In this episode, Maureen Kelleher, DVM, DACVS, DACVSMR, CVA, discussed diagnostic anesthesia for equine lameness exams. She talked about the types of lameness exams in which diagnostic anesthesia is useful, drug preferences, tips for maximum efficacy, and more.
Diagnostic Anesthesia in Equine Lameness Exams
Kelleher said she uses diagnostic anesthesia in about 98% of lameness cases. “The exceptions are going to be the extremes,” she said. These extremes include subtle, intermittent lameness cases and potential fractures. “But pretty much everything in the middle would be totally game for diagnostic anesthesia,” she said.
Drug Options for Diagnostic Anesthesia
The three main options for local anesthesia are lidocaine, mepivacaine, and bupivacaine. Kelleher said she mostly reaches for mepivacaine (more commonly known by the brand name Carbocaine), “because it has a relatively short onset of action, and it’s probably the most efficacious.”
Kelleher said she steers away from lidocaine for diagnostic purposes because one study found it to be variable in its ability to completely desensitize a foot. Bupivacaine has a longer onset time and duration, which makes it less practical for diagnostic purposes.
Perineural vs. Intra-Articular Anesthesia
Kelleher typically uses perineural anesthesia during initial lameness exams because it’s quicker, simpler, and allows her to reasonably estimate the location of the lameness. She will then use intra-articular anesthesia during follow-up lameness exams to get more precise localization.
When to Use Diagnostic Anesthesia in the Lameness Exam
Kelleher usually waits to use diagnostic anesthesia until she’s watched the horse go in as many circumstances as feasible. She wants to watch the horse move in a straight line, on the longe line, and under saddle if possible. She also prefers to perform flexions before blocking.
After blocking the horse, she watches them go in whichever situation the lameness was most severe. She often puts the rider back on the horse after blocking. “That gives me feedback from the rider on how much they feel like the horse has changed, so it’s not just my eye determining how much the horse is better,” she said. If the horse was sensitive to any joint flexions prior to blocking, she will repeat them to see how the block changed the flexion.
Administering Diagnostic Anesthesia for Maximum Precision
“I’ve been burned by trying to jump up the leg and start higher, or where I think the lameness is,” Kelleher said. “And because I’ve learned the hard way, I always start as low as possible on the leg and then work my way upward.” She works in the smallest feasible increments to obtain the most precise localization possible, taking time and patient constraints into account.
“Some horses are not going to tolerate all that blocking,” she said. “So at the very minimum, I’m going to try and break the leg up into reasonable sections for blocking and then subsequent imaging.”
She cautioned against jumping ahead when blocking up the leg. For example, she said she has started out by blocking a deep branch of the lateral plantar nerve when she was suspicious of a proximal suspensory injury. However, that has the potential to block out the entire lateral side of the limb down to the heel bulb.
“I’ve had at least one case where the horse had a lateral suspensory branch injury, and I’ve had at least one case where the horse had a lateral collateral ligament of the coffin joint injury, and those were missed right away because I interpreted the response as it had to have been the proximal suspensory, and it wasn’t,” she said.
Interpreting Diagnostic Anesthesia
Kelleher said you need to be cautious in how you interpret the results of diagnostic anesthesia, especially because it migrates quickly. “First, I’m going to check to make sure the block is working, meaning if I do a palmar digital nerve block, that the heel bulbs are desensitized,” she said. “But also in that situation, I’m going to check to make sure the dorsal aspect of my coffin joint, my pastern joint, and my fetlock joint are not desensitized.” If the horse has lost feeling in any of these joints and improves with the block, she assumes the lameness could be in any of these regions.
In that situation, she might decide to return in a day or two and start with intra-articular blocks to narrow down localization before performing diagnostic imaging.
Kelleher also said she would never rule out that a block has migrated proximally. “Maybe they still have skin sensation, but they may be blocked higher up,” she said. If a horse is not responding to the treatment plan based on your localization and diagnostic imaging, she recommends reblocking in a different fashion to confirm your localization and diagnostic imaging findings.
Final Thoughts
“Take-home messages would be to remember that the block is always going to migrate more proximal to what you think it is, and don’t be afraid to do some intra-articular anesthesia to really narrow down your diagnostic imaging and what’s going on with the horse,” Kelleher said.
About Dr. Maureen Kelleher
Maureen Kelleher, DVM, DACVS, DACVSMR, CVA, achieved her doctorate in veterinary medicine from the University of California at Davis. She then undertook an internship at Pioneer Equine Hospital in Oakdale and a residency in equine surgery. She gained several years of valuable experience in equine private practice in California, specializing in equine sports medicine and lameness, advanced diagnostic imaging, and acupuncture. In 2010, she obtained certification as a veterinary acupuncturist, and she gained Diplomate status with the American College of Veterinary Surgeons in 2013.
Kelleher relocated to The Marion duPont Scott Equine Medical Center in Leesburg, Virginia. Her primary focus is evaluating and treating performance-limiting issues in sport horses through nonsurgical methods. She collaborates closely with the center’s therapeutic farrier team, as well as its medicine and surgery teams, utilizing cutting-edge diagnostic imaging capabilities to deliver exceptional care to equine patients.
Related Reading
- Approach to Horses with Poor Performance
- Perineural Anesthetic Blocks Effects on Equine Posture
- How to Create a Joint Health Profit Center
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