AUTHOR AND EDITOR INFORMATION

Section 1 of 8  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Multimedia
• References

INTRODUCTION

Section 2 of 8  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Multimedia
• References

Background

Mononeuropathies can occur secondary to direct trauma, compression, stretch injury, ischemia, infection, or inflammatory disease.

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).

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

This neuropathy is uncommon in children but has been reported in all age groups.

CLINICAL

Section 3 of 8  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Multimedia
• References

History

• Patients 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 Image 1). With common peroneal lesions, sensory loss is noted over the lateral calf and dorsum of the foot but spares the fifth toe.

Causes

• Peroneal neuropathies classically are 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.
• Short casts or braces around this area can be factors in external compression.
• Other causes include operative trauma (knee surgery), fibular fracture, blunt or open trauma, and intrinsic masses (eg, ganglionic cysts, schwannoma).
• Lack of or loss of the fat pad over the fibular head due to sudden weight loss and/or a thin body habitus 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 the following:
• • 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, or hereditary neuropathy with liability to pressure palsy. 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.

DIFFERENTIALS

Section 4 of 8  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Multimedia
• References

Other Problems to be Considered

Generalized peripheral neuropathy of any cause
Sciatic nerve lesions
Lumbosacral plexus lesions
Lumbosacral disk syndromes
Metabolic neuropathy
Paraneoplastic neuropathy
Paraproteinemic neuropathy

WORKUP

Section 5 of 8  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Multimedia
• References

Imaging Studies

• MRI of the lower thigh or popliteal fossa may be indicated if a mass lesion is suspected.

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 hallicus 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.

TREATMENT

Section 6 of 8  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Multimedia
• References

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. Additionally, ankle foot orthosis (AFO) helps to stabilize the gait and prevent tripping due to the foot drop.

Surgical Care

Evaluation for surgical intervention 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.

MULTIMEDIA

Section 7 of 8  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Multimedia
• References

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.
	View Full Size Image
Media type:  Photo

REFERENCES

Section 8 of 8

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Multimedia
• References

• Campbell WW. Focal Neuropathies. Essentials of electrodiagnostic medicine. 1999;255-278.
• Katirji B. Peroneal neuropathy. Neurol Clin. Aug 1999;17(3):567-91, vii. [Medline].
• Katirji B, Wilbourn AJ. High sciatic lesion mimicking peroneal neuropathy at the fibular head. J Neurol Sci. Feb 1994;121(2):172-5. [Medline].
• Marciniak C, Armon C, Wilson J. Practice parameter: utility of electrodiagnostic techniques in evaluating patients with suspected peroneal neuropathy: an evidence-based review. Muscle Nerve. Apr 2005;31(4):520-7. [Medline].
• Turner OA, Taslitz N, Ward S. Common peroneal nerve entrapment. Handbook of peripheral nerve entrapments. 1990;119-124.
• Wilbourn AJ. AAEE case report #12: Common peroneal mononeuropathy at the fibular head. Muscle Nerve. Nov-Dec 1986;9(9):825-36. [Medline].
• Williams FH, Johns JS, Weiss JM, et al. Neuromuscular rehabilitation and electrodiagnosis. 1. Mononeuropathy. Arch Phys Med Rehabil. Mar 2005;86(3 Suppl 1):S3-10. [Medline].

Article Last Updated: Aug 9, 2005