Skip navigation
9

Components of a prosthetic leg

 

Wayne Derman etch 2“Every prosthetic leg starts with the design of a socket best suited to the anatomy of the individual: if the socket does not provide a good, comfortable fit, if the suspension that links the socket to the body doesn’t perform well and if all the components are not correctly aligned, even the most expensive prosthetic components will underperform and probably be inadequate.”

- Prof Wayne Derman

Socket

The socket connects your residual limb to the prosthesis and is the foundation of a good prosthesis. A proper fit is essential to ensure that you can function comfortably and effectively. Since no two residual limbs are the same, the socket is custom-designed and manufactured to suit the shape of your residual limb. Designing and manufacturing a well-fitting socket is the most difficult part of a prosthetist’s job, and the top prosthetists constantly work on improving their knowledge and skills in socket design.

Liner

The liner plays a key role in suspending the socket from the residual limb and as a protective barrier between your skin and the socket. There are three main ways to attach the liner to the socket; namely, with a locking pin at the end furthest from the residual limb (locking liner), with an extra sleeve applied over the liner and socket (cushion liner), and by creating a vacuum with a seal (seal-in liner). Lately, the effectiveness of seal-in liners, essentially a passive vacuum system, has been improved with the incorporation of a pump that sucks air out of the socket, creating an even stronger attachment. Considering how fundamental the socket and suspension are to the effective functioning of a prosthetic leg, it’s impossible to overstate the importance of selecting the right liner.

Prosthetic knee

A prosthetic knee aims to mimic the function of a natural knee by providing safety, symmetry and smooth movement when walking, stability when standing and a range of motion that makes sitting and kneeling possible. The knee is one of the most complicated joints in the human body, so designing a prosthesis that functions like a real knee is quite a challenge. If the design is poor and forces the user to walk in an unnatural way, back and hip pain may result, and if the knee doesn’t suit the user’s physical requirements, it may even cause the user to fall.

Prosthetic foot

A prosthetic foot should ideally imitate the function of a real foot as closely as possible by providing a safe platform, handling differences in terrain and allowing the user to walk in a natural, symmetrical way. It’s the main prosthetic component responsible for absorbing the shock generated by impact on the ground due to the absence of muscles from the amputated limb, and it should also help the user walk more easily by returning the energy generated by the impact of walking.

Adapters

An adapter is any prosthetic component that links the main components such as the liner, knee and foot together, and can vary from components such as a simple tube to an expulsion valve.

Cosmesis

A cosmesis is a lifelike limb covering made from a material such as silicone or PVC. Its purpose is to mimic the appearance of a real limb, complete with freckles, veins, hair or even tattoos. Some types of cosmeses are ready-made, but for a truly realistic appearance a cosmesis has to be custom designed and manufactured by a prosthetist specialising in this aspect of prosthetics. How important the look of a prosthesis is differs from individual to individual: in the final analysis, appearance has to be weighed up against the extra cost and the possible effects on functionality.

Specialised components

Thanks to the amazing versatility of the human body, even the best current prosthetic technology won’t work for the full spectrum of human activities. The technology has come a long way, though, and today a person can often use the same prosthesis for quite a range of activities, such as jogging, showering and swimming – something that simply wasn’t possible even a decade ago. But there are other activities − such as sprinting, long-distance running and swimming − in which a specialised prosthesis is more suitable and will give the user more enjoyment. For example, although some general-purpose prostheses can be used for running, if you plan to go sprinting regularly it’s better to use components made specifically for that, such as the Cheetah blade. A recent innovation by Össur is a unique crossover foot prosthesis inspired by the original Cheetah design. Although primarily designed for everyday use, the Cheetah Xplore allows the user to engage in various sports and activities as well. On the other hand, current prosthetic technology plays no active role in the swimming motion and is merely an extra weight on the body, so swimming is a typical area where the prosthetist can build a custom activity-specific device. Our advice is to discuss your ambitions and lifestyle requirements with your prosthetist – while, as always, taking personal responsibility to be informed.