Determination of functional and morphologic changes in palmar digital nerves after nonfocused extracorporeal shock wave treatment in horses

OBJECTIVE: To determine functional and morphologic changes in palmar digital nerves after nonfocused extracorporeal shock wave (ESW) treatment in horses. ANIMALS: 6 horses. PROCEDURES: The medial and lateral palmar digital nerves of the left forelimb were treated with nonfocused ESWs. The medial palmar digital nerve of the right forelimb served as a nontreated control nerve. At 3, 7, and 35 days after treatment, respectively, 2 horses each were anesthetized and nerves were surgically exposed. Sensory nerve conduction velocities (SNCVs) of treated and control nerves were recorded, after which palmar digital neurectomies were performed. Morphologic changes in nerves were assessed via transmission electron microscopy. RESULTS: Significantly lower SNCV in treated medial and lateral nerves, compared with control nerves, was found 3 and 7 days after treatment. A significantly lower SNCV was detected in treated medial but not lateral nerves 35 days after treatment. Transmission electron microscopy of treated nerves revealed disruption of the myelin sheath with no evidence of damage to Schwann cell bodies or axons, 3, 7, and 35 days after treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Nonfocused ESW treatment of the metacarpophalangeal area resulted in lower SNCV in palmar digital nerves. This effect likely contributes to the post-treatment analgesia observed in horses and may result in altered peripheral pain perception. Horses with preexisting lesions may be at greater risk of sustaining catastrophic injuries when exercised after treatment