Low-dose chlorhexidine found to be harmless for contaminated osteochondral allografts

The disinfectant chlorhexidine gluconate was found not to cause significant cell death up to 7 days when used in a low concentration to treat osteochondral allografts, according to a study presented at the 2011 Annual Meeting of the American Academy of Orthopaedic Surgeons.

A few years ago, an osteochondral allograft for transplantation was inadvertently contaminated by co-author Brian J. Cole, MD, MBA, section head of the Rush Cartilage Restoration Center at Rush University Medical Center in Chicago. “Fortunately, in this case we were able to remove a second plug from the graft with no untoward effects to the patient,” Cole said. “However, one could easily construe a clinical scenario where there may not be enough graft for a second plug.”

Cole and his colleagues contemplated what they could do to a contaminated graft that would likely render it sterile in the operating room without compromising chondrocyte viability and metabolic activity.

Multiple plugs

The study used multiple plugs from each of five donor femoral condyles rejected by the tissue bank due to potential contamination. The grafts were treated in one of four concentrations of chlorhexidine gluconate: 0.002%, 0.01%, 0.05% and 0.25%. Afterwards, the grafts were washed with 1 L of saline lavage.

Brian J. Cole

Grafts were then cultured using standard culture techniques (in media containing 10% fetal-bovine-serum and antibiotics) for 0, 1, 2 and 7 days. Cell viability was analyzed with LIVE/DEAD assays that use fluorescent dyes to distinguish between living and dead cells.

“We found that any concentration of chlorhexidine exceeding 0.002% compromised cell viability within 1 to 2 days after exposure,” Cole told Orthopedics Today. “This is in contrast to 0.002% concentration, which did not cause cell death, even upwards of 7 days of evaluation.” The authors believe a short exposure to the low-dose concentration of chlorhexidine may not only protect allograft from bacterial contamination, but will also provide a non-compromising cell effect.

Increased concentrations

Controls and the 0.002% chlorhexidine demonstrated similar cell viability, which ranged between 67% and 81% at all tested time points. However, with increased concentration — 0.01% chlorhexidine — cell viability was reduced by twofold already at day 2 post-treatment in comparison to the untreated control group and remained at that level until day 7 in culture. The 0.05% and 0.25% chlorhexidine groups attained a twofold reduction in cell viability even earlier, at day 1 after treatment.

At day 7, cell viability was reduced fourfold for 0.05% chlorhexidine and six-fold for 0.25% chlorhexidine.

Cole said currently there are no secondary sterilization techniques for osteochondral allograft tissue because all tissue is harvested in an aseptic environment. “In some tissue banks, more than 50% of the grafts are lost, due to inadvertent contamination,” he said. “At this point, the demand exceeds the supply of these grafts.”

Despite the literature showing that 0.05% chlorhexidine gluconate is antimicrobial, the authors are in the early stage of a follow-up study that duplicates the model to evaluate the antimicrobial properties of a lower concentration of chlorhexidine gluconate on the grafts after exposing them to typical OR organisms such as staph, strep, spore-forming agents and other common aerobes and anaerobes. “We want to ensure that the solution is antimicrobial in that clinically relevant setting,” Cole said. “Without this initial study, we wouldn’t know what concentration to assess.”

Saving viable tissue

If the low-dose concentration proves antimicrobial for common organisms, it is possible tissue banks could salvage a greater percentage of their osteochondral allograft tissue, “so that more patients can be positively affected,” Cole said. “We also need to do a more thorough analysis of the metabolic activity of these grafts, not just living and dead cells, in response to treatment with chlorhexidine.”

Furthermore, the long-term effect of the exposure to chlorhexidine on cell survival and activity “has to be proven in order to ensure that the public can safely undergo allograft transplantation,” Cole said.

Study results were presented at the AAOS annual meeting by co-author Robert C. Grumet, MD, an orthopedic surgeon at the Orthopaedic Specialty Institute, in Orange, Calif. – by Bob Kronemyer

Reference:

• Campbell J, Filardo G, Bajaj S, et al. Salvage of contaminated osteochondral allografts: chlorhexidine effects on human articular cartilage. Paper 208. Presented at the 2011 Annual Meeting of the American Academy of Orthopaedic Surgeons. Feb. 15-19. San Diego.

• Brian J. Cole, MD, MBA, can be reached at the Rush Cartilage Restoration Center, Rush University Medical Center, 1725 W. Harrison St., #1063, Chicago, IL 60612: 312-243-4244; e-mail: bcole@rushortho.com.
• Disclosure: Cole has no relevant financial disclosures