A review of the anatomy of the peroneal nerve is essential to understanding the causes and the clinical manifestations. The sciatic nerve is composed of 2 separate nerves: the common peroneal nerve (also called lateral popliteal nerve) and the tibial nerve (also called medial popliteal nerve). Both share a common sheath within the sciatic nerve but do not exchange any fascicles. In the upper thigh, the common peroneal nerve innervates the short head of biceps femoris only, whereas all other hamstring muscles (long head of biceps femoris, semitendinosus, and semimembranosus) are innervated by the tibial nerve. The common peroneal and tibial nerves separate completely in the upper popliteal fossa. Soon after this split, the common peroneal nerve gives off the lateral cutaneous nerve of the calf, which innervates the skin over the upper third of the lateral aspect of the leg. It winds around the fibular neck and passes through a tendinous tunnel between the edge of the peroneus longus muscle and the fibula (the fibular tunnel). Near that point, the common peroneal nerve divides into its terminal branches, the superficial and deep peroneal nerves. The superficial peroneal nerve innervates the peroneus longus and brevis and the skin of the lower two-thirds of the lateral aspect of the leg and the dorsum of the foot. The deep peroneal is primarily motor; it innervates all ankle and toe extensors (tibialis anterior, extensor hallucis, extensor digitorum longus and brevis) and peroneus tertius, in addition to the skin of the web space between the first and second toes.
More common causes of peroneal neuropathy include the following:
Knee dislocation and injury. Injury to the common peroneal nerve occurs in 25% of patients with dislocation of the knee. All underwent ligament reconstruction. In patients presenting with anterior or anteromedial dislocation with associated disruption of both cruciate ligaments and the posterolateral structures of the knee, common peroneal nerve palsy occurs in 41% of patients (Niall et al 2005).
Posterolateral knee injuries with disruption requiring surgery can be associated with displaced common peroneal nerves in cases with biceps avulsions or avulsion-fracture of the fibular head, with nerve injury believed to occur due to the nerve being pulled anteriorly by the biceps tendon (Bottomley et al 2005).
Knee surgery. In an Italian study, 22% of common peroneal neuropathies were due to surgery (Aprile et al 2005). Knee surgery is the most common surgical procedure associated with development of common peroneal neuropathy, which appears to occur with 0.3% to 1.3% of all knee arthroplasties (Nercessian et al 2005). Possible risk factors for post-operative peroneal neuropathy include valgus deformity, post-operative epidural anesthesia, previous nerve disease, and rheumatoid arthritis (Nercessian et al 2005). The presence of a preexisting peripheral neuropathy appears to be a significant risk factor for peroneal nerve palsy after knee or hip arthroplasty (Dellon 2005).
The use of a tourniquet was previously thought to be a risk for peroneal neuropathy development, but this appears to be unlikely (Nercessian et al 2005).
Other surgery. Common peroneal nerve injury appears to be the most common traumatic nerve palsy after total hip arthroplasty, composing more than 50% of known motor nerve palsies (Farrell et al 2005). Risk factors for common nerve palsy post-hip arthroplasty include developmental dysplasia of the hip, post-traumatic arthritis, lengthening of the extremity, cement-less femoral fixation, and a posterior surgical approach (Farrell et al 2005).
Uncommonly, peroneal nerve lesions may occur with thoracoabdominal surgery, perhaps related to surgical positioning (Aprile et al 2005a). Improper positioning of patients during gynecologic surgeries can also lead to compression neuropathies (Bradshaw and Advincula 2010).
Weight loss. In a prospective series, 15% of common peroneal neuropathies were associated and possibly attributed to weight loss (Aprile et al 2005a). Some of these patients have a concurrent polyneuropathy (Cruz-Martinez et al 2000). Relatives of patients with weight-loss induced common peroneal neuropathy can have genetic abnormalities consistent with hereditary liability to pressure palsies (Cruz-Martinez et al 2000). Weight loss is often associated with anorexia nervosa. The exact cause of common peroneal neuropathy in weight loss, however, remains unknown.
Prolonged maintenance of posture. Patients who are bedridden represent 7% to 23% of all cases of common peroneal neuropathy (Aprile et al 2005a; 2005b); in 1 series (Aprile et al 2005b), this was the most common cause of common peroneal nerve palsy.
External compression. External compression composes 5.8% of cases of common peroneal neuropathy in 1 prospective series (Aprile et al 2005a). Intraneural ganglion cysts of the peroneal nerve can be associated with the ‘wishbone’ sign on MRI with the ascending limb of the peroneal intraneural ganglion intersecting with the longitudinal limb of the vascular adventitial cyst in the axial plane (Spinner et al 2006). Arthrogenic cysts at the fibular head compresses the common peroneal nerve in 1.4% of cases (Aprile et al 2005a). Rare causes include extrinsic masses (osteomas, lipomas, ganglia, Baker cysts) or intrinsic nerve sheath tumors. Iatrogenic lesions include casts or tibial osteotomies. Bone tumors, such as osteochondromas, that cause peroneal neuropathies are more common than in adults.
Cast placement for broken bones may lead to as many as 6% of all common peroneal neuropathies (Aprile et al 2005b).
Trauma. This is responsible for 10% of cases of common peroneal neuropathy (Aprile et al 2005a) in 1 series and, likely, the second most common cause overall next to perioperative compression. Traumatic causes include fracture of the fibula, tibio-fibular fractures (Kim and Jung 2011), knee surgery and arthroscopy, lacerations, and blunt injuries. Common peroneal nerve injury is the most common nerve injury resulting from varicose vein removal surgeries; the injury tends to occur just before or as it crosses the fibular neck (Giannas et al 2006). Stretch injuries of the peroneal nerve may occur following severe inversion sprains of the ankle.
Common peroneal mononeuropathies in children are similar to those of adults with compression and trauma as the leading causes (Jones et al 1993). Neonatal peroneal nerve injuries are uncommon, usually associated with breech presentations and malpositioning, and often result in intrauterine stretching of the infant’s peroneal nerves (Godley 1998). Superficial nerve palsy has been reported in 1 patient with nerve herniation through a fascial defect which presented after exercise (Yang et al 2006). Compartment syndrome following pitviper envenomation has led to peroneal neuropathy (Hardy and Zamudio 2006).
Other rare causes include herpes zoster infection, tacrolimus neurotoxicity (Jain et al 2011), exertional compartment syndrome (Baker et al 2009), and hereditary neuropathy with pressure palsies.
Common causes of peroneal neuropathy are listed in Table 1.
Table 1. Causes of Common Peroneal Neuropathy
In most cases, peroneal neuropathy results from compression of the peroneal nerve between an external object and the fibular head. The second most common cause of acute peroneal neuropathy is trauma (second to perioperative compression). This includes fracture of the fibula, knee dislocation, knee surgery and arthroscopy, lacerations, and blunt injuries. Stretch injuries of the peroneal nerve may occur following severe inversion sprains of the ankle. Rare causes include extrinsic masses (osteomas, lipomas, ganglia, Baker cysts) or intrinsic nerve sheath tumors. Peroneal nerve entrapments at the fibular tunnel are extremely rare.
Common peroneal mononeuropathies in children are similar to those of adults with compression and trauma as the leading causes (Jones et al 1993). Weight loss is often associated with anorexia nervosa. Iatrogenic lesions include casts or tibial osteotomies. Bone tumors, such as osteochondromas, causing peroneal neuropathies are more common than in adults. Neonatal peroneal nerve injuries are uncommon, usually associated with breech presentations and malpositioning, and often result in intrauterine stretching of the infant’s peroneal nerves (Godley 1998).