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No description available.

Low back disorders (LBDs) comprise one of the major health issues in the United States. Previous research used isometric studies to understand the mechanisms that cause LBDs. Occupational tasks involving dynamic trunk movements, muscle fatigue, and spinal instability are identified as major risk factors for developing low back pain. Dynamic stability and muscle forces during trunk flexion-extension movements are studied in this dissertation. Torso muscle fatigue is known to affect the neuromuscular muscle recruitment that influences spinal stability. The first part of this dissertation investigates the effect of muscle fatigue on the stability of dynamic trunk flexion-extension movements. Participants with no self-reported low back pain history performed repetitive trunk flexion-extension exercises before and after extensor muscle fatigue. The extensor muscles were fatigued to 60% of their unfatigued isometric maximum voluntary exertion force. The maximum finite-time Lyapunov exponent, λ_Max, was used to quantify the dynamic stability. Values of λ_Max increased with fatigue, suggesting dynamic stability of the torso decreases with muscle fatigue. Fatigue-by-task asymmetry interactions did not influence spinal stability. The purpose of the second part of this dissertation was to predict time-dependent muscle forces and spinal loads during symmetric flexion-extension movements. A 2-dimensional sagittal plane, lumped parameter model was built with one thorax and five lumbar vertebrae stacked upon a stationary pelvis. Kinematics driven optimization was used to estimate time-dependent muscle forces. Muscle forces were determined by minimizing the metabolic power while satisfying the equations of motion. Spinal loads were calculated as the vector sum of the muscle forces and the trunk weight. Abdominal activity was observed at the onset of flexion and at the end of extension. The multifidus and psoas muscles played a major role in the spine dynamics. The compressive spinal loads were found to reach highest values at the onset of flexion, while the shear loads reached the highest values at large flexion angles. / Ph. D.

Measurement studies have linked paraspinal muscle reflexes to low back pain. However, the role of reflexes in stabilizing the spine is not clear. Previous studies enlisted biomechanical models to aid in understanding of how intrinsic stiffness stabilizes the spine. This work expands these previous studies by modeling the neuromuscular dynamic control of the spine. The presence of delay in the reflexive system limits the availability of traditional stability analyses. However it is possible to investigate how reflex delay affects stability of the spine model using methods in linear time delayed stability. Such analyses find the maximum reflex delay, i.e., the delay margin for which stability is possible. Therefore a biomechanical model of the spine was developed that used these methods for stability. The model was able to demonstrate how reflex gains and delays affect stability. It was shown that increased proportional reflex gain reduced the amount of co-contraction required for stability. However, increased reflex gain required a reduced delay margin of the system. Differential reflex gain had no effect on the amount of co-contraction required for stability. However, it was shown to increase the delay margin for small gains. As the differential reflex gain approached the magnitude of intrinsic muscle damping the trend was reversed, and increased gain caused the delay margin to approach zero. Increased intrinsic muscle damping did not affect the minimum co-contraction required for stability, but was shown to increase the delay margin in all cases. This study provided a theoretical explanation for the role of reflexes in stabilizing the spine. Results agree with the trends in the published literature regarding patients with low-back pain. Specifically, these patients demonstrate abnormally larger reflex delay. To maintain stability, atypically small reflex gain is necessary. Compensatory co-contraction is required to offset the small reflex gain. Co-contraction and instability is observed in low back pain patients. The results presented here agree with measurement studies, and should aid in the development of hypotheses for future measurement studies. / Master of Science

In developing a method of quantifying stability in the lumbar spine Cholewicki and McGill (1996) have also broached the notion of sufficient stability, where too much stiffness (and stability) would hinder motion. Thus people highly skilled at maintaining stability may use different and optimal strategies, where <i>sufficient</i> stability is maintained. The purpose of this work was to explore the contributors to <i>sufficient</i> stability, how they coordinate and relate to injury mechanisms. This work represents a cascade of investigations where. 1) To explore the balance of various sources of stiffness and their effect on the critical load and post-buckling behaviour, simulations were undertaken where the buckled configuration of the spine was predicted and its stability in this new configuration was assessed. 2) The various sources of stiffness contributing to stability in the lumbar spine have been in some cases found to be deficient. The question of how these deficiencies place individuals at risk of instability, if at all, remains unresolved. A challenged breathing task was used to determine if there was a difference in stabilizing potential between healthy individuals and low back pain sufferers. Given that differences in stabilizing potential are apparent, several tasks which included a predetermined motor strategy, such as 3)pressurizing the abdomen and 4) abdominal hollowing vs. muscle bracing, were evaluated to determine if individuals can utilize motor strategies to augment stability. The stabilizing potential of abdominal pressure (IAP) and its interaction with muscle activation was evaluated. Some individuals are more skilled at stabilizing their lumbar spine than others. Some consciously controlled motor strategies are better stabilizers than others. These strategies highlight the relative contributions of various components (posture, passive tissue, muscle activation, and load) in that no single muscle dominates stability and IAP appears to augment stability beyond muscle activation alone. The margin of safety is considerable and depends on the task at hand, but it is possible to speculate on which tissues are at greatest risk of injury.

