Finite element modelling of uncemented implants: Challenges in the representation of the press-fit condition

The primary stability of uncemented orthopaedic implants is dependent upon the production of a stable mechanical environment at surgery. Excessive movement between the prosthesis and the surrounding bone can lead to the formation of fibrous tissue instead of a direct bond with the bone. The establishment of an interference fit at surgery, called a press-fit, is widely used to limit such interfacial movement. Although this technique is very successful, bone fracture at surgery can occur if too high a fit is attempted. The question therefore arises as to what is the minimum level of interference that will help provide the mechanical environment in which osseointegration can occur. Computational approaches, such as the finite element methodology, are currently being explored in order to inform this discussion by identifying the characteristics of the mechanical environment which have most effect.