Common Fibular Nerve Injury: A Leading Cause of Foot Drop

Common Fibular Nerve Injury: A Leading Cause of Foot Drop

The common fibular nerve, also known as the common peroneal nerve, is a significant branch of the sciatic nerve. It travels down the outer side of the knee and curves around the neck of the fibula.

This sensitive area, being very close to bone and skin, makes the nerve highly susceptible to injury, fractures, pressure, and severe knee trauma. The most common and serious consequence of damage to this nerve is 'foot drop', where the front part of the foot droops downwards.

Causes of Common Fibular Nerve Injury

Several factors can cause injury to the common fibular nerve. Common culprits include fractures of the fibular head or neck, knee dislocations, severe ligament injuries, and damage to the proximal tibiofibular joint.

Additionally, direct cuts or other forms of penetrating trauma can also damage the nerve. Pressure from artificial devices, such as tight casts or splints, prolonged brace use, sitting with crossed legs for extended periods, and pressure during knee surgery or arthroplasty can also affect the nerve.

Other causes include traction injuries, prolonged immobility, tumor growth, or any other structural pressure.

Symptoms and Identification of Nerve Damage

When the motor function of the common fibular nerve is affected, the ability to lift the ankle (dorsiflexion) weakens, leading to foot drop. In this condition, individuals must lift their foot higher than normal while walking, a gait known as 'high-stepping gait'.

The ability to extend the toes and evert the foot may also be impaired. Sensory symptoms include numbness, tingling, or reduced sensation in the outer front part of the foot and the top of the foot (dorsum). Specifically, testing sensation in the first web space (skin between the first and second toes) can be a significant indicator of deep fibular nerve involvement.

Diagnostic Procedures and Tests

During a clinical examination, doctors conduct detailed tests of various muscle functions and nerve capabilities. The actions of ankle dorsiflexion and great-toe extension are primarily controlled by the deep fibular nerve.

Conversely, foot eversion reflects the function of the superficial fibular nerve. If both dorsiflexion and eversion are weak, but the ability to invert the foot remains normal, it is a strong sign of common fibular neuropathy.

Conversely, if inversion is also found to be weak, an L5 radiculopathy or a more proximal sciatic nerve injury is considered. Typically, significant deficits in deep tendon reflexes (like the knee-jerk reflex) are not observed in common fibular nerve injuries.

Diagnostic Imaging and Studies

Various imaging techniques are used to confirm the diagnosis. X-rays are used to examine the knee, fibular head, and associated fractures.

Advanced techniques such as MRI or ultrasound help detect nerve integrity, any form of compression, hematomas, tumors, or other structural abnormalities. Electromyography (EMG) and Nerve Conduction Studies (NCS) play a crucial role in assessing the precise location, severity, and potential for recovery from nerve injury.

These tests may be repeated as needed after the initial examination. In cases of severe trauma, it is also necessary to investigate other potential problems such as knee ligament injuries, blood vessel damage, and compartment syndrome.

Treatment Options and Rehabilitation

The treatment for common fibular nerve injury depends on the type and severity of the injury. For mild neuropraxia (temporary nerve blockage) or cases of compression, removing the source of pressure, appropriate treatment of associated fractures or dislocations, and regular neurological monitoring are key steps.

In cases of foot drop, an ankle-foot orthosis (AFO) is used to assist with mobility. Alongside this, physiotherapy, active and passive range of motion exercises, and prevention of equinus contracture are integral parts of treatment. If necessary, medications may be prescribed to manage nerve-related pain.

In severe cases, such as open wounds, complete nerve transection, progressive neurological deficits, or clear nerve compression, surgical intervention may be required. This includes surgical exploration of the nerve and decompression. If the nerve is completely damaged, primary nerve repair or nerve grafting may be necessary depending on the level and nature of the injury.

If weakness persists in the foot with inadequate recovery after prolonged treatment, reconstructive surgery options like tendon transfer may be considered for select patients.

Prognosis and Long-Term Management

The prognosis for common fibular nerve injury primarily depends on the severity of the injury. Mild injuries like neuropraxia often resolve spontaneously within weeks or months. However, recovery may be limited in cases of severe axonal injury or neurotmesis (complete nerve disruption).

Following knee dislocations or fibular head fractures, documenting initial motor and sensory examinations along with serial EMG/NCS tests proves vital in guiding treatment. This helps physicians determine if a patient requires only observation and rehabilitation, or if more invasive surgical procedures such as decompression, nerve repair, grafting, or future tendon transfer should be considered.