Zirconia ceramics were introduced in the seventhies for use as structural biomaterials after laboratory tests and simulator studies. However, nowadays concerns remain about their reliability in vivo, despite published clinical studies have already established the safety and the good tribological performance of these materials. It is still unclear what level of reliability can be achieved in ceramic biomaterials and how much their toughness level can be enhanced by microstructural design. The polycrystalline nature of ceramic materials may make both the observed properties and performance very scattered. In particular, the grain size and other microstructural features likely play a fundamental role in the mechanical behavior of the material. In this paper, we propose a set of fracture mechanics assessments, aimed to establish the quantitative amount of toughness achievable in a zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite), and in situ confocal Raman spectroscopy to visualize toughening mechanisms, including polymorph transformation and residual stress fields stored around the crack path.