What is the Common Peroneal Nerve?
The common peroneal nerve is a branch off the sciatic nerve which mainly supplies sensation to the top of the foot, the outside of the leg, and the web space between the great toe and the 1st toe. It controls the ability for one to extend (lift up) the great toe, the lesser toes, and the ankle, and to move the foot outwards (eversion). The common peroneal nerve is one of the most vulnerable to entrapment or injury in the body because it passes about 2 cm below the lateral aspect of the fibula, where it is very subcutaneous.
What Causes Peroneal Nerve Irritation?
Irritation of the common peroneal nerve can occur from a direct or indirect injury, prolonged pressure such as sleeping against a car console with one’s fibular head against it, or due to instability such as instability of the proximal tibiofibular joint. In addition, it is one of the most commonly injured nerves when there is an injury to the lateral (fibular) collateral ligament, posterolateral corner of the knee, or when there is a knee dislocation.
Because the common peroneal nerve is so subcutaneous, it can get caught up in scar tissue after injury and become irritated. The symptoms from this can range from numbness with prolonged activities, weakness of one’s ankle, a foot drop, or any combination of these. In particular, when one has scar tissue entrapment or a proximal tibiofibular joint instability problem, increasing one’s activities can cause some irritation of the nerve with some shooting pains on the outside of the leg down into the top of the foot.
It is very important to ensure that there are no other causes of common peroneal nerve irritation, which can include lumbar disc herniations, axonal damage to the sciatic nerve after a nerve block, or other sources that are closer to the spine.
How to Diagnose Common Peroneal Nerve Entrapment
A diagnosis of a common peroneal nerve entrapment is almost always based upon a physical examination. Palpation of the nerve where it crosses the fibular head, or slightly posterior to this, can cause zingers to go down the leg, which is called a Tinel sign. If this reproduces the patient’s symptoms, it can indicate that the common peroneal nerve is irritable and may be encased in scar. Nerve conduction tests or EMGs can be obtained, but these only tend to show positive results with more severe nerve injuries and I have seen patients with disabling pain who have normal EMGs and nerve conduction studies.