| Gradual screw loosening is a well-known failure mechanism in internal fixation. Loosening is primarily due to gradual bone loss caused by stress shielding, a phenomenon in which a disproportionate amount of load within the screw-bone construct is absorbed by a medical device. Magnesium's similar elastic modulus to bone, presents the potential for alleviating screw loosening by allowing optimum stress to be transferred between screw and bone and in turn supporting bone remodeling around the screw. In this study, performance of magnesium screw was studied by: (1) estimating the changes in young's modulus distribution cancellous bone around a magnesium rod, implanted in the femoral condyle of test rabbits and (2) applying a modified stress transfer parameter from a previous study to calculate the effect of screw thread geometry on stress transfer using a 2-D finite element model. Results showed an average increase of 19% in the young's modulus of cancellous bone around the magnesium screw from 4 to 6-weeks post-implantation, while also showing highest stress transfer in trapezoidal-shaped magnesium screw thread. In accordance, this study corroborates the potential for magnesium as an ultimate screw material to eliminate progressive screw loosening. |
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