Active Above-Knee Prosthesis: A Guide to a Smart Prosthetic Leg presents original research and development results, providing a firsthand overview of idea generation and prototype production. The book gives insights into the problem of stair ascent for people with above-knee amputation and offers a solution in the form of a physical prototype of an active above-knee prosthesis with an actuated ankle. The book's authors have developed and tested a physical prototype of an active above-knee prosthesis, giving anyone who is researching and designing prosthetic devices firsthand knowledge on how to build on, and continue with, work that has already been done. - Presents state-of-the-art technology in powered prosthetics - Helps readers evaluate design options and create new developments - Provides guidance on the evolution of advanced prosthetic design

The loss of a limb is extremely debilitating. Unfortunately, today's assistive technologies are still far from providing fully functional artificial limb replacements. Although lower extremity prostheses are currently better able to give assistance than their upper-extremity counterparts, important locomotion problems still remain for leg amputees. Instability, gait asymmetry, decreased walking speeds and high metabolic energy costs are some of the main challenges requiring the development of a new kind of prosthetic device. These challenges point to the need for highly versatile, fully integrated lower-extremity powered prostheses that can replicate the biological behavior of the intact human leg. This thesis presents the design and evaluation of a novel biomimetic active knee prosthesis capable of emulating intact knee biomechanics during level-ground walking. The knee design is motivated by a mono-articular prosthetic knee model comprised of a variable damper and two series elastic clutch units spanning the knee joint. The powered knee system is comprised of two series-elastic actuators positioned in parallel in an agonist-antagonist configuration. This investigation hypothesizes that the biomimetic active-knee prosthesis, with a variable impedance control, can improve unilateral transfemoral amputee locomotion in level-ground walking, reducing the metabolic cost of walking at selfselected speeds. To evaluate this hypothesis, a preliminary study investigated the clinical impact of the active knee prosthesis on the metabolic cost of walking of four unilateral above-knee amputees. This preliminary study compared the antagonistic active knee prosthesis with subjects' prescribed knee prostheses. The subjects' prescribed prostheses encompass four of the leading prosthetic knee technologies commercially available, including passive and electronically controlled variable-damping prosthetic systems. Use of the novel biomimetic active knee prosthesis resulted in a metabolic cost reduction for all four subjects by an average of 5.8%. Kinematic and kinetic analyses indicate that the active knee can increase self-selected walking speed in addition to reducing upper body vertical displacement during walking by an average of 16%. The results of this investigation report for the first time a metabolic cost reduction when walking with a prosthetic system comprised of an electrically powered active knee and passive foot-ankle prostheses, as compared to walking with a conventional transfemoral prosthesis. With this work I aim to advance the field of biomechatronics, contributing to the development of integral assistive technologies that adapt to the needs of the physically challenged.

With about 440,000 people with an above-knee amputation in India alone, there is a great need for high performance prosthetic knee. Due to socio-economic stigma associated with amputation, one of the main requirements for a lower limb prosthesis is achieving able-bodied kinematics. However, the prostheses available in developing countries, such as India, primarily focus the design on stability and low cost. This study presents a shear-based rotary viscous damper design for late stance and swing flexion for a passive single-axis knee prosthesis. The optimal normalized damping coefficient range of 0.012 - 0.014 ... was determined by optimizing a set of passive components to replicate a knee moment for an able-bodied subject and transtibial amputee wearing a fully characterized prosthetic foot. Dampers with a stacked fin architecture, where a highly viscous fluid is sheared between neighboring disks, were built with a range of damping coefficients from 0.37 to 1.80 Nm/(rad/s). The performance of dampers was evaluated through field and clinical testing with unilateral transfemoral amputees. The results of the studies showed that not only damping is required to prevent hyper flexion, but the optimal damping range allows achieve a peak knee flexion close to able-bodied. In future design, the validated damping selection framework will be used to expand the prosthetic knee design to other gait activities such as walking at different speeds, on slopes or uneven terrains.

