Diffusion of mepivacaine between adjacent synovial structures in the horse. Part 1: forelimb foot and carpus.

The research article investigates how the analgesic agent mepivacaine spreads between adjacent joint structures in the limbs of horses – a phenomenon reportedly more frequent than earlier anticipated.

Hypothesis and Objective

In this study, the researchers are challenging the commonly held view about the diffusion of mepivacaine, a local analgesic agent, between synovial (joint fluid) structures in equine forelimbs. They hypothesize that the diffusion is more frequent than what previous studies with latex, gelatine dye or contrast media have suggested.

Methodology

• The study used 31 fresh equine cadavers, examining their forelimbs specifically.
• Injection of mepivacaine into specific joints was performed: distal interphalangeal joint (DIPJ) of one forelimb, the navicular bursa (NB) of the other forelimb, and the radiocarpal (RC) joint of one forelimb and the intercarpal (IC) joint of the other forelimb.
• After performing flexion and extension of the joints, synovial fluid from joint structures adjacent to the injected ones was collected.
• The mepivacaine concentration in the fluid was assessed using enzyme-linked immunosorbent assay. For diluted samples, comparison of urea concentrations in the diluted synovial fluid and serum urea was used to determine mepivacaine concentration.

Findings

• The researchers found that mepivacaine diffused from the DIPJ to the NB or from the NB to the DIPJ in 100% of the limbs tested.
• Diffusion of mepivacaine from the IC to RC joints occurred in 96% of limbs and from the RC to IC joints in 84% of limbs.
• The detected levels of mepivacaine varied, from less than 0.3 mg/l in 36% of IC joints after RC joint injection to over 300 mg/l in 44% of DIPJ after NB injection.

Conclusion

• The findings reveal a much higher degree of mepivacaine diffusion across adjacent synovial structures than previous studies indicate.
• These results challenge the specificity of commonly performed intrasynovial analgesic techniques in the forelimbs of horses, indicating that they may not be as targeted as once thought, leading to more widespread effects of the analgesic.

This research provides valuable insight for the equine medical field, especially for veterinarians planning joint treatment or pain management strategies for horses.