Influence of the design for fixation implants on local infection: Experimental study of dynamic compression plates versus point contact fixators in rabbits

Objectives: Comparison of infection resistance after local bacterial challenge associated with two different designs for fixation implants: the conventional dynamic compression plate (DCP) and the point contact fixator (PC-Fix). Design: Randomized prospective study in experimental animals. Grouped sequential experimental procedure. Observation time was twenty-eight days, with twenty animals per group. Setting: Following surgery, animals were kept without restrictions in individual hutches. Animals: Forty White New Zealand rabbits. Thirty-eight animals, nineteen per group, were included in the final evaluation. Intervention: Under sterile conditions, specially manufactured titanium DCP or PC-Fix of identical dimensions were fixed to rabbit tibiae. After wound closure, different concentrations of Staphylococcus aureus, between 2 x 10(4) and 2 x 10(8) colony-forming units (CFU), were inoculated percutaneously at the implant site. Main Outcome Measurements: Implants, underlying bone, and surrounding soft tissues were removed under sterile conditions and quantitatively evaluated for bacterial growth. Infection was defined as positive bacterial growth at the bone-implant interface. Results: The overall infection rate was 45 percent. The infection dose of 50 percent (ID50) was 7.08 X 10(5) CFU for the DCP group and 8.51 X 10(6) CFU for the PC-Fix group. The infection rate was 63 percent (twelve of nineteen animals) for the DCP group and 26 percent (five of nineteen animals) for the PC-Fix group. This difference was statistically significant (p = 0.022). Conclusions: After local bacterial challenge, we found a statistically significant difference in the infection rates depending on the implant design. The higher infection resistance associated with the PC-Fix design seems to be related to the reduced contact area at the bone-implant interface.