Among vertebrates, whole-body movement is centered around the vertebral column. The bony vertebral column primarily consists of trabecular (spongy) bone that adapts in vivo to support mechanical demands respective to region, ontogeny, ecology, and locomotion. Previous work has extensively investigated the formfunction relationships of vertebral trabecular bone in terrestrial mammals, who use limb contact with a substrate as the primary support against gravity. However, we lack data from obligate swimming mammals whose locomotor ecology diverged from their terrestrial counterparts in two major ways: (1) body mass is supported by water’s uplifting buoyant forces and (2) swimmers power movement through dorsoventral loading of the axial body. This study examined vertebral trabecular bone mechanical properties and micoarchitecture from fully aquatic mammals, specifically sirenians (i.e. manatees) and cetaceans (i.e. dolphins and whales). We compression tested bone from several regions of the vertebral column among developmental stages in Florida manatees (Trichechus manatus latirostris) and among 10 cetacean species (Families Delphinidae and Kogiidae) with various swimming modes and diving behaviors. In addition, we microCT scanned a subset of cetacean vertebrae before subjecting them to mechanical tests. We demonstrated that in precocial manatee calves, vertebrae were the strongest and toughest in the posterior vertebral column, which may support rostrocaudal force propagation and increasing bending amplitudes towards the tail tip during undulatory swimming. Among cetaceans, we showed that greatest strength, stiffness, toughness, bone volume fraction, and degree of anisotropy were in rigidtorso shallow-divers, while properties had the smallest values in flexible-torso deep-divers. We propose that animals swimming in shallower waters actively swim more than species that conduct habitual glides during deep descents in the water column, and place comparatively greater loads on their vertebral columns. We found that cetacean bone volume fraction was the best predictor for mechanical properties. Due to the shared non-weight bearing conditions of water and microgravity, we present these data as a contribution to the body of work investigating bone adaptations in mammals that live in weightless conditions throughout life and evolutionary history. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

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Bone mechanics and traditional implant materials produce a recurring problem for patients of total hip arthroplasty (THA): the bone is “shielded” from the loading it has become accustomed to over many years of development. Bone adheres to what is called “Wolff’s Law”, meaning it is an adaptive structure which adjusts its geometry based on the loads experienced over its life (Pearson; Goldstein). As the new femoral hip implant transmits reduced stresses to the remaining bone, bone tissue atrophies at the interface, permitting loosening of the implant, pain, and thereby obliging additional surgery to correct the issue (Meade). In the present work, a methodology is endeavored for creating an innovative design for femoral hip implants. The approach uncouples the finite element implant model from the bone model, in order to focus solely on expected behavior within the implant while considering the varying material behavior in unique directions and locations. The implant’s internal geometry is optimized in order to better match typical, intact bone conditions. The eventual design reduces extreme changes in stresses within remnant bone such that the implant will remain implanted for greater periods of time without additional surgical attention.

[Truncated abstract] In this work a computer simulation program, similar to a finite element program, is used to study the relationship between skeletal tissue structure and function. Though other factors affect the shape of bone (e.g., genetics, hormones, blood supply), the skeleton adapts its shape mainly in response to the mechanical environment to which it is exposed throughout life. The specific relationship between the mechanical environment and the mechanical adaptation response of the skeleton is reviewed. Theories of mechanical adaptation are applied to the sites of tendon attachment to bone (entheses), the adaptation of generalised trabecular bone (i.e., Wolff’s Law of trabecular architecture), sesamoid bones that are often found where a tendon wraps around a bony pulley, and the internal trabecular structure of a whole bony sesamoid such as the patella. The relative importance of compression rather than tension in bone adaptation theories is still not fully understood. Some mechanical adaptation theories suggest that an overwhelming tensile stress at a skeletal location does not stimulate bone deposition, but would instead lead to bone resorption. The skeletal locations studied in this work were chosen because they have been proposed to be in tension. Computer simulations involving models are an ideal method to analyse the mechanical environment of a skeletal location. They are able to determine the mechanical stresses at, and the stress patterns around, complex biological situations. This study uses a two dimensional computer simulation program, Fast Lagrangian Analysis of Continua (Flac), to analyse the stress at the skeletal locations, and to test theories of mechanical adaptation over time by simulating physiological adaptation. The initial purpose of this study is to examine the stress in the skeletal tissue in generalised trabeculae, anatomical sites where a tendon wraps around a bony pulley, in the trabecular networks that fill the patella, and at tendon attachments. A secondary purpose, that follows directly from the first, is to relate the results of these initial stress analyses to existing and hypothetical skeletal tissue remodelling theories, to suggest how the complex skeletal structures might be generated solely in response to their mechanical environment. The term “remodelling” is used throughout this work to refer to mechanical adaptation of bone, usually at a surface of bone, rather than the internal regeneration of osteons (Haversion systems)

