Changes in equine carpal joint synovial fluid in response to the injection of two local anesthetic agents

The effects of repeated arthrocentesis and injection of local anesthetic agents, lidocaine HCl or mepivacaine HCl on the equine middle carpal joint were investigated. Synovial fluid samples were evaluated before, and 12, 24 and 48 hours following, treatment. The greatest changes from pretreatment values occurred in synovial fluid cellularity. Repeated arthrocentesis caused a moderate increase in cell counts, while injection of local anesthetics caused a greater increase. Alterations in mucin clot quality, hyaluronic acid content, fluid viscosity, total protein and immunoglobulin G were generally of no significance. The most sensitive sampling time to detect changes caused by a given treatment was 24 hours following treatment while the 12 hour sampling period appeared to be the best at detecting differences between treatments. Repeated arthrocentesis has a definite effect on synovial fluid composition but the effects appear to decrease with repeated centesis. Lidocaine HCl and mepivacaine HCl are irritating to the synovial environment. Clear differences between responses to the drugs could not be identified.