An Objective Assessment of the Effect of Anesthetizing the Median Nerve on Lameness Caused by Pain in the Cubital Joint

Abstract

The median nerve, along with the ulnar nerve, is often anesthetized when performing a lameness examination in horses. Because of the close proximity of the median nerve to the cubital joint, proximal migration of local anesthetic might ameliorate pain originating from the cubital joint. The objective of this study was to determine if a median nerve block will ameliorate lameness caused by pain in the cubital joint. A forelimb lameness was induced in six healthy horses by injecting 100 ng of recombinant equine interleukin 1 beta (IL-1β) into the cubital joint. The median nerve of the lame leg was anesthetized using 10 mL of 2% mepivacaine hydrochloride. A successful median nerve block was confirmed by loss of skin sensation at the medial aspect of the pastern and typical changes in thermographic images. Gait was assessed before and at 20, 40, and 60 minutes after the median nerve block using an inertial sensor-based motion analysis system (Lameness Locator; Equinosis LLC, Columbia, MO). A full-factorial repeated measures analysis of variance was used to compare treatment effect across time. IL-1β administration resulted in significant transient lameness in all horses (P < .0001). The median nerve block was successfully performed in all horses and did not result in significant improvement (P = .32) of lameness as quantified by the total differential head vector sum. This result has relevant clinical application as it suggests when performing a lameness examination, it is unlikely that blocking the median nerve with 10 mL of local anesthetic will ameliorate pain originating from the cubital joint.