Energy efficient lower limb prostheses

Unilateral trans-femoral amputee gait consumes up to 60% more energy than able-bodied gait. For higher level amputees, research suggests that energy efficiency drops by well over 80%. Recently it has been shown that energy consumption in high level amputees increases significantly when walking on slopes, suggesting studies in level walking may underestimate the extent of the problem. The negative effects of high energy consumption are compounded by reductions in walking speed of typically 40% for trans-femoral amputees with associated low activity levels, particularly in elderly amputees. These deficits are even greater in bilateral amputees. This has a tremendous impact on what amputees can achieve and the consequences for their quality of life.

The energy storage and return capabilities of prostheses are crucial to improving the situation and yet modern prostheses only store and return significant energy below the knee, and energy is not returned in a controlled manner. For example, stored energy is not available for plantar-flexion (push-off) at the end of stance. Furthermore, modern prosthetic systems don't transfer energy between joints, which is a lost opportunity as, for example, the excess of eccentric work at the knee could be stored and used in a controlled manner at other joints. For these reasons, we believe there is an opportunity for truly transformative research leading to a step change in the performance of lower limb prostheses.

We have been undertaking simulation studies to establish the potential for hydraulic technology to enable controlled storage, transfer between joints, and return of energy in lower limb prostheses. This work is showing great promise and we have held back from publishing our results because of the possibility of protecting the intellectual property rights. Although the work to date has focussed on prostheses for trans-tibial amputees, this approach has even greater potential for improving the energy efficiency of trans-femoral amputee gait. Therefore, in this project, we will explore storage, transfer between joints, and return of energy involving ankle, knee and hip; the latter being to evaluate the potential for amputees to benefit from some additional energy storage and return via a hip orthosis.

We are focussing on hydraulic designs because of their unique advantages for the prosthetics application. Because they typically operate at pressures of 200 to 400 bar, hydraulic systems have very high power densities and are therefore well suited to miniaturisation, an important requirement in prosthetics. Short term energy storage is another important requirement for which hydraulic accumulators are well suited. Finally, hydraulic actuation is ideally suited for transferring energy between joints because the transfer mechanism involves only pipes and fluid, rather than gears and linkages. This is of particular importance for higher level amputees who could benefit if the excess of eccentric work at the knee could be stored and used in a controlled manner at other joints.

To achieve our objectives we will build on our research in three areas, which correspond to the three main work packages (WPs). WP1 will develop and simulate alternative concept designs. WP2 will establish a methodology for predicting the ways in which amputees might adapt their gait to alternative prosthesis. WP3 will provide gait laboratory data for: validating the gait prediction methodology; and informing the concept designs.

The proposed research addresses three areas (prosthetics, gait simulation and hydraulics-based systems for energy storage and return), and involves both computational modelling and experimental work with amputee subjects. This will have major and broad impact on a range of beneficiaries. We believe that the primary beneficiaries will be:
1. Lower limb amputees
2. Blatchford Ltd.
3. Companies making other forms of body-worn devices (e.g. exoskeletons, orthoses, backpacks)
4. The general public
5. Trainee prosthetists, clinicians and clinical scientists
6. Researchers in gait simulation
7. Researchers in the design of body-worn assistive devices (prosthetics, exoskeletons, orthotics)
8. Researchers in experimental gait biomechanics

We have addressed academic beneficiaries elsewhere and we will limit ourselves here to focusing on industrial and societal impacts and public engagement with science (items 1-4).

LOWER LIMB AMPUTEES
Lower limb amputees typically consume up to 60% more energy in walking and are significantly less active than their age-matched counterparts, with major negative consequences for health and quality of life. By significantly improving energy efficiency we therefore have the potential to greatly improve this situation, particularly for older and higher level amputees. Our commercial partner, Blatchford Ltd, is ideally placed to facilitate this impact, as described below.

BLATCHFORD LTD
Our commercial partner, Blatchford Ltd, is the UK's leading manufacturer of prosthetics. Blatchford's experience with bespoke hydraulic product design extends over several decades and includes the recent Echelon foot (finalist in the prestigious Royal Academy of Engineering McRoberts Award 2010). Blatchford's are therefore ideally placed to exploit the emerging designs and have committed significant support for the project (see statement of support). Blatchford's expertise in practical hydraulic systems manufacture will allow for informed assessement of concept designs, guiding the direction of the academic research.

OTHER RELATED INDUSTRIES
At the most general level, the research will demonstrate to companies who work in the area of body-worn assistive devices the benefits of our approach (virtual prototyping including the prediction of gait adaptations), which we believe will greatly increase the number of possible design iterations and reduce costly human experimental work, when compared with current trials intensive methods. By adopting this approach a range of related industries, including manufacturers of exoskeletons, advanced orthoses and backpacks could radically improve their time to market. A concrete example of such a project would demonstrate its utility and we will show impact through articles in relevant trade journals and workshops.

PUBLIC ENGAGEMENT WITH SCIENCE
There is great interest in prosthetics (e.g. http://www.wellcomecollection.org/whats-on/exhibitions/superhuman.aspx) and the project will be an ideal opportunity to engage with schoolchildren, undergraduates and the general public. We will establish a project website and offer a session to Café Scientifique (http://www.cafescientifique.org/). Dr Kenney is an Academic Ambassador for IPEM and will discuss with them how to use the project to encourage undergraduates in physics and engineering to enter this field. We have growing links with the BBC through the University of Salford's Media City site and Prof Baker is already in discussions with them. We plan to exploit these links to advertise the project, with the aim of engaging with Big Bang or other popular science programmes.

We will also engage with amputee organisations (www.limbless-association.org/ and http://www.blesma.org/). We have good links to both organisations through Salford's UG programme in prosthetics. We will write brief articles for both organisations and suggest dissemination meetings.