Peroneal nerve entrapment can occur in either common peroneal nerve, superficial peroneal nerve or deep peroneal nerve. To understand these entrapments and their effects, it is important to understand the anatomy.
Relevant Anatomy Peroneal Nerve
About mid-thigh or lower, sciatic nerve divides into two branches – common peroneal nerve and tibial nerve. The common peroneal nerve descends to the popliteal fossa, gives a branch to biceps femoris and travels beneath the long and short heads of the biceps femoris on posterolateral aspect of the distal thigh.
As it crosses the knee, proximal to the fibular head, the common peroneal nerve gives off sural communicating branch, that along with branch from the tibial nerve forms the sural nerve. It also gives off the lateral cutaneous nerve of the calf that is responsible for skin sensation on the proximal and lateral aspect of the leg. It also gives articular branches to the knee.
After coursing around the fibular neck [It is secured to the fibular neck by fibrous tissue.] common peroneal nerve pierces through the fibro-osseous opening in the superficial head of the peroneus longus muscle.
Distal to this, the common peroneal nerve divides into the superficial and deep peroneal nerves
Superficial peroneal nerve travels in the lateral compartment of leg and supplies the peroneus longus and peroneus brevis. In most individuals, it pierces the deep fascia and emerges into the subcutaneous fat at approximately the level of the middle and lower third of the leg [10-15 cm above the tip of the lateral malleolus.]
About 5 cm [ or more in about 30%] proximal to the ankle joint, the superficial peroneal nerve divides into a medial and intermediate dorsal cutaneous nerve.
The medial dorsal cutaneous nerve supplies the skin of the dorsomedial ankle, the medial aspect of the great toe, and the second and third digits (First web space is not supplied)
The intermediate dorsal cutaneous nerve supplies the skin on the dorsolateral ankle and gives off dorsal digital nerves for the third, fourth, and fifth toes.
Deep peroneal nerve enters the anterior compartment after piercing interosseous membrane and travels lateral to the anterior tibial muscle, along with the anterior tibial artery and vein.
In the upper third of the leg, the nerve lies between the anterior tibial muscle and the extensor digitorum longus whereas, in the middle third, it is between the anterior tibial muscle and the extensor hallucis longus.
Near the ankle, the nerve lies between the extensor hallucis longus and the extensor digitorum because the extensor hallucis longus crosses over the deep peroneal nerve about 1.5 inches proximal to ankle mortise.
After crossing the mortise, the nerve divides into lateral and medial branches.
The lateral branch supplies the extensor digitorum brevis, the extensor hallucis brevis, the adjacent tarsal and tarsometatarsal joints and, occasionally, the second and third dorsal interosseous muscles.
The medial branch is just medial to the dorsalis pedis artery and travels between extensor hallucis longus tendon and extensor hallucis brevis muscle on the dorsum of the foot. At the metatarsophalangeal level, the nerve is between the extensor hallucis brevis and the extensor digitorum longus to the second toe joint level because the extensor hallucis brevis crosses over the nerve.
This nerve then divides into the dorsolateral cutaneous nerve of the great toe and the dorsomedial cutaneous nerve of the second toe. It supplies sensation to the first web space, the dorsalis pedis artery, and the adjacent metatarsophalangeal and interphalangeal joints.
It also supplies the first dorsal interosseous muscle and may occasionally supply the second and third interosseous muscles.
Causes of Peroneal Nerve Entrapment
Causes of Common Peroneal Nerve Entrapment
External Compression
The compression of the nerve may occur due to the positioning of the limb against other limbs as in habitual leg crossing or railing or hard mattress in infirm patients. Patients under anesthesia are prone to nerve compression.
Casts or braces may cause external compression.
In highly muscular athletes, the nerve may get compressed against fascial layers. These patients often complain of exercises related to pain.
Slimmer’s paralysis is peroneal nerve entrapment in persons who undergo rapid weight loss. This leads to loss of fat in fat pad around the nerve and predisposing the nerve to external compression.
Working for long hours in squatting position may lead to peroneal nerve compression at fibro-osseous opening when it pierces the peroneus longus muscle. It also is known as strawberry picker’s palsy.
Rarely, childbirth has also been associated [esp. in squatted position] with peroneal nerve palsy.
Trauma
- Wounds
- Contusions
- Proximal fibular fractures
- knee dislocations
- Tibial osteotomies
- Total knee
- Arthroscopy
- Limb lengthening procedure
Tumors
Tumors could be intraneural or extraneural. Following tumors are associated with peroneal nerve entrapment.
- Neurilemomas
- Schwannomas
- Desmoid tumors
- Angiomas
- Ganglia neuromas
- Fibrolipomatosis
- Hamartomas
- Exostosis
- Chondromatosis
- Baker cysts
- Vascular Tumors
Idiopathic
Many times the cause of the entrapment cannot be determined.
Causes of Superficial Peroneal Nerve Entrapment
Trauma
- Recurrent stretch injury due to frequent ankle sprains
- Posttraumatic perineural fibrosis at ankle the ankle after an inversion ankle sprain has been reported.
