gms | German Medical Science

Objectives: Infections after internal fixation of fractures remain a challenge. Antimicrobial coating of fractures fixation devices offers the possibility of improved infection prophylaxis. However, prior to clinical implementation, coated devices should be known to display good biocompatibility without negatively influencing fracture healing. Silver is known for its excellent antimicrobial activity, including activity against multiresistant strains. The silver technology used here has previously shown its antimicrobial efficacy in vitro. The aim of the current study was to analyze the biocompatibility and potential influence on the fracture healing process of this silver-coating technology for locking plates compared to silver-free locking plates in a rabbit model.

Methods: The implants used in this study were 7-hole titanium locking plates, and plasma electrolytic oxidation (PEO) silver coated equivalents. A total of 24 rabbits were used in this study (12 coated, 12 non-coated). An osteotomy of the midshaft of the humerus was created with an oscillating saw and the humerus stabilized with the 7 hole locking plates with a total of 6 screws. Radiographs were taken on day 0, week 2, 4, 6, 8, and 10 for continuous radiographical evaluation of the fracture healing. All animals were euthanized after 10 weeks and further assessment was performed using X-rays, micro-CT, non-destructive four-point bending biomechanical testing and histology. Furthermore, silver concentration was measured in the kidney, liver, spleen and brain.

Results and conclusion: Radiographs showed normal undisturbed healing of the osteotomy in all animals without any differences between the two groups over the entire observation period (Figure 1). Callus formation was observed up to week 4 to 5 followed by callus remodeling after 6 weeks indicating physiological fracture healing pattern in both the silver and in the silver free group. Micro CT analysis revealed overall tissue (callus and cortical bone) volume as well as tissue density to be comparable between the two groups. Mechanical testing showed comparable stiffness with an average stiffness relative to contralateral bones of 75.7 ± 16.1% in the silver free control group compared to 69.7 ± 18.5% (p-value: 0.46). Histology showed no remarkable difference in the analysis of the healed osteotomy gap or in the surrounding soft tissue area. Silver content in the analysed organs was found to be close to baseline values without differences between the two groups.

This study shows that the presented antimicrobial silver surface modification for locking plates has a good biocompatibility without any negative influence on the fracture healing processes compared to the silver free control group. This allows for further clinical investigation of this silver technology for locking plates in fracture patients with an elevated infection risk, e.g. in patients with open fractures.