Computed Tomography Validation of the Technique of Diagnostic Local Analgesia of the Caudal Part of the Infraorbital Nerve and Caudal Nasal Nerve Used for the Investigation of Idiopathic Headshaking in Horses

Abstract

IntroductionDiagnostic local analgesia of the caudal portion of the infraorbital nerve (CPIN) and caudal nasal nerve (CNN) is a valuable aid to the diagnosis of idiopathic headshaking in horses. The site of deposition of local anaesthetic has not been verified.AimsTo verify the site of deposition of local anaesthetic in this procedure, and to identify any correlation between accuracy of the technique and operator experience.MethodsThe procedure was performed bilaterally using contrast material on 30 cadaver horse heads by 3 groups of veterinarians and veterinary students with varying levels of experience in the technique. Location of deposition was identified by use of computed tomography (CT).ResultsContrast was deposited around the target site in 53.3% (32/60) of injections. The most experienced operator performed the procedure accurately significantly (P<0.05) more often (80% [16/20]) than did the less and nonexperienced performers (40% [16/40]).ConclusionsA negative response to diagnostic local analgesia of the CPIN and CNN in the investigation of headshaking does not disprove facial pain as the cause of headshaking in that horse. A negative response could arise due to failure to deposit local anaesthetic around the target area. Sufficient experience of performing the procedure decreases the probability of false negative results.Practical significanceClinicians performing diagnostic local analgesia of the CPIN and CNN must be aware of the possibility of false negative results. Experience improves the reliability of results.Ethical animal researchNot required by this Congress. Horse cadaver heads obtained from horses subjected to euthanasia for reasons other than this study were used. Sources of funding: The Langford Trust for Animal Health and Welfare funded this study and Langford Veterinary Services funded the first author's residency training. Competing interests: None.