Towards validation of computational analyses of peri-implant displacements by means of experimentally obtained displacement maps

Abstract

Micro-finite element (μFE) analysis has recently been introduced for the detailed quantification of the mechanical interaction between bone and implant. The technique has been validated at an apparent level. The aim of this study was to address the accuracy of μFE analysis at the trabecular level. Experimental displacement fields were obtained by deformable image registration, also known as strain mapping (SM), of dynamic hip screws implanted in three human femoral heads. In addition, displacement fields were calculated using μFE analysis. On a voxel-by-voxel basis, the coefficients of determination (R²) between experimental and μFE-calculated displacements ranged from 0.67 to 0.92. Linear regression of the mean displacements over nine volumes of interest yielded R² between 0.81 and 0.84. The lowest R² values were found in regions of very small displacements. In conclusion, we found that peri-implant bone displacements calculated with μFE analysis correlated well with displacements obtained from experimental SM.

Keywords:

• micro-finite element (μFE) analysis
• screw implant
• deformable image registration
• strain mapping
• local validation

Acknowledgements

This study was funded by the CPP1 network grant of the AO Foundation, Davos, Switzerland. Implants were manufactured by Synthes GmbH, Solothurn, Switzerland. Computational time was granted by the Swiss National Supercomputing Centre (CSCS), Manno, Switzerland. Specimens were provided by Prof. Jess Snedeker, Balgrist University Hospital, Zurich, Switzerland.