A 61-year-old woman had a 2-week history of painless weakness of her right foot.

A peroneal neuropathy is the most common isolated mononeuropathy of the lower extremities. The common peroneal nerve descends into the leg as the lateral division of the sciatic nerve. After rounding the head of the fibula, the common peroneal nerve splits into two branches: the deep peroneal nerve and the superficial peroneal nerve. Patients presenting with a foot drop often have either a peroneal neuropathy or an L5 radiculopathy (Table 10.1). Central nervous system (CNS) causes are rare.

Neuropathy of the common peroneal nerve is a frequent clinical condition, generally caused by compression at the fibular head. Chronic compression from habitual leg crossing is a common mechanism. Peroneal entrapment neuropathy has also been reported from sitting in a cross-legged position (yoga foot drop), tibial fracture, short casts or braces, arthroscopic knee surgery, excessive climbing, repetitive kicking, nerve infarcts, Baker cysts, hematoma, tumor, or leprosy. Peroneal nerve entrapment at the fibular head has also been reported in patients with hemiparetic strokes.