Veterans Affairs

Adaptive ankle prosthetic

Safe and efficient walking on sloped terrain, with improved stability for standing and swaying tasks

Medical & Biotechnology

Department of Veterans Affairs researchers have improved upon the design of prosthetic ankles with a new ankle-foot prosthetic (AFP) that can adapt its function for walking on sloped surfaces, providing stability and confidence. Patent licenses for the innovative design are available to businesses who would manufacture and sell the device. Contact TechLink for more information on this business opportunity.

Dr. Andrew Hansen, VA researcher and inventor of adaptive ankle prosthetics, works on a prosthetic foot with a screwdriver. (VA photo)

Many prosthetic ankles are spring-like structures that operate on one resting angle. These prosthetics may become unstable on sloped surfaces.

The AFP includes a foot plate attached to an ankle frame, a yoke pivotally connected to the ankle frame and including a member for attaching to a leg and a damper connected to the yoke and to the ankle frame.

The damper includes a microcontroller mechanism for switching the damper between low and high settings.

A pyramid-like attachment part 10, consistent with standard endoskeletal componentry in prosthetics, is provided at the top of a yoke 12, with holes drilled for front and rear pivotal attachments 14 and 16. The rear pivot attaches to one end 17 of a microprocessor controlled damper device 18. A neutralizing spring 20 is connected in parallel to the damper, such that its length change is equal to that of the damper. The damper device attaches on its other end 19 to an ankle frame 22, which has a yoke opening 24 and holes drilled at its posterior end 26 to pivotally attach to the damper by a shaft 28. The ankle of the device is a shaft 30 connecting the yoke with the apex 29 of the ankle frame. The ankle frame attaches with one or more bolts to the rear portion 32 of a flexible, yet deflectable rigid foot plate 34. The anterior end 36 of the ankle frame includes a follower or upwardly inclined surface 38 that limits the deflection of the foot plate such that the AFP will take a biomimetic ankle-foot roll-over shape during walking. The geometry of the surface is such that it provides the correct roll-over shape when the ankle is locked into a plantarflexed angle at the time of foot flat of walking, i.e., an angle of about 10 to 15 degrees.

The compression damping is set to a very low level and is unchanged throughout the walking gait cycle.

The extension damping for walking is set to a very high level at the beginning of the gait cycle and changes to low-level damping at the time of toe-off, which must be sensed using one or more sensors of force, acceleration, or other properties.

The extension damping can remain at a low level of damping for at least the time needed to return the ankle to a neutral or dorsiflexed position for swing phase and at most the time to the next foot flat event of the prosthesis.

For standing, both compression and extension damping levels can be controlled to be very high, providing a flatter effective shape and increasing the stability of the prosthesis user.

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