Landmark Technique vs Ultrasound-Guided Approach for Posterior Tibial Nerve Block in Cadaver Models.

Abstract

The use of ultrasound for peripheral nerve blocks has proven extremely useful for improving the accuracy and efficacy of many regional anesthetic techniques. There remain a few nerve blocks which have lagged behind in employing the assistance of ultrasound consistently, one of which is the ankle block. This block is commonly utilized for either surgical anesthesia or post-operative analgesia for a variety of foot and ankle procedures. The objective of this study was to compare the accuracy of traditional anatomical landmark-guided technique with an ultrasound-guided approach for ankle block by assessing the spread of injectate along the posterior tibial nerve (PTN) in cadaver models. Ten below-knee cadaver specimens were used for this study. Five were randomly chosen to undergo anatomical landmark-guided PTN blocks, and five were selected for ultrasound-guided PTN blocks. The anatomical landmark technique was performed by identifying the medial malleolus and Achilles tendon and inserting the needle (4cm long, 21G Braun® Stimuplex) at the midpoint of the two structures, aiming toward the medial malleolus and advancing until bone was contacted. The ultrasound technique was performed with a linear probe identifying the medial malleolus and the PTN, with the needle subsequently advanced in-plane with a posterior to anterior trajectory until the tip was adjacent to the nerve. Each specimen was injected with 2mL of acrylic dye. All the specimens were dissected following injection to determine which nerves had been successfully coated with dye. The PTN was successfully coated with dye in all five (100%) ultrasound-guided blocks. In the anatomical landmark group, two (40%) PTN were successfully coated with dye. Of the three unsuccessful attempts, two specimens were noted to have dye injected posterior to the PTN; dye was injected into the flexor digitorum longus tendon in one. The base of evidence has dramatically increased in recent years in support of the use of ultrasound in regional anesthesia. This study substantiates the superiority of ultrasound guidance for ankle block by demonstrating a 100% success rate of delivering a simulated nerve block to the correct anatomic location.