Objective. A large scale retrieval study of failed HA-coated acetabular cup was done by identifying and quantifying residual HA area on the surface of the retrieved cup for understanding the relevance between HA absorption and failure modes. Design. A total of 49 retrieved acetabular cups were collected through a long period of time for the study. Two main groups among the 49 cups were Landos and Osteonics cups. Methods. Image processing techniques and mathematical operation methods were used to quantify the residual HA area on the retrieved cups. Data incorporated with patients' histories and residual HA area for statistical analysis. Results. The HA coated surface of Landos cup disappears at a rate of 15.14% and 8.8% of the total surface per year for he unstable and the stable cups, respectively. The average loss rate of the HA coating of Osteonics cup in unstable cases is also faster than that in stable cases. Conclusions. The HA coating disappeared significant slower on the stable cups than did the unstable cups. The strong effect of mechanical fixation is necessary to achieve a good biological fixation result.