LOCAL-DISTRIBUTION OF MEPIVACAINE AFTER DISTAL INTERPHALANGEAL JOINT INJECTION IN HORSES

Objective-To evaluate the distribution of mepivacaine hydrochloride af ter distal interphalangeal (DIP) joint injection in horses. Design-Pro spective, uncontrolled study. Animals-10 adult horses. Procedure-30 mi nutes before euthanasia, 8 ml of 2% mepivacaine hydrochloride was inje cted into the dorsal pouch of a forelimb DIP joint. Synovial tissue fr om the DIP joint and podotrochlear (navicular) bursa and bone tissue f rom the medullary cavity of the distal sesamoid (navicular) bone were taken from both forelimbs immediately after death. All synovial and bo ne specimens were analyzed for tissue concentration of mepivacaine by high-performance liquid chromatography. Synovial tissue and bone speci men concentrations from the injected forelimb were compared with corre sponding specimens from the noninjected forelimb. All synovial tissue and bone specimen concentrations were compared with an estimated effec tive tissue concentration of mepivacaine (0.3 mu g/mg) for local anest hesia. Results-Specimen concentrations of mepivacaine from the injecte d forelimb were significantly greater (P < 0.05) than those in the cor responding tissues of the contralateral noninjected forelimb. All DIP joint and navicular bursa synovial tissue specimens from the injected forelimb had greater than the estimated effective tissue concentration of mepivacaine for local anesthesia. Of the 10 navicular bone specime ns from the injected forelimb, 4 were higher and 2 were within 20% of the estimated effective tissue concentration of mepivacaine for local anesthesia. Conclusions-Mepivacaine hydrochloride deposited into the D IP joint should anesthetize pain arising from navicular bursa synovia and may decrease pain arising from the medullary cavity of the navicul ar bone. Clinical Relevance-DIP joint injection of mepivacaine hydroch loride is not specific for DIP joint pain.