[home] [Personal Program] [Help]

---

Session: Poster session 2 (Odd numbers)
Session starts: Friday 27 January, 10:00
Presentation starts: 10:00

---

Esther de Kater (TU Delft)
Aimée Sakes (TU Delft)
Paul Breedveld (TU Delft)

Abstract:
Currently, pedicle screws are the conventional fixation method in spinal fusion surgery. However, the fixation strength of these pedicle screws may lack, preventing the desired fusion between the adjacent vertebrae and causing a need for revision surgery. Loosening of pedicle screws is a problem that is especially common in vertebrae with decreased bone density due to osteoporosis. The vertebra comprises a compact outer layer of cortical bone that surrounds the much softer cancellous bone. The conventional pedicle screw is for the major part in contact with the soft cancellous bone, only the small section of the screw located within the pedicle of the vertebra has purchase in the strong cortical bone. Although the purchase in the cortical bone is small due to the oval cross-section and the hourglass shape of the pedicle this small section accounts for 60% of the pull-out strength of the screw [1], [2]. Screw loosening is often caused by toggling, a cyclic loading that is exerted perpendicular to the screw axis causing the screw to pivot. During toggling, the cancellous bone surrounding the screw is compressed, compromising the fixation strength of the screw [1], [3]. Increasing the contact area between a spinal bone anchor and the strong cortical bone layer of the pedicle could increase the toggling resistance of the spinal bone anchor. A scaled-up two-dimensional prototype of a spinal bone anchor that can expand within the pedicle such that the anchor can shape to the hourglass shape of the pedicle was designed and manufactured. The prototype comprises ten stainless steel wedges that expand and mould to the hourglass shape of the pedicle by tensioning the central bolt. The prototype showed an increased toggling resistance compared to a non-expanding mock-up anchor. This preliminary prototype shows that an expandable in-pedicle anchor could be a feasible option to increase the contact between the anchor and the cortical bone layer, and increase toggling resistance and thus the fixation strength of spinal bone anchors.