Effect of anaesthesia of the palmar digital nerves on proximal interphalangeal joint pain in the horse.
Authors: Schumacher J, Livesey L, DeGraves F J, Schumacher J, Schramme M C, Hathcock J, Taintor J, Gomez J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Palmar Digital Nerve Blocks and PIP Joint Lameness Clinicians have long relied on palmar digital nerve blocks to identify and manage proximal interphalangeal (PIP) joint pain in lame horses, but this 2004 study questioned the anatomical assumptions underlying this diagnostic approach. Researchers video-recorded horses trotting before and after artificially inducing PIP joint pain, then assessed lameness response following mepivacaine injection at three different proximodistal sites along the palmar digital nerves. Whilst anaesthesia administered just 1 cm proximal to the cartilages of the foot produced negligible improvement in median lameness scores (P ≥ 0.05), injections 2 and 3 cm proximal to this landmark yielded significant improvements (P ≤ 0.05), suggesting a discrepancy between the block site and actual nerve distribution. The critical implication is that a negative response to a proximal digital block performed very distally does not reliably exclude PIP joint pain as a lameness cause—yet conversely, improvement from more proximal injections may reflect alternative pain sources rather than true PIP joint involvement. Practitioners should recognise that block location substantially influences which structures are truly desensitised, and diagnostic interpretation requires careful consideration of injection site in relation to anatomical landmarks.
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Practical Takeaways
- •Palmar digital nerve anaesthesia at the proximal cartilage margin does not reliably block PIP joint pain, so failure to improve lameness at this site does not rule out PIP joint involvement
- •Anaesthesia sites 2-3 cm proximal to the cartilages are more effective for assessing PIP joint pain, but improvement at these proximal sites may reflect blocking of periarticular tissues rather than the joint itself
- •Use palmar digital nerve blocks cautiously when diagnosing PIP joint lameness; anatomical site of injection significantly affects clinical outcome
Key Findings
- •Anaesthesia of palmar digital nerves 1 cm proximal to cartilages of foot did not significantly reduce lameness (P ≥ 0.05), with only 1 of 6 horses showing marked improvement
- •Anaesthesia of palmar digital nerves 2 and 3 cm proximal to cartilages of foot significantly improved median lameness scores (P ≤ 0.05)
- •The PIP joint is unlikely to be anaesthetised when palmar digital nerves are blocked at the proximal margin of the cartilages of the foot
- •PIP joint pain cannot be excluded as a cause of lameness when improvement occurs with palmar digital nerve anaesthesia at any proximal site