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Introduction
In 1976, Waters, Perry, Antonelli and Hislop measured the rate of oxygen consumption of both below-knee amputees and a control group (non-amputees) while they walked at their self-selected walking speed. The control group (N=50) consumed only 0.16 ml O2/kg/m while walking at a reasonably fast pace of 82 m/minute. However, patients (N=14) who suffered a trauma induced below-knee amputation needed 0.20 ml O2/kg/m to walk at slower pace of 71 m/minute. Even worse performance was exhibited by patients whose amputation arose from vascular problems. These patients (N=13) used 0.26 ml O2/kg/m to walk at only 45 m/minute.
While the control group had both lower limbs available to put energy into their gait, the below-knee amputee group did not. In fact, when broken down by joints, the hip contributes 22 joules/step, the knee 27 joules/step, and the ankle 36 joules/step (Gitter, Czerniecki, and DeGroot; 1991). Clearly, those with a lower limb amputation suffer a severe handicap.
Our research team is interested in testing the idea that if we could restore this lost energy, lower limb amputees would be able to walk better.
Approach
The idea of using powered prosthetic limbs has been around for a long time, however, most of the research and commercial activity has been on upper limb prosthetics. Among the differences between upper and lower limb devices are that upper limbs are used for fine manipulation tasks with small loads, while lower limbs are used for periodic motion (i.e. walking) with much greater loads. These differences result in some significant design challenges.
If a multi-disciplinary team were to develop the "perfect" lower limb prosthesis, the list of requirements might include:
Such a team might spend years developing a device which meets all of these requirements, yet it might not actually help an amputee walk any better. What if you had the perfect, portable, artificial limb to input energy into the amputee's gait, but they didn't walk any faster, use less oxygen, or have a lower perceived sense of effort? A lot of time and money would have been spent, but the goal of helping amputee's walk better wouldn't be achieved.
Our approach is to develop a limb for laboratory use to test the following hypotheses.
A powered prosthetic device for a below-knee amputee will:
To test these hypotheses, we don't need the "perfect" prosthesis, only one which can restore the lost energy to the amputee's gait while walking on a treadmill in the lab. If we're successful in this effort, we'll move on to some of the more difficult design challenges of the "perfect" prosthesis. Specific Aims