Nerve blocks are an integral part of the lameness exam. Following initial assessment of the horse at the trot, a flexion exam and the use of hoof testers, nerve blocks may be used to find or pinpoint the origin of the problem. This is especially true in cases where initial examination fails to isolate a cause.
Specific sensory nerve branches are numbed (blocked) at precise levels (lower to higher) by the vet with a local anesthetic. These nerve branches provide sensation to specific areas and structures within the limb. When local anesthetic is injected around the nerve at this level, the structures supplied below that level become numb. If the structure causing lameness happens to be within this “blocked” area, then the lameness improves. The effect lasts for several hours before wearing off.
Reasons to UseRelated Observations
Nerve blocks give concrete information about the region of the limb causing pain. This is a vital complement to radiography and ultrasound. Without this diagnostic, it can be very hard to know if a lesion found during imaging is the source of pain or is just an incidental finding.
Local anesthetic can be imprecise, spreading into the tissues around a nerve. Areas blocked may be higher or lower than a clinician would expect, complicating the analysis. There is also a great deal of individual variation between horses. Some horses have unique nerve branches that complicate interpretation of the results.
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