In toto microscopic scanning of ZTA femoral head retrievals using CAD-assisted confocal Raman spectroscopy

The purpose of this work is to establish a protocol, which combines CAD modeling to non-destructive microscopic techniques of confocal Raman micro-spectroscopy and laser microscopy, to assess the in-vivo hydrothermal stability of ZTA femoral head retrievals. The combined effects of wear, biological environment, and in vivo occurring peculiar events as metal staining were evaluated on five retrieved ZTA femoral heads with implantation time ranging from 9 to 106 months. The protocol relies on the application of a polar grid on the entire surface of the head, which divides it into small sectors; each sector is then automatically screened with micrometer resolution. Maps are finally linked to each other and an in-toto view of the retrieved head becomes available in three dimensions. Upon combining analytical techniques with a solid modeling computer-aided design (CAD) software, it becomes possible to develop a 3D model of the femoral head, which comprehensively describes topographic, crystallographic, and micromechanical characteristics of the entire surface and immediate sub-surface. The combination of CAD, polarized Raman spectroscopy, and laser microscopy has led to in-toto screening of femoral head with micrometer-scale resolution, thus providing a new and comprehensive protocol for both quality assessments on new components and failure analysis on retrievals.