Common Fibular Nerve
The common fibular nerve, also known as the common peroneal nerve, is one of two main muscular branches of the sciatic nerve. This common fibular nerve then divides into the deep and superficial fibular nerves, and innervates the muscles listed:
- Superficial fibular nerve: fibularis longus, fibularis brevis
- Deep fibular nerve: tibialis anterior, extensor digitorum longus, extensor digitorum brevis, extensor hallucis longus, extensor hallucis brevis, and fibularis tertius muscles.
Note: Do not confuse “peroneal” with “perineal”! The perineal nerve is a nerve arising from the pudendal nerve that supplies the perineum.
The sciatic nerve descends along the posterior thigh, and divides in the lower third of the thigh into the tibial nerve and common fibular nerve as it travels towards the popliteal fossa. Next, the common fibular nerve divides into the deep and superficial fibular nerves.
The common fibular nerve descends obliquely along the lateral side of the popliteal fossa to the head of the fibula, where it lies between the tendon of the medial biceps femoris and lateral head of the gastrocnemius muscle. At this location, the common fibular nerve winds around the head of the fibula (where it is palpable) to the front of the leg, between the fibularis longus and the bone. Immediately after it enters the fibularis longus, the nerve divides underneath the muscle into the superficial fibular nerve (superficial peroneal nerve) and deep fibular nerve (deep peroneal nerve).
Compared to the tibial nerve, the common fibular nerve is about one-half the size of the tibial nerve, and is derived from the dorsal branches of the fourth and fifth lumbar nerves and the first and second sacral nerves (L4-S2).
Prior to the division of the common fibular nerve, the articular and lateral sural cutaneous nerves branch off as:
- Articular branches (rami articulares) are three in number, where two of these branches accompany the superior and inferior lateral genicular arteries to the knee (the upper branch can occasionally arise from the trunk of the sciatic nerve), and the third branch is the (recurrent) articular nerve that is given off at the point of division of the common fibular nerve, which ascends with the anterior tibial artery through the tibialis anterior to the front of the knee.
- The lateral sural cutaneous nerve (nervus cutaneus surae lateralis; lateral cutaneous branch) supplies the skin on the posterior and lateral surfaces of the leg, and divides into two branches just below the head of the fibula (the superficial and deep fibular branches).
Branches of the Fibular Nerve
The superficial fibular nerve supplies the fibularis muscles and runs between the fibularis longus and the fibula to the dorsum of the foot. It innervates the fibularis longus and fibularis brevis muscles. These two muscles assist with eversion and plantar flexion of the foot. The cutaneous branches of the superficial fibular nerve extend into the medial dorsal cutaneous nerve and the intermediate dorsal cutaneous nerve.
The deep fibular nerve runs through the interosseus membrane to enter the extensor compartment and innervates the anterior compartment of the leg. After supplying the tibialis anterior, extensor digitorum longus, and extensor hallucis longus--these muscles are responsible for dorsiflexion of the foot and extension of the toes (along with fibularis tertius)-- it runs in a groove between tibialis anterior and extensor hallucis longus on the crural interosseous membrane, accompanied by the anterior tibial vessels, to the dorsum of the foot. The deep fibular nerve also innervates the intrinsic muscles: extensor digitorum brevis, extensor hallucis brevis. Its cutaneous branches supply the lateral cutaneous nerve of the big toe and the medial cutaneous nerve of the second toe.
- If the common fibular nerve is damaged at the fibular neck before it divides into its two terminal branches, there will be a resultant weakness or paralysis of the anterior and lateral compartment muscles that will cause foot drop with some inversion.
- If the common fibular nerve is damaged after it has divided, then the result will be an isolated weakness or paralysis of the anterior compartment or lateral muscles. This will depend on whether the deep fibular nerve or the superficial fibular nerve is affected. Weak dorsiflexion or weakness of eversion would result.
- An isolated lesion of the superficial fibular nerve would mostly affect only the sensory terminal branch, with pain that is felt in the distal leg and dorsum of the foot.
- An isolated lesion of the deep fibular nerve (especially in compartment syndrome, potentially caused by anterior compartment hemorrhage) would cause a gait disturbance that results from foot drop and a “steppage gait”. In this case, increased flexion of the hip and knee joints is necessary to compensate for this odd gait to keep the toe from dragging on the ground during the swing phase of gait.