ITAP (Intraosseous Transcutaneous Amputation Prosthesis), under development at UCL, is a prosthesis attachment system which uses a bone implant to anchor the prosthesis to the body; this allows more efficient transfer of the forces from the prosthesis to the human skeleton in comparison with conventional force transfer through human skin and tissue and can aid patient rehabilitation. The skin is encouraged to grow on to the implant to create a seal against infection. The project is currently undergoing clinical trials, with the first patient expected to be implanted with the developed novel type of prosthesis and fail-safe device by the end of 2008. Fail-safe mechanisms have been developed to protect patients with prosthetic limb prostheses which can be secured directly to human bone. Several prototypes have been built and world-wide patent protection has been obtained (patent no. WO2005087145). The fail-safe mechanism has been successfully tested to BS EN ISO 10328:2006 level P4. The mechanical interaction of the implant with bone has been investigated, developing a numerical continuum mechanics model. The detailed shape and inhomogeneous, orthotropic material properties of the femur were calculated from Computed Tomography (CT) scans of bone. Material types and properties were assigned according to the density obtained from ‘greyvalue’ (Hounsfield Units), dividing the bone in regions of varying orthotropic alignment. Numerical finite element analysis was used to investigate the fracture risk associated with different levels of amputation, geometry and bone quality.