Needle bevel orientation does not affect diffusion of contrast medium during perineural injection of the lateral palmar/plantar nerve and lateral palmar metacarpal/plantar metatarsal nerves

Summary Background Perineural anaesthesia is used to localise pain in horses presenting with lameness. Diffusion of local anaesthetics during perineural analgesia complicates clinical interpretation. Needle bevel orientation has been shown to affect drug diffusion in humans. Objectives To investigate the effects of needle bevel orientation and time on proximal diffusion following lateral palmar/plantar and palmar metacarpal/plantar metatarsal perineural analgesia (lateral low four‐point) in horses. Study Design Analytical experimental. Methods Twelve horses had lateral components of the low four‐point injections performed with contrast medium with the needle bevel oriented proximally on either the left or right limbs and distally on the contralateral limbs. Radiographs were taken at the time of injection and at 5, 10, 15 and 30 min post‐injection. Measurements of proximal and total diffusion of contrast medium were performed. Comparison between groups and time points were analysed with two‐way ANOVA and mixed model effects, with Dunnet's multiple comparison test and significance set at p < 0.05. Results There was no significant difference between proximal and total diffusion of contrast medium with needle bevel proximal versus bevel distal. An increase in proximal and total diffusion occurred over time regardless of needle bevel orientation. Main Limitations Use of contrast medium with a higher molecular weight than local anaesthetics. Use of radiography was used for diffusion evaluation rather than three‐dimensional imaging. Conclusion Needle bevel orientation does not affect diffusion of contrast medium. Analgesia of more proximal structures should be taken into consideration if horses are evaluated at later time points.