eMedicine Specialties > Neurology > Electromyography and Nerve Conduction Studies

Peroneal Mononeuropathy

Pinky Agarwal, MD, Clinical Assistant Professor, Department of Neurology, University of Washington; Attending Neurologist, Booth Gardner Parkinson's Care Center
Alida Griffith, MD, Movement Disorders Neurologist, Booth Gardner Parkinson's Care Center

Updated: Nov 18, 2009

Introduction

Background

Mononeuropathies can occur secondary to direct trauma, compression, stretch injury, ischemia, infection, or inflammatory disease. Dancers are also prone to superficial and deep peroneal nerve entrapments.¹

Nerve entrapments are due to compression of the nerve by either normal structures or an external source. The most common nerve entrapments are at the median nerve of the wrist (ie, carpal tunnel syndrome) and ulnar nerve of the elbow (ie, cubital tunnel syndrome). For more information, see eMedicine article Nerve Entrapment Syndromes.

In the lower extremity, peroneal neuropathy is the most common isolated mononeuropathy. In patients of our electrodiagnostic laboratory, it is the third most common mononeuropathy overall.

Pathophysiology

Compression and entrapment neuropathies are predominantly demyelinating.

Myelin loss results in slowing of the nerve conduction through the area involved.
When acute compression occurs, this may result in a conduction block. When the compression is more chronic, only slowing across the involved segment may be seen.
When compression is severe, ischemic changes occur that cause secondary axonal damage.
Pure demyelinating lesions typically have a better capacity to recover.

The pathophysiology of ischemic injuries and nerve transection is axonal damage. When axonal damage occurs, recovery is slower and longer and may not be complete.

This results in wallerian degeneration distally, and recovery requires the nerve to regenerate and reinnervate.
This process is slower than healing from other types of injuries and may not be complete.
Nerve conduction studies and electromyography (EMG) can aid in defining the lesion location and type.

Knowledge of peroneal nerve anatomy is essential to understanding the mechanism of its injury and to localizing the site of the lesion.

The peroneal nerve is a division of the sciatic nerve, which splits at or slightly above the popliteal fossa to form the tibial and common peroneal nerves.
The common peroneal nerve extends anterolaterally to wind around the neck of the fibula.
At this level, the nerve is superficial, covered only by skin and subcutaneous tissue. Here, it is predisposed to direct compression.
The nerve then dives into the peroneus longus muscle, where tethering can occur, making it susceptible to stretch injury at this level.
The nerve then divides into the superficial and deep peroneal branches.
- The superficial branch supplies the foot everters and sensation to the skin of the lateral calf and dorsum of the foot.
- The deep peroneal branch supplies the foot and toe dorsiflexors and has a small sensory component, which innervates only the skin of the web space between the first and second toes.

Race

No racial predilection is known.

Sex

No gender proclivity is known.

Age

Peroneal mononeuropathy is uncommon in children but has been reported in all age groups.

Clinical

History

Patients with peroneal mononeuropathy present with frequent tripping due to a foot drop.
Night cramps may occur in the anterior lower leg early in the course (if the compression is chronic).
If the compression is acute, the symptoms are likely to be maximal at onset.
Pain may occur at the site of compression.
Sensory disturbances (eg, tingling, numbness) in the lateral lower leg and foot may be noted.

Physical

If the lesion is severe, a complete foot drop that spares plantar flexion and foot inversion is noted.
The gait will be high-stepping with "foot slapping."
In milder cases, weakness of foot eversion and dorsiflexion may be noted only by asking the patient to walk on his or her heels.
Tapping of the nerve at the fibular head may produce pain and tingling in the peroneal sensory nerve distribution.
Distribution of peroneal sensory disturbance assists in localizing the lesion. Numbness in the lower part of the lateral distal leg suggests superficial peroneal sensory involvement, while numbness of the upper part of the lateral distal leg suggests deep peroneal sensory distribution (see Media file 1). With common peroneal lesions, sensory loss is noted over the lateral calf and dorsum of the foot but spares the fifth toe.
Peroneal sensory distribution: The striped area is the superficial peroneal sensory distribution. The green solid area represents the deep peroneal sensory distribution. All 3 areas shaded would be numb in a patient with a common peroneal nerve lesion.

Causes

Peroneal neuropathies are classically associated with external compression at the level of the fibular head.

