Equine cadaveric study suggests tibial and fibular nerve block is feasible with a single ultrasound-guided injection via a caudocranial midfemoral approach.

Abstract

OBJECTIVE: To describe anatomical references and sonoanatomy of an echo-guided injection for blocking the tibial and common fibular nerves with the use of a caudocranial midfemoral approach and to evaluate dye spreading in horse cadavers. METHODS: 1 horse cadaver preserved in glycerin was used for the anatomical study, and 14 fresh horse cadavers were used for the dye spreading study. The experimental procedures were conducted on the first cadaver on March 25, 2021, and on the last cadaver on October 5, 2022. A glycerin-preserved horse cadaver's pelvic limb was dissected to identify anatomical landmarks. In 14 horse cadavers, a convex probe was positioned perpendicular to the femur, at the level of the distal end of the third trochanter. The tibial and fibular nerves were located between the biceps femoris and semitendinosus muscles. A 21-cm needle was inserted at an approximately 60º angle in a caudocranial direction, aiming for the fascial plane. A 0.1-mL/kg solution of methylene blue-ropivacaine was injected. The spread of the dye was evaluated 15 minutes after the injection. This was a cadaveric experimental study. RESULTS: Technique execution and dissection times were 6.31 ± 3.44 minutes and 15 ± 6.33 minutes, respectively. Both nerves were successfully stained in 51.85% (14 of 27), only the tibial nerve in 7.41% (2 of 27), and the fibular nerve in 3.70% (1 of 27) of the limbs. The failure rate was 37.04% (10 of 27). CONCLUSIONS: With the technique described, it is possible to block both nerves, even for inexperienced operators. CLINICAL RELEVANCE: Blocking at the level of the third trochanter of the femur covers a larger area of desensitization in a single access point and can be used to promote analgesia in surgical procedures involving the pelvic limb.