Impact Force, Polar Gap and Modal Parameters Predict Acetabular Cup Fixation: A Study on a Composite Bone.

The balanced initial fixation of an implant makes up a crucial condition for its long-term survival. However, the quantification of initial fixation is no easy task and, to date, only qualitative assessments can be made. Although the concept of measuring fixation by means of vibration analysis is already widely used in dental implantology, the rigorous application of this method for the assessment of the fixation of femoral and acetabular components remains a challenge. Moreover, most studies on this subject have tended to focus solely on the femoral stem even though acetabular cup fixation is also important and even more difficult with respect to qualitative measurement. This study describes a comprehensive experiment aimed at assessing acetabular cup fixation. Fixation is expressed in terms of the impact force and polar gap variables, which are correlated with the modal properties of the acetabular implant during the various insertion stages. The predictive capabilities of modal frequencies and frequency functions were investigated by means of surrogate models based on the Gaussian process and functional principal component analysis. The prediction accuracy of the proposed models was in the range 82-94%. The results indicate that natural frequencies, reduced frequency, impact force and polar gap features provide great potential in terms of the prediction of implant fixation.