 |
Center for Nonlinear Studies |
This talk will describe our approach to full knee computational biomechanics modeling. This includes characterization of the soft tissues of the knee, particularly the anterior cruciate ligament (ACL) and the tibiofemoral cartilage, development of accurate constitutive models of these tissue structures, implementation into computational models of the knee, and simulations of impact loading and gait. Several challenges associated with obtaining accurate computational descriptions of the knee will be described. First among these is the non-linear, anisotropic, viscoelastic, heterogeneous nature of soft tissue structures. Pre-strain in the ACL and its complicated physiological configuration are other challenges. The necessity of accurate computational models of the soft tissues of the knee is examined with illustrative examples of healthy and diseased states. Articular cartilage focal defects within the knee are a common pathology that has been linked to the progression of degenerative soft tissue diseases, like osteoarthritis (OA). OA affects approximately 15% of the adult American population and typically presents initially as a decline in cartilage integrity, eventually developing into through-thickness lesions. Focal defects occur most frequently on the femoral cartilage, about 60% based on previous arthroscopy studies, with an average area of 2.1 cm2 and corresponding range of 0.5 – 4 cm2. While focal defects predominately appear in weight bearing and high wear regions, with prolonged joint use focal defects without intervention tend to expand and show signs of cartilage degeneration in the neighborhood around the original focal defect. It has been shown that the presence of focal defects influences both near and fear field strains during sliding contact typical of normal gait using bovine cartilage explants. However, the general and coupled contribution of focal defects within whole joints has not been fully explored. Moreover, the spatial heterogeneity of cartilage properties has implications for surgical intervention strategies that have not previously been elucidated. In this talk I will describe our efforts to examine the effects of focal defects on cartilage strains and knee motions. Anterior cruciate ligament (or ACL) tears are among the most common injuries in sports, with over 200,000 reconstructions per year in the US alone. ACL reconstruction has been linked to OA through associated alterations of knee joint biomechanics. Understanding ACL injury mechanisms requires accurate characterization of ACL strains in vivo. The ACL is comprised of two bundles that spiral around one another and twist approximately 90° as they course from the femur to the tibia. Some portion of the ACL bundles is always under strain in physiologically relevant states. Characterization from an unloaded, reference configuration is an arduous process involving separating the bundles and testing them individually, which will be described. I will discuss our utilization of digital image correlation analysis to measure the mechanical properties of the ACL bundles and its efficacy in reducing animal-to-animal variability. Then I will discuss our efforts to implement accurate constitutive models of the bundles, implement them into our computational framework using the unloaded configuration of the bundles, and restoring the physiological state in silico in order to examine ACL injury mechanisms in anterior tibial translation loading.
Host: Curt Bronkhorst