Bone bonding ability of a new biodegradable composite for internal fixation of bone fractures

Hydroxyapatite particles and poly(L-lactide) composites for internal fixation of bone fractures have been developed based on the hypothesis that incorporation of hydroxyapatite particles in a poly(L-lactide) matrix might enhance bone bonding. This study evaluated the bone bonding ability of these biodegradable composites. Two types of hydroxyapatite and poly(L-lactide) composite were used in this study: calcined hydroxyapatite/poly(L-lactide) and uncalcined hydroxyapatite/poly(L-lactide). Rectangular plates (2 x 10 x 15 mm) of each composite or poly(L-lactide) were implanted into the metaphysis of the tibiae of 33 male rabbits, and the failure load was measured by conducting a detaching test 8, 16, and 25 weeks after implantation. The failure loads of calcined hydroxyapatite/poly(L-lactide), uncalcined hydroxyapatite/poly(L-lactide), and poly(L-lactide), respectively, were 13.60, 13.95, and 0.46 N at 8 weeks; 29.84, 24.09, and 2.86 N at 16 weeks; and 25.50, 29.67, and 2.43 N at 25 weeks. Histologic observation revealed that the composites formed direct contact with the bone. The results in this study indicate that the composites improved the strength of the interface between bone and plate. This improved interfacial strength lead to a substantial decrease in the frequency of implant loosening in the treatment of fractured bones by internal fixation.