Posterior Tibial Nerve Block

Background

Posterior tibial nerve block allows for rapid anesthetization of the heel and plantar regions of the foot. Practitioners in the emergency department frequently encounter patients who have sustained trauma to the sole of the foot and require regional anesthesia for repair. However, this tender area is relatively difficult to anesthetize locally.

Posterior tibial nerve block is often overlooked in the emergency department, although it is safe, relatively easy to perform, and can provide excellent anesthesia to the foot. ^[1] In one study, regional anesthesia of the foot and ankle, when performed by surgeons, was completely successful 95% of the time. ^[2]

Regional blocks have several advantages compared to local infiltration, such as fewer injections necessary to attain adequate anesthesia, smaller volume of anesthetic required, and less distortion of the wound site. ^{[3, 4, 5]} Because of the lower number of injections, this procedure is better tolerated by the patient and limits the chance of a needle stick to the provider.

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Indications

Indications for posterior tibial nerve block include the following:

• Wound repair or exploration of the calcaneal or plantar regions of the foot

• As part of an ankle block required to manipulate a fractured or dislocated ankle

• Relief of tarsal tunnel syndrome ^[6]

• Incision and drainage of an abscess in the calcaneal or plantar regions of the foot

• Foreign body removal in the calcaneal or plantar regions of the foot

A combination of posterior tibial nerve block, saphenous nerve block, superficial peroneal nerve block, deep peroneal nerve block, and sural nerve block results in complete block of sensory perception beneath the ankle, as shown in the image below.

Contraindications

Contraindications to posterior tibial nerve block include the following:

• Allergy to anesthetic solution or additives (eg, ester, amide)

• Injection through infected tissue

• Severe bleeding disorder or coagulopathy

• Preexisting neurological damage

• Patient uncooperativeness (pediatric or elderly patients may need sedation)

Technical Considerations

Procedure Planning

Understanding the arborization of the tibial nerve is crucial to a successful posterior tibial nerve block. ^{[7, 8]} The posterior tibial nerve arises from the sciatic nerve and courses down the posterior thigh and posteromedial lower leg, as shown in the image below.

These nerves supply the intrinsic muscles of the foot, excluding the extensor digitorum brevis. They also supply sensory innervation to the plantar surface of the foot, as shown in the images below.

At the level of ankle, the posterior tibial nerve can be found midway between the medial malleolus and the heel. ^[9] The nerve lies beneath the flexor retinaculum between merging tendons and vessels, which have an anterior to posterior progression of tibialis posterior tendon, flexor digitorum tendon, posterior tibial artery, posterior tibial nerve, and flexor hallucis longus tendon (see the image below).

Complication Prevention

Infection can occur when the puncture site is not clean. Avoid puncture through infected skin or skin lesions. Be sure to use sterile technique during the procedure, as the risk of infection is insignificant when sterility is properly maintained.

Intra-arterial injection may result in vasospasm and lead to ischemia of the limb tissue. Intravenous injection can lead to systemic toxicity in high doses. Tissue texture changes revealing pallor, bogginess, and cool temperature may indicate that either intravascular injection or vascular compression has occurred. Always draw back the syringe to rule out intravascular placement before injection. Alpha-adrenergic antagonists (eg, phentolamine 0.5-5 mg diluted 1:1 with saline) can be administered by local infiltration to relieve arterial vasospasm secondary to intra-arterial injection. ^[10]

Patients may develop paresthesia, sensory deficits, or motor deficits secondary to inflammation of the nerve. Most often, this type of neuritis is transient and resolves completely. During the procedure, pull back gently after induction of paresthesia so as to not inject the nerve directly. Make sure to document a complete neuromuscular examination both before and after the procedure. ^[11]

Reports of significant hemorrhage during regional anesthesia are rare, even in patients with blood coagulopathies. ^[9] A hematoma may develop with intravascular puncture. If prolonged bleeding occurs, attempt to obtain hemostasis with direct pressure and elevation.

Allergic reactions to local anesthetics occur at a rate of 1%. ^{[12, 10]} Reactions range from delayed hypersensitivity (type IV) to anaphylactic (type I). Although rare, the most common cause of allergic reaction is the preservative in the local anesthetic solution. Cardiac lidocaine is an alternative because it does not contain the preservative. Alternatively, a 1-2% diphenhydramine solution can be used as a local anesthetic. ^[10]

The volume of 1% lidocaine without epinephrine should not exceed 5 mg/kg. If lidocaine with epinephrine is used, total volume should not exceed 7 mg/kg. Systemic toxicity manifests in the central nervous and cardiovascular systems. ^[12] Signs such as tremors, convulsions, tachycardia, or respiratory compromise should alert the physician to stop the procedure and reassess the patient.

