Superficial Peroneal Nerve Block at the Ankle

Indications and Clinical Considerations

Superficial peroneal nerve block is useful in evaluating and managing foot pain thought to be subserved by the superficial peroneal nerve. The technique also is useful for providing surgical anesthesia for the foot when combined with deep peroneal, tibial, and saphenous nerve block or lumbar plexus block. It is used for this indication primarily in patients who would not tolerate the sympathetic changes induced by spinal or epidural anesthesia and who need foot surgery, such as debridement, excision of Morton neuroma, or toe or forefoot amputation ( Fig. 182.1 ).

Superficial peroneal nerve block with local anesthetic can be used as a diagnostic tool when performing differential neural blockade on an anatomic basis in the evaluation of distal lower extremity pain. If destruction of the superficial peroneal nerve is being considered, this technique is useful as a prognostic indicator of the degree of motor and sensory impairment that the patient may experience. Superficial peroneal nerve block with local anesthetic may be used to palliate acute pain emergencies, including foot fractures and postoperative pain relief, when combined with the previously mentioned blocks, while waiting for pharmacologic methods to become effective. Superficial peroneal nerve block with local anesthetic and steroid occasionally is used in the treatment of persistent foot pain when the pain is thought to be secondary to inflammation or when entrapment of the superficial peroneal nerve as it passes underneath the dense fascia of the ankle is suspected. Superficial peroneal nerve block with local anesthetic and steroid also is indicated in the palliation of pain and motor dysfunction associated with diabetic neuropathy. Destruction of the superficial peroneal nerve occasionally is used in the palliation of persistent foot pain secondary to invasive tumor that is mediated by the superficial peroneal nerve and has not responded to more conservative measures.

Clinically Relevant Anatomy

The common peroneal nerve is one of the 2 major continuations of the sciatic nerve, and the other is the tibial nerve ( Fig. 182.2 ). The common peroneal nerve provides sensory innervation to the inferior portion of the knee joint and the posterior and lateral skin of the upper calf. The common peroneal nerve is derived from the posterior branches of the L4, L5, S1, and S2 nerve roots. The nerve splits from the sciatic nerve at the superior margin of the popliteal fossa and descends laterally behind the head of the fibula. The common peroneal nerve is subject to compression at this point by such circumstances as improperly applied casts and tourniquets. The nerve also is subject to compression as it continues its lateral course, winding around the fibula through the fibular tunnel, which is made up of the posterior border of the tendinous insertion of the peroneus longus muscle and the fibula itself. Just distal to the fibular tunnel, the nerve divides into its 2 terminal branches: the superficial and the deep peroneal nerves ( Figs. 182.3 and 182.4 ). Each of these branches is subject to trauma and may be blocked individually as a diagnostic and therapeutic maneuver. The deep branch continues down the leg in conjunction with the tibial artery and vein to provide sensory innervation to the web space of the first and second toes and adjacent dorsum of the foot ( Fig. 182.5 ). Although this distribution of sensory fibers is small, this area is often the site of Morton neuroma surgery; thus, it is important to the regional anesthesiologist. The deep peroneal nerve provides motor innervation to all of the toe extensors and the anterior tibialis muscles. The deep peroneal nerve passes beneath the dense superficial fascia of the ankle, where it is subject to an entrapment syndrome known as anterior tarsal tunnel syndrome. The superficial peroneal nerve provides sensory innervation to the majority of the skin on the dorsum of the foot, excluding the web space between the hallux and second digit, which is innervated by the deep peroneal nerve and the anterolateral distal one third of the leg ( Figs. 182.6 and 182.7 ).