How Long Does a Superficial Peroneal Nerve Block Last?

A superficial peroneal nerve block is an injection to numb the leg and top of the foot.

A superficial peroneal nerve block is a procedure to anesthetize a portion of the lower leg and the upper (dorsal) foot. A line of anesthetic injections are administered at the lower end of the front of the leg at the level of the bony projections (malleoli) on either side of the ankle. The anesthetic solution blocks the nerve from transmitting pain signals from the foot to the brain.

The superficial peroneal nerve is a branch of the common peroneal nerve, also known as the common fibular nerve, which arises from the sciatic nerve. Above the ankle the superficial peroneal nerve divides into two branches fanning over the upper foot.

The superficial peroneal nerve and its branches provide sensory and motor function to the lower third of the shin on the outer side, and the top of the foot and toes, except the web space between the big and its adjacent toe.

A superficial peroneal nerve block provides rapid regional anesthesia to the top of the foot. A nerve block is superior to local tissue infiltration anesthesia because it achieves anesthesia in a larger area with:

• lesser volume of the anesthetic agent
• fewer number of injections

A superficial peroneal nerve block may be performed solely or in combination with one or more of the other peripheral nerves in the lower leg. A superficial peroneal nerve block is performed:

• During surgical procedures in the dorsal foot for treatment of
  • Wound and laceration
  • Nail bed injuries
  • Fractures in the foot
• For superficial peroneal nerve pain relief from entrapment or injury
• As part of an ankle block for treatment of ankle dislocation or fracture
• Incision and drainage of abscesses in the dorsal foot
• Removal of foreign body in the dorsal foot
• Along with deep peroneal nerve block for 
  • Nail repair of the big toe or its adjacent toe
  • Pain relief from compression of common peroneal nerve

A superficial peroneal block is avoided if the individual has:

• Bleeding disorders
• Allergy to local anesthetics
• Cellulitis in the injection area
• Pre-existing nerve damage
• Local malignancy
• Diabetic neuropathy in the foot

A superficial peroneal nerve block is generally performed as an outpatient procedure.

Anesthesia

The anesthetic agent for a superficial peroneal nerve block is usually

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

For children 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, and also warm the anesthetic solution to body temperature, to reduce the injection pain. Children and elderly patients may require mild sedation as well.

Preparation

• The patient lies flat with the ankle elevated by a pillow.
• The doctor performs a physical examination to assess the patient’s neurovascular and musculoskeletal functions.

Procedure

The doctor

• Draws a line in the front of the lower leg, between the lower borders of the two malleoli.
• May use ultrasound guidance during the procedure.
• Sterilizes the area with antiseptic solution.
• Inserts the needle on the line near the outer malleolus.
• Injects a small amount of anesthetic into the skin to raise a bump (wheal).
• Inserts the needle through the wheal transversely along the line.
• Aspirates the syringe to make sure it is not inside a blood vessel.
• Slowly injects the anesthetic along the line up to the inner malleolus.
• 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 nerve block to take effect.

The duration of a superficial peroneal nerve block depends on the anesthetic agent used. The approximate durations are:

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

Post-procedural pain after the nerve block wears off can be relieved with oral painkillers.

• Infection at the injection site
• Allergic reaction to the local anesthetic
• Injection into an artery causing vascular spasm
• Injection into a vein leading to local anesthetic systemic toxicity
• Injury to a blood vessel causing bleeding and hematoma
• Injury to the superficial peroneal nerve causing neuropathy with
  • Tingling
  • Numbness
  • Muscle weakness
• Unsuccessful nerve block