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Veterinary surgery : VS2025; doi: 10.1111/vsu.70075

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

Abstract: 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. Methods: Experimental study. Methods: 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. Conclusions: A total of 20 L of lavage fluid was not sufficient to result in a sustained negative bacterial culture. Conclusions: High-volume arthroscopic lavage alone is not sufficient as a treatment for septic arthritis.
© 2025 The Author(s). Veterinary Surgery published by Wiley Periodicals LLC on behalf of American College of Veterinary Surgeons.
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Publication Date: 2025-12-26 PubMed ID: 41454562DOI: 10.1111/vsu.70075Google Scholar: Lookup
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Summary

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Overview

  • This study evaluated whether using a high volume of arthroscopic lavage fluid can clear bacteria from infected horse joints, making the fluid that comes out culture-negative, in an experimental model of septic arthritis and synovitis.

Background and Purpose

  • Septic arthritis, an infection of the joint, can be a serious condition in horses requiring treatment to remove infection.
  • Arthroscopic lavage involves flushing the joint with fluid to wash out bacteria and inflammatory debris.
  • The researchers wanted to know if using a very large volume of lavage fluid (up to 20 liters) would successfully clear bacteria from the joint, that is, make the fluid exiting (egress fluid) test negative for bacteria cultures.
  • This could inform veterinary treatment whether high-volume lavage alone is effective or not.

Methods

  • Eleven horses were divided into three groups for experimental infection of their middle carpal joint (a joint in the limb):
    • Group 1 (n=4): Injected with lipopolysaccharide (LPS) to induce synovitis (inflammation without bacterial infection).
    • Group 2 (n=4): Injected with Escherichia coli (E. coli) to induce septic arthritis.
    • Group 3 (n=3): Injected with Staphylococcus aureus (S. aureus) to induce septic arthritis.
  • 24 hours after injection, arthroscopic lavage was performed on the infected joint.
  • Fluid coming out from the joint was collected at each liter increment during lavage — specifically at 1, 5, 10, 15, and 20 liters — and tested for bacterial presence via culture.
  • Further cultures were done based on initial findings.

Results

  • For the LPS group (inflammation without infection), all fluid cultures were negative at all sample points, showing no bacterial growth as expected.
  • For the E. coli group:
    • Probability of positive bacterial culture decreased slightly with more lavage, from approximately 45% after 1 liter to about 35% after 20 liters.
    • However, cultures remained positive in a substantial portion of samples despite high volumes of lavage fluid.
  • For the S. aureus group:
    • Probability of positive bacterial culture started very high (over 98% after 1 liter) and decreased significantly with lavage volume but was still about 13.5% after 20 liters.
    • This indicates some bacteria remained despite large volumes of lavage.
  • After lavage, synovial fluid cultures remained positive in 50% of E. coli-infected horses and all S. aureus-infected horses.

Conclusions

  • Even with 20 liters of lavage fluid, bacterial cultures were not consistently negative in horses with septic arthritis caused by E. coli or S. aureus.
  • This indicates that high-volume arthroscopic lavage alone does not reliably eliminate bacteria from the joint.
  • Therefore, lavage should not be the sole treatment for septic arthritis—additional interventions such as antibiotics or other therapies are necessary.
  • The control group (LPS-induced synovitis) confirmed that inflammation without infection does not produce positive bacterial cultures, validating the experiment.

Cite This Article

APA
Friedlund AM, Bracamonte JL, Koziy RV, Epp T, Thomas KL. (2025). The effect of arthroscopic lavage volume on bacterial culture of egress fluid in horses with experimentally induced septic arthritis and synovitis. Vet Surg. https://doi.org/10.1111/vsu.70075

Publication

Veterinary surgery : VS
ISSN: 1532-950X
NlmUniqueID: 8113214
Country: United States
Language: English

Researcher Affiliations

Friedlund, Alannah M
  • Department Large Animal Clinical Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Bracamonte, Jose L
  • Department Large Animal Clinical Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Koziy, Roman V
  • Department of Veterinary Pathology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Epp, Tasha
  • Department Large Animal Clinical Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Thomas, Keri L

    Grant Funding

    • Mark and Pat DuMont Equine Orthopedic Research Fund

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