Common Peroneal Nerve (CPN) Compression

Background

The common peroneal nerve (CPN) is a critically important nerve the comes off the sciatic nerve in the back of the thigh and travels from the back of the knee, around the neck of the fibula bone, to end up in the front of the lower leg to provide electrical impulse to the important muscles that extend (pull up) the ankle and the toes. They also evert the foot. In addition, the nerve provides feeling the the outer aspect of the lower leg and foot. The nerve usually gets compressed where it travels from behind the knee to the front of the lower leg (at the fibular neck).

Causes

The CPN can be compressed for several reasons. Sometimes it occurs without trauma, but more often, there is a history of significant leg swelling and trauma or prior surgery that leads to thickening of fascia in this area that can impinge on the CPN.

Symptoms

The result of CPN compression is numbness, tingling, weakness (as in foot drop), and pain. Infrequently, all these symptoms occur at the same time. More often, we see a combination of a few of these symptoms, which makes diagnosis difficult.

Diagnosis

Nerve testing as in EMG’s can be helpful but not always. A dedicated MRI called MR neurography can be obtained. Alternatively, a high frequency ultrasound of the nerve can be more helpful in identifying more subtle changes in the nerve.

One specific circumstance which is almost an entity in itself is an acute CPN compression from a ganglion originating from the proximal tib-fib joint. This can lead to tearing and sudden pain in the nerve, often with weakness. An MRI usually shows the culprit and allows for an early diagnosis.

Treatment

Unfortunately, it is not widely known, even among neurologists and orthopedic surgeons that the CPN can be released/decompressed. This is a fairly routine procedure in which an incision is carried out over the course of the nerve on the outside of the knee. The nerve is identified and the various sites of compression are released. Just looking at the nerve and dissecting it at the outside of the knee is not sufficient. Known areas of compression should be explored. At least 4 common sites of compression exist and must be addressed.

An example is shown here. This patient had been followed by a spine clinic for foot drop which was considered to be originating from a nerve compression at his lower spine. Fortunately, the CPN compression was identified, and a simple decompression yielded a full recovery within 3 months.