- Injury from any procedure like ankle arthroscopy
- Chronic or exertional lateral compartment syndrome
Nontraumatic causes
- Fascial defects in the lateral lower leg where the nerve gets entrapped as it comes to the subcutaneous tissue
- Short proximal peroneal tunnel. The tunnel is present towards the ankle on outer aspect and is formed by the retromalleolar groove of the fibula [bony part] and a distal part of the posterior intermuscular septum of the leg fibrous part]. In very few cases, superficial peroneal nerve traverses through this.
Casues of Deep peroneal nerve entrapment
Entrapment of deep peroneal nerve at the ankle is called anterior tarsal tunnel syndrome and may occur due to osteophytes, exostosis, space-occupying lesions or related to foot posture.
Apart from anterior tarsal tunnel syndrome, deep peroneal nerve entrapment, however, can occur anywhere along the nerve’s course. Few of the causes are
- Space-occupying lesions about the proximal fibula
- Proximal tibial osteotomy
- Chronic anterior exertional compartment syndrome
Presentation of Peroneal Nerve Entrapment
Weakness of ankle dorsiflexion is the most common presentation of common peroneal nerve injury. There may or may not be a sensory loss in the upper lateral leg.
With superficial peroneal nerve entrapment, there is a vague pain over the dorsum of the foot and may be associated with numbness or paresthesia in the distribution of the nerve. The pain may occasionally be present in the lateral part of the leg. Depending upon the causation, the pain may be acute or chronic.
In cases, with exertional compartment syndrome, the symptoms increase with activity like running, walking, or squatting.
In vulnerable patients, crossing the leg over the opposite thigh can induce symptoms, as can tight clothing like elastic socks.
Patients with deep peroneal nerve entrapment have vague pain, a burning sensation, or a cramp over the dorsum of the foot. There might be a loss of sensation in the first dorsal web space.
Symptoms may always be not present and may appear or worsen only with a footwear or activity. Proximal entrapments may present with frequent tripping due to foot drop.
Investigations
Electrodiagnostic Evaluation
Electrodiagnostic evaluation is arguably the best method for assessing a potential peroneal nerve insult.
Evaluation of short head of biceps can differentiate between lesions proximal to knee and distal knee but it is difficult to do.
Electrodiagnostic tests include motor and sensory conduction studies, and electromyography.
Sensory conduction studies are able to tell if the lesions are distal to the dorsal root ganglion.
Motor conduction studies determine nerve conduction velocity across the fibular head region and distal. A comparison with the contralateral limb is often helpful.
Electromyography helps in confirming axonal loss and in assessing the degree of involvement of the muscles innervated by the superficial peroneal nerve. Electromyography can be used to define the proximal extent of the lesion
Note: The values of electrodiagnostic studies for superficial peroneal nerve injury are often normal because most of the cases have dynamic conditions that resolve at rest.
Electrodiagnostic studies of the deep peroneal nerve are helpful in further defining the zone of compression and in evaluating for concomitant radiculopathy or peripheral neuropathy.
Imaging
Xrays should include lower part of the thigh, knee, leg, ankle, and foot. These may be narrowed down to the suspected site of compression. Xrays may reveal injuries such as proximal fibular head fracture, bony tumors, angular deformities about the knee, lesions like osteochondromas, or fracture callus and osteophytes in the ankle.
CT can provide detailed information on bony anatomy and MRI may help to find compression along the course of the nerve. It also provides additional information about soft-tissue masses and their extent.
MRI is usually not necessary in superficial peroneal nerve entrapment.
Ultrasonography can be helpful in the localization of cystic masses impinging on the nerve.
Lab Studies
Blood studies are helpful in conditions such as diabetic neuropathy, alcoholic neuropathy, polyarteritis nodosa, and hyperthyroidism.
Treatment of Peroneal Nerve Entrapment
In cases where the cause or offending structure can be identified, the treatment should address that. Treatment of the underlying cause should be undertaken, as should release of the entrapped nerve and excision of existing neuromas.
In other cases, where there is no correctable cause and integrity of the nerve is determined by electrodiagnostic studies, it is prudent to put the patient on conservative treatment.
The treatment mainly consists of following –
Drugs
NSAIDs and/or oral corticosteroids are used to reduce inflammation. Antidepressants like amitriptyline are effective for chronic and neuropathic pain. Anticonvulsants like gabapentin and carbamazepine can also be used for controlling neuropathic pain.
Local Injections
Local corticosteroids injections reduce swelling and inflammation at the site can relieve the symptoms of peroneal nerve entrapment.
Ankle Foot Orthoses
Used in cases of foot drop, mostly associated with common peroneal nerve entrapment.
Footwear Modifications
Simple measures like padding of the tongue of the shoe, the elimination of shoes with laces and the avoidance of high heels, may be sufficient to resolve symptoms by decreasing the compression on dorsum of the foot
Physical Therapy
Physical therapy is useful for strengthening the peroneal muscles in cases associated with weakness and in individuals with chronic ankle instability. Physical therapy may also improve symptoms.
Orthopedic shoes
If ankle dynamics are abnormal and causing deep peroneal nerve entrapment symptoms, orthopedic shoes that provide dorsiflexion assistance could help in recovery.
In-shoe orthotics can help in the correction of a biomechanical malalignment in gait in severe flat or cavus foot.
Nonoperative management should continue for a minimum of 3-4 months.
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