Disinfection of contaminated metal implants with an Er:YAG laser

Abstract

Infections related to orthopedic procedures are considered particularly severe when implantation materials are used, because effective treatments for biofilm removal are lacking. In this study, the relatively new approach for infection control by using an erbium:yttrium-aluminum-garnet (Er:YAG) laser was tested. This laser vaporizes all water containing cells in a very effective, precise, and predictable manner and results in only minimal thermal damage. For preliminary testing, 42 steel plates and 42 pins were seeded with mixed cultures. First, the minimally necessary laser energy for biofilm removal was determined. Subsequently, the effectiveness of biofilm removal with the Er:YAG laser and the cleansing of the metal implants with octenidine-soaked gauze was compared. Then, we compared the effectiveness of biofilm removal on 207 steel pins from 41 patients directly after explantation. Sonication and scanning electron microscopy were used for analysis. Laser fluences exceeding 2.8 J/cm² caused a complete extinction of all living cells by a single-laser impulse. Cleansing with octenidine-soaked gauze and irradiation with the Er:YAG laser are both thoroughly effective when applied to seeded pins. In contrast, when explanted pins with fully developed biofilms were analyzed, we found a significant advantage of the laser procedure. The Er:YAG laser offers a secure, complete, and nontoxic eradication of all kinds of pathogens from metal implants without damaging the implant and without the possible development of resistance. The precise noncontact removal of adjacent tissue is a decisive advantage over conventional disinfectants. Therefore, laser irradiation could become a valuable method in every debridement, antibiotics, and implant retention procedure.

Keywords: Er:YAG laser; biofilm removal, DAIR; implant-related infection; laser disinfection; pin-tract infection.

Figure 1

Treatment of the extracted pins. A and B, Wiping with sterile gauze saturated with octenidine and exposed to the germicide for the appropriate minimum contact time of 3 minutes. C and D, Irradiation with the laser. The red spot serves as the guiding beam for the otherwise invisible infrared Er:YAG laser beam. Er:YAG, erbium:yttrium aluminum garnet [Color figure can be viewed at wileyonlinelibrary.com]

Figure 2

In vitro‐grown biofilm on steel plates. A, Macroscopic view of a crystal violet stained biofilm. B, Overview and C, detail SEM images showing several large yeast cells with bacteria in between. SEM, scanning electron microscopy [Color figure can be viewed at wileyonlinelibrary.com]

Figure 3

Determination of the minimally necessary laser energy for biofilm removal. Scanning electron micrographs of a cultivated metal plate after a single Er:YAG laser impulse show the discernible laser spots of 3 mm. Higher magnification reveals the complete removal of biofilm with 2 J. The very right images show the transition of the untreated biofilm and the lasered spot. A narrow transition area of homogenous residual material is found only in the periphery of the beam. Er:YAG, erbium:yttrium aluminum garnet

Figure 4

Comparison of the mean reduction in microbial contamination following different disinfection procedures in an in vitro model using cocultures. Median microbial colonization of in vitro‐cultivated pins (n = 42) after treatment. Whiskers indicate the 95% confidence intervals. Er:YAG, erbium:yttrium aluminum garnet

Figure 5

Temperature increase of steel pins after complete circumferential laser irradiation with 1.6 J. Pins of different diameter were analyzed at increasing laser frequencies [Color figure can be viewed at wileyonlinelibrary.com]

Figure 6

Titanium plates used for SEM examination were irradiated with the Er:YAG laser at two different power settings (22.8 J/cm²: middle third; 203 J/cm²: right third) or left untreated as control (left third). During the annealing process, no material is taken away, but a color change occurs through heating up the metal when high energy is used (right third). Despite this macroscopically visible change of color, neither SEM examination revealed a structural alteration of the titanium surface nor microbiology showed an altered bacterial opsonisation to the annealed surface. Er:YAG, erbium:yttrium aluminum garnet; SEM, scanning electron microscopy [Color figure can be viewed at wileyonlinelibrary.com]

Figure 7

Scanning electron micrograph of an extracted pin after linear unidirectional irradiation with the Er:YAG laser. A, Overview picture with the trace of the laser beam horizontally in the middle. B, Two circular Er:YAG laser spots lying next to each other with sharp borders towards the adherent biofilm (magnification: ×150). C, High‐magnification view of biofilm noted in (B) (magnification: ×10 000). D, High‐magnification view of the laser irradiated area noted in (B) (magnification: ×10 000). Er:YAG, erbium:yttrium aluminum garnet

Figure 8

We found sporadic remnants of bacterial biofilms or debris in samples of the octenidine group