Fibular (peroneal) nerve neuropathy

 

Symptoms and Clinical Presentation of Peroneal Nerve Neuropathy

The primary clinical manifestation of peroneal nerve neuropathy is foot drop, along with associated sensory changes.

 

Motor Deficits (Foot Drop)

When there is a lesion of the common peroneal nerve or its deep branch, the hallmark sign is weakness or inability to perform:

• Dorsiflexion of the foot: Difficulty or inability to lift the foot upwards at the ankle.
• Extension (dorsiflexion) of the toes.
• Eversion of the foot: Difficulty or inability to turn the foot outward (if the superficial peroneal nerve is also involved or if the lesion is at or proximal to the common peroneal nerve).

The foot characteristically hangs down (plantarflexed) and may be slightly turned inward (inverted) due to the unopposed action of the plantarflexor and invertor muscles, which are innervated by the tibial nerve. The Achilles reflex, which is mediated by the tibial nerve (S1-S2 roots), is typically preserved in isolated peroneal neuropathy.

Emaciation (atrophy) of the muscles in the anterolateral compartment of the lower leg may become noticeable with chronic or severe denervation.

 

Sensory Disturbances

Sensory loss or alterations (numbness, tingling, paresthesias) typically occur on the:

• Anterolateral surface of the lower leg.
• Dorsum (top) of the foot.
• Web space between the first and second toes (if the deep peroneal nerve is specifically affected).

The joint-muscular sense (proprioception) in the toes is generally not disturbed, as this sensation is largely carried by fibers that travel with the tibial nerve or other pathways. Pain associated with peroneal nerve neuropathy can vary; it may be significant in acute compressive or traumatic neuropathies, or it can be absent, especially in chronic or insidious onset cases. Trophic disorders (skin changes, ulcerations) are generally not prominent unless there are severe, long-standing sensory deficits or associated vascular issues.

Gait Abnormalities

The patient's gait with peroneal nerve neuritis (or neuropathy) becomes very typical due to the foot drop. This is often described as a "steppage gait" or "peroneal gait" (sometimes "cockerel" or "equine" gait):

• To avoid tripping over the toe of the hanging foot during the swing phase of walking, the patient lifts the leg unusually high by exaggerating hip and knee flexion (like climbing stairs).
• The foot then slaps down onto the floor, often with the toe or outer edge of the foot hitting the ground first, followed by the sole.

Basic functional tests for peroneal nerve involvement include:

1. Inability to perform active dorsiflexion and eversion of the foot.
2. Inability to perform active extension (dorsiflexion) of the toes.
3. Inability to stand on the heels or walk on the heels.

 

Diagnosis of Peroneal Nerve Neuropathy

The diagnosis is often made clinically, supported by electrodiagnostic studies and sometimes imaging.

 

Clinical Examination and Provocative Tests

• Motor Examination: Assessing strength of foot dorsiflexion, toe extension, and foot eversion. Observing gait.
• Sensory Examination: Testing light touch, pinprick, and temperature sensation in the distribution of the peroneal nerve.
• Reflexes: Achilles reflex is typically normal.
• Tinel's Sign: Tapping over the peroneal nerve at the fibular head may reproduce pain or paresthesias in its distribution if there is irritation or compression at that site.
• Palpation: Checking for tenderness, masses, or bony abnormalities around the fibular head.
• Assessment for predisposing factors (e.g., leg crossing habits, recent trauma, weight loss).

 

Electrodiagnostic Studies (EMG/NCS)

Electromyography (EMG) and Nerve Conduction Studies (NCS/ENG) are crucial for:

• Confirming the diagnosis of peroneal neuropathy.
• Localizing the site of nerve injury (e.g., at the fibular head, or more proximally as part of a sciatic neuropathy or L5 radiculopathy).
• Determining the type of nerve injury (axonal loss, demyelination, or mixed).
• Assessing the severity of the neuropathy.
• Providing prognostic information.

NCS typically show slowed conduction velocity or reduced amplitude of nerve signals across the segment of the peroneal nerve at the fibular head if compression is present there. EMG can show signs of denervation (e.g., fibrillation potentials, positive sharp waves) in the muscles innervated by the peroneal nerve.

