Excerpt from Peroneal Mononeuropathy

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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.

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