The fundamental motivation of this study is to develop two complementary computational assessment tools, based on finite element and multi-body dynamic simulation theory based on established musculoskeletal and parametric modeling techniques. We believe these computational tools will amend how knee stability is currently assessed and thus allow for potentially transformative changes in the current preventative and rehabilitative practices prescribed for ACL injuries. Currently, insufficient and inadequately corroborated quantitative measures exist of in-vivo knee stability and menisci/tibal plateau loads and displacements during intense dynamic activities. Ability to maintain kinematic stability is imperative in everyday tasks such as standing or rising from a chair and is especially critical during intense dynamic activities such as running or climbing stairs. Anterior cruciate ligament (ACL) injury and its involvement in knee stability and adverse intersegmental loading is an important and significant topic within biomechanics. Knee ligaments play a secondary role to muscles, which are the primary knee stabilizers. Nevertheless, the absence of ligaments makes stability more difficult, especially when muscle coordination is impaired or when loads are applied more quickly than neuromuscular response time allows. Thus, considerable interest has been given to knee stability and intersegmental forces, especially when associated with ligament failure. Our focus is to quantify knee [in]stability in ACL-Deficient (ACLD) subjects and the role that this [in]stability plays in increasing intersegmental forces including how variations in knee geometry contribute to changes in such measures. Intellectual Merit and Engineering Principles Applied: The project will (1) further develop a detailed finite element (FE) and anatomical musculoskeletal computer model to quantify knee ligament strain, anterior tibial translation (ATT), and intersegmental forces (ISF), (2) develop an improved load-generating knee specimen experimental apparatus used to verify and evaluate the computational models, (3) statistically assess the deviation between unimpaired and ACL-impaired knee stability parameters with emphasis on intersegmental forces and altered neuromuscular patterns, and (4) improve and extend our pilot FE models of the human knee to a high-fidelity parametric FE model using statistical shape modeling techniques. The improved load-generating cadaver experiment is a significant improvement to current knee studies as it accounts for time-varying muscle forces from multiple muscles in synchrony with joint position. Muscle activation and motion data will be obtained from healthy subjects (ACL-intact) and "coper" subjects (ACLD and functional). Ligament strain will be measured in eight knee ligament bundles of cadaver knee specimens during artificial time-varying multiple-muscle loading conditions derived from human trials. The FE and computational models will perform dynamic simulations to estimate ligament strain, and the results will be compared with data from the load-generating cadaver experiments. The computational model will also be refined to replicate the key characteristics of ligament strain, ATT, and ISF as measured in the experiment, as well as implement proven techniques of validation and verification within parametric probabilistic modeling. As a result, this research is to develop two complementary computational assessment tools (FE and multi-body dynamic simulations) that will change the way we are able to assess knee stability and ISF, and allow for potentially transformative changes in the current preventative and rehabilitative practices prescribed for ACL injuries. Broader Impacts: This research project is performed primarily by undergraduate students for academic credit and through research assistantships at LeTourneau University under the direction of the PI and in consultation with Dr. Dan Nicolella at Southwest Research Institute (SwRI). To enhance the research experience provided to these undergraduate students, half of the summer interns will spend the entire summer at the biomechanics and materials laboratory at SwRI, co-mentored by Dr. Nicolella and his professional staff as they work on the computational knee models and perform additional experiments. This project blends learning, discovery, and research into a unique undergraduate experience that will provide students with comprehensive preparation for future graduate studies in engineering.
