Cover Story | Orthopedics

Antimicrobial Prophylaxis: Evidence vs Habit

By Paul Basilio

Preventing surgical site infections is a critical goal for any orthopedic procedure in equine medicine, and antimicrobial prophylaxis is a common tool used to safeguard the success of those procedures. As the principles of antimicrobial stewardship move to the forefront of veterinary medicine, an increasingly relevant question is whether the routine use of antimicrobials truly is justified.

“The problem with treating orthopedic injuries in horses is the fact that it’s really hard,” said John Peroni, DVM, MS, DACVS, the Dr. Steeve Giguere Memorial Professor in Large Animal Medicine at the University of Georgia College of Veterinary Medicine. “Infections can show up a few weeks [after the procedure]. I once placed an implant in a horse that came back with an infection 6 months after the surgery.”

During a presentation at the 70th AAEP Annual Convention in Orlando, Dr. Peroni explained that regardless of the surgeon’s skill or the choice of antimicrobials, infection can still occur—potentially leading to implant failure and joint sepsis. This can add thousands of dollars to the owner’s bill, result in considerable suffering for the horse, and cause the surgeon to question their decisions.

“There are also intangibles, such as the impact on morale in veterinary personnel,” Dr. Peroni said. “Students, staff and faculty alike lose sleep—and their GI lining—over cases that become infected.”
On top of everything, some clients expect, or even demand, antimicrobials for routine procedures and may blame the veterinarian if an infection develops.

“Ultimately, you might be treating the client instead of the actual issue on some level,” he explained.

What the Science Says
Reported rates of surgical site infections by McDonald et al., have varied over the years. A study published in 1994 found that 10% of 452 cases developed surgical wound infections. Notably, 8% of infections occurred in procedures classified as clean (i.e., no break in sterile technique), while 52% occurred in clean-contaminated procedures (i.e., those with minor, controlled contamination). Bacterial isolates were recovered in only half of the infection cases.

The same study showed that surgeries lasting more than 90 minutes were almost 4 times as likely to result in infection.

“Everyone who performs in a surgical suite should be aware of that number,” Dr. Peroni said. “That magic number of 90 minutes has now been established across all types of surgical literature, including in human medicine.”
A 2013 study by found that only 3 of 636 joints (0.5%) became infected following elective equine arthroscopy performed without antimicrobial prophylaxis. Two of the infections were detected weeks later, significantly delaying treatment.

A 2018 study of 652 horses by Stöckle, et al., compared those that received antimicrobial prophylaxis (n=259) with those that did not (n=393). The overall complication rate was about 39% (antibiotics group, 37%; non-antibiotics group, 40%), with swelling being the most common complication. Septic joints were reported in 5 horses that received antimicrobials and 3 horses that did not.

“That’s a significant number of horses in the study,” Dr. Peroni said. “The use of antibiotics may be up for discussion—at least when it comes to clean procedures such as arthroscopy.”

A 2022 study comparing rates of equine synovial sepsis after intrasynovial injection in ambulatory versus hospital settings evaluated nearly 700 procedures. The results showed negligible sepsis rates, regardless of antimicrobial use or location.

“Why does this literature exist if we don’t pay close attention to it?” Dr. Peroni asked. “I feel that this supports [antimicrobial] practices more than hearsay or habit.”

Future Directions
The routine use of antimicrobials in cases where they are not shown to be effective is a significant driver of antimicrobial resistance.

“I’m not suggesting that antibiotics should never be used,” Dr. Peroni emphasized, “but the protocols by which they’re used should be reconsidered.”

The literature consistently shows that antimicrobial prophylaxis is most effective when administered 30 to 60 minutes before the surgical incision. While broad-spectrum antimicrobials still make sense for prophylaxis, prolonged use is not well supported.

Another strategy to counter habitual antimicrobial use is the implementation of care bundles—a concept long used in human medicine. These are collections of evidence-based, best-practice interventions tailored to manage a particular clinical situation.

“It involves the whole team collaborating to utilize evidence-based components backed by solid research,” Dr. Peroni said. “The bundle must be multifaceted, because it addresses pre-, intra- and postoperative stages. Once implemented, they ensure consistency. And if used regularly, they’ve been shown to reduce surgical site infections.” MeV

The Reading Room

MacDonald DG, Morley PS, Bailey JV, et al. An examination of the occurrence of surgical wound infection following equine orthopaedic surgery (1981-1990). Equine Vet J. 1994;26(4):323-6.
https://beva.onlinelibrary.wiley.com/doi/ abs/10.1111/j.2042-3306.1994.tb04394.x

Borg H, Carmalt JL. Postoperative septic arthritis after elective equine arthroscopy without antimicrobial prophylaxis. Vet Surg. 2013;42(3):262-266. https://onlinelibrary.wiley.com/doi/10.1111/j.1532-950X.2013.01106.x

Stöckle SD, Failing K, Koene M, et al. Postoperative complications in equine elective, clean orthopaedic surgery with/without antibiotic prophylaxis. Tierarztl Prax Ausg G Grosstiere Nutztiere. 2018;46(2):81-86.
https://www.thieme-connect.com/products/ejournals/abstract/10.15653/TPG-170491

Krause DM, Pezzanite LM, Griffenhagen GM, et al. Comparison of equine synovial sepsis rate following intrasynovial injection in ambulatory versus hospital settings. Equine Vet J. 2022;54(3):523-530.
https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.13485