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

This research study explores an ultrasound-guided technique for blocking the tibial and fibular nerves in horses. The approach used is a caudocranial midfemoral one, tested on horse cadavers to evaluate the spreading of a dye. Findings suggest if performed correctly, the technique can help in numbing a larger area, potentially useful for anesthesia in surgeries involving the pelvic limb of horses.

Study Design and Procedure

• The researchers conducted an anatomical study on a horse cadaver preserved in glycerin and a dye spreading study on 14 fresh horse cadavers. The investigations took place from March 25, 2021, to October 5, 2022.
• For the anatomical study, they dissected a glycerin-preserved horse cadaver’s pelvic limb to identify anatomical landmarks. They used a caudocranial midfemoral approach for the injection designed to block the tibial and fibular nerves.
• In the dye spreading study, they applied a convex probe perpendicular to the femur, at the level of the distal end of the third trochanter on the 14 fresh horse cadavers. They identified the tibial and fibular nerves situated between the biceps femoris and semitendinosus muscles.

The Injection Technique

• They inserted a 21-cm needle at an approximately 60º angle in a caudocranial direction, aiming for the fascial plane.
• A solution of methylene blue-ropivacaine was prepared and 0.1-mL/kg of the solution was injected into the targeted area. Methylene blue dye was used as a marker to track the extension of the nerve block.
• The researchers evaluated the spread of the dye 15 minutes after the injection to study nerve block extension and efficiency.

Results

• The execution of the procedure took about 6.31 ± 3.44 minutes and the dissection times were 15 ± 6.33 minutes.
• Both nerves were successfully stained in 51.85% (14 of 27), indicating successful blockage. Only the tibial nerve was stained in 7.41% (2 of 27), and the fibular nerve was stained in 3.70% (1 of 27) of the limbs, with a failure rate of 37.04% (10 of 27).

Conclusions and Implications

• Findings suggest that the described technique can potentially block both nerves, even for inexperienced operators, hence providing a useful tool for equine surgeries involving the pelvic limb.
• The nerve block technique, when executed at the level of the third trochanter of the femur, covers a larger area of desensitization in a single access point, hence it could be beneficial in surgical procedures requiring analgesia.