Deep Peroneal nerve
The deep peroneal/fibular nerve supplies some muscles in the leg, which are essential for normal gait and movement of the ankle. In this article we will discuss the anatomy of the deep peroneal nerve including its motor and sensory roles. We will also discuss its clinical relevance. Finally we will conclude with some review questions to test the reader’s understanding of the article content.
The sciatic nerve (ventral rami of L4-S3) bifurcates above the popliteal fossa into the common peroneal nerve (ventral rami of L4-S2) and the tibial nerve (ventral rami of L4-S3). The tibial nerve descends and supplies the posterior compartment of the leg, i.e. gastrocnemius, soleus and the deep posterior muscles (flexor hallucis longus, tibialis posterior and flexor digitorum longus). The common fibular/peroneal nerve runs laterally deep to the lateral collateral ligament of the knee, and winds around the neck of the fibula. It then divides into the deep and superficial branches. The superficial branch supplies the lateral compartment of the leg and sensation from the lateral surface of the leg.
The deep branch of the common peroneal nerve (L4-L5) supplies the anterior compartment of the leg, and sensation from the first dorsal web-space of the foot. The muscles of the anterior compartment are the extensor digitorum longus (dorsiflexes the ankle and extends the toes), extensor hallucis longus (extends the big toe/hallux), fibularis/peroneus tertius (dorsiflexes the ankle) and tibialis anterior (inverter and dorsiflexor of the foot). The ankle joint is a simple hinge joint in the formation of a mortice. It simply allows for dorsiflexion (caused by the anterior muscles) and plantar flexion (caused by the posterior muscles of the leg) of the ankle. The movements of inversion (tibialis anterior and tibialis posterior) and eversion (fibularis longus, fibularis brevis, fibularis tertius) occur at the subtalar joint. Innervation of the deep fibular nerve is functionally important since foot dorsiflexion is essential for the toe off phase of gait while foot inversion enables us to balance on uneven surfaces.
The deep branch of the common fibular nerve descends between the fibula and the superior part of peroneus longus, runs deep to extensor digitorum longus and anterior to the interosseus membrane. It begins lateral to the anterior tibial artery but terminates medial to it. It descends with the anterior tibial artery to the ankle and divides into a medial and lateral terminal branch. The medial terminal branch supplies the adjacent sides of the first two toes and the first dorsal web space. Before it branches to the web space it also gives an articular branch to the first metatarsophalangeal joint. The lateral terminal branch supplies extensor digitorum brevis, the tarsal joints as well as the middle three metatarsophalangeal joints.
Deep peroneal nerve palsy- The patient will be unable to dorsiflex their ankle. They will also lose sensation in the first dorsal web-space. This kind of isolated nerve palsy is caused by inflammatory disorders, demyelinating diseases, diabetes and lower motor neurone diseases. It can also be caused by trauma to the lateral surface of the knee. The symptom is clinically described as ‘foot drop.’
- The deep peroneal nerve (L4-L5) is a branch of the common peroneal nerve (ventral rami of L4-S2), which is itself a branch of the sciatic nerve (ventral rami of L4-S3).
- It supplies the anterior compartment of the leg (tibialis anterior, extensor hallucis longus, extensor digitorum longus). These muscles cause dorsiflexion and inversion of the foot.
- It relays sensation from the first web-space, and adjacent sides of the first two toes. It also supplies articular branches to the metatarsophalangeal joints and tarsal joints.