Peroneal neuropathy

1. What is the differential diagnosis of foot drop?
2. What is the etiology of peroneal nerve injury at the fibular head and what is the presentation? What are the EMG findings?
3. How is the deep peroneal nerve commonly injured? What is the presentation?
4. What muscles pass under the extensor retinaculum?
5. How is the superficial peroneal nerve commonly injured? What is the presentation?

Answers:
1. Diffuse polyneuropathy (diabetes), peroneal neuropathy, plexopathy, L4-L5 radiculopathy, tumor, CVA, AVM, SCI.
2. The peroneal nerve is injured at the fibular head by prolonged leg crossing, weight loss, poor positioning during surgery, poor cast application, prolonged squatting position (Strawberry picker's palsy), and metabolic disorders (diabetes). It presents with ankle DF weakness resulting in foot drop and steppage gait, with eversion weakness. EMG shows abnormal activity in peroneal-innervated muscles except for short head of biceps femoris.
3. The deep peroneal nerve is injured by compression from trauma or shoes as it passes under the extensor retinaculum (anterior tarsal tunnel syndrome). It presents with foot weakness (EDB) and atrophy with numbness in the first webspace. Pain is over dorsum of foot and relieved with motion. CMAP shows abnormal findings to EDB and EMG shows abnormal activity in the EDB.
4. Tibialis anterior, EHL, EDL.
5. Injury is by compression from trauma, ankle sprain, muscle herniation, or a lipoma. It presents with eversion weakness if injury is proximal and sensory loss.