Prosthetic components include the socket, suspension and control system(s), joints, and appendage. There are many different options for prostheses, but all options aim to achieve a stable, comfortable fit for maximum function. The prosthetist (an expert who designs, fits, builds, and adjusts prostheses) helps people choose the type of prosthesis and options they need to accomplish their goals. For example, prostheses can be designed for general daily mobility, for specific activities such as swimming, or for high-impact and competitive sports such as running. The person's physical and cognitive abilities and gadget tolerance are important in the initial selection of prosthetic components.
Limb prostheses are exoskeletal or endoskeletal.
Exoskeletal prostheses have a hard outer plastic or metal shell in the shape of the limb. They are permanently fixed and not adjustable. Exoskeletal prostheses are more durable and may be preferred by people who do physical labor or are in harsh environments that could damage the prosthesis.
Endoskeletal prostheses have a central inner skeletal structure and are adjustable, but less durable. The endoskeletal system is often covered with a soft material in the shape of the limb and a synthetic skin.
(See also Overview of Limb Prosthetics.)
Upper Limb Prostheses
The hand has psychosocial significance. Amputation can affect a person's self-perception and/or identity and impact relationships and career. Psychologic counseling can help a person cope.
The human hand is complex. Often two different prostheses are needed to provide optimal function for general daily activities and for specific activities.
General types of upper limb prosthesis
There are 5 general types of upper limb prostheses:
- Passive prostheses
- Body-powered prostheses
- Externally powered myoelectric prostheses
- Hybrid prostheses
- Activity-specific prostheses
Passive prostheses assist in balance, stabilization of objects (such as holding down paper when writing), and recreational/vocational activities. They look like a natural limb and are the lightest and cheapest, but they do not provide active hand and joint movement.
Body-powered prostheses are the most common because they tend to be less expensive, more durable, and require less maintenance. A strap-cable system holds the prosthesis on and uses the motion of the person's shoulder blade and upper arm to operate the hook, hand, and/or elbow joint. Some systems use the opposite arm to trigger one particular function; one end of a strap encircles the opposite arm at the armpit, and the other end connects to a cable that controls the terminal device (hook, hand, or specialty device for particular function). People involved in physical labor typically favor this type.
Externally powered myoelectric prostheses provide active hand and joint movement without needing shoulder or body motion. Sensors and other inputs use muscle movement of the residual limb or upper body control electrically powered actuators that provide greater grasp force than body-powered prostheses.
Hybrid prostheses are typically used for higher level upper-limb amputations. They combine specific features of body power and myoelectric power. For example, a body-powered elbow might be combined with an externally powered hand or terminal device.
Activity-specific prostheses are for people who participate in activities that could damage the residual limb or everyday prosthesis, or when the everyday prosthesis would not function effectively. These prostheses often include a specialty design interface, socket, suspension system, and terminal device. Activity-specific terminal devices can allow the person to grasp a hammer and other tools, a golf club, or baseball bat, or hold a baseball glove. Others aid in various specific activities (for example, swimming or fishing). These prostheses can be passive or controlled by the amputee.
Lower Limb Prostheses
There are many variables and options for lower limb prostheses—there are 350 different foot/ankle systems and 200 different knees. The amputee and prosthetist evaluate different joint and foot components to determine which provide optimal balance, safety, function, and gait efficiency.
Most lower limb prostheses are endoskeletal because they are adjustable.
There are 3 general types of lower limb prostheses:
- Prosthetic ankle and foot systems
- Prosthetic knee systems
- Sport-specific prosthetic foot and knee systems
Prosthetic ankle and foot systems may include a hydraulic system that dampens impact forces. Some automatically adjust to changes in walking speed. Microprocessor-controlled ankle/foot systems regulate function in real time based on user input and/or environmental conditions. Some are passive mechanisms; others provide active propulsion, which greatly reduces energy requirements for walking. Axial or horizontal rotation lost from amputations above the ankle can be replaced with an endoskeletal torsion unit; this feature is especially helpful for situations in which the limb needs to twist while bearing weight, such as when playing golf. People who like to wear shoes with different heel heights (sometimes wearing sneakers or flats and sometimes wearing cowboy boots or high heels) can choose a prosthetic ankle that adjusts to different heights.
Prosthetic knee systems include passive body-powered systems with a single- or multi-axis joint. Microprocessor-controlled knee systems lower the amount of effort people need to use while walking and provide greater safety and stability control of the prosthetic knee reducing risk of falling.
Sport-specific prosthetic foot and knee systems help people achieve the highest level of physical performance. Some systems are effective for multiple sport and recreational activities. Others are designed for specific events (such as sprinting, long-distance running, skiing, or swimming). Running is more challenging for above-knee amputees than for below-knee amputees. Socket and suspension are more critical for athletes.