The aim of this study was to redesign a soft stabilisation prototype, for use in the treatment of low back pain. The prototype consisted of a stainless steel spinous process hook joined by two loops of polyester braid to two stainless steel laminar hooks. The ends of the loops of braid passed through a stainless steel sleeve, allowing the loops to be secured by crimping the sleeve with three crimp actions. Preliminary mechanical testing of the prototype device revealed a weakness in the design of the spinous process work. Mechanical testing of the looped braid indicated that reducing the number of crimp actions to one, would ensure that if the device was overloaded, it would fail by slippage of the braid through the sleeves, avoiding fracture of the hooks. Finite element analysis provided information on the theoretical stresses in the hooks. It was used to redesign the both the laminar and spinous process hooks in a titanium alloy (for MR compatibility) with a greater range of sizes. The redesigned soft stabilisation construct was tested according to the standard for testing spinal implants (ASTM F1717). These tests verified the successful redesign of the construct. While redesigning the soft stabilisation device, information on its attachment to the spine was sought. Literature surveys and mechanical testing revealed that the strength of the spinous process is around 400 N; about half that of the lamina. The mean angulation of the spinous process in the sagittal plane was found to be in the range 74-84° on patient radiographs. Further literature surveys showed that movement of an implant relative to bone should be avoided. A mechanical investigation revealed that appreciable movement between the spinous process hook and its site of attachment is unlikely. A spinal implant and surgical instruments were developed in compliance with the Medical Devices Directive.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:592926 |
| Date | January 1999 |
| Creators | Leahy, J. C. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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