Other factors may be more significant
A study aiming to pinpoint the optimal timing of antibiotic administration to prevent surgical site infections (SSIs) following foot and ankle surgery found that timing of intravenous prophylaxis does not appear to significantly affect the risk of SSI. Results demonstrated that host factors and duration of surgery appear to play a much larger role in SSI incidence.

SSIs "can prove troublesome outcomes for both patients and providers," wrote the authors of the study, presented by Direk Tantigate, MD, of Columbia University Medical Center, at the 2016 American Orthopaedic Foot & Ankle Society annual meeting. Moreover, "SSI has been hailed by nonphysicians as something that should be a 'never-event.'"

Prior studies reported that optimal timing for antibiotic administration ranges from 15 minutes prior to incision in certain procedures to as high as 60 minutes prior to incision in general orthopaedic procedures. However, the authors noted, "the correlation between SSI occurrence and the timing of antibiotic administration in foot and ankle surgery and other orthopaedic subspecialties remains unclear."

Conducting the study
In this retrospective review of 1,933 foot and ankle procedures in 1,632 patients over 4 years, researchers recorded the following data:

• patient demographics
• type, amount, and timing of antibiotic administration
• incision and closure time

In addition, the investigators documented subsequent wound infection and incision and drainage procedure (I&D) within 30 days and 90 days. Outcomes and demographic variables were compared between procedures in which antibiotics were administered less than 15 minutes prior to incision and between 15 to 60 minutes prior to incision.

A total of 1,569 procedures met inclusion criteria. There were 17 cases (1.1 percent) of subsequent wound infection, of which 6 required a subsequent I&D within 30 days. In 63 additional cases (4 percent), wound complications occurred that did not meet SSI criteria.

The researchers found a significant 2.8-fold higher rate of SSIs when antibiotics were administered between 15 and 60 minutes prior to incision (P < 0.05). When comparing SSI and non-SSI groups, the only significant independent predictors were longer surgeries and non-ambulatory surgeries (both P < 0.05). Stepwise multivariate logistic regression analysis demonstrated that 91.8 percent of the risk of an SSI could be predicted by American Society of Anesthesiologists score and length of surgery alone.

In reference to the 4 percent of patients in the study who had wound complications—including mild erythema, swelling, and superficial wound dehiscence—that did not meet the criteria of a clear infection, the authors noted that many of these were treated with a short course of oral antibiotics. "However," they wrote, "it is ultimately not clear whether these patients actually had an infection or not." Therefore, they continued, "If we used the most liberal definition of SSI and counted all of those cases as infections (although many of them most certainly were not), the incidence of SSI in this study is 5 percent, which is comparable to the mean incidence of previous studies."

Drawing conclusions
The authors initiated this study "somewhat in response to the idea that optimal timing of antibiotic administration is between 15 and 60 minutes prior to incision." In foot and ankle surgery, they noted, "there is generally less set-up time than there is in other orthopaedic surgeries, most notably in hip/knee and spine procedures," where "much of the work in quality has focused." However, the authors reported that in their experience, most foot and ankle patients had historically received antibiotics less than 15 minutes prior to incision without any untoward sequelae or high infection rate. The results they presented do "corroborate that theory."

Overall, the authors asserted, "This work does not indicate an optimal timing of antibiotic administration, and we cannot conclude that administration of antibiotics less than 15 minutes prior to incision is better than 15 to 60 minutes prior to incision." Rather, they said, "This study illustrates that there are other variables that are much more relevant and affect the risk of infection to a much greater degree. However, many of those variables are not modifiable. It is certainly a worthwhile goal to attempt to identify the most appropriate timing of antibiotic administration for different surgical patients. However, performing this type of study would require a large database of patients and almost certainly a multicenter or even national effort."

Although Dr. Tantigate noted that the results of the study do not indicate an optimal timing for antibiotic administration in the set of patients included, "the authors still feel that standardization is a laudable and frankly necessary goal." The authors observed: "Indeed, decreasing variability and developing standards are perhaps one of the most direct ways to lead change toward better safety and ultimately better quality. As before, much of the work that has been done in this arena has focused on hip/knee replacement and spine procedures, which may or may not be as relevant to foot and ankle procedures, and this distinction likely merits further exploration. Furthermore, this work serves to highlight the absolute necessity of risk stratification, as the sicker patients with more complex procedures seem to be at greater risk for SSI."

Dr. Tantigate's coauthors are Eugene Jang, MD; Mani Seetharaman, MD; Peter C. Noback, BA; A. M. Heijne, BA; Justin K. Greisberg, MD; and J. Turner Vasseller, MD.

The authors' disclosure information can be accessed at www.aaos.org/disclosure

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org

Bottom Line

• Optimal timing of antibiotic prophylaxis for SSI after foot and ankle surgery remains unclear.
• This study reviewed 1,933 foot and ankle procedures in 1,632 patients documenting wound infection and incision and drainage procedure within 30 and 90 days, comparing timing of antibiotic administration less than 15 minutes prior to incision versus 15 to 60 minutes prior to incision.
• Late administration of ABx (within 15 minutes of incision) was not associated with a higher infection rate. Surprisingly, these patients were found to have a statistically significant, 2.5x, lower rate of infections. Even this difference was overwhelmed by host factors and the duration of surgery.
• The results support the importance of risk stratification, as sicker patients with more complex procedures seem to be at greater risk for SSI.