FIGURE 8.34 Medial aspect of the right foot. (From Tank PW, Gest TR. Lippincott Williams & Wilkins Atlas of Anatomy. Philadelphia, PA: Lippincott Williams & Wilkins, 2009.)
PATIENT POSITION
- Supine on the examination table with the hip in full external rotation, the knee slightly flexed, and the ankle in a neutral position.
- Alternatively, lying on the examination table on the affected side with the knee slightly flexed and the ankle in a neutral position.
- Rotate the patient’s head away from the side that is being injected. This minimizes anxiety and pain perception.
LANDMARKS
1. With the patient lying supine on the examination table, the clinician stands medial to the affected ankle.
2. Locate the medial malleolus of the tibia and then the insertion of the Achilles tendon into the calcaneus.
3. Midway between these two structures, palpate the posterior tibial artery.
4. The posterior tibial nerve is located about 0.5 cm posterior to the posterior tibial artery. Mark the nerve with ink.
5. At that site, press firmly on the skin with the retracted tip of a ballpoint pen. This indention represents the entry point for the needle.
6. After the landmarks are identified, the patient should not move the ankle.
ANESTHESIA
- Local anesthesia of the skin using a topical vapocoolant spray.
EQUIPMENT
- 3-mL syringe
- 25-gauge, 5/8 in. needle
- 0.5 mL of 1% lidocaine without epinephrine
- 0.5 mL of the steroid solution (20 mg of triamcinolone acetonide)
- One alcohol prep pad
- Two povidone–iodine prep pads
- Sterile gauze pads
- Sterile adhesive bandage
- Nonsterile, clean chucks pad
TECHNIQUE
1. Prep the insertion site with alcohol followed by the povidone–iodine pads.
2. Achieve good local anesthesia by using a topical vapocoolant spray.
3. Position the needle and syringe with the needle tip directed perpendicularly to the surface of the skin with the tip of the needle directed laterally toward the nerve.
4. Using the no-touch technique, introduce the needle at the insertion site (Fig. 8.35).
5. Advance the needle about 1 cm deep. If any pain, paresthesia, or numbness is encountered, back up the needle 1 to 2 mm.
6. Aspirate with the syringe to ensure that the needle tip is not in the posterior tibial artery or vein.
7. Slowly inject the volume of the syringe as a bolus around the posterior tibial nerve and into the tarsal tunnel. If increased resistance is encountered, advance or withdraw the needle slightly before attempting further injection.
8. Following injection of the corticosteroid solution, withdraw the needle.
9. Apply a sterile adhesive bandage.
10. Instruct the patient to move his or her ankle through its full range of motion. This movement distributes the steroid solution along the nerve and throughout the tarsal tunnel.
11. Reexamine the foot in 5 min to confirm pain relief or the development of numbness in the distribution of the posterior tibial nerve from the local anesthetic.
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