Material selection in the design of the femoral component of cemented total hip replacements

The paper is concerned with the selection of materials for use in the design of the femoral component of cemented hip replacement joints. The analysis was performed using a three-dimensional finite element model with a representative physiological loading condition. A range of materials was considered for the stem and cement, enabling the derivation of two equations predicting the maximum critical octahedral shear stress in either material when any combination of materials is used. The results show that simple substitution of a new material into an existing design could be disastrous, particularly with respect to the cement. For example, a stem manufactured from titanium rather than the usual stainless steel, might lead to an increase in cement stresses of up to 35%. Also, it is shown that carbon fibre reinforced cement should not be used with the basic design of stem considered here. An enlarged stem was modelled in the same femur, and designed so that, when manufactured from titanium, it had the same flexural stiffness as the basic stem manufactured from stainless steel. The performance of this large stem was also examined in combination with a range of different cement materials.