How is peroneal nerve entrapment diagnosed?

Updated: Oct 15, 2019
  • Author: Minoo Hadjari Hollis, MD; Chief Editor: Thomas M DeBerardino, MD  more...
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The history and physical examination are the most helpful initial clinical tools in establishing a high index of suspicion for a common peroneal nerve injury. Nerve biopsy, though largely unnecessary, may confirm the diagnosis.

Observation of the patient’s gait is useful in diagnosing ankle dorsiflexion weakness. A patient with common peroneal nerve entrapment often displays a steppage gait pattern, in which the affected foot is lifted excessively from the ground during the swing phase of ambulation in order to clear the foot. This results in excessive hip and knee flexion, and the appearance is as if the patient is stepping over an object in his or her path.

In addition, a foot slap may be heard on foot strike because of the inability of the ankle dorsiflexors to provide a controlled descent of the foot toward the floor. The patient may also stumble when walking as a consequence of the toes on the affected side dragging or catching on the floor during the swing-through phase of ambulation.

Examination often reveals a variable pattern of weakness, with the extensor digitorum brevis most profoundly affected. Ankle and toe dorsiflexion may be substantially altered. Dorsiflexion is best tested by having the patient place the ankle in the neutral position and then dorsiflex the foot and invert; this tests the anterior tibial muscle optimally. Often, ankle eversion is normal because the relevant muscles are relatively spared.

In a pure common peroneal neuropathy, plantar flexion should be spared. In fibular neck fractures, complete absence of sensation is possible along the anterodistal portion of the leg and the entire dorsum of the foot. Lateral calf sensation may be spared if the lesion is below the nerve branch to this region. When the neural insult occurs at the knee, the short head of the biceps femoris often is spared.

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