Background: This study investigated issues related to initial stability after stem fixation. Finite element models of the AI-Hip cementless stem were constructed for computer simulation.
Methods: Analysis was performed after implantation of two types of cementless hip stem for clinical use; and micromotion and stress were then calculated. Boundary and initial conditions were (1) rigid contact of the distal end of the model femur with a rigid base; (2) a stepping load of 1800 N was applied to the proximal top of the stem; (3) a load of 1440 N was pulled from the greater trochanter of the femur as muscle force; (4) a torsion load of 18.9 Nm was applied to the proximal femur as the intrarotation.
Results: Relative micromotion of the AI-Hip cementless stem showed a value as low as that of a conventional stem. The calculated von Mises stress was below the level that would cause destruction of the femur and stem.
Conclusions: Based on the relative micromotion and von Mises stress level, the AI-Hip cementless stem showed initial stability. The present experimental results should be compared with those obtained in clinical practice.