The most common etiology is habitual leg crossing (which compresses this area).
Prolonged positioning with pressure at this area (eg, sitting on an airplane or positioning during surgery) are other causes. Peroneal nerve entrapment has been reported at the fibular head on the hemiparetic side in stroke patients.²
Isolated acute repetitive strain injury such as repetitive kicking³ and dancing⁴.
Short casts or braces around this area can be factors in external compression.
Other causes include operative trauma (knee surgery), fibular fracture, fibular head osteochondroma⁵, blunt or open trauma, and intrinsic masses (eg, ganglionic cysts, schwannoma, lipoma)⁶.
Lack or loss of the fat pad over the fibular head due to a thin body habitus or sudden weight loss such as after bariatric surgery⁷ predisposes the nerve to external compression at this site.
The peroneal nerve, if tethered where it dives into the peroneus longus muscle, also may be damaged by stretch injury. Causes include prolonged squatting or a sudden stretch.
Other conditions that mimic peroneal mononeuropathy include sciatic nerve lesions. Sciatic nerve lesions involving predominantly the peroneal division are difficult to distinguish clinically. If the foot drop is associated temporally with hip surgery or trauma, then it is more likely to be due to sciatic nerve involvement.
Generalized neuropathy can present with slowly progressive, bilateral foot drop but also is associated with plantar flexion weakness and stocking-distribution sensory loss.
Clinically, the peroneal nerve may appear to be involved selectively in vasculitis, chronic inflammatory demyelinating neuropathy, hereditary neuropathy with liability to pressure palsy, or sarcoidosis.⁸ However, nerve conduction studies showing a more generalized or multifocal neuropathy may aid in the diagnosis.
L5 radiculopathy also can present with a foot drop but can be distinguished clinically from a peroneal mononeuropathy by involvement of the foot inverters.
The superficial peroneal nerve is at risk for traction injury during an ankle inversion sprain.⁹
Intermittent pneumatic compression to prevent deep vein thrombosis causing compression of the peroneal nerve at the fibula head may cause bilateral peroneal nerve palsy.¹⁰
Deep peroneal neuropathy resulting in foot drop with preserved toe extension has been rarely reported in patients with anatomical variation of an accessory deep peroneal nerve.¹¹

Differential Diagnoses

Diabetic Neuropathy	Toxic Neuropathy
HIV-1 Associated Multiple Mononeuropathies	Traumatic Peripheral Nerve Lesions
Leptomeningeal Carcinomatosis	Uremic Neuropathy
Nutritional Neuropathy	Vasculitic Neuropathy
Polyarteritis Nodosa
Sarcoidosis and Neuropathy
Systemic Lupus Erythematosus

Workup

Imaging Studies

The following imaging studies are useful in peroneal mononeuropathy.

MRI of the lower thigh or popliteal fossa may be indicated if a mass lesion is suspected. Peripheral nerve nodular mass lesions and inflammatory pseudotumors of the peripheral nerves may be detected and confirmed by pathological excision.¹²
MRI can also detect variations in the posterior and distal extents of the biceps femoris muscle, which can produce a tunnel in which the common peroneal nerve travels causing peroneal nerve compression.¹³
Color duplex ultrasonography and angiography can reveal a popliteal artery pseudoaneurysm in the popliteal fossa.¹⁴
High resolution sonography of the common peroneal nerve may identify structural lesions of the peroneal nerve such as intraneural ganglion¹⁵ and inflammatory changes in vasculitic neuropathy¹⁶.

Other Tests

Nerve conduction studies and needle EMG aid in defining the location and type of lesion.

Nerve conductions should show isolated peroneal nerve abnormalities. If the lesion is at the knee, then conduction block or, less commonly, conduction velocity slowing over that segment of the nerve should be documented. When axonal loss occurs in direct nerve trauma or with long-standing compression, a small compound muscle action potential may be noted. If other mononeuropathies with conduction blocks are found, then consideration should be made for an underlying vasculitis causing mononeuritis multiplex or possibly for hereditary neuropathy with liability to pressure palsy. If more diffuse nerve abnormalities are noted, then a generalized neuropathy should be considered, especially chronic demyelinating polyneuropathy.
EMG is useful to localize the lesion. It can be helpful in determining which nerve is involved primarily—the common peroneal nerve at the knee or one of its two branches, the superficial or deep peroneal nerve. The tibialis anterior or extensor hallucis longus muscles (ie, innervated by the deep peroneal) and the peroneus longus or brevis muscles (ie, innervated by the superficial peroneal) are useful to study for this purpose.
EMG also is helpful in determining if the foot drop is due to an L5 radiculopathy or a sciatic lesion. In an L5 radiculopathy, the tibialis posterior, which is a foot inverter, and the lumbosacral paraspinous muscles are involved.
Involvement of the peroneal division of the sciatic nerve in the thigh or hip area is more difficult to determine clinically. In the thigh, the peroneal division of the sciatic nerve innervates the short head of the biceps femoris muscle, a knee flexor. As isolating this muscle clinically is difficult, EMG may be necessary to determine involvement.
If lesions in the thigh are suspected on EMG, then MRI of the thigh (evaluating for cysts or tumors) is indicated.

