Knee replacement surgery is often performed in cases where the pain due to knee osteoarthritis can no longer be effectively controlled by conservative measures. The surgery—which replaces the articular surfaces of the tibia, femur and sometimes the patella with a mix of metal and polyethylene—is one of the most commonly performed lower limb surgeries. Despite patient reports of reduced pain and increased participation in activities of daily living, knee function following total knee arthroplasty (TKA) does not return to normal. Reductions in both passive and active knee range of motion, alterations in magnitude and timing of muscle activity, and changes in knee joint kinetics have all been reported. Comparatively little is known about why knee function is altered following TKA. In an attempt to address this gap in the literature, this thesis was designed to examine the biomechanical factors thought to contribute to reduced knee extensor moments following TKA. In particular, the contribution of alterations in passive knee moments, muscle moment arm lengths, and muscle activation magnitude and timing were examined in detail to determine which factors contributed to reduced knee extensor moment following TKA. To accomplish this goal, two groups--6 healthy controls and 6 individuals who were at least one year post-TKA—were examined in four different studies. The initial study of this thesis, a comprehensive examination of patients and controls during gait and stepping onto a raised surface, had two purposes. This moment data was needed to clearly define the knee moment deficits that existed in the patient – the remainder of the thesis focused on determining why these specific deficits existed. A secondary aim of this first study was to allow for the assessment of muscle activation patterns in this population during weight bearing tasks. Results of study one confirmed the existence of knee extensor moment deficits in the TKA group and also demonstrated that patients exhibited increased gastrocnemius EMG, prolonged stance phase activation of biceps femoris and reduced knee flexion during the loading phase of stance. Analysis of results across the two tasks suggested that reduced knee moments in members of the TKA group may be related to changes in gastrocnemi activation, however, differences in knee joint kinematics between patients and controls made it difficult to draw this conclusion. Study number two was designed to further probe the muscle activation strategies adopted by members of the TKA group. In order to avoid complications involved when comparing muscle activation patterns between groups using different kinematic strategies, seated knee extension was examined. This task was chosen as it challenged the knee musculature while at the same time restricting both groups of participants to use the same knee joint kinematics. The results of this analysis revealed that, while EMG magnitude for quadriceps and hamstrings were similar for both groups, patients exhibited increased amplitude of EMG in both the medial and lateral gastrocnemi. While the first two studies of this thesis focused on the active knee joint moment, in the third study the force required to passively move the knee from a flexed to an extended position was measured and used to estimate the passive moment of the knee joint. This study was based on the rational that if the passive knee moment was altered following TKA it could potentially affect the net knee joint moment. The comparison of patient and control results showed that, while small changes in passive moment were evident in patients, these differences were not large enough to account for changes in the knee extensor moment. The goal of the final thesis study was to examine moment arms of the knee musculature in an attempt to determine if TKA resulted in changes to this variable. However, various methodological issues arose in the course of completing this study. As a result, limited data were produced that sufficiently addressed the question posed. Despite the problems that arose, important issues regarding in vivo moment arm determination were realized and are included for discussion in this thesis. Together, the four studies provided a unique opportunity to observe knee function over a range of activities. The following conclusions were reached. • Changes in passive knee moment did not seem to contribute to reductions in knee extensor moment observed following TKA. • Quadriceps and hamstring muscle function, as evidenced by EMG recording during the seated knee extension task, appeared intact following TKA, suggesting that alteration in the function of these muscles were not directly responsible for reductions in knee extensor moments. • Changes in medial and lateral gastrocnemi activation were observed during knee extension and weight-bearing tasks. These changes may account for reduced knee extensor moment, particularly during the step-up task. • Knee extensor moment reductions during gait appear to be related to the reduced knee flexion exhibited by patients during the stance phase of gait . It was hypothesized that these changes in knee kinematics were directly linked to the increased activation of the gastrocnemi during gait. Although low subject numbers limited the generalizability of the results these conclusions will serve to guide future research in this area and ultimately help improve function and quality of life in this patient population.

