Anatomy of Superficial Peroneal Nerve
After division from the common peroneal nerve just distal to the fibular neck, superficial peroneal nerve (SPN) runs in the lateral (peroneal) compartment of the leg and innervates peroneus longus and brevis muscles. It then exits the compartment at the lower third of the leg and supplies sensory innervation to the dorsolateral aspect of the ankle and foot (sparing the first dorsal webspace which is innervated by the deep peroneal nerve). SPN has a highly variable course and becomes more superficial as it courses from the lower leg to the dorsum of the foot. It eventually divides into two terminal branches:
- Medial dorsal cutaneous nerve
- Intermediate dorsal cutaneous nerve
Nerve Injury
Because of the superficial position of the nerve around the ankle, it is vulnerable to injury from ankle trauma, ankle surgery employing the lateral approach and ankle arthroscopy.
Symptoms and Signs
- Shooting pain
- Tingling and altered sensation
- Allodynia (the above symptoms over the dermatome of SPN)
- Tinel's sign (the most important finding to localise the site of nerve irritation)
Investigation
A local anaesthetic (1 or 2% lidocaine) injection at the Tinel's spot followed by resolution of the above symptoms is regarded as a positive test for a focal nerve lesion. Should the symptoms return predictably as the local anaesthetic wears off (after 4 hours), that is taken as a further level of confirmation.
Treatment
Wound desensitisation may be tried but if there are corroborative symptoms and signs of a focal nerve lesion, surgery is a more reliable way of relieving the discomfort. At the time of exploration, if the nerve is found to be intact, neurolysis with a nerve wrap is performed. If the nerve has been cut or severely damaged, the proximal nerve end is buried in a muscle while the distal nerve end is sutured to a neighbouring healthy sensory branch (end-to-side repair).