Lai Yau Ming. / "August 2006." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 260-290). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese.

Bone is a composite material consisting of hydroxyapatite crystals deposited in an oriented manner on a collagen backbone. The arrangement of the mineral and organic phases provides bone tissue with the appropriate strength, stiffness, and fracture resistance properties required to protect vital internal organs and maintain the shape of the body. A remarkable feature of bone is the ability to alter its properties and geometry in response to changes in the mechanical environment. However, in cases of metabolic bone diseases or aging, bone can no longer successfully adapt to its environment, increasing its fragility. To elucidate the mechanisms of bone microdamage, this research project developed a specimen-specific approach that integrated 3D imaging, histological damage labeling, image registration, and image-based finite element analysis to correlate microdamage events with microstructural stresses and strains under compressive loading conditions. By applying this novel method to different ages of bovine and human bone, we have shown that the local mechanical environment at microdamage initiation is altered with age. We have also shown that formation of microdamage is time-dependent and may have implications in age-related microdamage progression with cyclic and/or sustained static loading. The work presented in this dissertation is significant because it improved our understanding of trabecular bone microdamage initiation and unlocked exciting future research directions that may contribute to the development of therapies for fragility diseases such as osteoporosis.

Skeletal fragility is characterized by low bone mass, negative changes in bone microarchitecture, and compromised tissue matrix properties, including accumulation of microdamage. Microdamage accumulates in vivo from daily physiological loading and is targeted for repair through a normal remodeling process, thus preventing microcrack growth and potential fracture. However, impaired remodeling is associated with aging and osteoporosis, resulting in an increased accumulation of microdamage which contributes to reduced bone mechanical properties. The current clinical method for assessing increased risk of fracture involves measuring bone mineral density (BMD) of the hip and spine, locations of trabecular bone where high rates of remodeling occur. The bisphosphonate alendronate (ALN) reduces clinical risk for fracture by significantly increasing BMD, but studies have shown a concomitant reduction in intrinsic properties that may be the underlying cause for recent reports of spontaneous fractures with long-term alendronate use. Another anti-resorptive agent called raloxifene (RAL) is a selective estrogen receptor modulator (SERM) and has been shown to modestly improve BMD while decreasing fracture risk to a similar degree as alendronate. The combination of RAL and ALN as a treatment for osteoporosis may provide the benefits of each drug without the negative effects of ALN. Therefore, the overall goal of this thesis was to address the effects of aging and anti-resorptive agents on the properties of bone through the formation of microdamage. Assessment of age-related effects on bone was conducted through quantification of microdamage progression. It was found that old bone results in greater incidences of microdamage progression, reflecting a compromised tissue matrix with reduced resistance to crack growth. Effects of combination treatment with RAL and ALN were evaluated through biomechanical testing, micro-CT imaging, and microdamage quantification. Results showed improved trabecular bone volume and ultimate load with positive effects on trabecular architecture. Combination treatment reduced the proportion of microdamage that may lead to catastrophic fracture, indicating an improvement in the local tissue matrix properties.

