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# Screw fixation of implants to the spine

Patel, Purvi Shantilal (2010)
Ph.D. thesis, University of Birmingham.

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## Abstract

Bone screws are used to fix various implants to the human spine. Screw fixation can be difficult in osteoporotic bone because of its reduced strength. This research aimed to investigate screw fixation techniques in the spine. A questionnaire study, representing British and Irish spine surgeons, confirmed the potential for a simple screw positioning device and identified the need for an improved screw for osteoporotic bone. Determination of the compressive mechanical properties of 0.32 g.cm$$^{-3}$$, 0.16 g.cm$$^{-3}$$ and 0.09 g.cm$$^{-3}$$ polyurethane foam enabled them to be used as models for normal, osteoporotic and very low density osteoporotic, human cancellous bone, respectively. The screw pullout force from these bone models decreased with polyurethane foam density, implying that the quality of bone principally influences the strength of screw fixation. The angle of screw insertion and thread design was also found to affect screw pullout force, but not a small amount of screw toggling prior to axial pullout. No benefits in pullout strength were found when placing screws at 40° in a normal bone model or when using closely placed multiple screws in an osteoporotic bone model.

Type of Work: Ph.D. thesis. Shepherd, Duncan E. T. and Hukins, David W. L. Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Mechanical Engineering TJ Mechanical engineering and machineryRD Surgery University of Birmingham 849
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