Anatomy, Bony Pelvis and Lower Limb: Calf Deep Peroneal Nerve (Deep Fibular Nerve)

Structure and Function

The deep fibular nerve is a terminal branch of the common fibular (common peroneal) nerve, arising in the lateral compartment of the leg where the common fibular nerve bifurcates into its superficial and deep branches. The deep fibular nerve's origin occurs between the upper segment of the fibularis longus (peroneus longus) muscle and the head of the fibula. The common fibular nerve (L4-S2) arises from the bifurcation of the sciatic nerve (L4-S3) into the tibial and common fibular nerves at the apex of the popliteal fossa.[3][4] (Source: Standring, 2016)

Following its origin near the proximal fibula, the deep fibular nerve travels obliquely forward beneath the extensor digitorum longus. The nerve passes through the intermuscular septum into the anterior compartment and comes into proximity with the anterior tibial artery in the upper 1/3 of the leg. The nerve and artery descend together within the anterior compartment. During this descent, the deep fibular nerve initially lies lateral to the anterior tibial artery, then crosses anterior to it, and ultimately returns to a lateral position as it approaches the ankle (see Image. Deep Fibular Nerve and Related Structures).[5]

Along its course, the deep fibular nerve gives off several motor branches that supply key muscles of the anterior compartment, including the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius. These muscles primarily produce dorsiflexion of the foot and assist with extension of the toes. The tibialis anterior also contributes to inversion of the foot.[6] The deep fibular nerve provides minimal sensory input to the anatomical leg, alongside an articular branch to the ankle joint. The nerve divides into lateral and medial terminal branches at the level of the ankle.

The lateral terminal branch courses deep to the extensor digitorum brevis, supplying motor innervation to both this muscle and the extensor hallucis brevis. Three interosseous branches arise from the lateral terminal branch and serve the tarsal and metatarsophalangeal (MTP) joints of the 2nd to 4th digits. A separate branch supplies the sinus tarsi, a small cone-shaped cavity located on the lateral aspect of the foot between the talus and calcaneus.[7]

The medial terminal branch continues along the dorsum of the foot, positioned just lateral to the dorsalis pedis artery, the distal continuation of the anterior tibial artery. An interosseous branch supplies the 1st MTP joint. This terminal branch then divides into 2 dorsal digital nerves that supply the 1st web space.

Embryology

The peripheral nervous system, including the deep fibular nerve, originates from neural crest cells during early embryogenesis. The deep fibular nerve arises from the posterior divisions of the L4 to S2 spinal nerves as a terminal branch of the common fibular nerve.

Blood Supply and Lymphatics

Peripheral nerves, including the deep fibular nerve, receive their blood supply from small arterial branches known as the vasa nervorum, which arise from adjacent vessels. Within the anterior compartment of the leg, the deep fibular nerve courses alongside the anterior tibial artery, which provides the predominant vascular input.

The vasa nervorum supply both the extrinsic (epineurial) and intrinsic (endoneurial) vascular systems. Along the nerve's course, these vessels form anastomoses that create a continuous microvascular network, preserving nerve viability even in regions with wider spacing between arterial sources, such as the anterior tibial artery.[8]

Compared to nerves such as the sciatic or tibial, which receive blood from multiple arteries, the deep fibular nerve typically demonstrates less vascular redundancy and may depend on a single dominant artery. This anatomical feature increases vulnerability to ischemic injury and may constrain recovery after trauma or surgical intervention.[9][10] In the foot, the distal segments of the nerve may also receive vascular supply from branches of the dorsalis pedis artery.[11]

Muscles

Within the anterior (extensor) compartment of the leg, the deep fibular nerve supplies the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius muscles. The tibialis anterior produces dorsiflexion and contributes to inversion of the foot. The extensor hallucis longus facilitates dorsiflexion and extends the hallux at the interphalangeal and MTP joints. The extensor digitorum longus contributes to dorsiflexion and extends the lateral 4 toes. The fibularis tertius assists in both dorsiflexion and eversion of the foot. In the foot, the deep fibular nerve also innervates the extensor hallucis brevis, which aids in extension of the hallux at the MTP joint, and the extensor digitorum brevis, which facilitates extension of the 2nd to 4th digits (see Image. Anterior Compartment Muscles of the Leg and Dorsum of the Foot).