The low back loading to which an individual is exposed has been linked to injury and the reporting of low back pain. Despite extensive research on the spine and workplace loading exposures, statistics indicate that efforts to date have not led to large reductions in the reporting of these injuries. One possible cause for the apparent ineffectiveness of interventions may be a poorly defined understanding of the mechanical exposures of the spine during work related activities. There are sophisticated models that can predict spine loads and are responsive to how an individual moves and uses their muscles, however the models are complex and require extensive data collection to be implemented. This fact has prevented these models from being employed in industrial settings and the simplified surrogate methods that are being employed may not be predicting load exposures well. Therefore, this work focused on examining surrogate methods that can produce estimates of spine loading equal to our most complex laboratory based models. In addition, our understanding of spine tolerance to combined motion and load has been based upon in-vitro work that has not accurately represented coupled physiologic compression and flexion or has not investigated potentially beneficial loading scenarios. The result has been a lack of clear data indicating when motion should be treated as the primary influence in injury development or when load is the likely injury causing exposure. As a result, research was conducted to determine the interplay between load and motion in cumulative injury development, as well as investigating the potential of static rest periods in mitigating the effects of cumulative compression. Study one examined the potential utility of artificial neural networks as a data reduction approach in obtaining estimates of time-varying loads and moments equal in magnitude to those of EMG-assisted and rigid link models. It was found that the neural network approach under predicted peak force and moment exposures, but produced strong predictions of average and cumulative exposures. Therefore this method may be a viable approach to document cumulative loads in industrial settings. Study two compared the load and moment estimates from a currently employed, posture match based ergonomic assessment tool (3DMatch) to those obtained with an EMG-assisted model and those predicted with a rigid link modeling approach. The results indicated that 3DMatch over predicted peak moments and cumulative compression. However, simple correction approaches were developed which can adjust the predictions to obtain more physiologic estimates. Study three employed flexion/extension motion with repetitive compression loading profiles in an in-vitro study, with both load and motion profiles being obtained from measures in study 1. It was found that at loads above 30% of a spine’s compressive tolerance, repetitive flexion/extension would not lead to intervertebral disc injury prior to an endplate or vertebral fracture occurring. However, as loads fall below 30% the likelihood of experiencing a herniation increases, while the overall likelihood of an injury occurring decreases. Comparison to relevant studies indicated that while repetitive flexion did not alter the site of injury it appeared to degrade the ability of the spine to tolerate compression. Finally, study four employed dynamic compression while the spine was maintained in a neutral posture to investigate the effects of ‘rest’, or periods of static low level loading, on altering the amount of load tolerated prior to injury. It was found that there was a non-linear relationship between load magnitude and compressive tolerance, with increasing load magnitude exposures leading to decreasing cumulative load tolerances. Periods of low level static loading did not alter the resistance of the spinal unit to cumulative compression or impact the number of cycles tolerated to failure. In summary, this work has examined methods that may allow for better predictions of spine loading in the workplace without the large data demands of sophisticated laboratory approaches. Where possible, suggestions for optimal implementation of these surrogates have been developed. Additionally, in-vitro work has indicated a load threshold of 30%, above which herniation is not likely to occur during dynamic repetitive loading. Furthermore, the insertion of static rest periods into dynamic loading scenarios did not improve the spine’s failure tolerance to loading, indicating that care should be exercised when determining optimal loading paradigms. In combination, the applied methods that have been developed and the information regarding injury development that has been obtained will help to refine our understanding of the exposures and tolerances that define mechanical injury in the spine.

