Fracture mechanics principles applied to implant medical devices--a review

Historically, the fatigue behavior of materials and structures, including biomaterials and implant devices, was analyzed using stress-life (S-N) techniques, i.e. by determining the number of cycles to failure at a calculated peak stress. The development of fracture mechanics technology has made the crack-growth aspect of fatigue analysis a more exact science, providing more precise data on the properties of materials, incorporating more geometric and metallurgical information from the structure, and, in some cases, providing for updated in-service lifetime predictions. Over the past decade, the medical implant industry and researchers have adopted this analytical tool to varying degrees. The result has been the development of some improved materials, operative procedures, and devices, based on a more exact knowledge of the properties most critical to assuring the long-term durability of devices. Examples of the application of fracture mechanics technology to orthopedic and cardiovascular devices and the potential for further applications are reviewed.