Proposal of a method for evaluating the bone affinity of pedicle screws and considering differences in bone affinity between carbon-fiber-reinforced plastic and titanium alloy pedicle screws

Abstract Bone affinity for materials is important for success of bone implants, including pedicle screws. Therefore, regarding medical devices using new materials, evaluating the biocompatibility and bone affinity for our recently developed posterior internal fixation device is important. Based on preliminary tests and past studies, no generalizable concepts or methods have been established for evaluating bone affinity for screw-shaped medical materials. Therefore, we developed a procedure for simple evaluations by combining implantation with strength tests using various jigs and preparations. We used this procedure for testing both titanium alloy and carbon-fiber-reinforced plastic screws and compared their pull-out strengths. The maximum pull-out strength of carbon-fiber-reinforced plastic and titanium alloy screws were 1298.9 ± 694.6 N and 1314.6 ± 811.0 N (P = 0.97), respectively. In conclusion, we developed a procedure for simple evaluations, which could also be applied to many types of bone screws. Carbon-fiber-reinforced plastic screws showed an affinity for bone and no significant difference with that of titanium alloys under testing conditions. Furthermore, in terms of bone affinity, carbon-fiber-reinforced plastic pedicle screws showed comparable properties to those of the existing products and can be evaluated and used similarly.