Imaging Studies

• Ultrasound: High-resolution ultrasound can visualize the peroneal nerve and identify compression, swelling, or structural lesions like ganglion cysts.
• MRI: May be used to evaluate for soft tissue masses, tumors, or to assess nerve inflammation or entrapment in more complex cases, or if a more proximal lesion (e.g., sciatic neuropathy, lumbosacral plexopathy) is suspected. MRI of the lumbar spine may be needed if an L5 radiculopathy is in the differential.
• X-rays: To assess for fractures or bony abnormalities around the knee and fibula.

 

Treatment of Peroneal Nerve Neuropathy

The treatment for peroneal nerve neuritis or neuropathy is selected individually for each case, based on the underlying cause, severity, and duration of symptoms. It often includes a combination of conservative procedures, and in some cases, surgical intervention.

 

Conservative Management

This is the initial approach for most cases, especially those due to compression or mild trauma.

• Avoidance of Precipitating Factors: Modifying behaviors like leg crossing, prolonged squatting, or pressure on the lateral knee.
• Ankle-Foot Orthosis (AFO): A brace worn on the lower leg and foot to support the ankle and prevent the foot from dropping, improving gait and reducing tripping risk.
• Physical Therapy:
  • Exercises to maintain or improve range of motion in the ankle and foot.
  • Strengthening exercises for weakened dorsiflexor and evertor muscles (once reinnervation begins).
  • Stretching exercises for tight calf muscles (which can develop due to foot drop).
  • Gait training.
• Padding or Protection: If external compression is a factor, padding the area around the fibular head.

 

Pharmacological Treatment

• Pain Management: For neuropathic pain or paresthesias, medications like gabapentin, pregabalin, tricyclic antidepressants (e.g., amitriptyline), or SNRIs (e.g., duloxetine) may be prescribed. NSAIDs can help with inflammatory pain.
• Corticosteroids: A short course of oral corticosteroids or a local corticosteroid injection near the site of compression may be considered in some cases to reduce inflammation and swelling around the nerve, though evidence for their routine use is limited.
• Vitamins: Vitamins of group "B" (B1, B6, B12), "C," and "E" are often given as supportive therapy for nerve health.
• Antiviral Drugs: If a viral cause is suspected (rare for isolated peroneal neuropathy but theoretically possible in the context of generalized neuritis), though this is not standard practice.
• Homeopathic Remedies: Some patients may explore homeopathic remedies, but scientific evidence for their efficacy in nerve regeneration is lacking.

 

Rehabilitative Therapies

Elimination of paresthesias and pain, along with restoration of the range of motion in the joints and muscles of the leg and foot affected by peroneal nerve neuropathy, can be accelerated with the use of physiotherapy and other rehabilitative modalities.

• Acupuncture: Can be very effective in managing neuropathic pain and potentially promoting nerve recovery.
• Electrical Stimulation:
  • Nerve Stimulation (e.g., TENS - Transcutaneous Electrical Nerve Stimulation): Can be used for pain relief. Functional Electrical Stimulation (FES) devices can stimulate the peroneal nerve during walking to help lift the foot, acting as an alternative to an AFO in some patients.
  • Muscle Stimulation: Electrical muscle stimulation (EMS) may be used to help maintain muscle mass and prevent atrophy in denervated muscles while awaiting reinnervation.

The TENS procedure can also contribute to the simultaneous stimulation of the patient's calf muscles if applied appropriately, though the primary target for foot drop is the anterior compartment muscles.

Surgical Intervention

Surgery is considered if:

• Conservative management fails after an adequate trial (typically 3-6 months).
• There is evidence of severe nerve damage (e.g., significant axonal loss on EMG/NCS) with no signs of recovery.
• A specific compressive lesion is identified (e.g., ganglion cyst, tumor, fibrous band).
• An open nerve injury (e.g., laceration) has occurred.

Surgical procedures may include:

• Neurolysis (Nerve Decompression): Releasing the nerve from any points of compression or scar tissue, particularly around the fibular head.
• Nerve Repair: For a transected nerve, direct end-to-end repair (neurorrhaphy) may be possible if done early.
• Nerve Grafting: If a segment of the nerve is severely damaged, a nerve graft (often using the sural nerve from the same leg) may be needed to bridge the gap.
• Tendon Transfers: In cases of permanent foot drop with no prospect of nerve recovery, tendon transfer procedures (e.g., transferring the tibialis posterior tendon to the dorsum of the foot) can help restore active dorsiflexion.
• Excision of a compressive mass (e.g., ganglion cyst).

