A cadaver study comparing two approaches to perform a maxillary nerve block in the horse

Abstract

Anaesthesia of the maxillary nerve of the horse has been described using several approaches, but sparse data exist to evaluate the accuracy of these methods. This study compared 2 previously described approaches to the maxillary nerve to assess their relative accuracies. Thirty severed heads from horse cadavers were arranged to approximate the position of a live horse. Methylene blue (0.25 or 0.1 ml) was injected using a 19 gauge 90 mm spinal needle by one of 2 approaches, the method used being randomly allocated in each instance. Method ANG: angulated needle insertion on the ventral border of the zygomatic process of the temporal bone and directed rostromedially. Method PER: needle inserted perpendicular to the skin surface, ventral to the zygomatic process of the malar bone, level with the temporal canthus of the eye. Accuracy of dye deposition was assessed following dissection. Placement was categorised as 'full hit' (complete nerve coverage or dye deposition centred on nerve), 'partial hit' (partial nerve discolouration but dye not centred on nerve) or 'miss' (no nerve discolouration). Deposition of dye relative to the nerve and whether injection was performed on the left or right side of the head was recorded. A Chi-squared test was performed to examine the relationship between the 2 methods. Method ANG was performed 31 times, Method PER 28 times. Full hits were 10/31 (32%) vs. 9/28 (32%), partial hits 15/31 (49%) vs. 14/28 (50%) and misses 6/31 (19%) vs. 5/28 (18%) (Methods ANG vs. PER, respectively). RESULTS were not statistically significantly different between the methods. Dye was deposited in the deep facial vein once by each method. Bone was contacted consistently with Method PER and 8/31 times with Method ANG. Both methods appeared equivalent in terms of accuracy. Aspiration should always precede injection.