Effect of Four Antimicrobial Lavage Solutions on the Tarsocrural Joint of Horses

Three concentrations of povidone‐iodine (0.1% w/v, 0.2% w/v, 0.5% w/v) and one concentration of chlorhexidine (0.5% w/v) were selected as antimicrobial joint lavage solutions. Through‐and‐through joint lavage was performed with one of these antimicrobial solutions on a tarsocrural joint of 12 horses. The contralateral tarsocrural joints (control limbs) were lavaged with a balanced electrolyte solution (BES). The effect of the lavage solution on the joints was evaluated with respect to lameness, foot flight pattern, soreness to joint palpation, articular and periarticular enlargement, and synovial fluid composition on Day 1,4, and 8 postlavage. On Day 8 postlavage, all horses were euthanized and the tarsocrural joints were examined. All solutions induced a synovitis. Based on clinical assessment, synovial fluid protein levels, color, clarity, mucin clot forming ability, gross appearance of the joint at necropsy, and synovial membrane histologic evaluation, a similar, mild, transient, synovitis was induced by the BES and 0.1% povidone‐iodine (PI) solution. The 0.2% PI solution induced a more prolonged neutrophilic response and poorer mucin clot forming ability in the synovial fluid as compared to the BES. The 0.5% PI and 0.5% chlorhexidine solutions produced severe lameness, soreness to joint palpation, and limb enlargement. The elevated synovial fluid total protein content persisted significantly longer (p < 0.05) than the corresponding control (BES) solution. Histologic evaluation of the synovial membrane confirmed the presence of a moderate to severe neutrophilic synovitis in these treatment groups.