Biomedical Engineering Reference
In-Depth Information
FIGURE 10-65
Mechanical design
of a powered
ankle-foot
prosthesis. [Adapted
from (Au, Weber
et al., 2007).]
FIGURE 10-66
Examples of active
prosthetic feet.
(a) PowerFoot from
iWalk Inc. (b) Proprio
Foot from Össur.
(Courtesy of iWalk
and Össur, with
permission.)
Examples of the state-of-the-art in active foot prosthetics are the PowerFoot
®
and the
Proprio Foot
TM
devices, shown in Figure 10-66. The PowerFoot is the latest lightweight
prosthesis developed by iWalk Inc. It integrates three microprocessors and 10 environmen-
tal sensors to evaluate and adjust ankle position, stiffness, and damping in real time
The
Proprio Foot is a motor-powered foot from Ossur with an integrated motion sensing system
that detects and adapts to terrain changes in real time. The active ankle motion identifies
slopes and stairs after the first step and instructs the ankle to flex appropriately and allows
wearers to more easily sit down or rise from a chair.
In even the most advanced passive foot prosthetics, some energy is lost during each
stride so less energy is provided at push-off than was absorbed during contact. However,
in these active prostheses, power assist provides additional spring at push-off to reduce
energy expenditure by the amputee.
.
10.10
PROSTHESIS SUSPENSION
One of the major problems with any prosthesis is the fact that that it cannot easily be
attached to the articulated support structure (skeleton) to which the original limb was
attached. This requires that the full weight of the device and any applied loads be supported
by soft tissue.
Often the contact between the soft tissue on the limb and the prosthetic attachment
causes problems such as blisters, cysts, edema, and other skin irritations. Another common
problem is that the weight load on a prosthetic limb can be painful and can restrict blood
