Sunday, June 10, 2018

The limited effectiveness of Vancomycin-containing spacers in treating periprosthetic infections

Vancomycin-Loaded Polymethylmethacrylate Spacers Fail to Eradicate Periprosthetic Joint Infection in a Clinically Representative Mouse Model

These authors developed a murine model of the first-stage surgery of a 2-stage revision for periprosthetic joint infection involving a 3-dimensionally printed Ti-6Al-4V tibial implant

 infected with Staphylococcus aureus and treated 2 weeks later with irrigation and debridement of the leg with revision of the implant to an articulating vancomycin-loaded PMMA spacer.
Postoperatively, mice underwent radiography and serum inflammatory-marker measurements. Following euthanasia of the mice at 6 weeks, bone and soft tissues were homogenized to quantify bacteria within periprosthetic tissues. Implants and articulating spacers were either sonicated to quantify adherent bacteria or examined under scanning electron microscopy (SEM) to characterize the biofilm.

They found that vancomycin-loaded PMMA spacers eluted vancomycin for 6 days with retained antimicrobial activity.

Control mice had elevated levels of inflammatory markers, radiographic evidence of septic loosening of the implant, and osseous destruction. Mice treated with the vancomycin-loaded PMMA spacer had significantly lower levels of inflammatory markers (p < 0.01), preserved tibial bone, and no intra-articular purulence. 

Retrieved vancomycin-loaded spacers exhibited significantly lower bacterial counts compared with implants (p < 0.001). SEM identified S. aureus encased within biofilm on control implants,
while vancomycin-loaded spacers contained no bacteria.

However, bacterial counts in periprosthetic tissue did not significantly differ between the groups.

The results suggest that the antimicrobial effects of PMMA spacers are tightly confined to the articular space and must be utilized in conjunction with thorough tissue debridement and systemic antibiotics to manage bacteria in the surrounding tissue.

Comment: This article once again demonstrates the remarkable propensity of titanium to enable biofilm formation. It also shows the effectiveness of Vancomycin spacers to resist biofilm formation and to help manage bacteria in the joint. However, it points to the relative ineffectiveness of spacers in managing infection in the tissues surrounding the joint. While they advocate "thorough tissue debridement," it is not always easy to discern what tissue needs to be debrided during surgical management of a periprosthetic infection. Hopefully a combination of debridement and systemic antibiotics will prove effective in managing bacteria in the tissues surrounding an infected prosthesis.

Interested readers may want to read these related posts:

Quantification of Peri-Implant Bacterial Load and in Vivo Biofilm Formation in an Innovative, Clinically Representative Mouse Model of Periprosthetic Joint Infection

Delayed Propionibacterium acnes surgical site infections occur only in the presence of an implant.

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