Cadaveric comparison of the accuracy of ultrasound-guided versus ‘blind’ perineural injection of the tibial nerve in horses.

This research article examines the accuracy of ultrasound-guided and traditional ‘blind’ techniques for injecting the tibial nerve in horses. The study concludes that ultrasound-guided injections are generally more accurate, but a single ultrasound-guided injection did not always effectively stain the nerve.

Background and Aim

• The application of nerve blocks in the diagnostic evaluation of hindlimb lameness in horses is a common standard procedure.
• Traditionally, a ‘blind’ technique using anatomical reference points has been used for these perineural injections. However, due to variances in patients’ bodies, achieving effective local anaesthesia using this method can be challenging.
• The accuracy of perineural injections could possibly be improved using ultrasound (US)-guided injections, hence this research study compares the accuracy of this technique with traditional blind injections.

Methodology

• Twenty-one pairs of cadaveric horse hindlimbs were included in the study and injected with 1ml methylene blue dye; one in each pair was subjected to a blind technique, while the other used ultrasound-guided injection.
• The success of each technique was evaluated based on the rate of successful nerve staining, indicated by the methylene blue dye, where the width and length of the dye stain as well as the length of the nerve coloured were measured.

Results

• There was no significant difference detected in the width and length of the stain dyes, as well as the coloured nerve length between the two techniques.
• Better success rates were noted with the US-guided technique, with an 85.7% success rate, as compared to a 47.6% success rate with the blind technique. The difference found was statistically significant.

Conclusion

• Despite concluding that the US-guided technique of perineural injection in horses is more accurate than the blind technique, the researchers acknowledge a limitation in the study, emphasising that in their samples, a single US-guided injection did not consistently result in successful nerve staining.
• Thus, although US-guided injections may generally be more accurate, multiple injections might be required to increase effectiveness.