Negative pressure wound therapy augmented with silver dressings decreases infection, study finds

Issue: November 2011

Daniel J. Stinner

The use of silver-impregnated dressings with negative pressure wound therapy for treatment of Staphylococcus aureus in an open fracture model significantly reduced the bacteria levels compared to standard negative pressure wound therapy alone, according to a study recently published in the Journal of Trauma.

“Just having the silver dressing actually blunted the increase in S. aureus that we normally see between debridements,” study investigator Daniel J. Stinner, MD, told Orthopedics Today. “Even after only 48 hours after the first debridement and irrigation, the addition of the silver dressing significantly reduced the bacteria when compared to standard negative pressure wound therapy,” Stinner said, adding that the silver dressing demonstrated a continual reduction of the S. aureus for the entire 6 days of the study. The silver decreased the amount of S. aureus by a factor of five compared to the control group.

Sharp decline in bacteria

For their study, Stinner and colleagues created complex fractures in the proximal legs of 13 goats and contaminated the wounds with either Pseudomonas aeruginosa or S. aureus. The bacteria were genetically modified to emit photons, giving the cells a bioluminescence that could be tracked with a photon-counting camera system.

The team debrided the wounds every 48 hours for 6 days. An Acticoat 7 dressing (Smith & Nephew; United Kingdom) containing silver was then applied to the wounds of each animal in the experimental group in combination with negative pressure wound therapy (NPWT). Imaging to quantify the bacteria was done before and after debridement. The investigators compared their results with those of a control group from a previous study that included 16 goats treated with NPWT alone.

A complex musculoskeletal wound (left) 6 hours after injury and contamination with bioluminescent bacteria is shown. There is minimal bacteria remaining within the wound after 6 days of treatment (right) using subsequent debridement and irrigations with negative pressure wound therapy augmented with silver dressings every 48 hours.

Image: Stinner DJ

They discovered that before each of the consecutive debridements there was less S. aureus in the experimental group compared to the control group. For the P. aeruginosa wounds, the investigators found a 50% decrease in the amount of bacteria in the silver dressing treated group at each subsequent time point. However, Stinner noted that this decrease was not statistically significant and may have been due to “the limitation of the numbers in the study.” He added, “However, with Staph aureus, there was a significant decrease.”

At the end of the study, P. aeruginosa wounds treated with silver dressings had 21% of the baseline bacterial load compared to 43% in the control group. Using S. aureus, the silver group contained 25% of the baseline bacterial load compared to 115% in the control group.

Augmented NPWT

Stinner said that his team chose to study silver because of its known bactericidal ability that works by the oligodynamic effect, he said in an interview. Joseph C. Wenke, PhD, co-author of the study, said that such an effect has never been proven to be effective in an orthopedic clinical trial.

“Silver is known to be able to kill both bacteria and eukaryotic (host) cells, but there is little to no evidence to support its use in traumatic orthopedic wounds,” Wenke told Orthopedics Today. “The goal for this study was to provide some evidence to support or dispute the use of silver. Because of the difficulty and expense to address this topic in a prospective clinical trial, this study, which uses a large complex musculoskeletal model, may be the most compelling data available for quite some time.”

The team plans to further research other adjunctive therapies to complement the existing standard of care.

“Our overarching goal is to work with companies and academic partners to develop a local treatment that will eradicate infection; we believe that a local treatment will have to be compatible with negative pressure wound therapy to be used fully by the surgical community,” Wenke said. – by Jeff Craven

Reference:

Stinner DJ, Waterman SM, Masini BD, Wenke JC. Silver dressings augment the ability of negative pressure wound therapy to reduce bacteria in a contaminated open-fracture model. J Trauma. 2011; 71:147-150.

Daniel J. Stinner, MD, can be reached at the Brook Army Medical Center, Fort Sam, Houston, TX; 210-916-4113; email: daniel.stinner@amedd.army.mil.

Joseph C. Wenke, PhD, can be reached at the Institute of Surgical Research, 3698 Chambers Pass, Fort Sam, Houston, TX; 210-539-9426; email: joseph.wenke@us.army.mil.

Disclosure: Stinner and Wenke were loaned devices for the study from Smith & Nephew.