Peroneal Mononeuropathy Clinical Presentation

Updated: May 22, 2017
  • Author: Shaheen E Lakhan, MD, PhD, MS, MEd; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Presentation

History

See the list below:

  • 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 and early in the lateral lower leg and foot.
  • Sensory disturbances (e.g. tingling, numbness) in the lateral lower leg and foot may be noted.
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Physical

See the list below:

  • If the lesion is severe, a complete foot drop that spares plantar flexion and foot inversion is noted (compared with L5 radiculopathy, lumbosacral plexopathy, or sciatic neuropathy).
  • 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 following image). 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 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.
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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 (e.g. 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. [7]
  • Isolated acute repetitive strain injury such as repetitive kicking [8] and dancing [4] .
  • Short casts or braces around this area can be factors in external compression.
  • Other causes include operative trauma (knee surgery), fibular fracture, fibular head osteochondroma [9] , blunt or open trauma, and intrinsic masses (e.g. ganglionic cysts, schwannoma, lipoma) [10] .
  • Knee dislocation or bicruciate injury can cause peroneal nerve injury in 10-40% of cases. [11] The superficial peroneal nerve is at risk for traction injury during an ankle inversion sprain. [12] Varus deformity in osteoarthritis of the knee can result in peroneal nerve injury with conduction block at the fibular neck. [13]
  • 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 surgery [14] or anorexia nervosa [15] 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.
  • Foot drop can be a presentation of exertional compartment syndrome. [16] It has been observed in weight lifters [6] and football players [17] and can be associated with anabolic steroid use. [18]
  • 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.
  • L5 radiculopathy can also present with a foot drop but can be distinguished clinically from a peroneal mononeuropathy by involvement of the foot inverters.
  • 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. [19] Lyme disease has been reported to cause peroneal nerve palsy. [20] However, nerve conduction studies showing a more generalized or multifocal neuropathy may aid in the diagnosis.
  • Intermittent pneumatic compression to prevent deep vein thrombosis causing compression of the peroneal nerve at the fibula head may cause bilateral peroneal nerve palsy. [21]
  • Peroneal neuropathy can occur following liver transplantation. Risk factors include intraoperative positioning, poor nutritional status, tall and slender body shape, and alcoholic liver disease. [22]
  • 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. [23]
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Physical Examination

Table 1. Physical Examination in Peroneal Mononeuropathy (Open Table in a new window)

Nerve Sensory Weakness
Common peroneal nerve Lateral calf and dorsum of foot Ankle dorsiflexion and eversion



Toe extension



Deep peroneal nerve Area between first and second toes Ankle dorsiflexion and partial eversion > inversion



Toe extension



Superficial peroneal nerve Lateral calf and dorsum of foot Ankle eversion
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