Affiliations: Division of Medical Devices, National Institute of Health Sciences, Tokyo, Japan | Department of Orthopedic Surgery, Graduate School of Medicine, Osaka City University, Osaka, Japan | Department of Orthopaedic Surgery, Graduate School of Medicine, Shinshu University, Matsumoto, Nagano, Japan
Note: [] Address for correspondence: Hideyuki Sakoda, Division of Medical Devices, National Institute of Health Sciences, Kamiyoga 1-18-1, Setagaya-ku, Tokyo 158-8501, Japan. Tel.: +81 3 3700 9264; Fax: +81 3 3700 9196; E-mail: sakoda@ nihs.go.jp.
Note: [] Present address: Center for Supporting Industries of Senior Necessities, Pusan, Korea.
Note: [] Present address: Medical Center for Translational Research, Osaka University Hospital, Osaka, Japan.
Abstract: Ultra-high molecular weight polyethylene (UHMWPE) has been widely used as a bearing surface of joint implants. Since wear of UHMWPE component has been the primal cause of implant failure, crosslinking of UHMWPE is now widely used to improve its wear property. On the other hand, crosslinking degrades its fatigue property and increase of fatigue related failure, such as delamination, is possible. However, the relationship between degraded fatigue property and implant failure is not clear, primarily because the fatigue properties of failed and retrieved UHMWPE components are not known. In this study, we propose a new test method to evaluate the fatigue property of retrieved UHMWPE components or final products using small specimens. First, the effects of test conditions were investigated using virgin UHMWPE. Then, tests were repeated using specimens from UHMWPE components of retrieved knee implants. The fatigue properties of virgin and retrieved UHMWPE were successfully evaluated by the new test method and a relationship was found among the extent of oxidation, the fatigue property, and occurrence of delamination. This result suggested that evaluation of fatigue property of UHMWPE component can predict the occurrence of fatigue related implant failure during operation in vivo.
Keywords: Joint implant, polyethylene, oxidation, degradation, fatigue, mechanical test