The human spine is an integral part of the human body. Its functions include mobilizing the torso, controlling postural stability, and transferring loads from upper body to lower body, all of which are essential for the activities of daily living. However, the many complex tasks of the spine leave it vulnerable to damage from a variety of sources. Prolonged walking with a heavy backpack can cause spinal injuries. Spinal diseases, such as scoliosis, can make the spine abnormally deform. Neurological disorders, such as cerebral palsy, can lead to a loss of torso control. External torso support has been used in these cases to mitigate the risk of spinal injuries, to halt the progression of spinal deformities, and to support the torso. However, current torso support designs are limited by rigid, passive, and non-sensorized structures. These limitations were the motivations for this work in developing the science for design of torso exoskeletons that can improve the effectiveness of current external torso support solutions. Central features to the design of these exoskeletons were the abilities to sense and actively control the motion of or the forces applied to the torso. Two applications of external torso support are the main focus in this study, backpack load carriage and correction of spine deformities. The goal was to develop torso exoskeletons for these two applications, evaluate their effectiveness, and exploit novel assistive and/or treatment paradigms. With regard to backpack load carriage, current torso support solutions are limited and do not provide any means to measure and/or adjust the load distribution between the shoulders and the pelvis, or to reduce dynamic loads induced by walking. Because of these limitations, determining the effects of modulating these loads between the shoulders and the pelvis has not been possible. Hence, the first scientific question that this work aims to address is What are the biomechanical and physiological effects of distributing the load and reducing the dynamic load of a backpack on human body during backpack load carriage? Concerning the correction of spinal deformities, the most common treatment is the use of a spine brace. This method has been shown to effectively slow down the progression of spinal deformity. However , a limitation in the effectiveness of this treatment is the lack of knowledge of the stiffness characteristics of the human torso. Previously, there has been no means to measure the stiffness of human torso. An improved understanding of this subject would directly affect treatment outcomes by better informing the appropriate external forces (or displacements) to apply in order to achieve the desired correction of the spine. Hence, the second scientific question that this work aims to address is How can we characterize three dimensional stiffness of the human torso for quantifiable assessment and targeted treatment of spinal deformities? In this work, a torso exoskeleton called the Wearable upper Body Suit (WEBS) was developed to address the first question. The WEBS distributes the backpack load between the shoulders and the pelvis, senses the vertical motion of the pelvis, and provides gait synchronized compensatory forces to reduce dynamic loads of a backpack during walking. It was hypothesized that during typical backpack load carriage, load distribution and dynamic load compensation reduce gait and postural adaptations, the user’s overall effort and metabolic cost. This hypothesis was supported by biomechanical and physiological measurements taken from twelve healthy male subjects while they walked on a treadmill with a 25 percent body weight backpack. In terms of load distribution and dynamic load compensation, the results showed reductions in gait and postural adaptations, muscle activity, vertical and braking ground reaction forces, and metabolic cost. Based on these results, it was concluded that the wearable upper body suit can potentially reduce the risk of musculoskeletal injuries and muscle fatigue associated with carrying heavy backpack loads, as well as reducing the metabolic cost of loaded walking. To address the second question, the Robotic Spine Exoskeleton (ROSE) was developed. The ROSE consists of two parallel robot platforms connected in series that can adjust to fit snugly at different levels of the human torso and dynamically modulate either the posture of the torso or the forces exerted on the torso. An experimental evaluation of the ROSE was performed with ten healthy male subjects that validated its efficacy in controlling three dimensional corrective forces exerted on the torso while providing flexibility for a wide range of torso motions. The feasibility of characterizing the three dimensional stiffness of the human torso was also validated using the ROSE. Based on these results, it was concluded that the ROSE may alleviate some of the limitations in current brace technology and treatment methods for spine deformities, and offer a means to explore new treatment approaches to potentially improve the therapeutic outcomes of the brace treatment.

