Common, Superficial & Deep Peroneal (Fibular) Nerve Anatomy

The common peroneal nerve is examined more than any other lower-limb nerve because it is the cause of foot drop and because it is so easily injured — it sits subcutaneously on the fibular neck with no protection. The clean way to hold the topic is a two-branch split: the deep peroneal nerve lifts the foot and toes (and owns the first web space), while the superficial peroneal nerve turns the foot out (and owns the dorsum of the foot). Everything clinical flows from that — foot drop, the sensory map, the distinction from an L5 root lesion (which adds inversion and hip-abduction weakness), and the entrapment/surgical danger points down the leg.

• Sensory (deep peroneal): a small but clinically vital zone in the first dorsal web space.
• Sensory (superficial peroneal): most of the dorsum of the foot (sparing the first web space and the lateral border, which is sural territory).
• Lateral sural cutaneous nerve: upper lateral leg, contributing to the sural nerve.

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Beyond the classic fibular-neck palsy, two distal entrapments and a set of operative danger points complete the examiner's picture.

• Superficial peroneal nerve entrapment. The superficial peroneal nerve becomes subcutaneous by piercing the deep fascia of the anterolateral leg about 10–12 cm above the lateral malleolus. It can be entrapped at this fascial exit (or by a fascial defect/muscle herniation, or after inversion ankle sprains), causing lateral leg / dorsal foot pain and altered sensation worse on activity — a cause of chronic exertional leg pain and a pitfall at lateral ankle arthroscopy portals.
• Deep peroneal nerve entrapment (anterior tarsal tunnel syndrome). The deep peroneal nerve can be compressed beneath the inferior extensor retinaculum at the ankle (tight footwear, osteophytes, ganglia), producing first-web-space numbness and, if the motor branch is involved, weakness/wasting of extensor digitorum brevis.
• Surgical danger at the fibular neck and proximal fibula. The subcutaneous course makes the nerve vulnerable in lateral approaches to the knee, proximal fibula resection/biopsy, high tibial osteotomy, multiligament knee reconstruction (PLC), and knee dislocation. It is also the graft/donor consideration site and the location of an intraneural ganglion arising from the superior tibiofibular joint (a recognised, recurrent cause of palsy).
• The peroneal nerves in the ankle block. Both terminal branches are anaesthetised as part of the five-nerve ankle block for foot surgery (the deep peroneal and superficial peroneal are two of the five, with the posterior tibial, sural and saphenous). The deep peroneal nerve is blocked at the front of the ankle between the tendons of tibialis anterior and extensor hallucis longus, just lateral to the dorsalis pedis (anterior tibial) artery, to anaesthetise the first web space; the superficial peroneal nerve is blocked by a subcutaneous ring across the dorsum of the ankle to cover the dorsum of the foot. Knowing which branch covers which territory tells you which to supplement when a block is patchy.

Global Practice Picture

Common peroneal neuropathy is a universal clinical problem - the leading lower-limb compressive neuropathy and the prototypical cause of foot drop. Internationally consistent teaching: protect the fibular neck (positioning, casts), localise the lesion clinically (deep vs superficial branch; peroneal vs L5), confirm with electrodiagnostics, and manage with cause removal, an AFO, and decompression or tendon transfer when indicated.

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