A comparison of the effects of two volumes of local analgesic solution in the distal interphalangeal joint of horses with lameness caused by solar toe or solar heel pain.
Authors: Schumacher J, Schumacher J, de Graves F, Steiger R, Schramme M, Smith R, Coker M
Journal: Equine veterinary journal
Summary
# Editorial Summary This 2001 study by Schumacher and colleagues investigated whether the volume of local anaesthetic injected into the distal interphalangeal joint influences its analgesic efficacy in horses with solar pain, a clinically relevant question given the frequency of foot lameness in equine practice. Seven horses were subjected to controlled solar pain stimuli (via set-screws in custom shoes) applied to either the dorsal sole margin or the sole angles, with lameness assessed via video analysis before and after injection of either 6 ml or 10 ml of local anaesthetic into the DIP joint. The findings revealed meaningful differences: whilst 6 ml proved insufficient to improve lameness scores when sole angle pain was induced, 10 ml significantly reduced lameness in this location; conversely, both volumes were equally effective at relieving dorsal sole margin pain. These results indicate that DIP joint analgesia penetrates and desensitises tissues unevenly across the solar surface, with deeper structures at the sole angles requiring higher anaesthetic volumes than more superficial dorsal margins. For practitioners diagnosing solar pain through intra-articular DIP analgesia, these findings suggest that inadequate response to a standard 6 ml injection warrants consideration of injecting a larger volume before dismissing DIP joint involvement, particularly when heel or palmar foot pain is suspected.
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Practical Takeaways
- •When performing DIP joint injections for solar pain, use 10 ml rather than 6 ml for pain localized to the angles of the sole to achieve significant analgesia
- •DIP joint injection is more reliably effective for dorsal sole pain than for pain at the heel angles, suggesting different pain pathways or anatomical considerations
- •Always consider the specific location of solar pain when selecting injection volume and predicting likelihood of diagnostic response to DIP joint analgesia
Key Findings
- •10 ml local analgesic solution into the DIP joint significantly reduced lameness scores for solar pain at the angles of the sole, while 6 ml did not (P < 0.05)
- •Both 6 ml and 10 ml local analgesic solution significantly reduced lameness scores for solar pain at the dorsal margin of the sole (P < 0.05)
- •DIP joint analgesia was less effective at desensitizing the angles of the sole compared to the dorsal margin of the sole
- •Volume of local analgesic solution (10 ml vs 6 ml) and location of solar pain both influenced the therapeutic response to DIP joint injection