Knee replacement surgery is often performed in cases where the pain due to knee osteoarthritis can no longer be effectively controlled by conservative measures. The surgery—which replaces the articular surfaces of the tibia, femur and sometimes the patella with a mix of metal and polyethylene—is one of the most commonly performed lower limb surgeries. Despite patient reports of reduced pain and increased participation in activities of daily living, knee function following total knee arthroplasty (TKA) does not return to normal. Reductions in both passive and active knee range of motion, alterations in magnitude and timing of muscle activity, and changes in knee joint kinetics have all been reported. Comparatively little is known about why knee function is altered following TKA. In an attempt to address this gap in the literature, this thesis was designed to examine the biomechanical factors thought to contribute to reduced knee extensor moments following TKA. In particular, the contribution of alterations in passive knee moments, muscle moment arm lengths, and muscle activation magnitude and timing were examined in detail to determine which factors contributed to reduced knee extensor moment following TKA. To accomplish this goal, two groups--6 healthy controls and 6 individuals who were at least one year post-TKA—were examined in four different studies. The initial study of this thesis, a comprehensive examination of patients and controls during gait and stepping onto a raised surface, had two purposes. This moment data was needed to clearly define the knee moment deficits that existed in the patient – the remainder of the thesis focused on determining why these specific deficits existed. A secondary aim of this first study was to allow for the assessment of muscle activation patterns in this population during weight bearing tasks. Results of study one confirmed the existence of knee extensor moment deficits in the TKA group and also demonstrated that patients exhibited increased gastrocnemius EMG, prolonged stance phase activation of biceps femoris and reduced knee flexion during the loading phase of stance. Analysis of results across the two tasks suggested that reduced knee moments in members of the TKA group may be related to changes in gastrocnemi activation, however, differences in knee joint kinematics between patients and controls made it difficult to draw this conclusion. Study number two was designed to further probe the muscle activation strategies adopted by members of the TKA group. In order to avoid complications involved when comparing muscle activation patterns between groups using different kinematic strategies, seated knee extension was examined. This task was chosen as it challenged the knee musculature while at the same time restricting both groups of participants to use the same knee joint kinematics. The results of this analysis revealed that, while EMG magnitude for quadriceps and hamstrings were similar for both groups, patients exhibited increased amplitude of EMG in both the medial and lateral gastrocnemi. While the first two studies of this thesis focused on the active knee joint moment, in the third study the force required to passively move the knee from a flexed to an extended position was measured and used to estimate the passive moment of the knee joint. This study was based on the rational that if the passive knee moment was altered following TKA it could potentially affect the net knee joint moment. The comparison of patient and control results showed that, while small changes in passive moment were evident in patients, these differences were not large enough to account for changes in the knee extensor moment. The goal of the final thesis study was to examine moment arms of the knee musculature in an attempt to determine if TKA resulted in changes to this variable. However, various methodological issues arose in the course of completing this study. As a result, limited data were produced that sufficiently addressed the question posed. Despite the problems that arose, important issues regarding in vivo moment arm determination were realized and are included for discussion in this thesis. Together, the four studies provided a unique opportunity to observe knee function over a range of activities. The following conclusions were reached. • Changes in passive knee moment did not seem to contribute to reductions in knee extensor moment observed following TKA. • Quadriceps and hamstring muscle function, as evidenced by EMG recording during the seated knee extension task, appeared intact following TKA, suggesting that alteration in the function of these muscles were not directly responsible for reductions in knee extensor moments. • Changes in medial and lateral gastrocnemi activation were observed during knee extension and weight-bearing tasks. These changes may account for reduced knee extensor moment, particularly during the step-up task. • Knee extensor moment reductions during gait appear to be related to the reduced knee flexion exhibited by patients during the stance phase of gait . It was hypothesized that these changes in knee kinematics were directly linked to the increased activation of the gastrocnemi during gait. Although low subject numbers limited the generalizability of the results these conclusions will serve to guide future research in this area and ultimately help improve function and quality of life in this patient population.

Cervical Spine injuries are a common occurrence during motor vehicle accidents, and they represent a significant economic cost to society. Numerical Finite Element (FE) models have been formulated to investigate the response of the neck under various loading scenarios and to improve vehicle safety. The Global Human Body Models Consortium (GHBMC) was formed to develop a detailed FE model capable of simulating occupant response and predicting subsequent soft tissue injuries in the cervical spine. The objective of this thesis was to validate the neck region of the GHBMC model at the segment level in flexion and extension, and at rotation rates observed during car crash scenarios. Nine cervical spines, under the age of 50, were procured from post mortem human subjects and they were dissected into segments. A segment consisted of two vertebrae with the ligaments and the intervertebral disc intact, and the muscle, nervous, and cardiovascular tissues removed. A custom built fixture was built to test each specimen three times in flexion and extension at two rotation rates: a low rate (one degree per second) and a high rate (500 degrees per second). To avoid damaging the specimens after the first test, the segments were only rotated up to ten degrees for the segments at the C2-C3 through C5-C6 level, and up to eight degrees for the C6-C7 and C7-T1 level. The segment response was represented by plots of the moment against the angle of rotation in the sagittal plane. The segment models were simulated at the same low and high rotation rates, and the model results were evaluated against the experimental response. The low speed experimental results were compared to existing quasi-static studies, but there was not an elevated rotation rate study at each segment level to compare with the high rate response. The segment response from the existing data was generally weaker than the results of this thesis because the earlier studies tested older specimens, and the exiting studies applied a step-wise loading protocol instead of a continuous one. A statistical analysis was conducted to determine the significance of the difference between the low and high rate experimental response. At the maximum angle of rotation, the analysis found moderate evidence (p < 0.05) of increased segment stiffness at the high rotation rate for the C5-C6 and C6-C7 segments in flexion and extension, and weak evidence of increased stiffness for the C3-C4 and C4-C5 segments in flexion and extension, and for the C2-C3 and C7-T1 segments in extension. Below six degrees of rotation, there was no statistical evidence that the low and high speed responses were significantly different for any segment. In flexion, the model response was within one standard deviation of the experimental mean at the C6-C7 and C7-T1 segment level. For the C2-C3 through C5-C6 segment levels, the model was stiffer than the experimental mean. In extension, the model was within one standard deviation at every segment level except at the C2-C3 and C7-T1 segment levels where the model response was weaker than the experimental response. For the high rate model analysis, the model predicted that the high rate simulations were stiffer than the low rate simulation at every segment level; however the difference was much greater in flexion than in extension. Recommendations for further research included studying the high rate behaviour of the intervertebral discs under compressive and bending loading, and investigating the translational and rotational displacement of the spine during flexion and extension and compare the results with the model. The procurement of more post mortem human subjects would increase the sample size and it could improve the significance of the statistical analysis, and additional spines would permit the analysis of other effects, such as the influence of gender.

