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Medial branch of deep fibular nerve

The medial branch of the deep fibular (peroneal) nerve is the terminal sensory division of the deep fibular nerve on the dorsum of the foot. It provides sensory innervation to the first interdigital (web) space between the hallux and second toe, and a small motor component to the extensor digitorum brevis and extensor hallucis brevis muscles before becoming purely cutaneous.

This branch is clinically significant because of its superficial course across the dorsum of the foot, making it prone to compression, trauma, or entrapment—commonly referred to as anterior tarsal tunnel syndrome. It is also a key nerve evaluated in neuropathy, ankle trauma, and surgical procedures involving the dorsum of the foot.

Synonyms

  • Medial dorsal cutaneous branch of deep fibular nerve

  • Medial terminal branch of deep peroneal nerve

  • Nerve of the first web space

Origin, Course, and Termination

  • Origin: Arises from the deep fibular nerve beneath the inferior extensor retinaculum of the ankle, after the nerve passes deep to the extensor hallucis longus tendon.

  • Course: Runs forward on the dorsum of the foot, lying lateral to the tendon of extensor hallucis longus and medial to extensor digitorum longus tendon. It accompanies the dorsalis pedis artery, supplying small twigs to adjacent muscles and skin.

  • Termination: Divides into two dorsal digital branches supplying the adjacent sides of the great toe and second toe in the first web space.

Relations

  • Superiorly: Extensor hallucis longus tendon

  • Inferiorly: Dorsal surface of the first metatarsal bones

  • Medially: Dorsalis pedis artery

  • Laterally: Tendon of extensor digitorum longus to the second toe

  • Anteriorly: Skin of the first interdigital cleft

  • Posteriorly: Capsule of the metatarsophalangeal joints

Function

  • Sensory: Provides cutaneous innervation to the skin of the first web space (between hallux and second toe)

  • Motor: Small branches to the extensor hallucis brevis and extensor digitorum brevis before becoming purely sensory

  • Proprioceptive: Contributes to proprioception of the first ray during dorsiflexion and toe extension

Clinical Significance

  • Entrapment: Occurs beneath the inferior extensor retinaculum (anterior tarsal tunnel syndrome)

  • Symptoms: Dorsal foot pain radiating to first web space, numbness, or burning sensation

  • Trauma: Nerve can be injured during ankle sprains, fractures, or dorsal foot incisions

  • Surgical relevance: At risk during anterior ankle approaches or tendon repairs

  • Imaging role: MRI and ultrasound used to detect nerve thickening, edema, or compression

MRI Appearance

  • T1-weighted images:

    • Normal nerve: low to intermediate signal, thin linear structure

    • Lies adjacent to the dorsalis pedis artery and between EHL and EDL tendons

    • Pathology: focal or diffuse thickening, intermediate signal increase in neuritis or entrapment

    • Fat planes around the nerve appear bright

  • T2-weighted images:

    • Normal: intermediate to mildly hyperintense compared to muscle

    • Pathology: increased T2 signal intensity in neuritis, compression, or trauma

    • Perineural edema appears as bright halo around the nerve

  • STIR:

    • Normal:  low to intermediate signal 

    • Entrapment or inflammation: marked hyperintensity, with perineural fluid signal under retinaculum

  • Proton Density Fat-Saturated (PD FS):

    • Normal: low to intermediate signal with uniform outline

    • Pathology: bright focal or diffuse signal changes indicating edema or inflammation

    • Excellent for detecting subtle entrapment neuropathy

  • T1 Fat-Sat Post-Contrast:

    • Normal nerve: minimal or no enhancement

    • Neuropathy: linear or nodular enhancement along nerve course

    • Entrapment or neuritis: patchy or diffuse enhancement with perineural soft tissue enhancement

CT Appearance

Non-Contrast CT:

  • Nerve not directly visible due to small caliber

  • Indirect findings: Soft tissue swelling or scarring near the extensor retinaculum

  • Bony abnormalities: Hypertrophic spurs or accessory ossicles compressing the nerve (e.g., os intermetatarseum)

 

MRI image

Medial branch of deep fibular nerve coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Medial branch of deep fibular nerve coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Medial branch of deep fibular nerve coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002