The common peroneal nerve represents a major nerve terminal of the sciatic nerve, providing the motor supply to the muscles of the anterior and lateral compartments of the leg. It is the most commonly damaged nerve in the lower limb and is relatively unprotected as it traverses the lateral aspect of the head of the fibula.
Damage may occur from direct trauma, pressure by plaster casts at the back of the fibula, or stretching after a prolonged period with the knee fully flexed, e.g. kneeling. Injury is not uncommon in patients lying in bed recovering from operations.
Clinical features include:
- foot drop
- weakness of dorsiflexion and eversion of the foot
- weakness of extensor hallucis longus
- inversion and plantar flexion are normal
- anaesthesia over the lower lateral part of the leg and dorsum of the foot; often with little or no sensory loss
- all reflexes are intact - the ankle jerk is lost in a sciatic nerve lesion
- wasting of the anterior tibial and peroneal muscles
Recovery occurs within a few weeks when the cause is simple compression. Full knee flexion should be avoided as in kneeling or squatting, and the patient should not sit with the legs crossed over the unaffected leg. To prevent foot drop the patient should wear an aluminium night-shoe at night and during the day, a shoe with plastic inserts.
Surgical exploration is indicated if the weakness progresses or fails to resolve within 1-2 months, or if there is an obvious local lesion.