Superficial peroneal nerve entrapment or compression syndrome is a nerve compression syndrome of the superficial peroneal nerve a mixed motor and sensory nerve providing the motor innervation of the peroneus longus and peroneus brevis muscles and sensory innervation of the dorsum of the foot and the two distal thirds of the lateral lower leg 1,2.
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Epidemiology
Superficial peroneal nerve entrapment is a rather rare type of nerve compression syndrome that might be seen in dancers and athletes 1-3.
Associations
Superficial peroneal nerve entrapment can be associated with muscle hernias of the peroneal compartment 1.
Diagnosis
The diagnosis is usually made on clinical grounds and difficult to diagnose with electrodiagnostic tests as nerve conduction studies and small fiber testing 3. Differential diagnosis as common peroneal nerve entrapment and radiculopathy need to be ruled out 4. Imaging such as MRI might provide additional clues 4.
Clinical presentation
Presenting symptoms include focal swelling pain and point tenderness in the area where the superficial peroneal nerve pierces the fascia approximately 10-15 cm above the ankle with paresthesia of the respective dermatome along the lateral aspect of the lower leg and the dorsum of the foot with sparing of the first web space and the fifth toe 1,2. This might be precipitated by walking as well as plantar flexion and inversion of the foot 3,4. A positive Tinel test can be elicited at the entrapment site 3. Peroneal muscle weakness is rather uncommon 2.
If a muscle herniation is associated with the condition this might be visualized at the spot as a focal swelling precipitated with dorsiflexion of the foot 1.
Pathology
The condition is caused by entrapment of the superficial peroneal nerve at the subfacial course and the site where the nerve leaves the lateral compartment of the lower leg through the lateral crural fascia about 10-15 cm above the ankle, which mainly leads to sensory deficits 1-5. The uncommon occurrence of peroneal muscle weakness can be explained by the location of the entrapment site 5.
Etiology
Causes of superficial peroneal nerve entrapment syndrome include the following 2,5:
- repetitive microtrauma due to stretching with forced inversion and plantar flexion
- muscle hernia
- ankle fractures
- ankle surgery
- other space-occupying lesions (e.g. ganglion cysts, tumors)
Radiographic features
Ultrasound
Starting at the ankle the superficial part of the nerve can be visualized in a small groove between the extensor digitorum longus and the peroneal muscles 5. Dynamic ultrasound with plantar and dorsiflexion of the foot can conveniently depict muscle hernias 1.
MRI
MRI might visualize the superficial peroneal nerve as it comes close and moves out of the fascia 1. Within the subcutaneous tissue of the lower leg and the ankle, the extensor digitorum longus muscle serves as a landmark for identification of the nerve 5. Enlarged diameter, caliper changes or increased signal intensity on T2 weighted images are features suggestive of superficial peroneal nerve compression 1.
Signal characteristics
- T2: high signal (compared to skeletal muscle) ref
- STIR/IMFS: high signal
Treatment and prognosis
Management includes conservative measures including comfortable footwear, physiotherapy with a strengthening of the peroneal muscles, local anesthetics, non-steroidal anti-inflammatory drugs and perineural corticosteroid injections 2. Surgery is rarely required in refractory or longstanding cases and involves simple decompression with fasciotomy and neurolysis around the nerve exit which usually leads to symptom relief 1-4. Recurrences in the case of surgery can happen in up to 20% and can be managed with repeat exploration 4.
History and etymology
Superficial peroneal nerve entrapment has been first reported by the Irish surgeon Arnold K Henry in 1945 3,6.
Differential diagnosis
The differential diagnosis of superficial peroneal nerve entrapment includes 4: