In England alone, the NHS carries out 30,000 total hip replacements each year, costing approximately £ 140 million. In some of these replacements loosening and subsidence are commonly seen within the initial six months post-operatively raising the possibility of secondary surgery. Revision surgery is more complex, risky and costly due to the increased amount of bone loss and bone damage associated with the removal of the primary prosthesis. Therefore, it makes perfect sense to focus resources towards alleviating early first implant failures and also prolonging the overall life of the implants. There is good evidence nowadays that many of these implant failure phenomena are brought about by the mechanical bone/implant interaction and are critically influenced by the bone tissue properties themselves. The present study focuses into the behaviour of cortical bone tissue under mechanical stress and in particular on the accumulation of both the recoverable (elastic) and irrecoverable (residual or 'plastic') strains. Strains are major contributors to either the deVelopment of damage within the bone matrix or to the bone remodelling process. Femoral bone specimens from 5 females (53-79 yrs old) and one 55 yr old male were fatigue cycled until failure in either tension, compression, or shear. This study found that the accumulation of both the elastic and plastic strain rates were dependent on the stress in each of the three loading modes (tension, compression, and shear) for each individual separately and also - when the data was pooled - regardless of the donor. However, the way plastic strain developed as function of elastic strain was independent of the applied stress. The material properties of the bone were also examined to see whether they had an effect on these strain patterns. The results showed that the two main contributors were the density of the tissue and the organic content of the test specimens. This is important in understanding how bone tissue will behave in fatigue, in general, and how it will behave around prostheses. It may also contribute towards predicting the long-term surgery outcome for various individuals of different ages and various bone characteristics. Therefore, the data and its analysis reported in this dissertation will be of particular benefit and interest to bioengineers working with FEA methods in applications of reconstructive surgery and in basic bone biomechanics research.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:413407 |
| Date | January 2003 |
| Creators | Winwood, Keith |
| Publisher | Cranfield University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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