The common peroneal nerve is the smaller terminal branch of the sciatic nerve. It appears in the lower third of the thigh just above the popliteal fossa. It enters into the popliteal fossa along its upper lateral boundary just below the border of the biceps tendon. Now, it runs over plantaris and the lateral head of gastrocnemius. It runs over the fibular connection of the soleus to wind around the lateral aspect of the neck of fibula to reach deep to peroneus longus where it splits into 2 endmost branches- deep and superficial peroneal nerves.
The motor branches of the deep peroneal Nerve Supply all the muscles of the anterior compartment of the leg consisting of extensor digitorum brevis on the dorsum of the foot.
The motor branches of the superficial peroneal Nerve Supply all the muscles of the lateral compartment of the leg.
The sensory branches of the deep peroneal Nerve Supply the skin of cleft between the great and 2nd toes.
The sensory branches of the superficial peroneal Nerve Supply majority of the skin on the dorsum of foot with the exception of in the cleft between the great and 2nd toes being provided by the deep peroneal nerve The lateral margin of the dorsum of foot consisting of the lateral margin of little toe is provided by the sural nerve. The medial margin of the dorsum of foot upto the ball of the great toe is being provided by the saphenous nerve.
In the popliteal fossa, the common peroneal Nerve Supplys rise to 2 cutaneous branches and 3 genicular branches.
All these are as follows:
- Sural conveying nerve: It originates opposite to the head of the fibula, and crosses superficially to the lateral head of gastrocnemius to join the sural nerve.
- Lateral cutaneous nerve (lateral sural nerve): It originates lower down and pierces the deep fascia to provide the skin on the upper part of the lateral side of the leg.
Genicular (articular) branches
All these are superior lateral genicular, inferior lateral genicular, and recurrent genicular nerves. The very first 2 provide the knee joint and the last 1 provides the superior tibiofibular joint.
The common peroneal nerve can be palpated against the neck of fibula. And the common peroneal Nerve Supplys no muscular branch in the popliteal fossa.
Effects of Injury To The Common Peroneal Nerve
Thecommon peroneal nerve is very susceptible to injury as it winds around the posterolateral aspect of the neck of the fibula. At this site it might be injured by the direct trauma, fracture neck of fibula, or closely applied plaster cast. The characteristic clinical features are as follows:
- Foot drop, as a result of paralysis of muscles of the anterior compartment of the leg (dorsiflexors of the foot).
- Loss of extension of toes, because of the paralysis of extensor digitorum longus and extensor hallucis longus.
- Loss of eversion of foot, because of the paralysis of peroneus longus and peroneus brevis (evertors of the foot).
- The sensory loss because of participation of the cutaneous branches, on the anterolateral aspect of the leg, and entire of dorsum foot with the exception of the regions provided by the saphenous and sural nerves.
Because of paralysis of the dorsiflexors and evertors of the foot, the patient can not stand on the heel. He’s high stepping gait, where foot is lifted higher compared to the normal so that the toes don’t hit the earth. Moreover, if the foot is put back on the earth unexpectedly, it generates a smacking sound termed foot smack.