In developing a method of quantifying stability in the lumbar spine Cholewicki and McGill (1996) have also broached the notion of sufficient stability, where too much stiffness (and stability) would hinder motion. Thus people highly skilled at maintaining stability may use different and optimal strategies, where <i>sufficient</i> stability is maintained. The purpose of this work was to explore the contributors to <i>sufficient</i> stability, how they coordinate and relate to injury mechanisms. This work represents a cascade of investigations where. 1) To explore the balance of various sources of stiffness and their effect on the critical load and post-buckling behaviour, simulations were undertaken where the buckled configuration of the spine was predicted and its stability in this new configuration was assessed. 2) The various sources of stiffness contributing to stability in the lumbar spine have been in some cases found to be deficient. The question of how these deficiencies place individuals at risk of instability, if at all, remains unresolved. A challenged breathing task was used to determine if there was a difference in stabilizing potential between healthy individuals and low back pain sufferers. Given that differences in stabilizing potential are apparent, several tasks which included a predetermined motor strategy, such as 3)pressurizing the abdomen and 4) abdominal hollowing vs. muscle bracing, were evaluated to determine if individuals can utilize motor strategies to augment stability. The stabilizing potential of abdominal pressure (IAP) and its interaction with muscle activation was evaluated. Some individuals are more skilled at stabilizing their lumbar spine than others. Some consciously controlled motor strategies are better stabilizers than others. These strategies highlight the relative contributions of various components (posture, passive tissue, muscle activation, and load) in that no single muscle dominates stability and IAP appears to augment stability beyond muscle activation alone. The margin of safety is considerable and depends on the task at hand, but it is possible to speculate on which tissues are at greatest risk of injury.

Up to date, only four cases of primary intradural extramedullary spinal cord melanoma (PIEM) have been reported. No previous reports have described a case of PIEM located in the lower thoracic spine with long-termfollow-up. Purpose. Demonstrating an unusual, extremely rare case of melanoma manifestation. Study Design. Case report. Methods. We report a case of a 57-year-old female suffering from increasing lower extremity pain, left-sided paresis, and paraesthesia due to spinal cord compression caused by PIEM in the lower thoracic spine. Results. Extensive investigation excluded other possible primary melanoma sites and metastases. For spinal cord decompression, the tumor at level T12 was resected, yet incompletely. Adjuvant radiotherapy was administered two weeks after surgery. The patient was recurrence-free at 104 weeks after radiotherapy but presents with unchanged neurological symptoms. Conclusion. Primary intradural extramedullary melanoma (PIEM) is extremely rare and its clinical course is unpredictable.

Jawed vertebrates (gnathostomes) consist of two clades with living representatives, the chondricthyans (cartilaginous fish including sharks, rays, and chimaeras) and the osteichthyans (bony fish and tetrapods), and two fossil groups, the "placoderms" and "acanthodians". These extinct forms were thought to be monophyletic, but are now considered to be paraphyletic partly due to the discovery of early chondrichthyans and osteichthyans with characters that had been previously used to define them. Among these are fin spines, large dermal structures that, when present, sit anterior to both median and/or paired fins in many extant and fossil jawed vertebrates. Making comparisons among early gnathostomes is difficult since the early chondrichthyans and "acanthodians", which have less mineralized skeleton, do not have large dermal bones on their skulls. As a result, fossil fin spines are potential sources for phylogenetic characters that could help in the study of the gnathostome evolutionary history. This thesis examines the development and internal structure of fin spines in jawed vertebrates using two-dimensional (2D) thin sections and three-dimensional (3D) synchrotron datasets. The development of the dorsal fin spine of the holocephalan, Callorhinchus milii, was described from embryos and compared to that of the neoselachian, Squalus acanthias, whose spine has been the model for studying fossil shark spines. It was found that the development of the C. milii fin presents differences from S. acanthias that suggest it might be a better candidate for studying "acanthodian" fin spines. The 3D histology of fossil fin spines was studied in Romundina stellina, a "placoderm"; Lophosteus superbus, a probable stem-osteichthyan; and sever­­al "acanthodians". The 3D vascularization reconstructed from synchrotron radiation microtomographic data reveal that "acanthodian" and Lophosteus spines grew similarly to what is observed in chondrichthyans, which differs slightly from the growth of the Romundina spine. Chondrichthyans and "acanthodians" also share similarities in their internal organization. Overall, Lophosteus and Romundina spines are more similar in terms of morphology and histology compared to chondrichthyans and "acanthodians". These results support the current hypothesis of gnathostome phylogeny, which places "acanthodians" on the chondrichthyan stem. They also emphasize the need for further study of vertebrate fin spines using 3D approaches.

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