Assistive Technology Notes: Lower Extremity Prosthetic Devices

Continuing to Farm with Lower Extremity Amputations

Technological advances in the development of new prosthetic devices have produced devices that are more comfortable and stable, provide a more natural gate, save energy, reduce fatigue, increase function, and withstand the forces that farmers experience when performing day-to-day farm tasks.

There are three categories for lower limb prosthetics: above knee, below knee, and partial foot. The basic components of a lower extremity prosthesis include: the socket, a sock or gel liner, a suspension system, a knee joint (articulating joint), the shank (a pylon), and a foot (terminal device) ⁷ (Fig. 1).

Figure 1: Lower extremity prosthesis components.

The socket enables the prosthesis to connect and fit to the stump (residual limb). This is the most important prosthetic component. A good fit is critical. A socket that is uncomfortable is a common reason why a prosthesis is rejected. Contoured sockets fit closer to the remaining bones, muscles, and soft tissues providing better support, and provide relief where it's needed for comfort. ⁸ Examples of contoured sockets include the Hanger ComfortFlex™ Socket System, Quadrilateral Socket, CAT/CAM Socket, ML socket, Acrylic socket, Total Contact Socket, Pump It Up system, the Otto Bock Air Cushion Socket system and more. Liners are sometimes used inside the socket to obtain a better fit and for comfort. A gel liner helps in pressure distribution, comfort, and skin smoothing.

The suspension system keeps the prosthesis from sliding off the residual limb. A suspension system may consist of a variety of belts, wedges, straps, suction, or any combination of these.

Individuals who have an above-the-knee amputation often use a prosthetic knee joint, a mechanical joint that replaces the knee joint and provides support and control when walking. Advances in prosthetic knees include a hydraulic, pneumatic, a single axis constant friction knee, or an electronic knee. The electronic microprocessor controlled knees, such as the Ottobock C-Leg System (Fig. 2) or the Endolite Adaptive Prosthesis, electronically sample the way a person walks and make immediate adjustments to pneumatic and hydraulic mechanisms in the knee joint. The electronic knee system provides better stability and can assist with stumble recovery to reduce falls and prevent the knee from buckling. ⁹ This is particularly important when farmers are walking up or down hilly surfaces or in fields with weeds, plants, or corn stalks that can increase potential stumbles.

A color photo of the Ottobock C-Leg system that displays all the various components used to make the above knee prosthetic.
Figure 2: Ottobock C-Leg System

The shank, also called a pylon, can be a hard shell, a tube, or even something that looks like a “leaf spring” and attaches the socket to the foot. Advances in the design of pylons include the ability to allow for axial rotation, shock absorption, and energy storage and release. For a farmer, these features may be particularly useful when getting on and off the tractor and walking around rough terrain. The pylon can be covered with a soft or hard covering for cosmetic purposes.

The foot, also called the terminal device is the part of the prosthesis that comes in contact with the ground, provides movement and a stable weight-bearing surface, and absorbs shock while walking. It may allow movement at the ankle or the foot itself may be flexible to allow movement. Figure 3 shows a wide variety of terminal devices that are available.

A color photo of 9 different terminal foot devices that can be used on prosthetics.
Figure 3: Variety of Foot or Terminal Devices

Active farmers may find the energy-storing multi-axis foot well suited to their work needs. This type of foot not only helps to absorb shock and save energy, it can also accommodate walking on uneven surfaces or dismounting a tractor. This foot “gives a little” in side to side motion and also adjusts to rotational forces that can occur when walking on rough terrain. Energy-storing feet can also be called a flex foot system, an energy storing foot, multi-axial ankle/foot, dynamic response foot, or flex-walk system. ¹⁰

Farmers who use prosthetic devices may also benefit from accommodations to their worksite and equipment. Adaptations or changes may reduce fatigue and stress to the prosthetic device and other parts of the body. Depending on the farmer’s needs and situation, modifications could be made to equipment or to how the work is performed; such as, additional steps and hand controls in tractors, automatic hitching systems, back saving solutions, outdoor mobility aids, and modifications to buildings, gates, and livestock handling facilities. To learn more about these worksite modifications and assistive technology solutions, explore the various resources and tip sheets available on the National AgrAbility Project Web site at http://www.agrabilityproject.org/assistivetech/

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In This Issue
Section 1: Client Story – Tractor hand clutches and a positive attitude keep an Indiana farmer going Section 2: Focus – Lower Extremity Amputations Section 3: Assistive Technology Notes – Lower Extremity Prosthetic Devices	Section 4: State Project Feature – Breaking New Ground-Indiana Section 5: References and Resources Section 6: Contacts