SLR - December 2016 - Marcus Richardson

Percutaneous External Fixator Pins with Bactericidal Micron-Thin sol-gel Films for the Prevention of Pin Tract Infection

Reference: Qu H, Knabe C, Radin S, Garino J, Ducheyne P. Percutaneous External Fixator Pins with Bactericidal Micron-Thin sol-gel Films for the Prevention of Pin Tract Infection. Biomaterials 2015 Sep; 62: 95–105

Reviewed By: Marcus Richardson, DPM
Residency Program: Grant Medical Center

Podiatric Relevance: Infections from external fixators are common and can be very difficult to treat. Deep infections rates are reported as high as 16 percent. Treatment is challenging and often involves prolonged course of IV antibiotics or removal of the external fixation pins with surgical debridement. Current approaches to reduce pin tract infections mainly entail daily pin dressing changes, which have proven mostly ineffective with no gold standard. This study investigates the use of coating rods with micron-thin sol-gel (MTSG) impregnated with antimicrobial agents and the reduction of infection rates.

Methods: This study was composed of in vitro and in vivo components, which were divided into four parts. The first experiment tested the release kinematics of MTSG triclosan-coated rods. This was performed by placing coated rods in a solution of 50 percent ethanol and PBS (pH 7.4) at 37 degrees to mimic physiological conditions for eight weeks. The aim of this experiment was to test how long the triclosan agent would remain on the rod and how much would be released into surrounding tissue. The concentration of triclosan was monitored at weekly intervals with spectrophotometrically for a period of eight weeks. The second components tested the bactericidal effects of the MTSG coated rods with triclosan. This was performed by incubating coated rods with staphylococcus aureus and monitoring bacterial growth, which was compared to noncoated controls. The third portion tested the clinical effectiveness of sol-gel triclosan-coated rods in preventing infection in an animal models. This was performed by placing percutaneous pins in the tibia of 34 rabbits. The aim of this study was to test clinical effectiveness of sol gel triclosan in preventing infection in animal models. The pins were inoculated with staphylococcus aureus at the pin insertion site. The pin sites were monitored for clinical and radiological signs of infection. The final part of the study tested the down growth of epithelium and bacteria at the pin sites. The hypothesis was that rods coated with MTSG would have less down growth, which would result in fewer infections and quicker healing times. This was performed by histologically analyzing the rabbits' soft tissue with 2 cm margins from the pin site. The rabbits were evaluated at weeks one, two and four. Histological analysis was performed to determine the epithelium down growth or “pocket depth” around the pin insertion site as well as bacterial down growth.

Results: Part 1: The release kinetics of the triclosan revealed that by the end of the eight-week study, 33 percent of the triclosan was released into the median. Statistical analysis revealed that the triclosan would continue to be released for more than 90 days.

Part 2: The antimicrobial activity of sol-gel triclosan coating showed a reduction in the number of bacteria. The control group grew 108 while the MTSG group displayed three to five orders of magnitude fewer bacterial growth even at the end of the four-week study.  

Part 3: Clinically, the rabbits with triclosan-coated rods had no clinical or radiographic signs of infection, as compared to the control group that had greater than 75 percent infection rates. 

Part 4: The coated group displayed significantly less epithelial down growth at .5 cm compared to that of the non-coated control group, which was almost 5 cm at the end of the four-week study.

Conclusions: The use of micron-thin sol-gel impregnated with antimicrobial agents shows promise in reducing the infection rates of external fixator pins. MTSG with triclosan displayed a steady release for a period of greater than eight weeks. It had statistically significant reduction in the amount bacteria and had no clinical infection in animal models with less down growth of epithelium and bacteria.  While more research is still needed, new technologies, such as impregnated MTSG, could be the future of external fixation. 

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