Integrating Multibody Dynamics and Computational Modeling
Computational Modeling Quick Facts:

Project Dates: December 2008 - Present

Funding Agency:
NIH T32 AG000213 (P.I. Sanjay Asthana)

Current NMBL Personnel:
Anne Schmitz, Kwang Won Choi, Darryl Thelen

External Collaborators:
Yasin Dhaher, Northwestern University
Dan Negrut, UW Mechanical Engineering

Publications from this work:
ASB 2010 - Providence, RI ,
Colloquium on Aging 2009 - Madison, WI
ASB 2012 - Gainesville, FL

Over 100,000 reconstructions of the anterior cruciate ligament (ACL) occur in the U.S. each year (Owings and Kozak 1998). Reconstructive knee surgery is often successful at restoring static joint stability in the short term, but the elevated risk for developing osteoarthritis (OA) in the long term remains. Abnormal kinematics following surgery may contribute to the onset of OA by altering tibiofemoral cartilage loading patterns in a way that contributes to cartilage degeneration. Computational models provide a mechanism by which to assess the influence of surgical factors, such as tunnel placement, on cartilage contact during functional movement. In this study, we will first empirically investigate the relevance of accounting for load-dependent variations in knee kinematics on muscle moment arms. We will then investigate the use of cosimulation techniques to describe this inherent coupling between functional movement and joint mechanics. Finally, we will use cosimulation models to predict the influence of ACL tunnel placement on tibiofemoral mechanics.

Aim 1. Investigate the influence of functional joint loading on knee muscle moment arms.
Rationale: Musculoskeletal models often assume that joints are simply kinematic constraints. However in reality, joint kinematics vary with loading (Westphal 2009), which can influence the line of action and moment arm of a muscle about the knee. Hypothesis: The three-dimensional patellar tendon moment arm will be significantly reduced with quadriceps loading in knee flexion, due to anterior translation of the tibia. Methods: Dynamic MRI imaging techniques will be used to measure three-dimensional knee kinematics under load. Eight subjects will perform cyclic knee flexion/extension tasks against inertial and elastic loads, which will induce quadriceps activity with knee flexion and extension, respectively. For both loading conditions, the instantaneous axis of rotation will be calculated as well as the patellar tendon’s moment arm with respect to this axis (Sheehan 2007; Sheehan 2007). Anticipated Outcomes: This study will demonstrate the importance of accounting for load-dependent variations in muscle moment arms, which directly influence the magnitude of muscle and joint contact loads.

Aim 2. Investigate the use of cosimulation to describe soft tissue deformations during movement.
Rationale: Injury and surgery can alter soft tissue material properties and lines of action, which in turn affects cartilage loading patterns. Current serial simulations do not capture this inherent coupling, which may be relevant to consider in the context of joint degeneration. Hypothesis: A cosimulation method will predict significantly different kinematics and cartilage contact patterns than an uncoupled approach. Methods: We will implement a cosimulation approach to simultaneously solve a multibody musculoskeletal dynamics model and a finite element model of the knee. The cosimulation approach will be used to simulate the knee flexion-extension tasks from Aim 1, with model predictions of knee kinematics compared to experimental measures. Anticipated Outcomes: This aim will establish a realistic computational framework to predict knee cartilage loading during movement.

Aim 3. Use the model to investigate how femoral tunnel placement affects cartilage contact.
Rationale: The position of the ACL graft is the most critical parameter during surgery (Beynnon, Johnson et al. 2005), with recent studies suggesting it may substantially influence tibiofemoral rotation during movement. Hypothesis: A femoral tunnel placed midway between the anteromedial and posterolateral bundle origins of the natural ACL will produce contact pressure points that agree most closely with normal. Methods: The ACL attachment to the femur will be modified in the FE model to attach at 10, 10:30, and 11 o’clock. The method developed in Aim 2 will then be used to predict contact points on the tibiofemoral cartilage. Anticipated Outcomes: This aim will give better insight into the sensitivity of cartilage loading patterns to femoral tunnel placement, which is important to consider when evaluating potential for developing OA. (Back to Research)

Email to: Darryl Thelen Last Updated: 4/14/2014