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The purpose of this study was to evaluate the efficacy of titanium dioxide photocatalyst in inhibition of bacterial colonization on percutaneous implants. Titanium dioxide photocatalyst was prepared by direct oxidization of pure titanium substrate, and a comparative study with pure titanium was performed. The bactericidal ability of the photocatalyst was examined using methicillin-resistant Staphylococcus aureus (MRSA) suspensions in a colony-forming assay according to the Japanese Industrial Standards committee standard. After exposing the MRSA suspension on sample plates to ultraviolet A (UVA) light, the number of surviving bacteria was estimated. Next, an animal model for inhibition of colonization was examined in vivo. Pins were inserted into the femurs of rabbits, were infected with 10(8) colony-forming units of MRSA suspension, and were illuminated with UVA light for 60 min daily; the number of colonizing bacteria was estimated after 7 days. The bactericidal ability of the photocatalyst was apparent after 60 min, when the bacteria had almost disappeared. The number of colonizing bacteria on photocatalytic pins was decreased significantly in vivo. The photocatalyst was effective even against resistant bacterial colonization. Clinically, the incidence of percutaneous implant infection such as pin tract infection in external fixation could be reduced using the titanium photocatalyst.

Background and purposeEvaluation of distraction callus is important for determination of the optimal time for removal of external fixation. We attempted to determine whether there might be a relationship between the electrical impedance of bone and callus maturation, with a view to using impedance as a way of knowing when to remove a fixator.MethodsWe applied an external lengthener to the right tibia of 24 rabbits and performed distraction at 1 mm/day for 10 days. Radiographs were taken and measurement of overall impedance between fixation pins was performed weekly after distraction. At weeks 2, 4, 6, and 8 after distraction (n = 6 each), resistivity of the bone to electrical conductivity was measured before killing. Cross-sectional area of the conduction pathway in callus and maximum bending stress were measured after excision of the tibia.ResultsThe overall impedance increased statistically significantly from 1 to 6 weeks after completion of distraction. The resistivity of bone decreased over 4 weeks and the cross-sectional area of callus decreased significantly over 6 weeks, while the maximum bending stress increased significantly over the same time. We observed a negative correlation between the cross-sectional area of callus and maximum bending stress.InterpretationThe impedance values, which are related to changes in electrical conductivity and the conduction pathway, increased due to the changes in the cross-sectional area of callus, despite the reduction in bone resistivity. Since the cross-sectional area of callus was correlated with maximum bending stress and the impedance values increased with the callus-remodeling process, we suggest that temporal increases in overall impedance reflect callus maturation.

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