Abstract
A clear discrepancy between predicted in vitro and actual in vivo surface phase stability of BIOLOX®delta zirconia-toughened alumina (ZTA) femoral heads has been demonstrated by several independent research groups. Data from retrievals challenge the validity of the standard method currently utilized in evaluating surface stability and raise a series of important questions: (1) Why do in vitro hydrothermal aging treatments conspicuously fail to model actual results from the in vivo environment? (2) What is the preponderant microscopic phenomenon triggering the accelerated transformation in vivo? (3) Ultimately, what revisions of the current in vitro standard are needed in order to obtain consistent predictions of ZTA transformation kinetics in vivo? Reported in this paper is a new in toto method for visualizing the surface stability of femoral heads. It is based on CAD-assisted Raman spectroscopy to quantitatively assess the phase transformation observed in ZTA retrievals. Using a series of independent analytical probes, an evaluation of the microscopic mechanisms responsible for the polymorphic transformation is also provided. An outline is given of the possible ways in which the current hydrothermal simulation standard for artificial joints can be improved in an attempt to reduce the gap between in vitro simulation and reality.
Highlights
A common tactic used in the marketing of highly technical products is the reduction of their message to its simplest possible terms—one that can be understood and remembered by end-customers
This paper started with a review of the observed phenomenological discrepancies between surface instabilities observed for short- and medium-term BIOLOX® delta zirconia-toughened alumina (ZTA) retrievals
F2345-03, the predicted transformation kinetics from in vitro exposed heads was several orders of magnitude slower than what was observed for time-matched actual retrievals
Summary
A common tactic used in the marketing of highly technical products is the reduction of their message to its simplest possible terms—one that can be understood and remembered by end-customers. This strategy is used in marketing of bioceramic medical devices. Scientific discovery is always multifaceted; and it can hardly be expressed by a single phrase. In this context, the use of this statement for zirconia-toughened alumina (ZTA) might be interpreted as indicating that the phase composition of this composite remains unchanged during its extended in vivo service.
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