Fracture to the neck of femur is frequently stabilised with a hip screw system, however the host bone is often weak or osteoporotic. This causes premature failure of the system, commonly by cut-out of the lag screw through the head of the femur. While augmentation of the fixation with bone cement improves the holding power and decreases failure rate, current methods of administering the cement are messy and inaccurate. This project proposes a lag screw design which allows for direct injection of the cement, via the lag screw itself, after the screw has been inserted and correctly positioned in the femur. A method is also suggested to reduce the risk of cement leakage into the joint space when the guide wire has punctured the head of the femur. The design uses a system of holes in the threaded section of a cannulated screw to allow delivery of cement to the desired area; the modified screw was also tested with and without the tip of the screw closed. These design and implantation techniques were compared to the standard design lag screw both with and without bone cement augmentation by traditional methods. Initial testing in a synthetic bone analogue looked promising. The modified screw with closed end performed better in push out tests than the standard screw alone and comparably with the standard screw with cement augmentation. A second phase of testing with the synthetic material was then conducted to more closely represent physiological loading conditions. In this case again the closed ended modified screw with cement augmentation outperformed the original screw and was comparable with the augmented original screw. However, during this phase of testing problems were observed with the synthetic testing material and it was decided to conduct further testing in paired porcine cadaveric femurs. Several further problems occurred in this phase of testing, including the bending of the test screws. It was concluded that the modified screw showed potential in being a more accurate and consistent method of cement augmentation, however neither the synthetic bone analogue or the porcine material was an adequate model of an osteoporotic human femur. If a suitable testing material could be found, continued study of this prototype may prove beneficial.
| Identifer | oai:union.ndltd.org:ADTP/265258 |
| Date | January 2006 |
| Creators | Grant, Caroline Ann |
| Publisher | Queensland University of Technology |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
| Rights | Copyright Caroline Ann Grant |
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