Diagnostic Block of the Posterior Tibial Nerve
Introduction
Tarsal tunnel syndrome is defined as the entrapment of the posterior tibial nerve (1). Entrapment of the nerve typically occurs in the tarsal tunnel, which is a canal that courses from the medial malleolus to the mid-foot (1). The posterior tibial nerve is a branch of the sciatica nerve (1). The nerve is typically found posterior to the tibial artery and nerve within the tarsal tunnel (1). The other structures found within the tunnel include the posterior tibialis tendon, flexor halluces longus, and flexor digitorum longus (5).
Cross section view of the tarsal tunnel under ultrasound visualization (8)
Symptoms of tarsal tunnel syndrome include posterior ankle burning, paresthesia, and pain that can radiate into the heel or forefoot (5). These symptoms have been found to worsen with standing and walking (5).
Procedure
Performing a block of the posterior tibial nerve can aid in diagnosis of an entrapment neuropathy. Ultrasound is the preferred approach compared to palpation. In a study comparing ultrasound vs. palpation when performing a posterior tibial nerve block, they found that landmark guided injections were only successful 40% of the time (2).
Approximate location of a posterior tibial nerve block (6)
The patient is placed in a supine position with an externally rotated leg (8). A posterior tibial nerve block typically uses a linear probe (2). The medial malleolus will first be identified (2). Then, using an in-plane approach, a 1 ½ inch 25 gauge needle will be guided in-plane from a posterior to anterior direction towards the posterior tibialis nerve. The injection can also be guided out of plane as visualized in the image below.
Out of plane approach to the posterior tibial nerve (8)
The in-plane approach should avoid contact with the posterior tibial artery, which is typically found anterior to the vein and nerve (6). Prior to injecting the anesthetic, the syringe should be aspirated due to its proximity to the artery (6). Then, approximately 5cc of an anesthetic can be injected around the nerve (2, 3). Typical anesthetics used are Xylocaine and Lidocaine due to their short mechanism of onset (6, 7). A successful nerve block will cause anesthesia to the sole of the foot from the heel to the toes (6).
Ultrasound images of a posterior tibial nerve block (3)
Conclusion
A diagnostic nerve block of the posterior tibial nerve can help aid in diagnosis of tarsal tunnel syndrome. Use of an ultrasound for the nerve block can aid in accuracy and help in avoidance of iatrogenic nerve or artery injury.
By Gregory Rubin, DO
rubinsportsmed.com
References
1) McSweeney, Simon C., and Matthew Cichero. “Tarsal Tunnel Syndrome-A Narrative Literature Review.” Foot (Edinburgh, Scotland), vol. 25, no. 4, Dec. 2015, pp. 244–50. PubMed, https://doi.org/10.1016/j.foot.2015.08.008.
2) Shah, Ashish, et al. “Landmark Technique vs Ultrasound-Guided Approach for Posterior Tibial Nerve Block in Cadaver Models.” Indian Journal of Orthopaedics, vol. 54, no. 1, Jan. 2020, pp. 38–42. PubMed Central, https://doi.org/10.1007/s43465-019-00012-6.
3) Burl, Taylor, et al. “Ultrasound-Guided Posterior Tibial Nerve Block for Frostbite of the Plantar Surfaces: A Case Series.” Clinical Practice and Cases in Emergency Medicine, vol. 6, no. 4, Nov. 2022, pp. 272–75. PubMed, https://doi.org/10.5811/cpcem.2022.7.56727.
4) Tran, De Quang Hieu, et al. “A Review of Approaches and Techniques for Lower Extremity Nerve Blocks.” Canadian Journal of Anaesthesia = Journal Canadien D’anesthesie, vol. 54, no. 11, Nov. 2007, pp. 922–34. PubMed, https://doi.org/10.1007/BF03026798.
5) Ferkel, Eric, et al. “Entrapment Neuropathies of the Foot and Ankle.” Clinics in Sports Medicine, vol. 34, no. 4, Oct. 2015, pp. 791–801. PubMed, https://doi.org/10.1016/j.csm.2015.06.002.
6) Offierski, Chris. “Peripheral Nerve Blocks for Distal Extremity Surgery.” Clinics in Plastic Surgery, vol. 40, no. 4, Oct. 2013, pp. 551–55. PubMed, https://doi.org/10.1016/j.cps.2013.07.005.
7) Yelnik, Alain P., et al. “French Clinical Guidelines for Peripheral Motor Nerve Blocks in a PRM Setting.” Annals of Physical and Rehabilitation Medicine, vol. 62, no. 4, July 2019, pp. 252–64. PubMed, https://doi.org/10.1016/j.rehab.2019.06.001.
8) Waldman, Steven. “Posterior Tibial Nerve Block at the Ankle.” Atlas of Pain Management Injection Techniques, Elsevier.
