This paper evaluates the mechanical behavior of an uncemented hip stem using finite element analysis. The analysis is focused on the stem-bone interaction which is assessed by simulation of distinct conditions encountered daily on orthopedic practice of hip implants. Logical uncemented femoral stem was used in this work. Three distinct conditions have been modeled: a) exposed neck with fully embedded fins, b) partially exposed anti-rotational fins and c) fully exposed fins, representing real femoral hip conditions. Anthropometric variations and different angulations for the stem neck were investigated for typical body weight of populations submitted to implants. The ratio of mobilized stress to yield stress is shown to be lower than 55% indicating a safety factor against stem failure. Although small displacements are observed in all conditions, the displacement increases with the increase of both the length of exposed fins and the magnitude of applied forces. Even for the extreme condition of fully exposed fins, the prostheses will support the working loads, and the risk of bone fracture still has a safety factor. Stresses and displacements change considerably with neck angulations suggesting that anthropometric variations should be considered in the future to optimize prostheses performance. Numerical analysis of the used uncemented femoral stem demonstrated that small stresses and strains are generated under working load conditions indicating that a proper factor of safety is obtained for the static conditions tested in the present study.
Numerical analysis; Hip surgery; Uncemented stem; Prosthesis
