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Longer leg prosthetics are used for high amputations.
Prosthetics are artificial body parts designed to replace damaged or missing limbs. Leg prosthetics allow a person to walk after leg amputation due to injury or disease. There are many different types of leg prosthetics with 4 main components: the foot-ankle assembly, shank, socket and suspension. Variations in these components allow for a leg prosthesis designed to fit an individual's lifestyle.
Different types of foot-ankle assemblies are available that can accommodate a person's activity level, occupation and hobbies. The SACH -- solid ankle cushioned heel -- is commonly used for children to improve standing balance and for adults with lower activity levels. The single axis foot allows some movement at the ankle, pointing the toes down and bringing them up to make it easier to walk on uneven terrain. Bumpers keep the foot from moving too far in either direction. Multiaxial feet allow movement in multiple directions. The toe can point down or up, and the foot can turn inward and outward. This type of foot-ankle assembly handles uneven terrain better, but it requires more training than the single-axis or SACH feet. Dynamic response, or energy-storing, feet are used by people with more active lifestyles. These feet are typically made of carbon graphite, which is strong and lightweight. Energy is stored in the foot as a person steps on the heel, which helps propel the body forward when the toe pushes off the ground. Dynamic response feet can also be custom-made for athletes, including runners and swimmers.
Shank and Knee Component
The shank is the lower leg portion of the prosthesis. It can have an internal framework with a silicone covering or a rigid structure that is hollow on the inside. The knee component of a leg prosthetic is picked based on a person's balance and muscle strength. A manual locking knee provides the most stability but requires the most energy for walking. This knee is locked or unlocked by the user with a cable. Weight-activated stance control components swing the knee while walking but can be locked in a slightly bent position by putting weight on the foot. This is an appropriate option for people with weak muscles. Hydraulic knee joints use compressed air or fluid to move. These joints allow a person to walk at different speeds. Some of these knees also have a microprocessor that detects leg movement and automatically adjusts the hydraulic component.
Sockets and Liners
A leg prosthesis is attached to the remaining or residual limb by a socket. These are custom-made out of plastic materials using a plaster mold of the residual limb. The socket distributes body weight appropriately, either on a tendon that crosses the kneecap for a below-knee amputation or the bottom of the thigh for an above-knee amputation. Swelling fluctuates, causing the size of the leg to change frequently. Liners are worn under the socket to adjust the fit on a daily basis.
Prosthetic legs are held in place with a variety of suspension systems. The suction method is commonly used. A silicone sleeve slides over the residual limb with a pin sticking out of the bottom. The pin locks into the socket, securing the prosthesis to the leg. Other suspension systems include cuffs that wrap around the end of the thigh bone, a waist belt with an elastic strap on the front of the thigh or a thigh corset.