Every month, JBJS publishes a Specialty Update—a review of the most pertinent and impactful studies published in the orthopaedic literature during the previous year in 13 subspecialties. Click here for a collection of all OrthoBuzz Specialty Update summaries.
This month, Arvind Nana, MD, co-author of the July 20, 2016 Specialty Update on musculoskeletal infection, selected the three most compelling discoveries from among the more than 100 studies cited in the Specialty Update, which focused on biofilms.
Dr. Nana and his co-authors provide a concise primer on the biology of biofilms, the network of microorganisms that adhere to implant surfaces and form a complex structure surrounded by a self-generated extracellular polymeric matrix. This matrix not only anchors bacteria to orthopaedic implants, but also provides a nearly impenetrable defense mechanism against the host immune system. Staphylococci are the most common biofilm-forming bacteria found in orthopaedics.
Persister Cells in Biofilms
So-called persister cells have an inherent tolerance to antimicrobial agents. Misconceptions about persisters have permeated the literature. The authors provide clarification about persisters:
- Persister cells CAN be reliably killed when the antimicrobial concentration is high enough. The minimum biofilm eradication concentration (MBEC) is lower when antimicrobial exposure is continuous and prolonged.1
- Decreasing the number of microorganisms with antimicrobial intervention is NOT good enough. Cure requires the total elimination of all viable microbes.
Biofilm in Orthopaedic Trauma
Biofilm formation in the setting of open fractures is concerning because biofilm can develop on bone and in soft tissues in a matter of hours. The assumption is that appropriate surgical techniques for open fractures, including therapeutic antibiotic administration, can decrease bioburden and provide fracture stability, thus modulating the acute, local inflammatory response and minimizing biofilm formation.2 However, current technology does not enable noninvasive quantification of biofilm activity and presence in a stable open fracture following wound closure.
Biofilm in Total Joint Arthroplasty
Traditionally, prosthesis-related biofilm infections in the US have been treated by a 2-stage exchange arthroplasty. Although biofilm from the implant is removed by extraction of the components, the potential exists for persistence of biofilm in the surrounding soft tissues. Most patients treated for periprosthetic joint infections also receive intravenous antibiotics, but a recent in vitro study demonstrated that administering cefazolin even at increased concentrations still resulted in persistent Staphylococcus biofilm on cobalt-chromium, polymethylmethacrylate, and polyethylene,3 which supports the need for explantation.
There is still room to develop novel treatment methods for eradicating biofilm in periprosthetic joint infections. Future novel treatment methods for eradicating implant biofilm will help minimize the morbidity associated with current accepted periprosthetic joint infection treatment options.
- Castaneda P, McLaren A, Tavaziva G, Overstreet D. Biofilm antimicrobial susceptibility increases with antimicrobial exposure time. Clin Orthop Relat Res. 2016 Jan 21.
- Pfeifer R, Darwiche S, Kohut L, Billiar TR, Pape HC. Cumulative effects of bone and soft tissue injury on systemic inflammation: a pilot study. Clin Orthop Relat Res. 2013 Sep;471(9):2815-21.
- Urish KL, DeMuth PW, Kwan BW, Craft DW, Ma D, Haider H, Tuan RS, Wood TK, Davis CM 3rd..Antibiotic-tolerant Staphylococcus aureus biofilm persists on arthroplasty materials. Clin Orthop Relat Res.2016 Feb 1.