M.Ing. (Mechanical Engineering) / A stand-alone anterior lumbar interbody fusion device is used to stabilise the spine and restore the disc space height without any other instrumentation. The stand-alone anterior lumbar interbody device is fixed to the adjacent vertebrae using titanium screws. In this research an experimental and numerical investigation on the structural strength of the SASCATM stand-alone anterior lumbar interbody fusion device are presented. The outcome of the investigation will be used as part of the device validation documentation necessary for market approval. The SASCATM device is manufactured from PEEK (a high strength polymer). Tensile and compressive testing was conducted to determine the appropriate mechanical properties of PEEK. The structural integrity of the SASCA device was evaluated by conducting full scale compression testing on a limited number of different design revisions. Comparisons as regards to their loaddisplacement behaviour were made. All specimens were visually inspected. The Finite Element Analysis (FEA) method was used in the numerical investigation of the SASCATM stand-alone anterior lumbar interbody device. Three studies were conducted. The first study aimed at comparing the full scale experimental compressive testing results with the FEA simulation. Although the desired results weren’t achieved, the model gave a fair representation of the initial region of the experimental setup in the sense that it had a similar slope. It was concluded that the nominal stress (4.1 MPa) fell within the proportional limit (35 MPa) as measured during the materials testing. The second study was aimed at determining the displacement at a worst-case load determined from the literature (2.7 kN). The study showed that the maximum Von Mises stress does not exceed the yield strength of the material. The third and final (parametric) study aimed at geometric optimisation of the cages. The motivation for the changes was based on the literature and customer suggestions for improvement. The geometric optimisation intended to show whether a desired increase in graft hole size would have an effect on the structural integrity of the device. The suggestion to move the screw holes of the threehole version closer to the center of the cage was also assessed. It was shown that enlarging the two graft holes does have an effect on the compressive strength. Higher stresses were presented in all but one case. Combining the holes also had an effect on the compressive strength. Movement of the screw holes more medially did have an impact on the compressive strength of the cages. The effect was significant. The closer the holes were to the center of the cage, the higher the Von Mises stress was. This change should therefore be considered before implementation. The results showed that different shapes and sizes of the graft holes do have an impact on the stress of this particular cage. None of the models exceeded the compressive yield strength of the material. The proposed graft hole opening design changes are therefore not warranted for the current SASCATM stand-alone anterior lumbar interbody device.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:7801 |
| Date | 25 November 2013 |
| Creators | Rossouw, M.M. |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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