An Objective Assessment of the Effect of Anesthetizing the Median Nerve on Lameness Caused by Pain in the Cubital Joint.
Authors: McGlinchey Leah, Agne Gustavo, Passler Thomas, Cole Robert, Schumacher John
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Median Nerve Blocks and Cubital Joint Lameness When investigating forelimb lameness, clinicians routinely perform median nerve blocks as part of the diagnostic protocol, partly based on anatomical proximity between the nerve and cubital joint. This study sought to determine whether proximal spread of local anaesthetic during median nerve blockade could inadvertently resolve cubital joint pain, potentially confounding lameness localisation. Six healthy horses received intra-articular recombinant equine interleukin-1β to induce acute cubital pain; their lame limbs were then blocked using 10 mL of 2% mepivacaine, with gait assessed via inertial sensor analysis at 20, 40, and 60 minutes post-block. Despite successful median nerve anaesthesia (confirmed by loss of pastern sensation and thermographic changes), lameness showed no significant improvement compared to baseline (P = 0.32). These findings carry important clinical weight: median nerve blocks performed with standard anaesthetic volumes are unlikely to mask cubital joint pain during diagnostic work, allowing practitioners greater confidence in their lameness interpretation when this block fails to improve gait. The study reinforces that anatomical proximity alone does not guarantee therapeutic spread, and results should refine how clinicians weight negative median blocks in their differential diagnosis algorithms.
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Practical Takeaways
- •When performing diagnostic median nerve blocks during lameness examinations, clinicians should not expect improvement in gait if pain originates from the cubital joint, despite the anatomical proximity of the nerve to the joint
- •A failed response to median nerve blocking can help localize pain to the cubital joint rather than structures distal to the block site
- •The standard 10 mL volume of 2% mepivacaine used for median nerve blocks is insufficient to anesthetize the cubital joint itself
Key Findings
- •IL-1β injection into the cubital joint successfully induced significant transient lameness in all 6 horses (P < 0.0001)
- •Median nerve block with 10 mL of 2% mepivacaine did not significantly improve lameness as measured by total differential head vector sum (P = 0.32)
- •Successful median nerve blocks were confirmed by loss of medial pastern skin sensation and characteristic thermographic changes
- •Anesthetizing the median nerve is unlikely to ameliorate pain originating from the cubital joint during clinical lameness examinations