The effect of arthroscopic lavage volume on bacterial culture of egress fluid in horses with experimentally induced septic arthritis and synovitis.
Authors: Friedlund Alannah M, Bracamonte Jose L, Koziy Roman V, Epp Tasha, Thomas Keri L
Journal: Veterinary surgery : VS
Summary
# Editorial Summary: Arthroscopic Lavage Volume in Equine Septic Arthritis Determining adequate lavage volume during arthroscopic treatment of septic joints remains clinically challenging, prompting this experimental study to assess whether high-volume irrigation reliably sterilises synovial fluid regardless of causative pathogen. Eleven horses received intra-articular injections of lipopolysaccharide (inducing sterile synovitis), *Escherichia coli*, or *Staphylococcus aureus*, followed by arthroscopic lavage 24 hours later, with egress fluid sampled at 1, 5, 10, 15, and 20-litre intervals and cultured for bacterial growth. Both bacterial species demonstrated persistently high positive culture rates: *S. aureus* proved particularly resistant, with 98.3% positive cultures after just 1 litre declining only to 13.5% by 20 litres, whilst *E. coli* showed lower but still significant positivity (44.7% at 1 litre, 35.2% at 20 litres); critically, 100% of *S. aureus* cases and 50% of *E. coli* cases retained positive synovial cultures after lavage completion. These findings challenge the assumption that mechanical irrigation alone—even at 20 litres—can achieve bacterial sterilisation and suggest that arthroscopic lavage must be combined with systemic antimicrobial therapy, extended treatment protocols, or alternative surgical approaches to effectively manage septic arthritis, particularly when *Staphylococcus* species are involved.
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Practical Takeaways
- •High-volume arthroscopic lavage alone is insufficient treatment for septic arthritis—expect persistent positive cultures even after 20 liters, particularly with S. aureus infections
- •Post-lavage bacterial culture should not be used as the sole indicator of treatment success; adjunctive systemic antibiotics and additional therapeutic interventions are essential
- •S. aureus infections require more aggressive treatment protocols than gram-negative organisms; expect greater bacterial persistence regardless of lavage volume
Key Findings
- •20 liters of arthroscopic lavage did not reliably eliminate bacteria from egress fluid, with E. coli showing 35.2% positive cultures and S. aureus 13.5% positive cultures after 20L
- •S. aureus demonstrated greater persistence than E. coli, with 98.3% positive cultures after 1L versus 44.7% for E. coli
- •Post-lavage synovial fluid cultures remained positive in 50% of E. coli-infected horses and 100% of S. aureus-infected horses despite high-volume lavage
- •LPS-induced synovitis showed negative cultures at all timepoints, suggesting inflammatory synovitis differs significantly from bacterial septic arthritis