Using multibody dynamics to design total knee replacement implants

Abstract

Computational mechanics methods, such as finite element analysis or multibody dynamics, are usually employed toward the end of the design phase of a total joint implant system. It is of greater benefit, however, to utilize these methods early in the design process as a benchmarking tool to compare competitive products, as a screening tool to eliminate poor design concepts, and as a means to virtually test selected designs to determine if they meet the functional requirements prior to cadaver testing in an experimental knee rig. The use of a purpose-written commercial multibody dynamics program has provided computational advantages for this purpose in an industrial setting, saving an unprecedented amount of time required for addressing design questions, prior to prototype manufacturing and testing. Such methods can be successfully employed to deal with challenging and clinically motivated design questions. This paper illustrates the use of computational mechanics as an enabling technology to discover design-related factors that contribute to unsatisfactory functional performance in some patients. As an illustrative example, it is demonstrated that the sagittal design of the femoral component of a total knee replacement is responsible for the observed phenomenon of paradoxical anterior motion in knee bending activities and that minor design modifications can reduce or eliminate and even reverse paradoxical anterior displacement.