RESORBABLE POLYMERIC INSERTS AS A MEANS OF ENHANCING FIXATION OF FRACTURES OF POROTIC BONES .1. STABILITY OF MECHANICAL-PROPERTIES AND VISCOELASTICITY OF THE INSERTS AGED IN-VITRO

A titanium screw-poly(L-lactide) medullary insert system intended for use in the fixation of porotic bone fractures was subjected to in vitr o ageing at 37 degrees C and pH = 7.4 for up to 6 months. The pull-out force of the screw from the insert and the viscoelastic properties of the insert were measured. The pull-out force did not change up to 6 m onths of ageing, indicating that the polymeric insert provides a good purchase for the screws. The viscoelastic properties of the inserts at 37 degrees C resembled those of bone and did not change substantially with temperatures up to 52 degrees C. This indicates that the medulla ry insert would maintain its properties in vivo even if the body tempe rature was increased. The molecular weight of the insert at 6 months w as reduced by 60%, but the molecular weight reduction did not affect t he mechanical properties of the insert. (C) 1997 Elsevier Science Limi ted. All rights reserved.