No description available.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains vii, 56 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 48-50).

Thesis (Ph. D.)--University of Chicago, Committee on Evolutionary Biology, June 2001. / Includes bibliographical references. Also available on the Internet.

In cardiac biomechanics, people have been developing a complete model of the patient-specific heart. A finite element bi-ventricular model involves several critical steps. First is the acquisition of patient-specific heart geometry. Second is the definition of material model and its constitutive parameters which is suitable to model the behavior of heart muscle. Third is the integration of fiber orientation of myocardium into the bi-ventricular model. The first objective of this study is to investigate some significant aspects in ventricular biomechanics using a simple model of prolate spheroidal left ventricle (LV). These critical aspects include the geometry of LV, the material model, constitutive parameters and fiber orientations. Results of this simplified model are useful in developing a patient-specific model. For example, parametric study of hyper-elastic material is instructive in determining constitutive parameters of myocardium in a patient-specific model. The second objective of this study is to develop a workflow of building a patient-specific bi-ventricular model. It involves working with experimental data like CT images, DTMRI data and so on. A user defined Fung material model is also reviewed in detail. Two methods of assigning fiber orientation are discussed. Finally, the report points out the future work needed to get a valid patient-specific model which can be useful in research and clinical case. / text

Cerebral palsy (CP) is a heterogeneous disorder in which movement and posture are affected. Increased excitation of the central nervous system leads to neural symptoms, which can cause spasticity and muscle weakness. These neural abnormalities result in secondary CP-related mechanical adaptations of muscles and tendons, which can lead to muscle contracture, joint deformities and pain. Therapeutic interventions are therefore essential to treat CP-induced abnormalities. Passive stretching in particular is a popular treatment method in clinical practice. However, due to a lack of scientific evidence, clinicians often have to make assumptions about the mechanical adaptability of muscles and tendons. Currently, the mechanical properties of muscles and tendons in children with CP and their adaptability are not well understood, which makes it difficult to implement evidence-based practice in clinical settings. Therefore, the overall purpose of this research was to examine the mechanical properties of the medial gastrocnemius muscle and Achilles tendon in children with spastic CP, and the adaptations of the muscle and tendon to acute and long-term passive stretching. The first experimental Chapter (3) was carried out in healthy adults, to assess the agreement between two methods of deriving Achilles tendon stiffness (i) active contraction of the triceps surae muscles to elongate the Achilles tendon, or (ii) passive rotation of the ankle joint. Taking into consideration the tendon’s viscoelastic response, the effects of strain-rate on Achilles tendon stiffness were also described. Results revealed that tendon stiffness measured using the “active method” was 6% greater than the “passive method”. There was also a significant increase in Achilles tendon stiffness in response to increased strain-rate. As the more commonly used active method is problematic to be used in children with CP, due to muscle weakness and excessive co-contraction, the passive method of deriving tendon stiffness was used in subsequent experimental studies. In experimental Chapter 4, differences in the mechanical properties of the Achilles tendon and triceps surae muscles between children with CP and their typically developing (TD) peers, were investigated. The results revealed that estimates of triceps surae muscle stiffness were significantly greater in children with CP compared to TD children. The results also showed that despite a smaller tendon cross-sectional area in children with CP, Achilles tendon stiffness was not different between groups. In addition, children with CP had a steeper tendon stiffness-strain-rate relationship compared to TD children. These results have significant clinical implications regarding the diagnosis of spasticity using the current clinical methods. Experimental Chapters 5 and 6 examined the muscle’s and tendon’s response to stretch. Passive stretching, implemented by a clinician or by the children themselves, is a commonly used intervention for children with CP with the aim of inducing structural alterations in muscles and tendons to improve function. In order for these alterations to take place, elongation of the muscle and fascicles would presumably need to occur with acute stretching. To date, this assumption has not been tested. Thus, the purpose of Chapter 5 was to investigate the medial gastrocnemius and muscle fascicle