Pertinent Insights On Surgical Decompression For Common Peroneal Nerve Entrapment

Stephen L. Barrett, DPM, MBA, FACFAS, FAENS

   For patients who come in with only the complaint of ankle pain, in addition to the examination I described above, there should be radiographic and clinical evaluation of the ankle joint. Before making the diagnosis of sinus tarsi syndrome, which frequently coexists with proximal nerve entrapments of the common peroneal (fibular) and superficial peroneal (fibular) nerves, the provider must rule these out.

   If there are no clinical signs of proximal entrapment, no motor weakness, no decrease in sensation to light touch and two-point discrimination, then one can usually make a reliable sole diagnosis of sinus tarsi syndrome but physicians often miss this. However, if it appears that both or one of these etiologies are present, then confirmation of the diagnosis with peripheral nerve blocks can be extremely reliable.

   The use of peripheral nerve blocks with just lidocaine (Lidoderm, Endo Pharmaceuticals) is an extremely powerful and helpful adjunct in the diagnosis of peripheral nerve entrapments. In the case of the common and superficial peroneal (fibular) nerves, I recommend blocking the more distal known site of entrapment (the superficial peroneal (fibular) nerve) at the foraminal level with just 1 cc of the local anesthetic. If this eliminates all the “ankle” pain, then the physician can feel assured that this is the level of the pain generator. However, if in this same situation, the practitioner had blocked the more proximal common peroneal (fibular) nerve site and the pain went away, he or she would not know if there really was a more distal entrapment causing or at least contributing to the pain in the sinus tarsi.

   A neurosensory testing report will shows an elevated two-point discrimination threshold with axonal degeneration for only the distribution of the common peroneal (fibular) nerve in a patient with an isolated single entrapment. The report shows widespread loss of sensation in a patient with diabetic peripheral neuropathy—both one point and two point.

Current Insights On Performing SurgicalNeurolysis/Decompression

Decompression of the common peroneal (fibular) nerve is a technically easy surgery for the experienced peripheral nerve surgeon, and a difficult and dangerous one for the inexperienced surgeon. Surgeons who are not formally trained in lower extremity peripheral nerve surgery should not perform this surgery as the potential complication of nerve injury resulting in a permanent drop foot condition is disastrous for the unfortunate patient.
However, for the trained surgeon who can provide judicious technique, this is one of the most immediate and gratifying surgeries for the lower extremity.

   Patient positioning and incision placement are critical to the success of any surgery. This is especially the case with decompression of the common peroneal (fibular) nerve. One should ensure the patient is in a supine position with the knee flexed and a weight placed on the OR table holds the knee in that position. When placing the incision, the surgeon marks the level of the fibular neck, which is easily palpable in patients with a normal body mass index (BMI).

   However, in those patients with high BMIs, this can be difficult to palpate. In these patients, one can palpate this anatomic marker with the leg extended. In very serious cases in which there is no osseous palpation of the fibula, one can use intraoperative fluoroscopy. As most patients tend to abduct their lower extremities when they are relaxed (as in general anesthesia), the OR table can tilt slightly away from the surgeon, holding the leg in better position.

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