Evaluation of the equine mental foramen block: cadaveric and in vivo injectate diffusion.

The research studies the effects of two nerve block techniques on equine mental foramen, identifying which methods and volumes of injectate result in optimal dissemination and efficacy. It was discovered that neither the technique nor the volume of injection significantly affected the circumferential nerve staining, but the diffusion patterns and volumes in the mandibular canal varied, impacting the overall efficiency of the nerve block.

Methods

• The study uses both a descriptive anatomic study and live horses to evaluate and describe injectate diffusion for two equine mental foramen block techniques.
• A total of 12 equine heads were longitudinally sectioned to create 24 hemi-heads for testing the two techniques (T1 and T2) and the impact of two injectate volumes (3 and 5 mL) of a mixed dye and contrast medium.
• Technique T1 had needles directed rostrocaudally into the mental foramen for 3 cm, while T2’s needles were directed dorsolaterally to ventromedially into the foramen for 1 cm.
• The chosen technique and volume were randomly assigned to the hemi-heads.
• Radiographs were used to evaluate the needle tip positioning, measure the distance traveled by the injectate, and assess the injectate diffusion pattern.
• The specimens were then dissected to measure the length of the circumferential nerve staining.
• The most effective technique was applied to three live horses and evaluated further using computed tomography.

Results

• The researchers found no significant difference between the effects of the two injection techniques and injectate volumes on the circumferential nerve staining. They noted a median of 15 mm circumferential nerve staining for T1 and 10 mm for T2.
• They identified differing diffusion patterns for each technique. T1 was more likely to thread alongside the inferior alveolar nerve, while T2 was more likely to form a bolus around the rostral inferior alveolar nerve.
• The bolus diffusion patterns were associated with an increased level of circumferential nerve staining of at least 1 cm.
• They observed the diffusion of the injectate within the mandibular canal was greater with a 5 mL volume compared to 3 mL.
• When tested in vivo, using T2 with 5 mL of injectate resulted in a decreased incidence of circumferential nerve staining of ≥1 cm.

Conclusion

• Overall, T2 created an injection diffusion pattern more likely to result in circumferential nerve staining of at least 1 cm.
• The low frequency of in vivo circumferential nerve staining of at least 1 cm using this method indicates that the effectiveness of the block can vary.