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Also known as the deep peroneal nerve, the deep fibular nerve is a nervous system vessel located on the front outside portion of the lower leg. Along with the superficial fibular nerve, it arises from a large vessel called the common fibular nerve, which in turn is a branch of the tibial nerve, the large nerve that runs down the center of the posterior side of the leg. The deep fibular nerve crosses from the side of the leg to the anterior compartment, where it communicates with the muscles found here: the tibialis anterior, extensor digitorum longus, extensor digitorum brevis, and the peroneus tertius. It also transmits sensory signals from the skin on the adjacent sides of the first and second toes.
The splitting of the common fibular nerve into the superficial fibular nerve and deep fibular nerve occurs alongside the bottom of the knee on the outside of the leg. At approximately the height of the upper end of the peroneus longus muscle, the common fibular sends its superficial branch down the outside of the leg through the peroneal muscles and its deep branch under the extensor digitorum longus muscle toward the center of the front of the leg. The deep fibular nerve runs directly alongside the anterior tibial artery and just in front of the interosseous membrane, a thin, flat ligament that unites the fibula and tibia bones along their length, as it descends through the shin.
Staying on a nearly vertical course through the anterior compartment of the leg, the deep fibular nerve sends motor signals to the muscles found to the front of the interosseous membrane: the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius. These are the muscles that dorsiflex the foot, or lift it upward at the ankle joint, and extend or lift all five toes. Toward its lower end, the deep fibular nerve passes beneath the extensor hallucis longus before crossing the front of the ankle and entering the dorsum, the top side of the foot. Here it innervates the muscles that assist those of the lower leg in extending the toes, the extensor digitorum brevis, and extensor hallucis brevis.
In addition to sending signals that produce muscle contractions, the deep fibular nerve also returns sensory input from the skin between the first and second toes, or what is known as the first webspace, to the central nervous system. Since the vessels and structures in the anterior compartment of the leg are packed in fairly tightly, the supply of blood to the nerve or the nerve itself can become cut off in a condition known as anterior compartment syndrome. This compression or other injury to the nerve can result in an inability to dorsiflex the foot, a condition known as “footdrop,” as well as difficulty extending the toes or reduced sensation in the webspace between the big toe and second toe.