The decision for surgical treatment, including options like neurolysis or stitching of the nerve trunk (neurorrhaphy), is made on an individual basis after thorough evaluation.

 

Differential Diagnosis of Foot Drop and Lower Leg Neuropathy

Foot drop can be caused by lesions at various levels of the nervous system. It's crucial to differentiate peroneal neuropathy from:

Condition	Key Differentiating Features
Common Peroneal Neuropathy (at Fibular Head)	Foot drop (weak dorsiflexion/eversion), sensory loss over anterolateral leg and foot dorsum. Ankle inversion and plantarflexion are normal. Achilles reflex normal. Often history of compression/trauma at fibular head.
L5 Radiculopathy (Sciatic Nerve Root L5)	Foot drop PLUS weakness of foot inversion (tibialis posterior, also L5 innervated via tibial nerve) and often hip abduction (gluteus medius, L5). Sensory loss in L5 dermatome. Back pain/sciatica common. Reflexes may be altered depending on other root involvement. Hamstring reflex may be diminished.
Sciatic Neuropathy (Proximal to Peroneal Branching)	Foot drop PLUS weakness of plantarflexion (tibial nerve) and knee flexion (hamstrings). Sensory loss in both peroneal and tibial distributions. Absent Achilles reflex.
Lumbosacral Plexopathy	More widespread weakness and sensory loss in the leg, often asymmetrical, involving multiple nerve distributions. Can be caused by trauma, tumor, inflammation, diabetes.
Motor Neuron Disease (e.g., ALS)	Progressive weakness, may start with foot drop, but often associated with fasciculations, muscle atrophy, hyperreflexia (or mixed UMN/LMN signs). Sensory examination usually normal.
Peripheral Polyneuropathy (e.g., Diabetic, Alcoholic, CIDP)	Usually symmetrical, distal weakness and sensory loss ("stocking-glove" pattern). Foot drop can be a feature if severe. Other nerves often involved.
Central Causes (Stroke, Brain Tumor, Spinal Cord Lesion - Rare for isolated foot drop)	Associated with upper motor neuron signs (spasticity, hyperreflexia, Babinski sign) and other neurological deficits.
Anterior Compartment Syndrome (Acute)	Severe pain, swelling, tenseness in anterior leg compartment, often after trauma or exertion. Foot drop is a late sign. Medical emergency.

 

Prognosis and Potential Complications

The prognosis for peroneal nerve neuropathy depends on the cause, severity, and duration of nerve injury, as well as the timeliness of treatment.

• Neurapraxia (mild compression, conduction block without axonal damage): Often has a good prognosis with full recovery within weeks to a few months once the compression is relieved.
• Axonotmesis (axonal damage but nerve sheath intact): Recovery is possible through axonal regeneration (about 1 mm/day or 1 inch/month) but may be slow and incomplete.
• Neurotmesis (complete nerve transection or severe damage): Recovery is poor without surgical repair, and even then, outcomes can be variable.

Potential complications include:

• Persistent foot drop and gait disturbance.
• Chronic pain or paresthesias.
• Muscle atrophy in the anterolateral leg compartment.
• Ankle instability and increased risk of falls or ankle sprains.
• Development of contractures (e.g., Achilles tendon tightness).
• Skin breakdown or injury on the foot due to sensory loss and altered gait.

 

Prevention Strategies

Preventive measures can reduce the risk of some types of peroneal neuropathy:

• Avoid prolonged leg crossing or squatting.
• Ensure proper positioning during surgery or prolonged bed rest to avoid pressure on the fibular head.
• Use caution with tight casts or braces around the knee.
• Manage underlying conditions like diabetes effectively.
• Be mindful of activities that could lead to direct trauma to the lateral knee.

 

When to Consult a Neurologist or Neurosurgeon

Medical evaluation by a neurologist, neurosurgeon, or physiatrist (rehabilitation physician) is recommended if an individual experiences:

• Sudden or gradual onset of foot drop (difficulty lifting the foot or toes).
• Tripping or stumbling frequently.
• Numbness, tingling, or pain on the outer aspect of the lower leg or top of the foot.
• Noticeable weakness in foot or ankle movements.
• A "steppage" gait.
• Following an injury to the knee or lower leg that results in these symptoms.

Early diagnosis and appropriate management can optimize the chances of recovery and prevent long-term disability.