Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015.
Authors: Malton R, Nagy A
Journal: Equine veterinary journal
Summary
# Editorial Summary The anatomical spread of local anaesthetic during mid-pastern ring blocks has received little scientific attention despite widespread clinical use, prompting researchers to map diffusion patterns using radiodense contrast medium injected into twelve horses' forelimbs. Using both 2 ml and 5 ml volumes, injections at the dorsal aspect of the proximal phalanx demonstrated substantial proximal migration—reaching up to 94.2% of the proximal phalanx length with larger volumes—with significant movement occurring within the first 10 minutes and continuing dorsally up to 20 minutes post-injection. Notably, the dorsal and palmar injection sites created separate contrast patches that did not merge, indicating compartmentalised diffusion patterns. These findings have direct clinical implications: the extensive proximal spread suggests that mid-pastern ring blocks may inadvertently anaesthetise structures at the fetlock joint level, which could confound diagnostic analgesia or provide unexpected therapeutic benefit in fetlock-related pain, whilst the volume-dependent spread indicates that injection technique and volume merit careful consideration when precision of analgesia is required.
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Practical Takeaways
- •Mid-pastern ring blocks provide anesthetic coverage extending well proximal to the injection site, potentially affecting fetlock region pain perception
- •Larger injection volumes (5 ml) produce significantly greater proximal and dorsal spread than smaller volumes (2 ml), which may be beneficial or require adjustment based on clinical goals
- •Anesthetic diffusion is dynamic within the first 10-20 minutes, so timing of clinical assessment post-injection should account for ongoing diffusion
Key Findings
- •Dorsal contrast medium diffused proximally to 89.0% of proximal phalanx length after 2 ml injection and 94.2% after 5 ml injection
- •Significant proximal diffusion occurred within first 10 minutes of injection, with continued dorsal diffusion at 20 minutes (P<0.01)
- •5 ml injected volume resulted in significantly greater dorsal diffusion than 2 ml (P<0.01)
- •Mid-pastern ring block may influence fetlock region pain due to proximal anesthetic diffusion