Arises beneath the flexor retinaculum from the tibial nerve, posterior to the medial malleolus.
Course:
- Runs obliquely anterolaterally between the flexor digitorum brevis and quadratus plantae.
- Crosses the sole toward the base of the fifth metatarsal.
- Divides into superficial and deep branches.
Branches:
- Superficial branch: Supplies the flexor digiti minimi brevis and the lateral side of the fifth toe; also provides a common digital nerve for the fourth interdigital space.
- Deep branch: Courses medially with the plantar arterial arch and supplies adductor hallucis, quadratus plantae, interossei, and lumbrical III and IV.

Relations

Superiorly: Quadratus plantae and flexor digitorum longus tendons
Inferiorly: Flexor digitorum brevis and plantar aponeurosis
Medially: Medial plantar nerve
Laterally: Abductor digiti minimi muscle
Anteriorly: Deep branch runs alongside the plantar arterial arch beneath adductor hallucis

Function

Motor supply:
- Innervates all intrinsic foot muscles except those supplied by the medial plantar nerve (first lumbrical, abductor hallucis, flexor hallucis brevis, flexor digitorum brevis).
- Controls toe abduction, adduction, and flexion movements.
Sensory supply:
- Provides cutaneous sensation to the lateral one and a half toes (fourth interdigital cleft and fifth toe).
Clinical role:
- Important in toe stability, balance, and gait control.
- Dysfunction leads to weakness of toe abduction and claw toe deformity.

Clinical Significance

Entrapment neuropathy (Baxter’s nerve entrapment): Compression of the first branch of the lateral plantar nerve between the abductor hallucis and quadratus plantae causes heel pain mimicking plantar fasciitis.
Tarsal tunnel syndrome: May involve both medial and lateral plantar nerves, resulting in sensory loss and intrinsic muscle weakness.
Injury: Lacerations or post-surgical scarring may cause pain and sensory deficits in the lateral foot.
Diabetic neuropathy: Can affect plantar nerve function bilaterally, leading to gait imbalance and ulcer risk.
Clinical testing: Loss of sensation in the lateral plantar area and weakness of abductor digiti minimi indicates lesion of this nerve.

MRI Appearance

T1-weighted images:
- Normal nerve: low-to-intermediate signal surrounded by bright plantar fat.
- Course visualized as a thin tubular structure lateral to the medial plantar nerve.
- Entrapment or fibrosis: focal thickening or signal alteration with surrounding fat obliteration.
- Denervation of supplied muscles: increased intramuscular signal (chronic cases show fatty infiltration).
T2-weighted images:
- Normal nerve: intermediate signal, darker than on T1.
- Pathology (neuritis, compression, trauma): hyperintense signal within or around the nerve.
- Denervated muscles: bright hyperintense signal in early edema stage; becomes intermediate in chronic fatty replacement.
- Fluid-sensitive T2 improves visualization of perineural edema or mass effect.
STIR:
- Normal: nerve appears dark.
- Pathology: bright hyperintense signal indicating neuritis, entrapment, or inflammatory edema.
Proton Density Fat-Saturated (PD FS):
- Nerve: low-to-intermediate signal intensity.
- Abnormal: bright focal or diffuse signal in entrapment, neuritis, or trauma.
- Helps delineate relationship with surrounding muscles, fascia, or fibrous bands.
T1 Fat-Sat Post-Contrast:
- Normal nerve: minimal enhancement.
- Pathology: enhancement of the nerve sheath or adjacent fibrosis in neuritis or scarring.
- Entrapment neuropathy: may show linear or nodular enhancement depending on severity.

CT Appearance

Non-Contrast CT:

Nerve not distinctly visible (soft tissue density).
May show secondary signs such as muscle atrophy in the lateral plantar group or fascial thickening in entrapment.
Fat plane loss near abductor hallucis may suggest nerve compression.

MRI images

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