What is a sural nerve block?

A sural nerve block is a procedure to numb the outer (lateral) side of the calf, lower leg, heel, edge of the foot and the top part of the little toe. A sural nerve block is most often performed as an outpatient procedure in the emergency department to treat injuries in the lower leg.

A sural nerve block may be performed alone or in combination with other peripheral nerve blocks depending on the area that requires anesthesia.

What is the anesthesia used in a sural nerve block?

Anesthetic agents used for a sural nerve block include:

  • Lidocaine for short and fast acting blocks
  • Ropivacaine for longer lasting blocks

Doctors mostly avoid adding epinephrine to the anesthetic agent for nerve blocks in the foot but may add diluted epinephrine to achieve a longer-lasting anesthetic effect and reduced blood flow in the operating area.

For children and noncompliant adults the doctor may also use a topical application of lidocaine mixed with

  • Tetracaine or
  • Prilocaine

The doctor may add a buffering solution such as sodium bicarbonate.  The anesthetic solution may also be warmed to body temperature to further reduce the injection pain. Children and elderly patients may require mild sedation as well.

How is a sural nerve block performed?

Preparation

  • The patient lies on their stomach with the ankle elevated by a pillow or lies on their back with the ankle rotated internally.
  • The doctor performs a physical examination to assess the patient’s muscle, nerve, and circulation functions in the lower leg and sensation in the calf and the little toe.

Procedure

The doctor

  • May apply a tourniquet in the calf or above the ankle to expose the vein (saphenous vein) which lies adjacent to the sural nerve.
  • Marks the injection site between the Achilles tendon and the bony projection (malleolus) on the outer ankle.
  • Sterilizes the injection site with an antiseptic solution.
  • May use ultrasound guidance during the procedure for accurate positioning of the needle.
  • Inserts the needle and injects a small amount of anesthetic into the tissue under the skin to raise a bump (wheal).
  • Advances the needle through the skin wheal towards the lateral malleolus.
  • Aspirates the syringe to be certain it is not inside a blood vessel.
  • Slowly injects the anesthetic close to the sural nerve avoiding direct contact with the nerve.
  • Withdraws the needle and massages the injection site gently to help the solution spread in the tissues.
  • Waits for up to 10 minutes for the sural nerve block to take effect.
  • If there is a fracture and hematoma, may also administer an injection into the hematoma.

QUESTION

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How long does a sural nerve block last?

The duration of a sural nerve block depends on the anesthetic agent used. Approximate durations of a sural nerve block’s effect are:

  • Lidocaine: Up to three hours
  • Lidocaine with diluted epinephrine: Up to seven hours
  • Ropivacaine: Up to six hours

Post-procedural pain can be relieved with oral painkillers.

What are the risks and complications of a sural nerve block?

The sural nerve block area is superficial, and complications are unusual. Potential complications include:

  • Infection at the injection site
  • Injection into an artery, leading to arterial spasm
  • Injection into a vein causing local anesthetic systemic toxicity
  • Injury to the sural nerve, leading to tingling (paresthesia), hypersensitivity, numbness or muscle weakness
  • Bleeding and hematoma
  • Allergic reaction to local anesthetics
  • Unsuccessful nerve block

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Medically Reviewed on 6/15/2020
References
Medscape Medical Reference
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