Stress analysis in ceramic hip-joint heads of various shape and fitting.

The stress distributions in models of ceramic hip-joint heads are investigated using the three-dimensional photoelastic freezing technique. It is shown that the most dangerous tensile stresses occur on the bottom of the conical hole. Slight changes of the shape (curvature of the bottom, cone angle) and mismatching of the connection between head and stem does not influence the maximum stresses significantly. Only a reduction of the wall thickness as a whole causes a remarkable increase. The estimation for the real stresses in situ - assuming normal loading conditions as well as extreme ones by high body-weight and fast walking - results in values at which a failure of the head seems to be very improbable under these conditions.