Conditions & Treatments - Peroneal Nerve Entrapment                                      

The common peroneal nerve, also known as the common fibular nerve, external popliteal nerve, peroneal nerve, or lateral popliteal nerve, is formed from the L4, L5, S1, and S2 nerve roots. The nerve separates from the sciatic nerve in the upper popliteal fossa, runs behind the fibular head, travels down the fibula behind the peroneus longus muscle, and splits into the superficial and deep peroneal nerves. The superficial peroneal nerve innervates the peroneus longus and brevis and provides cutaneous innervation to the anterolateral lower leg and the dorsum of the foot (excluding the webspace between the great and second toes). The deep peroneal nerve innervates the tibialis anterior, extensor digitorum longus, peroneus tertius, and extensor hallucis longus. As the deep peroneal nerve courses past the ankle joint, the nerve divides into lateral and medial terminal branches. The lateral terminal branch innervates extensor digitorum brevis and extensor hallucis brevis, while the medial terminal branch provides cutaneous innervation to the webspace between the great and second toes (1).

Etiology and Management
An entrapment neuropathy refers to an isolated peripheral nerve injury that occurs when a nerve is mechanically constricted in a fibrous or fibro-osseous tunnel or deformed by a fibrous band (2). Before the common peroneal nerve splits into the superficial and deep peroneal nerves, the nerve passes through a fibrous arch (3). This arch consists of a deep portion, formed by the deep aponeurosis of the peroneus longus muscle, and a superficial portion, which stretches from the soleus to the aponeurosis of the peroneus longus (3). This fibrous arch may compress the common peroneal nerve, causing peroneal nerve entrapment and neuropathy (3). Peroneal neuropathy can also arise from acute trauma to the lateral knee, chronic leg crossing, systemic disease, exposure to chemicals, tumor growth, or iatrogenic injury (4).
 

Conservative therapy is advocated for peroneal nerve entrapment and neuropathies (4). For patients with electrophysiological studies confirming peroneal entrapment who fail three to four months of conservative therapy, an operative decompression may be performed (4).

Subjective and Objective PT Exam Findings
In the physical therapy clinic, a patient with peroneal nerve entrapment may complain of lateral knee and calf pain, numbness or tingling in the foot, or weakness of the ankle and foot (5). The patient may have suffered trauma to his or her lateral knee or may report wearing a constrictive garment or brace around his or her upper calf (5).

 
The peroneal nerve tension test (a variation of the SLR where the ankle is plantarflexed and inverted at the point of first resistance) may reproduce symptoms (5). Palpation or tapping of the nerve (Tinel's) around the fibular head may also reproduce symptoms (5). Asking the patient to walk on their heels serves as a quick, gross screen of the deep peroneal nerve (dorsiflexors, L4, L5). Asking the patient to toe walk serves as a quick, gross screen of the tibial nerve (S1-2) and superficial peroneal nerve (L5, S1) (6). Manual muscle tests may further reveal weakness of the peroneus longus, peroneus brevis, peroneus tertius, tibialis anterior, extensor digitorum longus and brevis, and extensor hallucis longus and brevis. During gait analysis, the PT may notice foot drop, a "slapping" gait, or toe drag during swing phase (5).

PT Intervention
Goals of physical therapy intervention include minimizing edema, increasing neural mobility, and maintaining or increasing the strength and endurance of unaffected sites (5). A variety of modalities may prove useful to reduce edema and inflammation, including ultrasound, iontophoresis, and cryotherapy (5). If paresis is present, electrical stimulation may help maintain muscle function (5). Manual therapy techniques, including soft tissue mobilization, proximal tibiofibular joint mobilizations, patellofemoral joint mobilizations, and tibiofemoral joint mobilizations, should be utilized when appropriate (5). Therapeutic exercises, including strengthening of unaffected musculature and neural mobility exercises, should be included in the plan of care. An AFO may be necessary until ankle dorsiflexion strength returns, especially if foot drop significantly impairs the patient's gait (5).