Common peroneal neuropathy

Last revised by Mostafa Elfeky on 10 Jun 2023

Common peroneal neuropathy, also known as fibular neuropathy is a nerve compression syndrome of the common peroneal nerve (CPN) at the level of the fibular head. It is the most common cause of spontaneous painless foot drop.

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  • spontaneous painless foot drop

  • weak foot eversion

  • sensory loss over anterolateral lower leg and dorsum of the foot

It occurs as the common peroneal nerve exits the popliteal fossa over the lateral head of gastrocnemius and popliteus and wraps around the fibula head and neck to enter the lateral compartment of the leg. 

Most commonly the cause is trauma 1

  • habitual leg crossing

  • prolonged kneeling

  • blunt trauma

  • fibular fracture

  • knee dislocation

  • casts

  • hematoma 

Less commonly the cause is by compression

Ultrasound examination can be normal but nerve enlargement and hypoechoic spots within the nerve have been described. Ultrasound can also aid in identifying any ganglion cysts, hematomas or flabella that may compress the common peroneal nerve 2,3. 

MRI demonstrates general features of peripheral neuropathy including nerve enlargement, signal alteration (most commonly high T2-weighted signal intensity) and loss of fascicular architecture 4. It can also help identify any compressive etiology such as ganglion cysts in patient's with no history of trauma, kneeling or habitual leg crossing. In patient's with a history of significant trauma such as knee dislocation, MRI can identify nerve disruption and neuroma formation. 

Treatment, as well as prognosis, depends on the cause. For patients with a history of mechanical external pressure (eg habitual leg crossing or kneeling), the prognosis is generally favorable after behavioral modifications. In patients with complete nerve disruption and neuroma formation, they will not regain function without intervention with neurological recovery depending on the length of the segment of nerve injury. 

  • imaging is rarely needed in patients with a straightforward history of mechanical external pressure

  • in patients with persistent or increasing symptoms despite behavioral modifications, MRI can help verify the common peroneal nerve as the suspected location and excluding a compressive mass

  • L5 radiculopathy and sciatic neuropathy are also common causes of foot drop so if imaging findings are negative these sites should be considered

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