Common Peroneal Nerve Palsy

From: e-medicine

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.
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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