Severe damage of alumina-on-alumina hip implants: wear assessments at a microscopic level

Six retrieved alumina hip implants were investigated for severe damage after a mean follow-up of 13 years (range: 8–21 years) using a multivariable approach: a coordinate measuring machine was used to quantify volumetric wear, the surface was characterized by scanning electron microscopy, and fluorescence and Raman spectroscopy were used to investigate the phenomenon on a micrometer crystal scale. All the femoral heads exhibited significant loss of roundness with heavy deviation from the original sphericity, showing an average volumetric wear of 602±3 mm3. A smooth surface with occasional pits and agglomerates was observed; formation of craters and loss of surface integrity was revealed. The femoral heads characterized by the highest volumetric wear underwent the most significant stress on a micrometer crystal scale (i.e. the most pronounced changes in the width of the fluorescence and Raman bands).