Passive knee prostheses in developing countries use low-cost components driven primarily by the need to prevent falls, resulting in undesirable gait deviations during walking. There is a severe lack of reliable data on the specific needs of low-income amputees, which poses a significant challenge towards developing globally appropriate prosthetic technology. This thesis presents the analysis of user-centered needs and relevant lower leg dynamics as frameworks for the design of passive prosthetic knee components that can enable transfemoral (above-knee) amputees to ambulate with minimal gait deviations leading to higher user satisfaction. The goal of developing these frameworks is ultimately to design a low cost, fully passive prosthetic knee device for persons with transfemoral amputations living in the developing world. To identify user needs, structured oral interviews of 19 transfemoral amputees in India were conducted regarding 22 different Activities of Daily Living (ADLs). A scale of relative importance for different needs was compiled, which can help designers, doctors, and administrators provide better clinical solutions to amputees. Cross-legged sitting was identified as the most critical user need with the potential for highest improvement in the quality of life of amputees. Two identical rotator prototypes were designed and validated for cross-legged sitting on 9 amputees in India. To compute and replicate the target knee moment profile for a prosthetic knee device, the dynamics of level-ground walking were analyzed using a conceptual link-segment model of the prosthetic leg with the knee joint modeled as a combination of passive linear springs and dampers. The effects of changes in inertial properties (mass, radius of gyration, and center of mass location) of the prosthetic leg on the lower leg kinetics were also quantified in the model. The knee moment required for achieving normative joint kinematics at the hip, knee and ankle by the optimal engagement of spring and dampers was replicated computationally with a maximum R2=0.90 in an idealized clutching scheme. Multiple prototypes of modular knee mechanisms were built to replicate the model, including (i) an automatic locking module for stability during early stance, (ii) a linear spring module for facilitating knee flexion-extension during early stance, and (iii) a rotary damping module for control during terminal stance and swing. Qualitative feedback from two unilateral transfemoral amputees in India showed the automatic locking module provided the predicted performance for timely stance to swing transition. Fluid-based viscous damping was found to provide more optimal control compared to friction-based damping. A comprehensive biomechanical framework was developed that predicted the range of optimal damping coefficients for transfemoral amputees. The framework used the results from the link-segment model and empirical data of transfemoral gait characteristics such as slower walking speeds and asymmetries in the stance-swing duration. An experimental prosthetic knee with five different damping conditions was built and tested on three subjects with unilateral transfemoral amputation in a motion capture lab. Increased damping led to reduced peak knee flexion during terminal stance and swing, as predicted by the framework. The framework predicted the optimal damping value for achieving normative peak knee flexion to within one standard deviation of the able-bodied value during the swing phase.

In January 2012, a partnership was initiated between the Massachusetts Institute of Technology and Bhagwan Mahaveer Viklang Sahayata Samiti (BMVSS, a.k.a., Jaipur Foot) to design a high-performance, low-cost, passive prosthetic knee for transfemoral amputees in India. The knee was primarily intended to improve the walking gait of amputees relative to existing low-cost devices. This thesis aimed to identify detailed design requirements for the prosthetic knee through user analysis and dynamic simulation. User analysis identified the needs and constraints of numerous stakeholders in the prosthesis development process. Members of the Indian biomechanics, prosthetics, and rehabilitation communities were interviewed to identify general requirements for the design, manufacturing, evaluation, and fitting of a prosthetic knee, and a structured survey of Indian amputees was conducted to quantify the demographics, functional capabilities, and functional needs of future end users. Dynamic simulation identified methods to enable transfemoral amputees to walk with reduced energy expenditure and normative gait kinematics. 2-dimensional inverse dynamics simulations were used to calculate the effects of inertial alterations of a prosthetic leg on the energy expenditure required to walk with normative kinematics. In addition, simulations were performed to compute the effects of inertial alterations on the knee moment required to walk with normative kinematics. Mechanical power analysis, sensitivity analysis, and optimization were used to formulate a passive mechanical model that could accurately reproduce the specified knee moment. The effects of walking cadence on critical results were also examined. Through the identification of user-centered and biomechanical requirements, the thesis provides a blueprint for the mechanism design comprising the next phase of the project.

An estimated 230,000 above-knee amputees are in need of prosthetic devices in India with a majority of them facing severe socio-economic constraints in their daily lives. However, only a few passive prosthetic knee devices in the market have been designed to enable normative gait and to meet the unique daily life needs of above-knee amputees in the developing world. This thesis builds upon a past study at MIT, which established optimal mechanical component coefficients in prosthetic knee function required for achieving able-bodied kinematics. A mechanism for the design of a fully passive, low-cost prosthetic knee device, which aims to facilitate able-bodied kinematics at a low metabolic cost is presented. The mechanism is implemented using an automatic early stance lock for stability, a linear spring for early stance flexionextension and a differential friction damping system for late stance and swing control. For preliminary validation of the knee mechanism two field trials were carried out on five above-knee amputees in India, which showed satisfactory performance of the early stance lock and enabled smooth stance to swing transition by timely initiation of late stance flexion.