Initial fixation of a finite element model of an AI-Hip cementless stem evaluated by micromotion and stress.

Abstract

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. 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. 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. 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.