Effects of cryotherapy on the palmar and plantar digital nerves in the horse.

The duration of anesthetic effect and the histopathologic changes resulting from a controlled freeze of the palmar and plantar digital nerves in the horse were evaluated. Two techniques were compared: (i) nerves were frozen by direct application of the cryoprobe after surgical exposure and (ii) nerves were frozen by percutaneous application of the cryoprobe to the overlying skin. Return of skin sensation and ability to detect a stimulus were used to determine return of nerve function. The duration of anesthetic effect was significantly (P less than 0.005) longer for nerves frozen after surgical exposure than for those frozen by the percutaneous technique (mean 156 days vs 47.5 days). At the termination of the study, horses were euthanatized and all nerves were examined histologically. Neuromas-in-continuity were observed in 10 of 28 frozen nerves. Classification was based on the involvement of the supporting fibrous connective tissues of the nerve, endoneurium, perineurium, and epineurium. The direct technique of freezing the nerve after surgical exposure was repeatable and could be used to provide temporary neurectomy in the horse. The percutaneous technique caused a temporary loss of pain perception, but could not be relied on to interrupt nerve function for longer than a few weeks.