Fixation properties of a biodegradable "free-form" osteosynthesis plate with screws with cut-off screw heads: biomechanical evaluation over 26 weeks.

OBJECTIVE: The aim of this study was to compare the postoperative fixation properties of a biodegradable osteosynthesis "free-form" plate achieved with countersunk screws with those provided by screws with cut-off screw heads. STUDY DESIGN: Acrylic pipes were fixed together to simulate fracture fixation for tensile testing. Additional plates were fixed to a polyurethane block with a single screw for plate-screw pullout testing. Specimens were incubated in phosphate buffer solution at 37 degrees C, and testing was conducted at various time points during hydrolytic degradation of 26 weeks. In both tests the specimens were loaded at a speed of 5 mm/min until failure. The yield load, maximum load, and stiffness were recorded, and failure mode was visually determined. RESULTS: Both countersunk screws and screws with cut-off screw heads provided similar plate fixation properties over degradation time. CONCLUSION: According to these results, fixation of the biodegradable osteosynthesis free-form plate with screws with cut-off screw heads seems to be feasible.