STRENGTH RETENTION OF SELF-REINFORCED POLY-L-LACTIDE SCREWS AND PLATES - AN INVIVO AND INVITRO STUDY

Self-reinforced poly-L-lactide (SR-PLLA) screws and multilayer plates were studied for their initial mechanical shear and/or tensile strength and strength retention in vivo and in vitro up to 48 weeks. The plates were studied in vitro up to 68 weeks. The loss of strength was faster in vivo than in vitro. The screws retained more than half of their initial shear strength up to 12 weeks in vivo and over 24 weeks in vitro. By 48 weeks they had lost nearly all of their mechanical strength in both groups. The plates retained over 54% of their initial tensile and 71% of shear strength up to 24 weeks in vivo. The shear strength did not particularly diminish up to 52 weeks of follow-up in vitro whereas the tensile strength was slightly decreased after 36 weeks. After this follow-up time the loss of strength was more rapid and by 68 weeks the shear strength had decreased to 17% and the tensile strength to 0%.