Peroneal Nerve Injury

The peroneal nerve, or the fibular nerve, is a significant nerve innervating the lower extremity. With fibers originating from the posterior divisions of L4–S2, the peroneal and tibial nerves are the primary branches of the sciatic nerve, which bifurcates into the tibial and common peroneal nerves proximal to the popliteal fossa in the distal posterior thigh. The common peroneal nerve (CPN) then courses posterolaterally behind the long head of the biceps femoris muscle before moving anteriorly to wrap around the fibular neck and pass beneath the lateral compartment of the calf. The CPN divides into deep and superficial branches after curving around the fibular neck. The deep peroneal nerve (DPN) courses between the tibialis anterior and hallucis longus muscles in the anterior compartment of the leg, then continues along the anterior tibia before terminating in the webspace between the first and second toes. The superficial peroneal nerve (SPN) descends through the lateral compartment of the leg before terminating at the dorsum of the ankle and foot. Anatomical variation is possible. As an example, the accessory fibular nerve, present in approximately 25% of the general population, is an anatomic variant innervating the extensor digitorum brevis muscle. The peroneal nerve subserves both sensory and motor functions. Motor function of the DPN permits dorsiflexion of the foot and extension of the great toe; the SPN subserves ankle eversion. Sensory function of the SPN supplies the dorsum of the foot except for the interdigital space between the first and second toes, which is supplied by the DPN. After median and ulnar neuropathies, peroneal neuropathy is the most common focal neuropathy; peroneal neuropathy is the most common compressive neuropathy of the lower extremity. Symptoms of CPN mononeuropathy classically include numbness of the dorsum of the foot and the lateral leg along with foot drop—the latter occurring secondary to paresis of ankle and toe dorsiflexion plus weakness of foot eversion—with its distinctive accompanying steppage gait. Traumatic and behavioral causes alike can precipitate peroneal neuropathy, with trauma usually occurring acutely, whereas behavior contributes more to chronic presentations. Compressive peroneal neuropathy commonly afflicts athletes and individuals whose work otherwise necessitates substantial kneeling and squatting. This topic reviews injuries to the common peroneal nerve and its branches, including etiology, epidemiology, salient features of the history and physical exam findings, plus diagnosis and treatment.