Browsing by Author "Donahue, Tammy, committee member"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Open Access A Haversian bone model of fracture healing in a simulated microgravity environment(Colorado State University. Libraries, 2015) Gadomski, Benjamin C., author; Puttlitz, Christian M., advisor; Browning, Raymond, committee member; Donahue, Tammy, committee member; Heyliger, Paul, committee memberGround-based models of weightlessness and microgravity have provided valuable insights into how dynamic physiological systems adapt or react to reduced loading. Almost all of these models have used rodent hindlimb unloading as the means to simulate microgravity on isolated physiological systems. Unfortunately, results derived from rodent studies are significantly limited when one tries to translate them to the human condition due to significant anatomical and physiological differences between the two species. Therefore, it is clear that a novel animal model of ground-based weightlessness that is directly translatable to the human condition must be developed in order for substantial progress to be made in the knowledge of how microgravity affects fracture healing. In light of this, four specific aims are proposed: (1) develop a ground-based, ovine model of skeletal unloading in order to simulate weightlessness, (2) interrogate the effects of the simulated microgravity environment on bone fracture healing using this large animal model, (3) develop a computational model of weightbearing in ovine bone under different experimental conditions in order to characterize the loads experienced by the fracture site, and (4) develop countermeasures that enhance bone fracture healing in the presence of simulated microgravity. Successful completion of this project will substantially elevate the understanding of how fracture site loading affects the subsequent healing cascade in the presence of microgravity and will form the foundation for designing future rehabilitation protocols to facilitate bone healing during long-duration spaceflight.Item Open Access Quantifying the effects of pediatric obesity on musculoskeletal function and biomechanical loading during walking(Colorado State University. Libraries, 2015) Lerner, Zachary F., author; Browning, Raymond, advisor; Davidson, Bradley, committee member; Donahue, Tammy, committee member; Puttlitz, Christian, committee member; Reiser, Raoul, committee memberWith the high prevalence of pediatric obesity worldwide, there is a critical need for structured physical activity interventions during childhood. However, obese children exhibit altered walking mechanics that are associated with decreased gait stability, reduced walking performance and an increased prevalence of musculoskeletal pain and pathology. Left unaddressed, the increased pain and orthopedic conditions associated with pediatric obesity may lead to reduced physical activity and a cycle of perpetual weight gain for the child and future adult. To enhance the efficacy of health and weight loss interventions, clinicians could benefit from an improved understanding of how pediatric obesity affects the neuromuscular and musculoskeletal systems during walking, the most common form of daily activity. The mechanisms for the altered gait and associated risks to the developing musculoskeletal system in obese children are not well understood, particularly as they relate to excess adiposity and exercise related fatigue. This void in the literature may be attributed in part to the lack of experimental and computational tools necessary to accurately quantify muscle function and joint loads during walking in obese and healthy-weight adults and children. Therefore, to improve our understanding of the musculoskeletal mechanisms for the altered gait mechanics and orthopedic disorders exhibited by obese children, this dissertation sought to first, establish the proper methods to adequately quantify the necessary biomechanical measures in obese and healthy-weight individuals, and second, determine the effects of obesity and duration on muscle function and tibiofemoral loading during walking in children. The accuracy of muscle and joint contact forces estimated from dynamic musculoskeletal simulations is dependent upon the experimental kinematic data used as inputs. Subcutaneous adipose tissue makes the measurement of representative kinematics from motion analysis particularly challenging in overweight and obese individuals. We developed an obesity-specific kinematic marker set and methodology that accounted for subcutaneous adiposity. Next, we determined how this methodology affected muscle and joint contact forces predicted from musculoskeletal simulations of walking in obese individuals. The marker set methodology had a significant effect on model quantified lower-extremity kinematics, muscle forces, and hip and knee joint contact forces. We demonstrated the need for biomechanists to account for subcutaneous adiposity during kinematic data collection and proposed a feasible solution that likely improves the accuracy of musculoskeletal simulations in overweight and obese people. Understanding orthopedic disorders of biological and prosthetic knee joints requires knowledge of the in-vivo loading environment during activities of daily living. Anthropometric and orthopedic differences between individuals make accurate predictions from generic musculoskeletal models a challenge. We developed a knee mechanism within a full-body OpenSim musculoskeletal model that incorporated subject-specific knee parameters to predict medial and lateral tibiofemoral contact forces. To assess the accuracy of our model, we compared measured to predicted medial and lateral compartment contact forces during walking in an individual with an instrumented knee replacement. We determined the importance of specifying subject-specific tibiofemoral alignment and contact locations and validated a simple approach to measure and specify these parameters on a subject-specific basis using radiography. The biomechanical mechanisms responsible for the altered gait mechanics in obese children are not well understood. We investigated the relationship between adiposity and lower extremity kinematics, muscle force requirements, and individual muscle contributions to whole body dynamics by generating musculoskeletal simulations of walking in a group of children with a range of adiposity. Body fat percentage was correlated with average knee flexion angle during stance and pelvic obliquity range of motion, as well as with relative vasti, gluteus medius and soleus force production. The functional demands and relative force requirements of the hip abductors during walking in pediatric obesity likely contribute to the altered gait mechanics in obese children. The combination of larger magnitude and altered application of tibiofemoral loads during physical activity in obese children is commonly theorized to contribute to their increased risk of orthopedic disorders of the knee, such as growth-plate suppression leading to conditions of malalignment. To evaluate this theory and determine how prolonged activity affects knee loading, we quantified the effects of pediatric obesity and walking duration on medial and lateral tibiofemoral contact forces. We found that obese children have elevated medial compartment magnitudes, loading rates, and load share, which further increased with walking duration. The altered tibiofemoral loading environment during walking in obese children likely contributes to their increased risk of knee pain and pathology. These risks may increase with activity duration. This dissertation provides a foundation for improved understanding of the effects of pediatric obesity on the neuromuscular and musculoskeletal systems during walking. The main research outcomes from this dissertation aim to improve rehabilitation and activity guidelines that minimize the risk of musculoskeletal pain and pathology in obese children, address degenerative gait mechanics, and assist in breaking the cycle of weight gain.Item Open Access Weak Galerkin finite element methods for the Darcy equation(Colorado State University. Libraries, 2018) Wang, Zhuoran, author; Liu, Jiangguo, advisor; Tavener, Simon, advisor; Donahue, Tammy, committee memberThe Darcy equation models pressure-driven flow in porous media. Because of the importance of ground water flow in oil recovery and waste mitigation, several types of numerical methods have been developed for solving the Darcy equation, such as continuous Galerkin finite element methods (CGFEMs) and mixed finite element methods (MFEMs). This thesis describes the lowest-order weak Galerkin (WG) finite element method to solve the Darcy equation and compares it to those well-known methods. In this method, we approximate the pressure by constants inside elements and on edges. Pressure values in interiors and on edges might be different. The discrete weak gradients specified in the local Raviart-Thomas spaces are used to approximate the classical gradients. The WG finite element method has nice features, e.g., locally mass conservation, continuous normal fluxes and easy implementation. Numerical experiments on quadrilateral and hybrid meshes are presented to demonstrate its good approximation and expected convergence rates. We discuss the extension of WG finite element methods to three-dimensional domains.