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Materials 2017, 10(5), 466;

In Vitro versus In Vivo Phase Instability of Zirconia-Toughened Alumina Femoral Heads: A Critical Comparative Assessment

Ceramic Physics Laboratory, Kyoto Institute of Technology, Kyoto 606-8585, Japan
Department of Orthopaedic Surgery, Tokyo Medical University, Tokyo 160-0023, Japan
Medical Technology Laboratory, Rizzoli Orthopaedic Institute, Bologna 40136, Italy
Department of Medical Engineering for Treatment of Bone and Joint Disorders, Osaka University, Osaka 565-0854, Japan
Amedica Corporation, Salt Lake City, UT 84119, USA
Department of Orthopaedic Surgery, University of Missouri, Columbia, MO 65212, USA
Author to whom correspondence should be addressed.
Academic Editor: Maryam Tabrizian
Received: 22 March 2017 / Revised: 14 April 2017 / Accepted: 21 April 2017 / Published: 28 April 2017
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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. View Full-Text
Keywords: ZTA; femoral head; Raman spectroscopy; in vivo; in vitro; hydrothermal aging ZTA; femoral head; Raman spectroscopy; in vivo; in vitro; hydrothermal aging

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Pezzotti, G.; Affatato, S.; Rondinella, A.; Yorifuji, M.; Marin, E.; Zhu, W.; McEntire, B.; Bal, S.B.; Yamamoto, K. In Vitro versus In Vivo Phase Instability of Zirconia-Toughened Alumina Femoral Heads: A Critical Comparative Assessment. Materials 2017, 10, 466.

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