Structural safety and stress distributions in ceramic hip-joint-heads for different neck lengths

The stress distributions analysed for the three different head types show that the highest tensile stresses mainly occur in the center of the curvature at the inner surface. At equal loading conditions the amount of stress and consequently the risk of failure is different, for the three head types. In the head type with the thinnest shell (type 1) the stresses may be 4 to 8 times higher compared to type 3. The stress level is also increased especially if bad fitted cups or other irregular conditions lead to small contact areas between cup and head. A proof test which can be applied to all head types makes the risk of mechanical failure of implanted heads very small.