Histologic Findings

Peroneal neuropathy from intraneural ganglia of the peroneal nerve may have various patterns: outer (epifascicular) epineurial, inner (interfascicular) epineurial, and combined outer and inner epineurial.¹⁷

Treatment

Medical Care

Most peroneal nerve lesions respond to conservative management with rest and elimination of triggering factors such as leg crossing. Physical therapy is helpful in recovery of function. A large Italian study showed good spontaneous improvement in patients with peroneal mononeuropathy and rehabilitation helped with recovery of deambulation.¹⁸ Additionally, ankle foot orthosis (AFO) helps to stabilize the gait and prevent tripping due to the foot drop.

Surgical Care

Evaluation for surgical intervention for peroneal nerve repair is rarely necessary except in the following situations:

The lesion is due to a mass compressing the nerve.
Release of nerve tethering is indicated.
Severe or complete transection is suspected as with blunt or open trauma.

A group from Turkey has reported good results after tibialis posterior tendon transfer for persistent foot drop after peroneal nerve repair.¹⁹

Another group has reported good results from patients with deep peroneal nerve injuries resulting in foot drop undergoing nerve transfer of functional fascicles of either the superficial peroneal nerve or of the tibial nerve as donor for deep peroneal-innervated muscle groups.²⁰

A group from Italy has reported good motor improvement with a double tendon transfer method from the tibialis posterior to tibialis anterior, and flexor digitorum longus transfer to the extensor digitorum longus and extensor hallucis longus tendons.²¹

Follow-up

Prognosis

Common peroneal nerve decompression is a useful procedure to improve sensation and strength as well as to decrease pain.²²

Multimedia

Media file 1: Peroneal sensory distribution: The striped area is the superficial peroneal sensory distribution. The green solid area represents the deep peroneal sensory distribution. All 3 areas shaded would be numb in a patient with a common peroneal nerve lesion.

References

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Keywords

peroneal neuropathy, nerve entrapment, nerve compression, entrapment neuropathy, compression neuropathy, carpal tunnel syndrome, cubital tunnel syndrome, axonal damage, peroneal nerve anatomy

Contributor Information and Disclosures

Author

Pinky Agarwal, MD, Clinical Assistant Professor, Department of Neurology, University of Washington; Attending Neurologist, Booth Gardner Parkinson's Care Center
Pinky Agarwal, MD is a member of the following medical societies: American Academy of Neurology, American Medical Association, Association of Clinical Research Professionals, and Movement Disorders Society
Disclosure: Nothing to disclose.

Coauthor(s)

Alida Griffith, MD, Movement Disorders Neurologist, Booth Gardner Parkinson's Care Center
Disclosure: TEVA Honoraria Speaking and teaching; Novartis Honoraria Speaking and teaching

Medical Editor

Aashit K Shah, MD, Associate Professor of Neurology, Wayne State University; Program Director, Clinical Neurophysiology Fellowship, Department of Neurology, Detroit Medical Center
Aashit K Shah, MD is a member of the following medical societies: American Academy of Neurology, American Clinical Neurophysiology Society, and American Epilepsy Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Glenn Lopate, MD, Associate Professor, Department of Neurology, Division of Neuromuscular Diseases, Washington University School of Medicine; Chief of Neurology, St Louis ConnectCare, Consulting Staff, Barnes Jewish Hospital
Glenn Lopate, MD is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and Phi Beta Kappa
Disclosure: Nothing to disclose.

Chief Editor

Nicholas Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants
Nicholas Lorenzo, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Neurology
Disclosure: Nothing to disclose.

Further Reading