How securely is the testicular artery occluded in the spermatic cord by using a ligature?

REASONS FOR PERFORMING STUDY: There are no studies on the ideal ligature technique for the spermatic cord. OBJECTIVES: To compare the maximal resistance pressure in the testicular artery and the maximal tensile forces to produce failure of 2 different ligature techniques used for ligation of the equine spermatic cord. METHODS: The capabilities of 2 types of ligatures, single knot loop and double knot loop, were assessed using a pressure-resistance test in testicular arteries and with an in vitro mechanical evaluation of the tensile strength by single cycle-to-failure testing. RESULTS: In the pressure-resistance test, the mean ± s.d. peak force at failure of the single knot loop was 354.4 ± 91.7 mmHg and for the double knot loop 303.2 ± 62.0 mmHg. There was no significant difference between the maximal load to failure of the single knot loop and double knot loop technique. The pressure needed for rupture was significantly higher (P = 0.001) than for leakage. The maximal tensile force at failure of the single knot loop was significantly higher than the double knot loop (P = 0.028). There was no significant difference in load elongation properties to failure between the single knot loop and double knot loop. CONCLUSIONS: Although no significant differences were obtained in the pressure-resistance test, the single knot loop sustained significantly greater load to failure than the double knot loop in single cycle-to-failure testing. Based on these findings, it would appear that the performance of the single knot loop should be superior to the double knot loop. POTENTIAL RELEVANCE: Both ligature techniques are able to withstand the normal physiological intravascular pressure. The single knot loop has the greater breaking strength of the 2 ligatures tested and is less time consuming to perform and may therefore have advantages during equine castration.

Anatomy and anaesthesia of the equine external ear canal.

Anaesthesia of the external ear canal (external acoustic meatus) is usually performed by blocking both the great and internal auricular nerves by regional infiltration. However, exact landmarks for blocking the internal auricular nerve to accomplish effective anaesthesia have not been described yet. In this study, detailed anatomical dissection of the equine external ear canal and its nerve supply was carried out on fifteen cadaver heads. Tissue samples of the dissected nerves were taken from two cadaver heads processed and were evaluated microscopically. Prior to the dissection, the region of interest was evaluated ultrasonographically, and injection of a local anaesthetic was simulated with an injection of methylene blue on ten cadaver heads. The tympanic membranes of three cadaver heads were obtained by microdissection and processed for microscopic evaluation. The entrance point of the internal auricular nerve, which is a branch of the facial nerve, into the ear canal is formed by the styloid process of the auricular cartilage. Using ultrasound, the styloid process presented as a thin hyperechoic line 2.17-2.97 cm deep, based on the skin surface. Landmarks for performing a complete and reliable anaesthesia of the external ear canal were established, and the simulated anaesthesia with methylene blue injection was evaluated as successful in all ten cases. Additionally, the histological composition of the equine tympanic membrane is described and illustrated.