What is a posterior tibial nerve block?
A posterior tibial nerve block is used to deaden sensation in the foot, usually as part of a surgical procedure.
A posterior tibial nerve block is a procedure for numbing a portion of the foot. An anesthetic injection is administered near the ankle on the inside of the leg, close to the posterior tibial nerve, blocking the transmission of pain signals to the brain.
The posterior tibial nerve is one of the two main branches of the sciatic nerve. The posterior tibial nerve runs down the back of the leg and calf and enables sensory and motor functions of the lower leg and the foot. The posterior tibial nerve block provides anesthesia to the heel, sole of the foot, and the underside of the toes.
Below the ankle, the sensory part of the posterior tibial nerve branches are
- Medial and lateral plantar nerves: transmit sensation of the ball and arch of the foot
- Medial and inferior calcaneal nerves: transmit sensation of the heel pad and the back of the heel
Why is a posterior tibial nerve block performed?
The sole of the foot is extremely tender and sensitive, and direct injection of local tissue infiltration anesthesia in the sole can be difficult and painful. The posterior tibial nerve block provides effective and rapid anesthesia to the heel and sole with fewer injections and less volume of anesthetic agent.
The posterior tibial nerve block is performed:
- For wound repair in the plantar and calcaneal region of the foot
- As part of an ankle block for treatment of ankle dislocation or fracture
- To relieve tarsal tunnel syndrome due to compression of the posterior tibial nerve causing symptoms such as:
- Numbness
- Pain
- Tingling
- Incision and drainage of abscess in the sole of the foot
- Foreign body removal from the sole of the foot
A tibial nerve block is avoided with the following conditions:
- Allergy to local anesthetics
- Infection at the injection site
- Bleeding disorders
- Pre-existing nerve damage
How is a posterior tibial nerve block performed?
A posterior tibial nerve block is an outpatient procedure, most often performed in the emergency department.
Anesthesia
The anesthetic agent for a tibial nerve block may be
- Lidocaine for short and fast acting blocks
- Ropivacaine for longer lasting blocks
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 be warmed to body temperature to reduce the injection pain. Children and elderly patients may require mild sedation as well.
Doctors generally avoid adding epinephrine to the anesthetic agent for nerve blocks in the foot but may occasionally add diluted epinephrine to achieve longer-lasting anesthetic effect and a bloodless operating area (epinephrine constricts the blood vessels).
Preparation
- The patient lies flat with the inside of the ankle turned out.
- The doctor performs a physical examination to assess the patient’s muscle, nerve, and circulation functions.
- The doctor palpates (prods with fingers) the region next to the ankle to locate the tibial artery and mark the injection site.
- The injection site is sterilized with an antiseptic solution.
Procedure
The doctor
- 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 deeper and close to the tibial nerve.
- Aspirates the syringe to make sure it is not inside a blood vessel.
- Slowly injects the anesthetic in the space between the tibial artery and the posterior tibial 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 nerve block to take effect.
- If there is a fracture and hematoma, may also administer an injection into the hematoma.
How long does a posterior tibial nerve block last?
The duration of the posterior tibial nerve block’s effects depends on the kind and quantity of anesthetic agent used. Approximate period of anesthetic effects is:
- 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.
What are the risks and complications of a posterior tibial nerve block?
A posterior tibial nerve block is a low-risk procedure. Potential complications include:
- Infection at the injection site
- Injection into an artery leading to vascular spasm
- Injection into a vein leading to systemic toxicity
- Injury to the tibial nerve or a blood vessel
- Bleeding and hematoma
- Tingling, numbness or muscle weakness (neuropathy)
- Allergic reaction to the anesthetic
- Unsuccessful nerve block