Failures of Stainless Steel Orthopedic Devices - Causes and Remedies

Orthopaedic implants are exposed to the biochemical and dynamic environments of the human body; their design is dictated by anatomy and restricted by physiological conditions. In every failure of an orthopaedic implant, the concerned patient is made to experience the trauma of repeated surgeries, besides the severe pain experienced during the process of rejection of the device. The removal of the failed implant will cause great expense and hardship to the patient. Therefore, it is highly desirable to keep the number of failures to a minimum. The determination of the mechanism by which failure of an implant occurred is important, but it is also necessary to explore the event, or sequence of events, that had caused a particular mechanism or mechanisms to be operative. Furthermore, failure analyses can help improving the overall performance of implant devices through revision engineering. In the framework of this study, a survey of failure investigations of stainless steel implants was undertaken. The use of advanced stainless steels and the application of nitrogen ion implantation and bioceramic hydroxyapatite coatings as potential remedies are evaluated. Failure analyses reveal the occurrence of significant localized corrosion attack viz., pitting and crevice corrosion. These findings support the need for the development of some innovative implant materials exhibiting resistance to localized corrosion attack. Cooperative efforts by the materials and medical/surgical disciplines may result in even greater improvements in the future with respect to the durability and safety of these implant devices.