Biomedical Engineering – From Theory to Applications

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Biomedical Engineering – From Theory to Applications
displacements diagrams for bone, for plate modules and for staples, for each of the three
process steps are obtained.
Step 1. The upper and lower plates are fixed with screws on the bone. It simulates the
mounting of head off for holding elements on the fixed plates on the bone, the
holding elements having the other head already mounted in the middle plates
(common nodes). The temperature of all the elements and of the holding elements
is 23 0 C. Resultant displacements in plate modules and resultant displacements in
femur bone are presented.
Step 2. The ends of the nitinol elements are considered mounted in plates, considering the
pretension of step 1, eliminating imposed movements, and realizing the state of
tension for mounting the implant.
Step 3. Starting from the final state of tension obtained in step 2 we are simulating the
increase of temperature for holding elements from room temperature to body
temperature 36.5 0 C. Resultant displacements in plate modules, Von Mises stress in
Nitinol staples and resultant displacements in femur bone are presented.
The use of nitinol elements makes contact pressure between the two bone segments to grow
by 58%. The values of maximum tensions on the plates and on the fixing screws are placed
below the limit of proportionality.
Fig. 19. The finite element model of the femur-implant assembly
Step 1
Fig. 20. Total displacements of the second module (a), total displacements for the femur (b),
von Mises stress in the element (c), von Mises stress in the plates (d)