Patient Education & Consent

Explain the procedure, benefits, risks, and complications to the patient and/or patient’s representative, and inform the patient of the possibility of paresthesia during the procedure.

Obtain informed consent in accordance with hospital protocol.

Equipment

Equipment for posterior tibial nerve block includes the following:

• Needle, 4 cm, 25 G

• Needle, 18 G

• Syringe, 10 mL

• Marking pen

• Sterile gloves

• Antiseptic solution (eg, povidone iodine [Betadine], chlorhexidine gluconate [Hibiclens]) with skin swabs

• Alcohol swabs

• Sterile drape

• Lidocaine 1%, 10 mL

• Facial mask with eye shield

• Sterile gauze

This equipment is shown in the image below.

Patient Preparation

Anesthesia

The 2 main classes of local anesthetics currently in use are amino esters and amino amides. Both inhibit ionic fluxes required for the initiation and conduction of nerve impulses. ^[13]

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. ^{[12, 13]} The total cumulative dose of lidocaine to be infiltrated is 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.

Anesthetic preparations that contain epinephrine are commonly used in the emergency department. Epinephrine induces vasoconstriction, decreasing the amount of local bleeding at the site of injection. In addition, it increases the duration of action of the anesthetic with which it is combined. Despite these advantages, the vasoconstrictive properties of epinephrine may contribute to tissue hypoxia, and its use should be avoided in areas of poor perfusion (ie, fingers, toes, penis, ears, nose).

In children or noncompliant adults, consider using topical anesthetic mixtures, such as lidocaine, epinephrine, and tetracaine or a eutectic mixture of lidocaine and prilocaine.

Pediatric or elderly patients may require additional sedation for compliance.

Positioning

Position the patient supine and as comfortably as possible.

Alternatively, the patient may sit and face the physician.

Approach Considerations

Equipment preparation and proper patient positioning may make the difference between success and failure.

Consider a hematoma block or bier block when a fracture exists or when more extensive manipulation of the foot is expected to attain more effective analgesia. ^[14]

Adding a buffering solution, like sodium bicarbonate, can significantly decrease the pain of the injection when performing a nerve block. ^{[9, 10]} Add 1 mL of sodium bicarbonate (44 mEq/50 mL) to 9 mL of lidocaine.

Warming the anesthetic solution to body temperature can significantly decrease the pain of the injection. ^[10]

When unassisted, tape a bottle of lidocaine upside down to the wall prior to the procedure. If more anesthetic is needed during the procedure, it can be obtained from this bottle without compromising the sterility of gloves and equipment.

Approach for Posterior Tibial Nerve Block

Perform and document neurovascular and musculoskeletal examinations prior to the procedure. Testing the posterior tibial nerve prior to block includes the following:

• Sensation of sole of the foot, as shown in the image below

  Cutaneous innervation by the medial and lateral branches of the posterior tibial nerve.

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• Flexion, abduction, and adduction of the digits

Using nonsterile gloves, expose the area of injection and identify the landmarks, as depicted in the image below.

Start by palpating the medial malleolus and advance posteroinferiorly toward the Achilles tendon, as shown below, until the pulsation of the posterior tibial artery is felt.

Mark the point that is 0.5-1 cm superior to the posterior tibial artery, as shown below.

If the artery is not palpable, mark a point 1 cm superior to the medial malleolus and slightly anterior to the Achilles tendon (see the image below).

Wipe the area with an alcohol pad, and clean site thoroughly with an antiseptic solution, moving outwards in a circular fashion, as shown in the image below.

Open sterile drape and place the syringe, needle, and gauze on the tray, maintaining sterility.

Put on sterile gloves. Attach the 18-G needle to the 10-mL syringe and draw up the lidocaine. Then, change to the 25-G needle.

With the needle, place a skin wheal, as shown below, at the marked injection site.

Advance the needle through the skin wheal toward the tibia at a 45-degree angle in a mediolateral plane, just posterior to the artery. Wiggle the needle slightly to induce paresthesia. If elicited, aspirate to make sure the needle is not in a vessel, wait for the paresthesia to resolve, and inject 3-5 mL.

If paresthesia is not elicited, advance the needle at a 45-degree angle until it meets the posterior tibia. Withdraw 1 cm and inject 5-7 mL of anesthetic while withdrawing needle another 1 cm, as shown below.

Calor and rubor of the foot due to loss of sympathetic tone may initially be noted.

Successful anesthesia of the areas noted heralds a successful posterior tibial nerve block. ^{[15, 16, 17]}