Sural Nerve Block at the Ankle

Indications and Clinical Considerations

Sural nerve block at the ankle is useful in evaluating and managing foot and ankle pain thought to be subserved by the sural nerve. The technique also is useful for providing surgical anesthesia for the posterior ankle and plantar surface of the foot when combined with common peroneal, posterior 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 distal lower extremity surgery, such as debridement or tendon repair.

Sural nerve block at the ankle with local anesthetic can be used as a diagnostic tool when performing differential neural blockade on an anatomic basis in the evaluation of lower extremity pain. If destruction of the sural 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. Sural nerve block at the ankle with local anesthetic may be used to palliate acute pain emergencies, including heel and foot fractures and postoperative pain relief, when combined with the previously mentioned blocks while waiting for pharmacologic methods to become effective. Sural nerve block at the ankle with local anesthetic and steroid occasionally is used in the treatment of persistent ankle, heel, and foot pain when the pain is thought to be secondary to inflammation or when entrapment of the sural nerve at the ankle is suspected. Sural nerve block at the ankle with local anesthetic and steroid also is indicated in the palliation of pain associated with diabetic neuropathy. Destruction of the sural nerve by block at the ankle occasionally is used in the palliation of persistent lower extremity pain secondary to invasive tumor that is mediated by the sural nerve and has not responded to more conservative measures.

Clinically Relevant Anatomy

The sural nerve is a branch of the posterior tibial nerve ( Fig. 184.1 ). The sural nerve passes from the posterior calf around the lateral malleolus to provide sensory innervation of the posterior lateral aspect of the calf and the lateral surface of the foot and fifth toe and the plantar surface of the heel ( Figs. 184.2 and 184.3 ). The sural nerve is subject to compression at the ankle and is known as boot syndrome because it is associated with compression of the nerve by boots that are too tight. The nerve can also be compressed by ganglion cysts, lipomas, neural tumors, and fractures of the fifth metatarsal ( Fig. 184.4 ).