Leg

Summary

A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element capable of changing length and rotating about an omnidirectional "hip" joint. As an anatomical animal structure it is used for locomotion. The distal end is often modified to distribute force (such as a foot). Most animals have an even number of legs. As a component of furniture, it is used for the economy of materials needed to provide the support for the useful surface, such as the table top or chair seat. Terminology *Uniped: 1 leg, such as clams *Biped: 2 legs, such as humans and birds *Triped: 3 legs, which typically does not occur naturally in healthy animals *Quadruped: 4 legs, such as dogs and horses Many taxa are characterized by the number of legs: *Tetrapods have four legs. Squamates of genus Bipes have only two. Caecilians

Official source

https://en.wikipedia.org/wiki/Leg

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Neuroprosthetic Technologies to Evaluate and Train Leg Motor Control in Neurologically Impaired Individuals

Camille Georgette Marie Le Goff-Mignardot

Spinal cord injury (SCI) disrupts many essential sensorimotor and autonomic functions. Consequently, individuals with SCI can face decades with permanent disabilities. Advances in clinical management have decreased morbidity, but no clinical trial has yet demonstrated the efficacy of a repair strategy. In the past decade, Courtine lab has developed neurotechnologies that restored volitional control of locomotion in animal models of SCI. The intervention acts over two-time windows. In the short-term, the delivery of epidural electrical stimulation (EES) targeting the posterior lumbar roots with timing that mimics the natural activation of the spinal cord enables stepping in otherwise paralyzed rats. In the long-term, this targeted EES with intensive robot-assisted overground training triggers a reorganization of descending pathways that reestablished voluntary control of the paralyzed legs, even without EES. These results in animal models encouraged the transfer of these technologies and concepts to clinical applications. My contribution to this translational research program forms the core of my thesis. The first section presents a software that I developed in order to enable a comprehensive yet semi-automated analysis of kinematics and muscle activity underlying locomotor functions in humans. This toolbox allows to evaluate gait features of people with neuromotor deficits, quantify locomotor performance compared to healthy people or to monitor changes in different experimental conditions or over the time course of interventions, and automatically generate comprehensive gait reports directly understandable by scientists and clinicians. The second section introduces a paradigm shift in robotic postural assistance: the gravity-assist. We demonstrated the detrimental impact of high levels of body weight support on gravity-dependent interactions during standing and walking. We developed a gravity-assist algorithm that fine-tunes the forward and upward body weight support to reestablish these interactions based on each patientâs residual capacities. We validated the personalized gravity-assist in 30 individuals with SCI or stroke. Compared to other conditions of support, the gravity-assist enabled all the patients to improve their locomotion performance. This platform establishes refined conditions to empower and train overground locomotion in a safe yet ecological environment. The third section reports the development of targeted EES in patients with chronic SCI, and the impact of an intensive 5-month rehabilitation with gravity-assist and targeted EES on the recovery of motor functions. The key findings can be summarized as follows: We established procedures to configure targeted EES that immediately enabled voluntary control of weak or paralyzed muscles; Targeted EES boosts the residual supraspinal inputs to the lumbar spinal cord, enabling all the patients to adapt their gait to specific tasks; Locomotor performance improved during the rehabilitation; All the patients regained voluntary control over previously paralyzed muscles without EES. These combined results establish the proof-of-concept on the therapeutic potential of targeted EES and intensive, robot-assisted rehabilitation to restore locomotion after SCI. Together with similar results obtained in the US in patients with severe SCI, our findings are establishing a pathway towards the development of a viable treatment to support motor functions and improve recovery after SCI.

EPFL2019

Spatiotemporal stimulation strategies in neuroprostheses to improve locomotion after spinal cord injury

