Pertinent Insights On Surgical Decompression For Common Peroneal Nerve Entrapment

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

   The use of bipolar cautery is mandatory for hemostasis and avoids the potential of thermal nerve injury, which is problematic with monopolar cautery. As there is no way to know to what depth of thermal injury occurs with monopolar cautery, even in cases in which the surgeon “just likes to use it to make the skin incision,” this nerve can lie just millimeters deep to the dermis. There is no way to know how superficial this nerve is this until surgical exposure. Additionally, there is nothing from a hemostatic standpoint that the surgeon cannot address adequately with bipolar cautery, thus obviating any need for the potential risk associated with monopolar cautery. The use of monopolar cautery in lower extremity peripheral nerve surgery is dangerous and below the standard of care.

   Prior to making the actual skin incision, I recommend preemptive local anesthesia with lidocaine to prevent the potential for centralization of nociception. Depending on the morphology of the patient, there can be virtually no subcutaneous fat to dissect bluntly or a very thick amount in the high BMI patient, making the surgery very difficult. Then identify the deep fascia and lift it off the tissues below, which includes the nerve itself.

   One area of caution is that once through this tissue plane, the nerve can appear like a fatty globule. The surgeon cannot safely excise anything from this area and must only use blunt dissection to release the nerve from the surrounding fat due to longstanding entrapment. In patients with metabolic disease such as diabetes, this nerve can take on the appearance of subcutaneous fat. Inexperienced surgeons have sadly mistaken this nerve as a lipoma only to discover their mistake after they removed it.

   After delineating the nerve at this level, the surgeon can perform proximal dissection to release the nerve from any fascia in the popliteal fossa. The surgeon can safely use a finger to dissect this proximally into the fossa but should never perform this maneuver distally as the potential to harm motor innervation is high. In all reality, this is usually not the level of nerve entrapment as the true entrapment is beneath the peroneus (fibular) longus muscle belly as it courses into the lateral compartment.

   The next step is to perform a fasciotomy of the superficial fascia of the muscle belly, and then retract the muscle anteriorly and medially. This will leave the surgeon with good visualization of the true site of entrapment as the nerve can be visible before and after entering the lateral compartment. There is often an “hourglass” deformity at this level of entrapment.

   At this point, one can perform neurolysis of the nerve distally with extreme care to prevent any damage to the motor branches coming off under the muscle. There can be a 1 to 2 cm length of entrapment medially from where the nerve enters the lateral compartment that one must release in order to ensure a complete neurolysis. At this time, the nerve decompression is essentially complete with the only remaining step to remove or shrink any remaining redundant fascia with bipolar cautery, which will only serve to increase fibrosis. The surgeon must again take care to lift this tissue as far as possible from the nerve when using the bipolar cautery or excising the tissue.

   Closure of the skin usually entails both an intradermal interrupted suture such as 4-0 or 5-0 Monocryl (Ethicon) followed by 5-0 nylon sutures of the surgeon’s choice. One can inject bupivacaine (Marcaine) in the skin edges prior to closure so as to avoid any local anesthesia coming in contact with the common peroneal nerve itself. This allows for postoperative pain management but at the same time allows the surgeon to immediately evaluate the motor function of the patient in the post-anesthesia care unit.

What You Should Know About Postoperative Management

Patients may be fully weightbearing immediately after surgery and one should encourage them to begin walking modestly that day. In order to avoid the potential for hematoma, advise patients to walk only to the point of necessity the first 48 hours. Strongly recommend that they begin flexion and extension of the knee repeatedly.

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