A new approach for perineural injection of the lateral palmar nerve in the horse.

To evaluate the accuracy of a new technique for perineural injection of the lateral palmar nerve and to determine frequency of inadvertent injection into the carpal synovial sheath with this technique. Prospective experimental study. Thirty equine cadaver forelimbs. Each of 3 clinicians injected 0.5 mL of a 1% aqueous solution of new methylene blue as a marker at the medial aspect of the accessory carpal bone of 10 limbs. Immediately after each injection, the lateral palmar nerve was identified by dissection of and inspected for proximity of dye, and the carpal synovial sheath was inspected for the presence of dye. New methylene blue solution was observed to surround the nerve (29 limbs) or to lie within 2 mm of it (1 limb). Dye was not found in the carpal synovial sheath of any specimen. Using this technique, perineural injection of the lateral palmar nerve can be consistently achieved, and the carpal synovial sheath is unlikely to be penetrated by the needle during the procedure. The technique described provides an accurate and simple method for perineural injection of the lateral palmar nerve proximal to the origin of its deep branch. This technique can be used to anesthetize the lateral palmar nerve for diagnosis of pain originating in the palmaroproximal aspect of the metacarpus without risk of inadvertently desensitizing structures within the carpal synovial sheath.