The biomechanical characteristics of the anterior cruciate ligament (ACL) of the knee include non-linearity, anisotropy, and viscoelasticity. The tissue structures that make up the ACL also exhibit mechanical heterogeneity. Soft tissue characterization is further complicated by the possibility of the tissue properties changing during testing. The ACL is particularly challenging to experimentally characterize; in its anatomically relevant state, it is twisted and partially extended regardless of knee flexion angle. The ACL consists of two bundles that are not simultaneously unloaded under any configuration, and an approach to accurately characterize each bundle is described. Our experimental methods involve mechanically testing in uniaxial loading as well as anatomical positions using digital image correlation analysis to describe the strain fields arising from mechanical heterogeneity in each experimental condition. We demonstrate that the anterior bundle of the ACL may be functionally graded along its length whereas the posterior bundle appears to be mechanically homogeneous axially. We have developed a non-linear viscoelastic mathematical model of the ACL bundles and implemented it into a finite element framework for computational analysis of the ACL during physiologically relevant loading conditions. In our computational environment we can transition from the uniaxial loading state to the anatomically correct loading state and predict the strain fields in the ACL during an anterior tibial translation. This motion is relevant to ACL injury as the ACL tears when the tibia anteriorly translates excessively relative to the femur. Our computational model is able to predict the location of ACL tears in the proximal third of the tissue.

The tibiofemoral cartilages are mechanically heterogeneous. It is understood that local cartilage properties vary through the thickness, however we have recently established that the cartilage properties also vary with position throughout the tibial and femoral surfaces.  The effect of neglecting this spatial heterogeneity on cartilage and ACL strains during impact loading is discussed.

~BME Faculty Host: Sarah Calve~

***Coffee and juice will be provided at West Lafayette***

(via live streaming to SL165 at IUPUI)