This presentation was made at CAASE18, The Conference on Advancing Analysis & Simulation in Engineering. CAASE18 brought together the leading visionaries, developers, and practitioners of CAE-related technologies in an open forum, to share experiences, discuss relevant trends, discover common themes, and explore future issues.

Resource Abstract

Rheumatoid arthritis is an autoimmune disorder that frequently affects the fingers and results in swollen and/or painful joints. Total joint replacement surgery is commonly required, in which a silicone elastomer prosthetic is implanted, to restore patient hand/finger function and alleviate pain. Design qualification requirements specify that the prosthetic must endure at least 10 million cycles in which the finger joint is flexed through 90 degrees, which is typically determined and verified through a battery of costly physical testing routines. However, physics-based simulation is becoming a commonly used method by medical device companies to enhance or replace physical testing, which can potentially save time and money when submitting for device approval to the US Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA). The workflow presented here describes why and how to leverage patient-specific anatomical data, non-linear structural simulation, fatigue simulation and shape optimization to generate a customized simulation workflow to enhance device design of a total finger joint replacement.

Standard treatment consists of removing the joint tissue and replacing with an off the shelf prosthetic. This workflow aims to customize both the implant and the excised joint tissue. The patient-specific CT scan data is provided by the open source Visible Korean project (Park et al. 2006). The Simpleware Software platform is used to import the image data of the hand, segment out the various tissue types by density, integrate the CAD geometry, from Catia, of the implant and generate the volumetric finite element mesh. With the geometric boundaries established for the tissues the implant is aligned with the anatomy and a boolean operation is performed to remove the tissue occupying the same space as the implant. In order to optimize the prosthetic and ensure compliance to the durability specification, a non-linear finite element model is created in Abaqus of the proposed treatment plan and of typical post-treatment duty cycle of the finger joint. Stress-strain behavior for the silicone elastomer is represented via a 3rd order Ogden hyperelastic law. Fatigue simulations are performed Durability calculations are made with Endurica’s technology in fe-safe/rubber via Critical Plane Analysis to address the multiaxiality of loads experienced by the implant. Fracture mechanical behavior is defined via a non-crystallizing Thomas law. The calculation returns the number of duty cycle repeats required to grow a crack precursor from its naturally occurring initial size to its end-of-life size. Tosca is then used to both modify geometry of the tissue removal and the prosthetic shape with shape optimization. This entire workflow gives confidence of adequate durability and maximize patient outcome.

Park et al. 2006. Visible Korean Human: Its Techniques and Applications. Clinical Anatomy 19:216–224