I. Superficial Peroneal Nerve (SPN)
Definition
· Compression neuropathy of superficial peroneal nerve
· Usually seen in transition of the nerve from lateral compartment to anterior ankle
Anatomy
· SPN is a purely sensory branch
· Branches from the common peroneal nerve at the level of fibular neck
· Proceeds distally in the lateral compartment between peroneus longus & brevis
· It becomes superficial in the distal third of the leg, approximately 12 cm proximal to the tip of lateral malleolus
· Branches into medial- and intermediate dorsal cutaneous nerves
o Intermediate dorsal cutaneous nerve: sensation from third, fourth and fifth toes
o Medial dorsal cutaneous nerve: passes lateral to EHL and provides sensation from the medial aspect of dorsal foot
· Compression can be seen anywhere along its course
· Usually posttraumatic – after inversion injuries
· Iatrogenic injury
o open management of lateral malleolus fractures
o placement of anterolateral portal for ankle arthroscopy
Evaluation
· Burning pain and paresthesias in dorsal foot
· Pain distribution is similar to L5 dermatome
· Symptoms are aggrevated by plantar flexion and inversion
· Tinel sign is usually seen over where the nerve pierces the fascia
· Motor findings are normal unless more proximal compression
· Sensory nerve conducting velocities may be prolonged
· Electrodiagnostic tests are useful for excluding a more proximal cause of compression
· Diagnosis is usually made based on clinical examination
Imaging
· Radiographs are helpful for detecting osseous impingement
· MRI for soft tissue masses
Treatment
· Non-surgical
o Injection of local anesthetics and steroids
o Orthoses to prevent inversion of the ankle
o Physical therapy to strengthen the muscles around ankle
· Surgical
o If the pain doesn’t response to non surgical treatments
o Should begin at the level at which the nerve exits fascia
o Neurolysis should proceed distal to the site of compression
o Fasciotomy is indicated in chronic compartment syndrome
o 80% of patients experience improvement
II. Sural Nerve
Anatomy
· Purely sensory nerve that is formed by branches of peroneal and tibial nerves
· It lies at the midline at the musculotendinous junction of gastrocnemius muscle
· Descends distally lateral to the Achilles tendon and lies posterior to peroneal tendons
· Proceeds distally and crosses base of the fifth metatarsal
· Entrapment can result from fractures of the calcaneus, talus, fifth metatarsal
· Iatrogenic injury: during ORIF of these fractures and gastrocnemius recession
Evaluation
· Lateral foot and ankle pain radiating proximally
· Associated numbness in the same area
· Positive percussion test typically reproduces paresthesias in the lateral foot
· Electrophysiological studies are rarely helpful
Imaging
· Radiographs are helpful for excluding fractures and exostosis
· MRI for soft tissue masses
Treatment
· Non-surgical
o Shoe modification to relieve pressure on the sural nerve
o Injections can be both diagnostic and therapeutic
· Surgical
o Neurolysis is beneficial especially in malreduced fractures
o In cases of posttraumatic neuroma: excision and burying of proximal stump is recommended
III. Saphenous Nerve
· Provides sensation to the medial ankle and dorsomedial foot
· Follows greater saphenous vein
· Can be injured during anteromedial arthroscopic portal placement
· Saphenous nerve entrapment is rare and usually occur in medial aspect of the knee
· If a true neuroma present, resection and burying of the proximal stump is recommended because of its subcutaneous location