Introduction

Emergency practitioners and other clinicians working in acute care settings frequently encounter patients who have trauma to or pathology of the dorsum of the foot and require anesthesia for treatment and repair.

Regional block of the superficial peroneal nerve allows for rapid anesthetization of the dorsum of the foot, which allows for management of lacerations, fractures, nail bed injuries, or other pathology involving the dorsum of the foot. Regional blocks have several advantages compared to local infiltration, such as fewer injections required to attain adequate anesthesia, smaller volume of anesthetic required, and less distortion of the wound site. Because of the lower number of injections, this procedure is better tolerated by the patient and limits the chance of a needle stick injury to the provider.

This procedure, often overlooked in the emergency department, is safe, is relatively easy to perform, and can provide excellent anesthesia to the foot. In one study, regional anesthesia of the foot and ankle, when performed by surgeons, was completely successful 95% of the time.

Anatomy

Understanding the anatomical distribution of the superficial peroneal nerve is helpful in performing a successful blockade of this nerve. The superficial peroneal nerve arises from the common peroneal nerve, which also gives rise to the deep peroneal nerve. The superficial peroneal nerve originates between the peroneus longus muscle and the fibula. It courses down the lateral compartment of the lower leg along with the peroneus longus muscle and the peroneus brevis muscle. It then descends posterolaterally to the anterior crural intermuscular septum. It runs anterolateral to the fibula between the peroneal muscles and the extensor digitorum longus, eventually supplying the peroneal muscles.

In the distal third of the leg, it pierces the deep fascia to become superficial. The nerve splits into the medial dorsal cutaneous nerve and the intermediate dorsal cutaneous nerve, which give rise to the dorsal digital nerves. These nerves supply the skin of the anterolateral distal third of the leg, most of the dorsal foot, and the digits. However, this nerve does not supply the web space between the first and second digits or the lateral fifth digit. At the level of ankle, the superficial peroneal nerve splits to fan out between the medial and lateral malleoli.

Dermatome of the superficial peroneal nerve at the level of posterior calf.

Superficial peroneal nerve dermatome at the level of the anterior lower leg.

Indications

• Wound repair or exploration of the dorsal regions of the foot
• As part of an ankle block required to manipulate a fracture or dislocated ankle (A combination of posterior tibial, saphenous, superficial peroneal, deep peroneal, and sural nerve blocks results in complete block of sensory perception beneath the ankle. Compared with more proximal approaches to the ankle block, motor block is rarely a concern with the ankle block. 

Areas of anesthetization to complete an ankle block. This block requires anesthetization of 5 nerves for complete sensory block below the ankle. The areas to anesthetize include a line along the anterior ankle for the superficial peroneal nerve (blue line), the deep peroneal nerve (red star), the saphenous nerve (pink star), the sural nerve (green arrow), and the posterior tibial nerve (orange arrow).

• Incision and drainage of an abscess in the dorsal regions of the foot
• Removal of foreign body in the dorsal regions of the foot
• Toenail repair (Toenail repair on the lateral first digit and medial second digit also requires deep peroneal nerve block.)
• Symptomatic relief of compression of the common peroneal nerve (along with the deep peroneal nerve block)

Contraindications

• Allergy to anesthetic solution or additives (eg, ester, amide)
• Overlying cellulitis
• Severe bleeding disorder or coagulopathy
• Preexisting neurological damage
• Patient uncooperativeness (Pediatric or elderly patients may need sedation.)

Anesthesia

• Lidocaine, the most commonly used anesthetic, has a fast onset of action and a duration of action of 30-120 minutes, which is increased to 60-400 minutes with the addition of epinephrine. The total cumulative dose of lidocaine to be infiltrated is 4.5-5 mg/kg (not to exceed 300 mg) if lidocaine without epinephrine is used, and 7 mg/kg (not to exceed 500 mg) if lidocaine with epinephrine is used.
• Topical anesthetics may be needed in children or uncooperative adults.

Equipment

• Needle, 4 cm, 25 gauge (ga)
• Needle, 18 ga
• Syringe, 10 mL
• Marking pen
• Sterile gloves
• Antiseptic solution (eg, povidone iodine [Betadine] or chlorhexidine gluconate [Hibiclens]) with skin swabs
• Alcohol swabs
• Sterile drape
• Lidocaine 1%, 10 mL
• Facial mask with eye shield
• Sterile gauze

Positioning

• Position the patient supine, with the ankle supported by a pillow or rolled sheet, optimizing comfort.
• Alternatively, the patient may sit and face the physician while maintaining a similar leg elevation.