- 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.
- 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 below
- 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.
Posterior tibial nerve block landmarks. Medial malleolus (MM) is at the left and Achilles tendon is at right. Posterior tibial artery (A) is approximately 1 cm inferior to the site marked for needle insertion (arrow).
- 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.
Palpation of the posterior tibial artery.
- Mark the point that is 0.5-1 cm superior to the posterior tibial artery, as shown below.
Marking the injection site, which is 0.5-1 cm superior to the posterior tibial artery.
If the artery is not palpable, mark a point 1 cm superior to the medial malleolus and slightly anterior to the Achilles tendon, as shown below.
Location of injection site when unable to palpate the posterior tibial artery.
- Wipe the area with an alcohol pad, and clean site thoroughly with an antiseptic solution, moving outwards in a circular fashion, as depicted 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-ga needle to the 10-mL syringe and draw up the lidocaine. Then, change to the 25-ga 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° 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.
Placing a skin wheal.
- 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.
Injection posterior and superior to the posterior tibial artery.
- 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.
- Equipment preparation and proper patient positioning may make the difference between success and failure.
- In children or noncompliant adults, consider using topical anesthetic mixtures, such as lidocaine, epinephrine, tetracaine (LET) or a eutectic mixture of lidocaine and prilocaine (EMLA cream).
- Pediatric or elderly patients may require additional sedation for compliance.
- 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.
- Adding a buffering solution, like sodium bicarbonate, can significantly decrease the pain of the injection when performing a nerve block. 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.
- 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.
- Infection: Infection occurs 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.
- Intravascular injection: 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 intraarterial injection.
- Nerve injury: 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.
- Hemorrhage: Reports of significant hemorrhage during regional anesthesia are rare, even in patients with blood coagulopathies. A hematoma may develop with intravascular puncture. If prolonged bleeding occurs, attempt to obtain hemostasis with direct pressure and elevation.
- Allergic reaction: Allergic reactions to local anesthetics occur at a rate of 1%. 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, as it does not contain the preservative. Alternatively, a 1-2% diphenhydramine solution can be used as a local anesthetic.
- Exceeding total volume of anesthesia: 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. Signs such as tremors, convulsions, tachycardia, or respiratory compromise should alert the physician to stop the procedure and reassess the patient.