Simplified ultrasound-guided technique improves accuracy of median nerve perineural injection compared to “blind” techniques in equine ex vivo specimens.

Overview

• This study evaluated a simplified ultrasound-guided technique (SUGT) for injecting dye around the median nerve in horse limbs, comparing it to traditional “blind” injection methods without ultrasound guidance.
• The research tested if SUGT improved accuracy and dye distribution in perineural injections on equine ex vivo specimens.

Study Objective

• To assess the feasibility of a simplified ultrasound-guided technique for perineural injection of the median nerve on horse limbs outside the living animal (ex vivo).
• To compare the accuracy of three injection methods: SUGT, blind proximal, and blind distal injections.
• To evaluate and compare the distribution of injected dye following each technique.

Methodology

• Design: Experimental study conducted on 22 equine thoracic limbs collected from April to October 2025.
• Techniques Tested:
  • Simplified Ultrasound-Guided Technique (SUGT)
  • Blind Proximal Injection (no ultrasound, injection near the proximal median nerve)
  • Blind Distal Injection (no ultrasound, injection near the distal median nerve)
• Procedure:
  • Each technique involved injecting 1 mL of methylene blue dye around the median nerve.
  • SUGT and blind proximal injections were performed in paired limbs (comparing both on the same horse limb pairs).
  • Blind distal injections were performed on a separate group of limbs.
  • After 5 minutes, limbs were dissected to:
    • Determine whether the median nerve was stained (indicating accurate perineural injection).
    • Measure dye diffusion in two directions: proximodistal (along the length of the limb) and craniocaudal (from front to back).
• Statistical Analysis:
  • Accuracy compared using McNemar and Fisher exact tests.
  • Dye diffusion compared using the Wilcoxon signed-rank test.
  • Significance threshold set at P < .05.

Results

• Total number of forelimbs tested: 22
• Accuracy of median nerve staining:
  • SUGT: 100% success (11 out of 11 limbs showed accurate staining of the median nerve)
  • Blind Proximal: 27.3% success (3 out of 11 limbs)
  • Blind Distal: 0% success (0 out of 11 limbs)
• Statistical significance:
  • SUGT was significantly more accurate than both blind proximal and blind distal techniques.
  • No significant difference in accuracy between blind proximal and blind distal injection methods.
• Dye Diffusion:
  • No significant differences in the extent of dye spread among the three techniques in either proximodistal or craniocaudal directions.

Conclusions

• The simplified ultrasound-guided technique is superior to blind injection methods for accurately delivering dye around the median nerve in horse limbs.
• Despite better accuracy, the extent of dye diffusion did not differ significantly, suggesting that when the injection is correctly placed, the dye spreads similarly regardless of technique.
• Implementing the SUGT in clinical settings is recommended for improved diagnostic analgesia (nerve blocking) of the median nerve in horses.
• Use of ultrasound guidance enhances the precision of perineural nerve blocks, potentially improving diagnostic outcomes and treatment efficacy in equine medicine.