[Adaptation of the viscoelastic behavior of bone cement to bone as a stabilizing factor in endoprostheses]

Incompatibility of viscoelastic properties is a major factor contributing to the development and enlargement of microscopic cracks between bone and bone cement. In the study reported here the viscoelastic characteristics of fresh long bones were studied in vitro and compared with those of bone cement. Using strain gauges, creep elongation was measured over time spans ranging from 10(-2) to 10(3) seconds with an applied stress of 10 MPa. On the basis of these measurements creep compliance and permanent elongation at two points on a sheep femur were calculated by means of a rheologic Kelvin model with three parameters. The possibility of obtaining an optimal bone/cement bond was studied in the light of these results and of data published in the literature on bone cement creep related to cement composition factors.