Affiliations: [a] Department of Orthopedic Surgery, Tokyo Medical University, Nishishinjuku, Shinjuku-ku, Tokyo, Japan | [b] Department of Bone and Joint Biomaterial Research, Tokyo Medical University, Nishishinjuku, Shinjuku-ku, Tokyo, Japan | [c] Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, Kyoto, Japan
Correspondence:
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Corresponding author: Yasuhito Takahashi, Department of Orthopedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan; and Department of Bone and Joint Biomaterial Research, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan. Tel.: +81 3 3342 6111; Fax: +81 3 3342 5295; E-mail: yasuhito@tokyo-med.ac.jp
Abstract: BACKGROUND:Accelerated hydrothermal aging has long been one of the most widely accepted quality control tests for simulating low-temperature degradation (LTD) in zirconia-containing implants used in total hip arthroplasty (THA). However, it is still unclear how much consistency there is between the experimental prediction from the internationally-standardized tests and the actual measurements from surgically-removed implants after a long period of implantation. This question is fundamentally related to a lack of understanding of mechanical/tribological contribution to the in-vivo LTD kinetics. OBJECTIVE:The main purpose of this study is to validate the clinical relevance of standardized accelerated aging by comparing artificially-aged and in-vivo used prostheses, and to clarify the long-term effects of in-vivo mechanics/tribology on the LTD progression upon service in the body environment. METHODS:Surface magnitudes of phase transformation and residual stress in zirconia femoral head retrievals (13.1–18.4 yrs) were evaluated by using confocal Raman microspectroscopy. RESULTS:The long-term aging behavior in unworn head surface was in agreement with the experimental prediction estimated as 1 h aging at 134 °C = 4 years in-vivo. However, the current aging protocols based on ASTM and ISO criteria were not accurately predictive for the worn surfaces, and the tribologically-induced phase transformation and tensile stress were up to 6.5-times and 3.3-times higher than the environmentally-induced ones. CONCLUSION:Our study suggests that wear/scratching, frictional heating, tribochemical reactions, and metal transfer may become far more intense triggers to phase transformation than the mere exposure to body fluid.
