Long-term survival of massive prostheses used to treat bone cancers is associated with extra-cortical bone growth and osteointegration into a grooved hydroxyapatite coated collar positioned adjacent to the transection site on the implant shaft [1]. The survivorship at 10 years reduces from 98% to 75% where osteointegration of the shaft does not occur. Although current finite element (FE) methods successfully model bone adaption, optimisation of adventitious new bone growth and osteointegration is difficult to predict. There is thus a need to improve existing FE models by including biological processes of osteoconduction and osteoinduction.

The principal bone adaptation criteria is based on the standard strain-energy remodeling algorithm, where the rate of remodeling is controlled by the difference in the stimulus against the reference value [3]. The additional concept of bone connectivity was introduced, to limit bone growth to neighbouring elements (cells) adjoining existing bone elements. The algorithm was developed on a cylindrical model before it was used on an ovine model.

The geometry and material properties from two ovine tibiae were obtained from computed tomography (CT) scans and used to develop FE models of the tibiae implanted with a grooved collar. The bones were assigned inhomogeneous material properties based on the CT grey values and typical ovine walking load conditions were applied. The FE results show a region of bone tissue growth below the implanted collar and a small amount of osteointegration with the implant, which is in good agreement to clinical results. Some histological results suggest that further bone growth is possible and potential improvements to the model will be discussed. In summary, by including an algorithm that describes osteoconduction, adventitious bone growth can be predicted.

To try and aid the formation of a soft tissue seal to promote dermal and epidermal attachment to Intraosseous Transcutaneous Amputation Prostheses we compared the effect of titanium surfaces functionalised with fibronectin (fn) or YRGD peptide sequences on human dermal cell (HDF) attachment. We hypothesise that YRGD and fn coatings will significantly increase HDF attachment to titanium alloy substrates. Titanium alloy 10mm discs were polished and acted as control substrates, functionalised surfaces had YRGD or fn adsorbed or silanised onto the polished surface. HDFs were seeded at 10,000/disc and cultured for 1, 4, 24 and 96 hours, fixed and fluorescent immnolocalisation for vinculin was performed. Individual vinculin markers were counted and density calculated as a measure of cell attachment. All assays were performed in triplicate and data were analysed in SPSS 19.0 and results were considered significant at the 0.05 level. Results showed an up-regulation of Focal adhesion density (FA) against controls at all time-points (excluding ad-fn at 4 hours, p=0.057), p values < 0.05, the use of functionalised titanium surfaces may lead to long-term clinical success of ITAP. We have shown a significant positive effect on cell attachment when a synthetic peptide sequence is used. Using synthetic peptide sequence may also be more beneficial from a regulatory stand-point compared with using isolated proteins.