Common Peroneal Nerve Injury – When the Foot Stops Lifting

Suddenly the foot starts to drop when walking, the toes can no longer be lifted, and there is numbness on the top of the foot – such symptoms may point to an injury of the common peroneal nerve at the level of the fibular head. This condition is known as a common peroneal nerve palsy or fibular head neuropathy, and is one of the most common peripheral nerve injuries in the lower limb. Early diagnosis can help prevent long-term impairment.

What is the Common Peroneal Nerve?

The common peroneal nerve (also called the common fibular nerve) is a branch of the sciatic nerve. It curves around the head of the fibula (fibular head) from behind and then divides into two main branches:

the superficial peroneal nerve, which supplies the evertor muscles of the foot (such as the peroneus longus and brevis) and provides sensation to the lower leg and top of the foot
and the deep peroneal nerve, which controls the muscles that lift the foot and provides sensation between the first and second toes.

At the level of the fibular head, the nerve runs very close to the skin and has little protection. Even minor pressure or stretching can lead to functional problems.

Schematic illustration of the common peroneal nerve branching into superficial and deep branches, with a circle highlighting the typical injury site near the fibular head. — Course of the common peroneal nerve with division into superficial and deep branches. The typical injury site at the fibular head is marked with a circle.

Typical Symptoms

A lesion of the common peroneal nerve may cause a range of symptoms, depending on the location and severity of the injury:

Foot drop – the toes cannot be lifted while walking (“steppage gait”)
Numbness or tingling on the top of the foot or outer lower leg
Loss of sensation between the big toe and the second toe
In severe cases: complete paralysis of the foot lifting muscles

Illustration showing a woman who cannot lift her left foot following leg crossing, indicating possible nerve involvement. — Crossing the legs can cause peroneal nerve palsy with weakness in lifting the foot.

Some people notice symptoms immediately after an accident or surgery; in others, they develop gradually.

Causes and Risk Factors

The most common causes of common peroneal nerve injury at the fibular head include:

1. Trauma and fractures

Fibular head fracture (e.g. after twisting the ankle or falling)
Knee dislocation or complex ligament injury, which may stretch or compress the nerve
Tibial plateau fractures with associated nerve involvement

2. Prolonged pressure or positioning

Lying on one side for an extended period
Poor padding during surgery
Prolonged immobility (e.g. in intensive care or unconscious patients)

3. External compression

Sitting with one leg crossed over the other
Kneeling activities on the ground
Tight plaster casts, braces, or splints
Bandages or pressure from medical devices

Illustration of a woman experiencing foot lift weakness after kneeling during gardening, indicating possible peroneal nerve involvement. — Kneeling activities, such as gardening, can cause damage to the peroneal nerve, leading to weakness in lifting the foot.

4. Other causes

Space-occupying lesions such as cysts or tumors
Scarring from previous surgery

Because the nerve is fixed against the fibula and not well protected, it is particularly vulnerable to injury.

Differential Diagnoses

Other conditions can cause similar symptoms, so accurate diagnosis is essential. Important alternatives to consider include:

Lumbar disc herniation (L5 radiculopathy)
Lumbosacral plexus injury
Sciatic nerve damage (e.g. in the buttock or thigh)
Central nervous system conditions (e.g. stroke)

Additionally, diabetes mellitus can lead to nerve problems and should be distinguished from localized compression.

Diagnostic Evaluation

Clinical examination

The first step is a thorough neurological exam to assess strength, reflexes, and sensation. A combination of foot drop and numbness on the foot dorsum often points to the common peroneal nerve.

Nerve conduction studies and EMG

Electrodiagnostic tests such as nerve conduction studies (NCS) and electromyography (EMG) can help assess how well the nerve is functioning.
The exact lesion site can be difficult to localize using electrodiagnostic tests alone, since nerve conduction studies assess long-range signal flow and EMG reflects downstream muscle activity rather than structural nerve changes.

High-resolution nerve ultrasound

Particularly for superficial nerves like the common peroneal nerve, high-resolution nerve ultrasound has become a valuable tool. It allows for direct visualization of the nerve’s course at the fibular head and can help detect structural abnormalities. Metal implants do not pose a limitation.

What ultrasound may reveal:

Swelling or thickening of the nerve
Compression by adjacent structures (e.g. fracture, cyst, external pressure)
Disruption or discontinuity of the nerve
Lack of mobility of the nerve during movement
Scar tissue or adhesions after trauma or surgery

The nerve can also be traced distally to detect more diffuse involvement or to differentiate it from more proximal lesions.

A major advantage of ultrasound is the ability to perform a dynamic evaluation – meaning the nerve can be assessed during movement or positional changes. This can provide functional information beyond what static imaging or electrical testing can offer.

Why Early Diagnosis Matters

Timely and structured evaluation is especially important in cases of common peroneal nerve injury. If there is complete loss of nerve function and no sign of recovery, surgical decompression (neurolysis) may be considered after thorough evaluation.

Even in milder cases, identifying the cause early on – such as a poorly positioned cast or local pressure – can help relieve the nerve and prevent worsening of symptoms.

Conclusion: When the Nerve at the Fibular Head Is Affected

Common peroneal nerve palsy at the fibular head is a relatively common but often underestimated cause of foot drop and sensory disturbances in the lower leg. It may result from trauma, positioning, or mechanical compression.

Accurate diagnosis is key. High-resolution nerve ultrasound plays an increasingly important role in evaluating this nerve – offering structural insights without radiation and allowing real-time, individualized assessment.

Disclaimer: The information provided on this page is for general informational purposes only and does not constitute medical advice. It is not a substitute for personal consultation, examination, or treatment by a physician or other qualified healthcare professional. No guarantees of healing or cure are made. While we strive for accuracy and completeness, we cannot guarantee that all content is up to date or free from errors, and we accept no liability for any inaccuracies.