| Popis: |
The a1m of this thesis was to design and evaluate implants used m the treatment of intervertebral disc disorders. A new cervical PEEK-on-PEEK disc device, combining a ball-on-socket mechanism with an elastomeric core, was designed. To find a material for the core, quasi-static compression tests were performed; on the basis of which an elastomer MED 4780 was selected for further testing. Finite element analysis (FEA) was used to investigate the maximum stresses in the device during static compression. The results showed that maximum stresses did not exceed PEEK's compressive or fatigue strength. The comparison of the mechanical properties of pedicle screws (cylindrical and dual-core), used as an integral part of the posterior lumbar stabilisation system, was performed. The screws were tested in axial pullout, quasi-static and dynamic bending, as well as subjected to the static bending, using FEA. The results of the pullout tests, performed using three polyurethane foams (0.16, 0.32 and 0.64 g/cm) showed no significant difference between pullout strength values. However, dual-core screws had significantly higher bending strength and a longer fatigue life. The FEA showed lower stress values for the dual-core screw. Furthermore, a critical assessment of explanted screws has shown that fatigue bending was the cause of failure in vivo. |
