Superficial Peroneal Nerve Biopsy

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Anesthesia

Procedure is done with an LMA, no need for endotracheal intubation

Positioning

Supine on a regular OR table. No need to turn the bed.

Place a large bump under the ipsilateral hip to medially rotate the leg.

Place pillows between the knees and between the ankles.

Marking

Mark the head of the fibula and the lateral malleolus. The incision lies along a line drawn between these two marks. Mentally divide this line into quarters and again into thirds. The incision itself is the overlap between the distal third and the third quarter mark.

As a backup, also mark an incision over the sural nerve, which lies ~1cm posterior to the posterior border of the lateral malleolus. This is demonstrated as the thick line in the photo below. The hashed line posterior to it is an incorrect marking.

Procedure

Use lidocaine with epi to locally anesthetize the incision.

Peroneal Nerve Biopsy

Prep and drape in standard fashion.

Incise the skin to the subcutaneous fat. Use Metzenbaum scissors to spread the subcutaneous fat to the fascia of the muscle. The course of the superficial peroneal nerve is parallel with and deep to the incision. It is sometimes above the fascia. If it is not found above the fascia, incise the fascia and search below it as well. Below the fascia there are several tendons which can, at first glance, be confused for the nerve. Tendons are bright white, shiny, and iridescent, however.

Once the nerve is found, cut out a 2-cm section with microscissors. Take care that the ends are sharply cut and the nerve bundles within are not splayed. The ends of the cut nerve will retract slightly after cutting.

Fibularis Brevis Biopsy

Use the muscle biopsy forceps to grab a piece of the muscle and slide the locking mechanism on the side of the instrument to lock the bite in place. Use Metzenbaum scissors (not the Bovie!) to cut the muscle on the outside of the forceps to free up the bite. Keep the forceps locked and hand the sample to the scrub tech. Instruct the scrub tech to send the forceps with muscle as-is and not to release the muscle from the forceps.

Nerve Interposition Graft

Measure the diameter of the cut end of the nerve as well as the length of the graft required. Because the ends of the cut nerve retract, the graft will have to be longer than the 2 cm portion of nerve that was excised.

Call for a cadaveric nerve interposition graft that approximates the required dimensions. Should be something like 2-3 mm by 30 mm.

Go under scope.

Using 9-0 nylon suture and microsurgical instruments, perform an end-to-end anastamosis between the cut ends of the superficial peroneal nerve and the graft. Use 3 to 4 interrupted sutures at each end. Take bites through the perineurium. Evert the edges of the suture line.

Closure

Irrigate with antibiotic irrigation. Close the fascia of the muscle with 3-0 polys. Close the dermal layer with 3-0 polys. Close the skin with a running subcuticular 4-0 Biosyn. Put a small amount of skin glue over the incision. Dress with a Primapore.

Place a JP drain if necessary. It is rarely necessary.

Postop Orders

Prophylactic Ancef for 24 hours. Pain meds. No SBP cap, no imaging, no special labs, no special meds.

Complications

All patients will have loss of sensation in the distribution of the biopsied nerve. Some will also have dysesthetic pain (20%) or paresthesias (50%).

With microsurgical repair of the nerve, post-biopsy hypesthesia persists for 4 to 8 weeks and improves to preoperative levels as early as 6 months after the nerve repair.

For the peroneal nerve: