Chapter 82G: Cutaneous Nerve Blocks of the Lower Extremity

INTRODUCTION

Blocks of the lateral femoral cutaneous, posterior femoral cutaneous, saphenous, sural, and superficial peroneal nerves are useful anesthetic techniques for a variety of superficial surgical procedures and carry a low risk of complications.^1,2

Indications and Contraindications

The lateral femoral cutaneous nerve block has been used to provide anesthesia for pediatric patients undergoing muscle biopsy³ and to provide analgesia after femoral neck surgery in older patients.^4,5 The posterior femoral cutaneous nerve block is used for any surgical procedure performed on the posterior aspect of the thigh.⁶ The saphenous, sural, and superficial peroneal nerve blocks can be used as part of an ankle block to provide complete anesthesia to the foot and ankle, or they can be used separately to provide anesthesia to specific portions of the foot and ankle.

The contraindications to performing cutaneous nerve blocks of the lower extremity are few, but include local infection at the sites of needle insertion, and allergy to local anesthetic.

Functional Anatomy

The cutaneous nerves of the extremities are blocked by injection of local anesthetic in the subcutaneous layers above the muscle fascia. The subcutaneous tissue contains a variable amount of fat, superficial nerves, and vessels. Deep to this area lies a tough membranous layer, deep fascia of the lower extremity enclosing muscles of the leg. This deep fascia is penetrated by numerous superficial nerves and vessels.

The cutaneous innervation of the lower extremity is accomplished by nerves that are part of the lumbar and sciatic plexuses (Figures 82G–1 and 82G–2). A more detailed review of the relevant anatomy is provided with a description of the individual block procedures in Chapter 3.

Choice of Local Anesthetic

Any local anesthetic can be used for cutaneous blocks of the lower extremity; the choice is based primarily on the desired duration of blockade. Because these blocks do not result in motor block, longer-cting local anesthetics are most commonly chosen (e.g., 0.2%–0.5% ropivacaine or 0.25%-0.5% bupivacaine). When performing blocks in the ankle area, it is always prudent to avoid using epinephrine owing to the risk of decreasing blood flow to the toes. Onset time for the block depends on the local anesthetic used⁷ (Table 82G–1).