Resorbable polymeric inserts as a means of enhancing fixation of fractures of porotic bones : I. Stability of mechanical properties and viscoelasticity of the inserts aged in vitro

A titanium screw-poly(image-lactide) medullary insert system intended for use in the fixation of porotic bone fractures was subjected to in vitro ageing at 37 °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 months of ageing, indicating that the polymeric insert provides a good purchase for the screws. The viscoelastic properties of the inserts at 37 °C resembled those of bone and did not change substantially with temperatures up to 52 °C. This indicates that the medullary insert would maintain its properties in vivo even if the body temperature was increased. The molecular weight of the insert at 6 months was reduced by 60%, but the molecular weight reduction did not affect the mechanical properties of the insert.