The effect of arthroscopic lavage volume on bacterial culture of egress fluid in horses with experimentally induced septic arthritis and synovitis

Abstract

Objective: To evaluate if high-volume lavage results in a negative bacterial culture of egress fluid, regardless of pathogen in an experimental model of equine septic arthritis. Study design: Experimental study. Animals: A total of 11 horses in three groups (lipopolysaccharide [LPS] Group 1, n = 4; Escherichia coli [E. coli] Group 2, n = 4; Staphylococcus aureus [S. aureus] Group 3, n = 3). Methods: A middle carpal joint of each horse was injected with LPS (synovitis Group 1), E. coli (septic arthritis Group 2) or S. aureus (septic arthritis Group 3). Arthroscopic lavage of the middle carpal joint was performed 24-h post-injection. Egress fluid samples were collected every liter for bacterial culture. Liter samples 1, 5, 10, 15, and 20 were submitted for bacterial culture. Subsequent samples were submitted based on the results of the initial dataset. Results: Predicted probability of a positive culture after 1, 5, 10, 15, and 20 L for E. coli and S. aureus, respectively were: 44.7% (p =.04) and 98.3% (p ≤.001) after 1 L, 42.6% (p =.02) and 94.3% (p ≤.001) after 5 L, 40.1% (p =.02) and 77.8% (p =.001) after 10 L, 37.6% (p =.04) and 42.5% (p =.08) after 15 L, and 35.2% (p =.09) and 13.5% (p =.32) after 20 L. LPS cultures (n = 4) were negative at every timepoint. Post-lavage 50% (2/4) of E coli. and 100% (3/3) S. aureus horses had positive synovial fluid cultures. Conclusion: A total of 20 L of lavage fluid was not sufficient to result in a sustained negative bacterial culture. Clinical significance: High-volume arthroscopic lavage alone is not sufficient as a treatment for septic arthritis.