  Since the recent failure events of two particular series of zirconia femoral
heads for total hip replacement prosthesis, a large decrease in the use of
zirconia ceramics for orthopaedic implants has been observed. In spite of the
biomedical success of this material during the last ten years, this was
required for safety reasons, until the cause of the failures is known. It has
been shown that these failures were related to the low temperature hydrothermal
degradation (also known as ageing). Thus it is crucial to better understand the
ageing behaviour, in order to be able to assess its importance and then control
it if required. In this paper, various techniques relevant to assess the
hydrothermal degradation sensitivity of biomedical grade yttria stabilized
zirconia are discussed and compared. The expected outputs of conventional
methods, i.e. X-Ray diffraction and scanning electron microscopy are examined.
More recent methods like optical interferometry and atomic force microscopy are
presented, with their respective benefits and drawbacks. An up to date
comparison of these different techniques is provided, and their use for
ensuring the long term reliability of a particular batch of zirconia in terms
of ageing degradation is demonstrated.
