The purpose of this study was to acquire information about the effect of an antibacterial and biodegradable
poly-L-lactide (PLLA) coated
titanium plate osteosynthesis on local
infection resistance. For our in vitro and in vivo experiments, we used six-hole AO DC minifragment
titanium plates. The implants were coated with biodegradable, semiamorphous PLLA (coating about 30 microm thick). This acted as a carrier substance to which either
antibiotics or
antiseptics were added. The
antibiotic we applied was a combination of
Rifampicin and
fusidic acid; the
antiseptic was a combination of Octenidin and
Irgasan. This produced the following groups: Group I: six-hole AO DC minifragment
titanium plate without PLLA; Group II: six-hole AO DC minifragment
titanium plate with PLLA without
antibiotics/
antiseptics; Group III: six-hole AO DC minifragment
titanium plate with PLLA + 3%
Rifampicin and 7%
fusidic acid; Group IV: six-hole AO DC minifragment
titanium plate with PLLA + 2% Octenidin and 8%
Irgasan. In vitro, we investigated the degradation and the release of the PLLA coating over a period of 6 weeks, the bactericidal efficacy of
antibiotics/
antiseptics after their release from the coating and the bacterial adhesion of Staphylococcus aureus to the implants. In vivo, we compared the
infection rates in white New Zealand rabbits after
titanium plate osteosynthesis of the tibia with or without antibacterial coating after local percutaneous bacterial inoculations at different concentrations (2 x 10(5)-2 x 10(8)): The plate, the contaminated soft tissues and the underlying bone were removed under sterile conditions after 28 days and quantitatively evaluated for bacterial growth. A stepwise experimental design with an "up-and-down" dosage technique was used to adjust the bacterial challenge in the area of the ID50 (50%
infection dose). Statistical evaluation of the differences between the
infection rates of both groups was performed using the two-sided Fisher exact test (p < 0.05). Over a period of 6 weeks, a continuous degradation of the PLLA coating of 13%, on average, was seen in vitro in
0.9% NaCl solution. The elution tests on
titanium implants with
antibiotic or
antiseptic coatings produced average release values of 60% of the incorporated
antibiotic or 62% of the incorporated
antiseptic within the first 60 min. This was followed by a much slower, but nevertheless continuous, release of the incorporated
antibiotic and
antiseptic over days and weeks. At the end of the test period of 42 days, 20% of the incorporated
antibiotic and 15% of the incorporated
antiseptic had not yet been released from the coating. The antibacterial effect of the
antibiotic/
antiseptic is not lost by integrating it into the PLLA coating. The overall
infection rate in the in vivo investigation was 50%. For Groups I and II the
infection rate was both 83% (10 of 12 animals). In Groups III and IV with antibacterial coating, the
infection rate was both 17% (2 of 12 animals). The ID50 in the antibacterial coated Groups III and IV was recorded as 1 x 10(8) CFU, whereas the ID50 values in the Groups I and II without antibacterial coating were a hundred times lower at 1 x 10(6) CFU, respectively. The difference between the groups with and without antibacterial coating was statistically significant (p = 0.033). Using an antibacterial biodegradable PLLA coating on
titanium plates, a significant reduction of
infection rate in an in vitro and in vivo investigation could be demonstrated. For the first time, to our knowledge, we were able to show, under standardized and reproducible conditions, that an
antiseptic coating leads to the same reduction in
infection rate as an
antibiotic coating. Taking the problem of
antibiotic-induced bacterial resistance into consideration, we thus regard the
antiseptic coating, which shows the same level of effectiveness, as advantageous.