Modified abaxial sesamoid nerve block provides enhanced proximal diffusion compared to basisesamoid block and lower proximal diffusion than traditional low plantar nerve block in equine hind limbs: ex vivo and in vivo study.

This research compares the proximal diffusion of nerve blocking techniques in horses, including modified sesamoid nerve block (MASB), basisesamoid block (BSB), and traditional low plantar block (TLPB). The study found that MASB had significantly more proximal diffusion than BSB and less diffusion compared to TLPB. The risk of injecting into the blood or synovial fluid was low with all methods.

Methodology

• The testing was divided into two models, ex vivo and in vivo. In the ex vivo model, the hind limbs from 18 horses were used, while the in vivo model involved 5 live horses in a crossover study.
• In the ex vivo model, a solution of mepivacaine/methylene blue was injected into the hind limb of the horse to measure and compare the diffusion distance of the three different injection techniques: MASB, BSB, and TLPB.
• 10 minutes after injection, the skin was dissected and the diffusion distance of the dye was measured.
• For the in vivo model, a radiopaque contrast medium was injected in both hind limbs of the horses using either the MASB or TLPB techniques. After 10 minutes, a radiograph was taken and the diffusion distance of the injection was measured.

Results

• In the ex vivo model, the diffusion of the MASB was significantly longer than the BSB but shorter than the TLPB. However, all techniques managed to reach the proximal aspect of the Deep Flexor Tendon Sheath (DFTS) in a similar manner.
• In terms of the risk of injecting into the blood or synovial fluid (intravascular or intrasynovial injections), there was no significant difference between the techniques.
• In the in vivo model, the contrast medium diffusion was shorter for the MASB compared to the TLPB. The incidence of intrasynovial or intravascular injections with both techniques was not significantly different.
• Across all techniques, the proportion of injections that diffused to the proximal aspect of the DFTS was not significantly different.

Conclusions

• Overall, the results show that the MASB technique resulted in a significantly longer diffusion than the BSB method and a shorter diffusion than the TLPB method, but consistently reached the proximal aspect of DFTS in both ex vivo and in vivo models.
• The study concludes that the risk of intrasynovial or intravascular injections for all the methods is relatively low, making these techniques safe for use in veterinary practice for equine species.