Jérôme Gandar

Spinal cord injury (SCI) disrupts communication within central nervous system and lead to range of neurological disorders including paralysis. Current rehabilitation strategies to restore locomotion are poorly effective in people with severe SCI. Epidural electrical stimulation (EES) showed promising results in animal models and humans to improve recovery. However, EES protocols have remained empirical, which has limited the efficacy of this paradigm. In this thesis, I report my contribution to the development of EES related software and hardware that were driven by the under- standing of the mechanisms underlying EES. These neurotechnologies showed a remarkable efficacy to reestablish locomotion in animal models of leg paralysis. EES protocols have primarily been delivered with continuous stimulations applied over the middle of the spinal cord, independently of current limb positions. However the natural activity of the spinal cord does not correspond to this limited monotone modulation. In the first part of this thesis, we developed spatiotemporal stimulation protocols that seek to reproduce the natural activity of the spinal cord during walking. Using computational models, we identified optimal electrode locations that target individual posterior roots. These simulations steered the design of spatially selective spinal implants. Control software triggered stimulation trains in real-time to engage extensor and flexor synergies according to limb positions. This spatiotemporal neuro- modulation therapy enhanced locomotor performances in rats with severe SCI. However, these spatiotemporal neuromodulation protocols were controlled via an external computer. The animal had no control over the occurrence of the stimulation. To remedy this limitation, we designed a brain-spine interface. We linked motor states decoded from leg motor cortex activity to spinal cord stimulation protocols to elicited the intended movements. We implemented this brain-spine interface in a nonhuman primate models of transient unilateral leg paralysis. All the animals immediately regained movements of the paralyzed leg. There is often a mechanical mismatch between current stiff implants and the soft neural tissues of the host. The third part of this thesis is dedicated to the design and fabrication of soft neural implants that present the same elasticity as the dura mater. These implants maintain the ability to deliver electrochemical stimulation while being stretched. Such interfaces can be applied to multiple neuroprosthetic applications, including the restoration of locomotion in paralyzed rats. In the last part of this thesis, I addressed the current limitations of spinal implant specificity. We found that EES activates the large afferent fibers within the dorsal rots and developed novel implants that take advantage of the known trajectories of the dorsal roots to increase the specificity of EES. First, we built a precise anatomical computational model of the lumbosacral roots. We then ran simulations that identi- fied multipolar electrode configurations capable of steering the current specifcally. These results drove the fabrication of soft neural implants that we inserted chronically in rat models of severe SCI. Experiments showed that multipolar EES increases the specificity of the stimulation compared to conventional protocols. All the concepts developed and validated in my thesis are already applied or are steering applications in humans with SCI.

EPFL2019

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Neuroprostheses based on electrical stimulation are becoming a therapeutic reality, dramatically improving the life of disabled people. They are based on neural interfaces that are designed to create an intimate contact with neural cells. These devices speak the language of electron currents, while the human nervous system uses ionic currents to communicate. A deep understanding of the complex interplay between these currents, during the electrical stimulation, is essential for the development of optimized neuroprostheses. Neural electrodes can have different geometries, placement within the nervous system, and the stimulation protocols (paradigms of use). This high-dimensional problem is not tractable by an empiric, brute-force approach and should be tackled by exact computational models, making use of our accumulated knowledge. In pursuit of this goal, a hybrid finite element method-NEURON modeling-is used for a solution of electrical field generated by stimulation, within the different neural structures having anisotropic conductivity, and a corresponding neural response computation. In this work, an important correction of perineurium electrical conductivity is computed. Models of median and sciatic nerves, innervating the hand and foot areas, relevant to the development of bionic hands and legs with sensory feedback, are implemented. The obtained results have the potential to optimize the design of neural interfaces, in terms of shape and number of stimulating contacts. Guidelines for the neurosurgical planning are proposed, by indicating the optimal number of implants for a specific nerve to obtain the best efficacy with the lowest invasiveness. The interpretation is proposed for one of the basic problems of neural interfaces, consisting in the change of the stimulation threshold due to fibrotic reaction of tissue. We show that it is possible to use human microstimulation as an experimental setup for testing of afferent stimulation paradigms, which can be translated to further chronic implants. In the future, models will have a key role in the decision of the most appropriate design of customized neuroprostheses, their optimal modality of use, understanding the effects that occur during their use, and minimizing animal and human experimentation.

Ieee-Inst Electrical Electronics Engineers Inc2017

Neuroprosthetic Technologies to Evaluate and Train Leg Motor Control in Neurologically Impaired Individuals

Camille Georgette Marie Le Goff-Mignardot

EPFL2019

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Ieee-Inst Electrical Electronics Engineers Inc2017

Spatiotemporal stimulation strategies in neuroprostheses to improve locomotion after spinal cord injury

Jérôme Gandar

EPFL2019