Physiologic Variants

The accessory deep fibular nerve is a physiological variant that typically arises from the superficial fibular nerve or one of its branches. This structure provides motor innervation to the extensor digitorum brevis and sensory innervation to the lateral aspect of the ankle and foot. Although the extensor digitorum brevis is usually solely supplied by the deep fibular nerve, studies have indicated that in up to 28% of individuals, one or both of the extensor digitorum brevis muscles may receive partial or complete innervation from the accessory deep fibular nerve. This anatomical variation occurs equally among male and female individuals and is believed to follow an autosomal dominant inheritance pattern with incomplete penetrance.[12]

A recent electrophysiological study conducted in Bosnia and Herzegovina identified the accessory deep fibular nerve in 14.5% of the lower limbs examined. Bilateral involvement was observed in 5.8% of the subjects, and no significant differences were found based on sex or laterality (right vs. left).[13]

Surgical Considerations

Fasciotomy

The deep fibular nerve is at risk of injury during anterior compartment fasciotomy due to its close proximity to the anterior tibial artery and vein. Surgical release of the anterior compartment fascia requires careful dissection to prevent iatrogenic damage. Injury to the deep fibular nerve may result in foot drop due to loss of dorsiflexion, along with sensory loss in the 1st web space. Prompt recognition of compartment syndrome and anatomically precise dissection are critical to preserving nerve integrity and function.[14]

Anterior Tarsal Tunnel Decompression

Anterior tarsal tunnel decompression is a surgical procedure performed to relieve entrapment of the deep fibular nerve beneath the inferior extensor retinaculum. This intervention is indicated in patients with persistent symptoms despite conservative therapy. Intraoperative care is required to avoid injury to the nerve and adjacent vascular structures. Successful decompression can reduce dorsal foot pain, motor weakness, or numbness attributable to anterior tarsal tunnel syndrome. Reported complications include iatrogenic nerve injury and atrophy of the extensor hallucis brevis, particularly in advanced or delayed presentations.[15]

External Fixation and Anterior Tibial Pin Placement

The tibia can be divided into 4 longitudinal zones to evaluate the risk of deep fibular nerve injury during anterior tibial pin placement for external fixation. In Zone 1, the nerve curves around the fibular neck and courses along the interosseous membrane near the proximal tibia. In Zone 2, the nerve remains on the interosseous membrane but is positioned along the posterior margin of the lateral tibial cortex. In Zone 3, the nerve shifts anteriorly, leaving the interosseous membrane to lie directly against the tibial surface. In Zone 4, the nerve traverses the anterior aspect of the distal tibia. Cadaveric studies have demonstrated that Zones 2 and 3 carry the highest risk of iatrogenic injury to the deep fibular nerve during external fixator pin placement.[16]

Clinical Significance

Deep fibular nerve injury or dysfunction may result in several clinically significant conditions. These conditions include anterior compartment syndrome, anterior tarsal tunnel syndrome, and foot drop.

Compartment syndrome constitutes a surgical emergency defined by elevated pressure within a closed fascial compartment, leading to compromised perfusion, ischemia, and potential tissue necrosis. Anterior compartment syndrome of the leg may occur secondary to tibial fractures, soft tissue trauma, crush injuries, vascular compromise, tight circumferential dressings, or extreme physical exertion. Although most cases follow direct trauma, reports have described atraumatic anterior compartment syndrome in pediatric patients with leukemia.

Pain out of proportion to the injury, particularly with passive stretch, is among the earliest and most reliable clinical findings. Additional features may include paresthesia in the 1st web space, firm swelling of the anterior leg, and progressive motor weakness. Diagnosis is primarily clinical, although an intracompartmental pressure of at least 30 mm Hg warrants fasciotomy. Timely surgical decompression, ideally within 6 hours, is essential to avoid permanent neuromuscular damage.[17]

The classic clinical features of compartment syndrome are summarized by the “6 Ps”: pain, poikilothermia, paresthesia, paralysis, pulselessness, and pallor. These findings may occur in compartment syndromes involving any extremity or anatomical region, not limited to the leg.

Anterior tarsal tunnel syndrome is a compression neuropathy of the deep fibular nerve as it passes beneath the inferior extensor retinaculum at the anterior ankle. Possible causes include acute trauma, repetitive microtrauma, and external compression from tight footwear, athletic equipment, or military boots. Space-occupying lesions, such as ganglion cysts, varicosities, or dorsal osteophytes, as well as a hypertrophied extensor hallucis brevis muscle, may also contribute to entrapment.

Clinical manifestations include dorsal foot pain, sensory disturbance in the 1st web space, and, in some cases, weakness of toe extension. Diagnosis is based on clinical findings but may be supported by electromyography, nerve conduction studies, magnetic resonance imaging, or ultrasonography. Initial treatment involves conservative measures such as footwear modification and activity restriction. Surgical decompression of the inferior extensor retinaculum may be indicated for persistent or functionally limiting cases.

Foot drop refers to impaired dorsiflexion of the foot, often resulting in a high-stepping gait pattern and increased fall risk. This condition arises from weakness or paralysis of the anterior compartment muscles, which control dorsiflexion. Common causes include injury to the deep or common fibular nerve, radiculopathy of the 5th lumbar spinal nerve, and upper motor neuron lesions. Contributing factors may include direct trauma, prolonged external compression, nerve root impingement, or underlying neuromuscular disorders. Less frequently, metabolic and autoimmune conditions, such as diabetes mellitus, vasculitis, or Guillain-Barré syndrome, may result in foot drop. Diagnostic evaluation begins with a comprehensive neurologic and musculoskeletal examination, followed by imaging and electrodiagnostic studies to localize the lesion and determine the condition's severity.