Effect of an edge at cup rim on contact stress during micro-separation in ceramic-on-ceramic hip joints

- Head-cup rim contact due to micro-separation was studied for ceramic total hip joints.
- An edge formed between the cup bearing surface and the cup rim was analysed.
- Finite element model was developed to predict contact stress distribution and intensity.
- A non-smooth edge led to substantially increased stress concentration and high contact stress.
- The resulting high contact stresses can lead to ceramic bearing wear and damage.

Alumina ceramic total hip joint bearings have shown superior wear properties. The joint bearing may undergo adverse conditions such as micro-separation causing head contact on the cup rim. As a transition, an edge is formed between the cup bearing and the rim. The aim of this study was to predict the effect of the edge on contact stresses in order to better understand the mechanisms of wear. A finite element contact model was developed under the conditions of the head displacements 0.5-2 mm and vertical loads 0.5-3 kN. The edge contact produced the most severe stresses capable of causing elevated wear and damage to ceramic bearings. The study shows that the bearing design should be considered in association with clinical conditions to eliminate severe stress.