Fibular (Peroneal) Nerve


This nerve next passes between the two heads of the fibularis (peroneus) longus (L5) muscle; here it is particularly vulnerable to being compressed against the fibular bone, leading to footdrop. The CFN divides into the superficial and deep fibular nerves here. Concomitantly, two superficial sensory nerves take origin. The lateral sural cutaneous nerve supplies the skin and fascia on the lateral and adjacent parts of the anteroposterior leg. The peroneal communicating branch joins the sural nerve, a branch of the tibial nerve, to be distributed with it.


The superficial fibular nerve initially descends between the extensor digitorum longus and brevis (L5, S1) muscles to innervate the fibularis (peroneus) longus (L5) and brevis (L5) muscles. The accessory fibular (peroneal) nerve, a motor branch of the superficial fibular nerve, is an important anatomic variation found in 10% of individuals. This provides partial innervation to the extensor digitorum brevis. Subsequently, the superficial fibular nerve pierces the deep fascia in the lower leg, dividing into two cutaneous nerves. The medial dorsal cutaneous nerve innervates the skin on the anterior distal leg; then it travels across the anterior ankle to the dorsum of the foot and across the lower inferior extensor retinaculum. It divides into two medial dorsal digital nerves; one supplies the medial and posterior aspects of the foot and great toe, and the other innervates the second and third toes. The intermediate dorsal cutaneous nerve courses along the lateral dorsal foot, supplying its adjacent skin and fascia. The lateral dorsal digital nerves innervate the skin and fascia of the third through fifth toes.


The deep fibular (peroneal) nerve (DFN) originates at the fibular head, passing obliquely downward around the proximal fibular neck, between the fibularis (peroneus) longus and extensor digitorum longus (L5, S1), muscles that it innervates, to then descend lateral to the tibialis anterior (L4, 5) and medial to the extensor digitorum longus and brevis (L5, S1) and extensor hallucis longus (L5, S1). The DFN innervates each of these muscles and the fibularis (peroneus) tertius muscles. The DFN divides at the ankle. Its medial terminal branch gives rise to a dorsal digital nerve, whose two branches supply the contiguous surfaces of the first two toes. Its lateral terminal branch curves outward under the extensor digitorum brevis muscle, which it supplies.


Clinical. Most fibular (peroneal) neuropathies occur at the fibular head with 60% of cases involving the CFN, whereas about 10% affect the deep fibular, and 5% the superficial fibular nerve. The other 25% are difficult to localize precisely. Compression is the primary pathophysiologic mechanism for fibular neuropathies; a typical example occurs when sleeping on one’s side on a hard surface, resting directly on the fibular head, and thereby compressing this nerve as it winds around the fibular neck. This typically occurs in a narcotized, often alcoholically intoxicated individual not moving during deep sleep. Anorectic malnourished adolescents often sit for long periods with legs crossed, compressing their fibular heads and the CFN, and leading to a footdrop. When this occurs among patients who are on strict diets, it is known as “slimmer’s palsy.” Occupations requiring prolonged squatting, such as farm laborers, strawberry pickers, and carpet layers, may compress this nerve between the biceps femoris tendon and lateral gastrocnemius origin. Very occasionally, iatrogenic mechanisms lead to compression injuries and footdrop; these include too tightly applied casts at the fibular head, Buck traction, Velcro straps, and intravenous footboards.


Entrapment. Sometimes a progressive footdrop develops secondary to common or deep fibular nerve entrapment at the knee. The proximal tendon of the fibularis longus rarely entraps the fibular nerve within the fibular tunnel at the fibular head. Mass lesions, including schwannomas, hemangiomas, bony exostoses, osteochondromas, perineuromas, or intraneural ganglia or synovial cysts within the popliteal fossa, may variably entrap the fibular nerves. Occasionally, runners inadvertently step into a hole, inverting the ankle and concomitantly stretching and/or avulsing the CFN at its anatomic fixation to the fibular head, producing a footdrop. A post-traumatic anterior tibial compartment syndrome rarely leads to similar outcomes. An urgent limited fasciectomy is indicated. The lateral cutaneous nerve of the calf can be entrapped in the lateral popliteal fossa, leading to popliteal fossa and lateral calf pain, exacerbated when seated and aided by extension of the knee.


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Sep 2, 2016 | Posted by in NEUROLOGY | Comments Off on Fibular (Peroneal) Nerve

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