response to acute stretching, using two commonly used stretch techniques. Results of this study revealed that 100 s of stretching caused a transient increase in tendon (1.0 cm), muscle (0.8 cm) and fascicle lengths (0.6 cm). This effect was independent of stretch technique. These results provide evidence that the muscle and fascicles are capable of elongating in response to stretch in children with spastic CP. They provide a basis for the hypothesis that the spastic muscle may be able to adapt in response to long-term stretching. Thus, the purpose of the final experimental Chapter (6) was to assess the effects of a six week passive stretching intervention (four days per week, 15 minutes per day) on muscle and tendon properties, and gait parameters in children with CP. Results revealed there was a significant reduction in joint stiffness in the experimental group following six weeks of stretching. This was accompanied by a reduction in muscle stiffness, but with no alterations in Achilles tendon stiffness. Additionally, there were no positive effects of passive stretching on gait parameters. Together, the results of the present series of investigations demonstrates how fundamental knowledge of muscle and tendon mechanics in children with spastic CP, can be implemented to support evidence-based clinical practice.

<p> Artificial neural networks (ANNs) have been used successfully in various practical problems. Though extensive improvements on different types of ANNs have been made to improve their performance, each ANN design still experiences its own limitations. The existing digital human models are mature enough to provide accurate and useful results for different tasks and scenarios under various conditions. There is, however, a critical need for these models to run in real time, especially those with large-scale problems like motion prediction which can be computationally demanding. For even small changes to the task conditions, the motion simulation needs to run for a relatively long time (minutes to tens of minutes). Thus, there can be a limited number of training cases due to the computational time and cost associated with collecting training data. In addition, the motion problem is relatively large with respect to the number of outputs, where there are hundreds of outputs (between 500-700 outputs) to predict for a single problem. Therefore, the aforementioned necessities in motion problems lead to the use of tools like the ANN in this work. </p><p> This work introduces new algorithms for the design of the radial-basis network (RBN) for problems with minimal available training data. The new RBN design incorporates new training stages with approaches to facilitate proper setting of necessary network parameters. The use of training algorithms with minimal heuristics allows the new RBN design to produce results with quality that none of the competing methods have achieved. The new RBN design, called Opt_RBN, is tested on experimental and practical problems, and the results outperform those produced from standard regression and ANN models. In general, the Opt_RBN shows stable and robust performance for a given set of training cases. </p><p> When the Opt_RBN is applied on the large-scale motion prediction application, the network experiences a CPU memory issue when performing the optimization step in the training process. Therefore, new algorithms are introduced to modify some steps of the new Opt_RBN training process to address the memory issue. The modified steps should only be used for large-scale applications similar to the motion problem. The new RBN design proposes an ANN that is capable of improved learning without needing more training data. Although the new design is driven by its use with motion prediction problems, the consequent ANN design can be used with a broad range of large-scale problems in various engineering and industrial fields that experience delay issues when running computational tools that require a massive number of procedures and a great deal of CPU memory. </p><p> The results of evaluating the modified Opt_RBN design on two motion problems are promising, with relatively small errors obtained when predicting approximately 500-700 outputs. In addition, new methods for constraint implementation within the new RBN design are introduced. Moreover, the new RBN design and its associated parameters are used as a tool for simulated task analysis. This work initiates the idea that output weights (<i>W</i>) can be used to determine the most critical basis functions that cause the greatest reduction in the network test error. Then, the critical basis functions can specify the most significant training cases that are responsible for the proper performance achieved by the network. The inputs with the most change in value can be extracted from the basis function centers (<i>U</i>) in order to determine the dominant inputs. The outputs with the most change in value and their corresponding key body degrees-of-freedom for a motion task can also be specified using the training cases that are used to create the network's basis functions. </p>