Abstract
We introduce a new prosthetic leg design, adapted to elderly trans-femoral amputees. Technical progress in prosthesis design mainly concerns active individuals. An important number of elderly amputees are not very mobile, tire easily, present reduced muscle strength, and have difficulties managing their balance. Therefore, the needs and characteristics of this specific population are very different from those of younger ones and the prosthetic solutions are not adapted. Our artificial knee has been designed to fulfill the specific requirements of this population in terms of capabilities, transfer assistance, security, intuitiveness, simplicity of use, and types of physical activity to be performed. We particularly focused our efforts on ensuring safe and secure stand-to-sit transfers. We developed an approach to control the different states of the prosthetic joint (blocked, free, resistant), associated with different physical activities. Amputee posture and motion are observed through a single multi-axis force sensor embedded in the prosthesis. The patient behaves naturally, while the controller analyses his movements in order to detect his intention to sit down. The detection algorithm is based on a reference pattern, calibrated individually, to which the sensor data are compared, and submitted to a set of tests allowing the discrimination of the intention to sit down from other activities. Preliminary validation of the system has been performed in order to verify the applicability of the prosthesis to different tasks: walking, standing, sitting down, standing up, picking up an object from a chair, slope and stair climbing.
Highlights
Amputation of the lower limb is a growing problem in the elderly population
The context of our article is prosthetic rehabilitation, the goal being to compensate for the loss of an amputated lower limb in order to encourage activity and achieve a level of autonomy as close as possible to that prior to amputation
We performed preliminary experiments with two elderly amputees in order to analyze the stand-to-sit transfer: we recorded the dynamic efforts applied to the ground via instrumented insoles (3 contact points recording normal forces). 3D acceleration and orientation of the trunk were measured using a sensor placed at the C7 cervical level
Summary
Amputation of the lower limb is a growing problem in the elderly population. the number of elderly persons is increasing, together with their susceptibility to atherosclerotic troubles. As a consequence, locking is not perfect, and these prostheses fold slowly, but irremediably, if load is exerted on the artificial limb They are intended to flex during the swing phase of walking in order to increase gait aesthetics and efficiency, which can make them insufficiently secure for some elderly people. What is proposed here is a compromise between the previously described solutions (Fig. 1, right picture): 1) a micro-processordriven leg prosthesis that detects the patient’s intent to sit down and releases the knee appropriately, 2) a knee which remains mechanically locked the rest of the time, 3) a knee which offers mechanical assistance when sitting by resisting against motion, without being totally free, for safety reasons. Preliminary feasibility validations have been carried out to evaluate the applicability of the prosthesis prototype
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