Dynamic finite element knee simulation for evaluation of knee replacement mechanics Mark A. Baldwin a , Chadd W. Clary a,b , Clare K. Fitzpatrick a , James S. Deacy a , Lorin P. Maletsky b , Paul J. Rullkoetter a,n a Computational Biomechanics Lab, University of Denver, 2390 South York Street, Denver, CO 80208, USA b University of Kansas, Lawrence, KS, USA article info Article history: Accepted 27 November 2011 Keywords: Knee kinematics Finite element Model verification Implant mechanics abstract In vitro pre-clinical testing of total knee replacement (TKR) devices is a necessary step in the evaluation of new implant designs. Whole joint knee simulators, like the Kansas knee simulator (KKS), provide a controlled and repeatable loading environment for comparative evaluation of component designs or surgical alignment under dynamic conditions. Experimental testing, however, is time and cost prohibitive for design-phase evaluation of tens or hundreds of design variations. Experimentally- verified computational models provide an efficient platform for analysis of multiple components, sizes, and alignment conditions. The purpose of the current study was to develop and verify a computational model of a dynamic, whole joint knee simulator. Experimental internal–external and valgus–varus laxity tests, followed by dynamic deep knee bend and gait simulations in the KKS were performed on three cadaveric specimens. Specimen-specific finite element (FE) models of posterior-stabilized TKR were created from magnetic resonance images and CAD geometry. The laxity data was used to optimize mechanical properties of tibiofemoral soft-tissue structures on a specimen-specific basis. Each speci- men was subsequently analyzed in a computational model of the experimental KKS, simulating both dynamic activities. The computational model represented all joints and actuators in the experimental setup, including a proportional-integral-derivative (PID) controller to drive quadriceps actuation. The computational model was verified against six degree-of-freedom patellofemoral (PF) and tibiofemoral (TF) kinematics and actuator loading during both deep knee bend and gait activities, with good agreement in trends and magnitudes between model predictions and experimental kinematics; differences were less than 1.8 mm and 2.21 for PF and TF translations and rotations. The whole joint FE simulator described in this study can be applied to investigate a wide range of clinical and research questions. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Assessing long-term in-vivo performance of total knee replace- ment (TKR) is complicated by the relationship between compo- nent design, surgical alignment, patient-specific anatomy, and ligamentous constraint. The difficulty and variability associated with implant evaluation under in-vivo conditions have driven manufacturers to characterize component designs in the more controlled and repeatable loading environment provided by dynamic mechanical simulators. In-vitro force-controlled mechani- cal simulators have been developed to elucidate the relationship between natural and implanted constraint and whole joint kinetics and kinematics under simulated dynamic activities (Maletsky and Hillberry, 2005; Withrow et al., 2006; Zavatsky, 1997). Whole joint cadaveric testing of implanted specimens provides a useful indica- tion of implant performance under applied loads and realistic soft tissue constraint, but becomes cost-prohibitive as a design-phase tool in evaluating multiple component designs, sizes, and alignment conditions. Computational models represent an efficient way to perform component design evaluations under a variety of dynamic loading conditions that would otherwise be difficult and costly to accomplish experimentally. A host of finite element (FE) models of the knee, varying in complexity and functionality have been presented in the literature. A substantial portion of these are static or quasi-static in nature (Elias et al., 2004; Heegaard et al., 2001; Li et al., 1999; Powers et al., 2006). Some have focused on the patellofemoral (PF) (Baldwin et al., 2009a; Dhaher and Kahn, 2002) or tibiofemoral (TF) (Godest et al., 2002; Halloran et al., 2005c; Shirazi-Adl and Moglo, 2005; Perillo-Marcone and Taylor, 2007) joint, rather than a full knee model Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics 0021-9290/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbiomech.2011.11.052 n Corresponding author: Tel.: þ1 303 871 3614; fax: þ1 303 871 4450. E-mail address: prullkoe@du.edu (P.J. Rullkoetter). Journal of Biomechanics 45 (2012) 474–483