Deep Fibular (Peroneal) Nerve: Anatomy, Course, Function, and Imaging

Topic

Deep fibular nerve

The deep fibular (peroneal) nerve is the terminal branch of the common fibular (peroneal) nerve, arising near the neck of the fibula. It is a mixed motor and sensory nerve that supplies the anterior compartment muscles of the leg, the dorsum of the foot, and provides cutaneous sensation to the web space between the great and second toes.

This nerve plays a key role in ankle dorsiflexion, toe extension, and foot stabilization. It runs alongside the anterior tibial artery and is clinically important because of its involvement in foot drop, entrapment neuropathies, and traumatic injuries at the ankle or fibular neck.

Synonyms

Deep peroneal nerve
Anterior tibial nerve
Internal popliteal division (historical term)

Origin, Course, and Branches

Origin: Arises as a terminal branch of the common fibular nerve at the bifurcation near the fibular neck.
Course:
- Enters the anterior compartment of the leg by piercing the anterior intermuscular septum and the extensor digitorum longus.
- Descends on the anterior surface of the interosseous membrane, accompanied by the anterior tibial artery.
- At the ankle, it lies between the tendons of the extensor hallucis longus and extensor digitorum longus.
- Divides beneath the extensor retinaculum into medial and lateral terminal branches on the dorsum of the foot.
Branches:
- Muscular branches: To tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius.
- Articular branches: To ankle and tarsal joints.
- Cutaneous branch: Provides sensation to the first interdigital cleft (between hallux and 2nd toe).
- Terminal branches:
  - Medial branch: Sensory to the first web space.
  - Lateral branch: Motor to the extensor digitorum brevis and extensor hallucis brevis.

Relations

Superiorly: Originates near the neck of fibula, deep to the fibularis longus.
In the leg: Lies on the anterior surface of the interosseous membrane with the anterior tibial artery.
At the ankle: Between the tendons of the extensor hallucis longus (medially) and extensor digitorum longus (laterally).
On the dorsum of the foot: Divides into medial (sensory) and lateral (motor) branches beneath the extensor retinaculum.

Function

Motor:
- Controls anterior compartment muscles responsible for ankle dorsiflexion and toe extension.
- Lateral branch innervates extensor digitorum brevis and extensor hallucis brevis on the dorsum of the foot.
Sensory:
- Supplies the first interdigital cleft (between the hallux and second toe).
Reflex and proprioceptive role:
- Provides proprioceptive feedback from the dorsum of the foot and anterior leg.

Clinical Significance

Entrapment neuropathy: Common at the ankle under the extensor retinaculum (anterior tarsal tunnel syndrome).
Foot drop: Caused by injury to the nerve at or near the fibular neck, leading to paralysis of ankle dorsiflexors.
Trauma: May occur due to fractures of the fibula, tight casts, or external compression.
Surgical relevance: Important during ankle arthroscopy, external fixation, or tibial nailing.
Symptoms: Numbness in first web space, weakness of dorsiflexion, or deep aching over dorsum of the foot.

MRI Appearance

T1-weighted images:
- Nerve appears as a thin, low-to-intermediate signal intensity structure surrounded by bright subcutaneous fat.
- Lies adjacent to the anterior tibial artery in the anterior compartment.
- In entrapment or trauma: nerve becomes thickened or shows intermediate signal change.
T2-weighted images:
- Normal nerve shows intermediate signal, slightly darker than on T1.
- Pathologic nerve: bright hyperintense signal compared to muscle (indicative of neuritis, edema, or compression).
- Loss of fascicular architecture seen in severe injury or neuroma formation.
STIR:
- Normal: low-to-intermediate signal.
- Pathology: bright hyperintense nerve with surrounding soft tissue edema or fluid signal.
Proton Density Fat-Saturated (PD FS):
- Normal: well-defined, low-to-intermediate signal fascicular pattern.
- Pathology: diffuse or focal bright signal with surrounding fat suppression, best for subtle neuritis.
T1 Fat-Sat Post-Contrast:
- Normal nerve: no or minimal enhancement.
- Pathology: nodular or diffuse enhancement in inflammatory or post-traumatic neuropathy.
- Perineural scarring enhances; neuromas show irregular enhancement patterns.

CT Appearance

Non-Contrast CT:

Nerve itself poorly visualized due to soft-tissue density similar to surrounding structures.
Indirect signs: adjacent soft tissue swelling, fractures near fibular neck or ankle joint compression.
Useful for detecting osseous causes of nerve entrapment such as osteophytes or fracture callus.

Post-Contrast CT (standard):

Nerve does not enhance distinctly.
Enhancing perineural tissue may indicate inflammation or postoperative fibrosis.
High-resolution CT delineates bony anatomy contributing to compression or entrapment.

MRI images

Topics