Indiana University-Purdue University Indianapolis (IUPUI) / Bone is a dynamic tissue that is constantly remodeling to repair damage and strengthen regions exposed to loads during everyday activities. However, certain conditions, including long-term unloading of the skeleton, hormonal imbalances, and aging can disrupt the normal bone remodeling cycle and lead to low bone mass and osteoporosis, increasing risk of fracture. While numerous treatments for low bone mass have been devised, dynamic mechanical loading modalities, such as axial loading of long bones and lateral loading of joints, have recently been examined as potential methods of stimulating bone formation. The effectiveness of mechanical loading in strengthening bone is dependent both on the structural and geometric characteristics of the bone and the properties of the applied load. For instance, curvature in the structure of a bone causes bending and increased strain in response to an axial load, which may contribute to increased bone formation. In addition, frequency of the applied load has been determined to impact the degree of new bone formation; however, the mechanism behind this relationship remains unknown. In this thesis, the application of mechanical loading to treat osteoporotic conditions is examined and two questions are addressed: What role does the structural geometry of bone play in the mechanical damping of forces applied during loading? Does mechanical resonance enhance geometric effects, leading to localized areas of elevated bone formation dependent on loading frequency? Curvature in the structure of bone was hypothesized to enhance its damping ability and lead to increased bone formation through bending. In addition, loading at frequencies near the resonant frequencies of bone was predicted to cause increased bone formation, specifically in areas that experienced high principal strains due to localized displacements during resonant vibration. To test the hypothesis, mechanical loading experiments and simulations using finite element (FE) analysis were conducted to characterize the dynamic properties of bone. Results demonstrate that while surrounding joints contribute to the greatest portion of the damping capacity of the lower limb, bone absorbs a significant amount of energy through curvature-driven bending. In addition, results show that enhanced mechanical responses at loading frequencies near the resonant frequencies of bone may lead to increased bone formation in areas that experience the greatest principal strain during vibration. These findings demonstrate the potential therapeutic effects of mechanical loading in preventing costly osteoporotic fractures, and explore characteristics of bone that may lead to optimization of mechanical loading techniques. Further investigation of biomechanical properties of bone may lead to the prescribing of personalized mechanical loading treatments to treat osteoporotic diseases.

Indiana University-Purdue University Indianapolis (IUPUI) / Mechanical loading associated with exercise is known to benefit bone health; however, most studies explore exercise benefits on bone mass independent of bone structure and strength. The purpose of this dissertation is to explore the response of the skeleton to exercise across the translational divide between animal- and human-based studies, with a particular emphasis on exercise-induced changes in bone structure and estimated strength. To explore the skeletal benefits of exercise, models were used wherein loading is introduced unilaterally to one extremity. Unilateral exercise enables the contralateral, non-exercised extremity to be used as an internal control site for the influences of systemic factors, such as genetics and circulating hormones. In study 1, a dose response between load magnitude and tibial midshaft cortical bone adaptation was observed in mice that had their right tibia loaded in axial compression at one of three load magnitudes for 3 d/wk over 4 weeks. In study 2, the ability of peripheral quantitative computed tomography to provide very good prediction of midshaft humerus mechanical properties with good short-term precision in human subjects was demonstrated. In study 3, collegiate-level jumping (long and/or high jump) athletes were shown to have larger side-to-side differences in tibial midshaft structure and estimated strength between their jump and lead legs than observed in non-jumping athletes. In study 4, prepubertal baseball players followed for 12 months were shown to gain more bone mass, structure and estimated strength in their throwing arm relative to their nonthrowing arm over the course of 12 months. These cumulative data using a combination of experimental models ranging from animal to cross-sectional and longitudinal human models demonstrate the ability of the skeleton to adapt its structure and estimated strength to the mechanical loading associated with exercise. Study of these models in future work may aid in optimizing skeletal responses to exercise.