Deep peroneal nerve
The deep peroneal nerve, more commonly known as the deep fibular nerve innervates a number of muscles in the leg and foot, which are essential for normal gait and movement of the ankle.
In this article we will discuss the anatomy of the deep fibular (peroneal) nerve including its motor and sensory roles and relevant clinical aspects.
The sciatic nerve (root values:L4-S3) bifurcates above the popliteal fossa into the common fibular (peroneal) nerve (root values: L4-S2) and the tibial nerve (root values: 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 however 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 fibular (peroneal) nerve descends between the fibula and the superior part of fibularis/peroneus longus, runs deep to extensor digitorum longus and anterior to the interosseus membrane.
The deep peroneal (fibular) nerve, provides innervation to the muscles of the anterior compartment of the leg, also known as the dorsiflexor compartment of the leg. These include 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 deep fibular nerve 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 provides cutaneous innervation to the adjacent sides of the first two toes as well as the web space between these digits. In addition, the medial branch of the deep fibular (peroneal) nerve gives an articular branch to the first metatarsophalangeal joint.
- The lateral terminal branch supplies extensor digitorum brevis and extensor hallucis brevis muscles, the tarsal joints as well as the middle three metatarsophalangeal joints.
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 by the deep fibular nerve is functionally important since dorsiflexion of the foot is essential for the midstance and heel strike phases of gait, while foot inversion enables us to balance on uneven surfaces.
Deep fibular (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 ‘drop foot.’
- 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.