Introduction

Clinicians in the emergency department and other acute care settings frequently encounter patients who have sustained trauma to the lower leg or foot and require anesthesia for repair.

Regional block of the saphenous nerve, a pure sensory nerve of the leg, allows for rapid anesthetization of the anteromedial lower extremity, including the medial malleolus. Regional blocks have several advantages compared with 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 needlestick injury to the provider.

The saphenous nerve block is gaining popularity not only for procedural anesthesia but also for treatment of pain after procedures. Recently, its use has been demonstrated to be an effective regional technique for post-meniscectomy pain.

While the saphenous nerve can be blocked above the knee, at the level of the knee, below the knee, or just above the medial malleolus, this nerve is commonly blocked at the ankle because of its predictable and superficial location.

Anatomy

Understanding the anatomical distribution of the saphenous nerve helps when performing a successful saphenous nerve block. The saphenous nerve is a cutaneous branch of the femoral nerve originating from the L2-L4 nerve roots. It descends anteroinferiorly through the femoral triangle, lateral to the femoral sheath, accompanying the femoral artery in the adductor canal, and then courses between the sartorius and gracilis muscles across the anterior thigh.

Descent of the saphenous nerve down the anteromedial aspect of the leg.

After piercing the deep fascia on the medial aspect of the knee, the nerve courses superficially down the anteromedial lower leg. The infrapatellar branches supply innervation to the knee. The saphenous nerve runs laterally alongside the saphenous vein, giving off a medial cutaneous nerve that supplies the skin of the anterior thigh and anteromedial leg. The saphenous nerve travels to the dorsum of the foot, medial malleolus, and the area of the head of the first metatarsal. At the level of ankle, the saphenous nerve is found between the medial malleolus and the anterior tibial tendon, just lateral to the saphenous vein.

Saphenous nerve dermatome of the anteromedial leg.

Saphenous nerve dermatome at the level of the foot.

Indications

• Wound repair or exploration of the medial malleolus or anteromedial lower extremity
• As part of an ankle block required to manipulate a fractured 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.)

  

  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 medial malleolus or anteromedial lower extremity
• Foreign body removal in the anteromedial lower extremity or medial malleolus
• Pain after partial meniscectomy

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.
• Newer studies have shown that the addition of clonidine 100 mcg to 30 mL of 0.375% bupivacaine (with 5 mcg/mL epinephrine) significantly prolongs duration of the block. The use of clonidine is not yet well-studied, and the authors cannot recommend its use as standard of care at this time.
• 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 (povidone [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 leg externally rotated and the ankle elevated (if anesthetizing at the level of the ankle) or knee elevated (if anesthetizing at the level of the knee).
• Alternatively, the patient may sit and face the clinician.