Ultrasonographic guided block of the tibial nerve

Summary Tibial nerve anaesthesia is often utilised in the diagnostic evaluation of hindlimb lameness, but effective analgesia is sometimes difficult to achieve using a blind injection. The objectives of this paper are to describe the ultrasonographic anatomy of the caudomedial aspect of the superficial caudal crural compartment containing the tibial nerve and to describe a technique to perform an ultrasonographic guided block of this nerve. The tibial nerve is imaged by the use of a microconvex probe on a transverse section of the caudomedial part of the crus made approximately 8–10 cm proximal to the point of the hock. The needle is first inserted caudally to the probe, through the superficial caudal crural fascia, directed to the caudal aspect of the nerve where half of the volume of anaesthetic solution is injected (5–8 mL). A second injection is made similarly, cranial to the probe. Ultrasonographic guided injection of the tibial nerve increases accuracy of the nerve block by avoiding erroneous intravascular injections or injections under the deep caudal crural fascia that reduces diffusion of the anaesthetic solution. As deposit of anaesthetic solution can be done closer to the nerve, specificity of the block increases with quicker anaesthesia of the distal part of the limb. In addition, a smaller volume of anaesthetic solution (10–12 mL) can be used, thereby reducing the risk of proximal diffusion.