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.
Summary
Median nerve anaesthesia is sometimes indicated in the diagnosis of forelimb lameness in the horse in conjunction with the ulnar nerve block, but the localisation of the nerve to perform a precise deposition of the anaesthetic solution around and close to the nerve is difficult to achieve using the conventional blind technique. The objectives of this paper are to describe the ultrasonographic anatomy of the median nerve and the technique for performing an ultrasound‐guided anaesthetic block of the nerve. The median nerve is imaged using a microconvex (or linear) probe in transverse section performed proximally to the chestnut on the medial aspect of the forearm. Distribution of the anaesthetic solution around the nerve is done by initially inserting the needle caudally and then cranially to the nerve and injecting 4–6 mL at each site. Control of the needle penetration avoids erroneous intravascular or intramuscular injections or sudden horse reaction. Ultrasound‐guided injection has the potential to safely and accurately block the median nerve.
Summary
Thoracolumbar lesions are common in horses, but their identification and location remain a challenge in field practice. A precise diagnostis improves therapeutic strategy and, thus, the prognosis of affected horses. Although radiography remains the preferred diagnostic imaging modality used for the back, ultrasound is a useful complementary technique that offers valuable information and can be performed as a stand‐alone procedure when high‐output radiographic equipment is not available. The aim of this paper is to describe thoracolumbar articular process joint pathology that can be visualised with ultrasound.
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