Robust contact modeling using trimmed NURBS surfaces for dynamic simulations of articular contact

Computational simulation of the behavior of orthopaedic implants in a realistic in vivo environment is rapidly growing in importance as a test applied to prospective designs as younger patients place greater functional demands on their new joints. In addition to muscle and ligament forces, forces caused by implant contact must be computed and applied in an accurate and efficient manner during these simulations. A method is presented by which implant contact forces are computed from the contact nodes on one implant as the nodes penetrate into NURBS surface patches that comprise a second implant using a rigid-body-spring-model (RBSM). A scheme for placing evenly-distributed contact nodes is described, as well as methods for unambiguously interpreting whether a node is in contact with a specific surface. The ability to represent the surface properly was then evaluated using various spring-spacings. Spacing contact nodes 3 mm apart using this scheme appears to produce simulated implant motions that are similar to those obtained using smaller spacings, and results in simulations that are more stable than those possible when a similar number of spring nodes are placed using triangulation.