Superficial Peroneal Nerve (SPN) Compression
Background
The superficial peroneal nerve (SPN) is a sensory nerve branch that comes off the common peroneal nerve in the lower leg. It can get compressed along its path through the thick fascia of the lower leg. It can lead to pain and occasionally numbness/tingling in the top and side of the foot.
Causes
The SPN is most often compressed at the point where it exits the fascia at approximately 10-15 cm from the ankle joint. Thickening of the fascia is a known cause of this compression and can happen after trauma, in cases of exertional compartment syndrome, but also when the patient has experienced bouts of swelling and edema that can occur after knee or ankle operations.
Symptoms
The result of SPN compression is most often pain that is located along the course of the nerve. The exit point through fascia at approximately 10 cm from the ankle is often point tender. Numbness and tingling in the distribution of the nerve can also be present.
Diagnosis
Nerve testing (EMG) is often not helpful / non-diagnostic. The physical examination is the mainstay of diagnosis.. 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 as it exits the fascia. If the patient presents with pain, a diagnostic local anesthetic injection performed in the office under ultrasound guidance can provide helpful prognostic information.
Treatment
Unfortunately, it is not widely known, even among neurologists and orthopedic surgeons that the SPN 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 anterolateral aspect of the calf. The nerve is identified and released. Since often the fascia is thickened, concomitant fasciotomies/a focused fasciectomy is completed at the same time of the anterior and lateral compartment.
On occasion, if the patient has already undergone several injections, dry needling or other interventions such as failed decompression, a denervation may be indicated. This involves dividing the nerve more proximally, and performing TMR (Targeted Muscle Reinnervation) to prevent formation of a painful neuroma. On occasion, protective feeling in the distribution of the SPN can be restored using an end-to-side transfer of the distal nerve end into the sural nerve.
This is the case of a patient with a longstanding history of pain with ambulation. The point of maximum tenderness, seen in the photograph, corresponds to the anatomic location of the transition point of the SPN from deep to superficial. The compressive fascia is seen on the following images. The final photograph shows the nerve and its branches after the decompression is complete. A neuroma in continuity of one of the SPN branches is seen.
