An above knee prosthetic socket is the most important component of the above knee prosthesis. The socket is what comes into direct contact with the user and dictates the success or failure of the prosthetic rehabilitation.
There are many socket designs for the above knee prosthesis, depending on the anatomy, activity level, and personal preference of the user. The suspension system refers to how the socket attaches to the user’s residual limb.
The main options for above knee prosthetic socket designs, or transfemoral suspension systems, are:
Suction suspension , where there is no interface between the residual limb and socket. This type of suspension relies heavily on total contact, as gapping can lead to suction failure. The prosthetic user usually pulls into the socket using a pull sock and a suction valve eliminates air. When it is time to remove the prosthesis, the user releases the suction valve, air is introduced into the socket, and the prosthesis is easily removed.
This type of design:
· Allows the user to have better control of the prosthesis, as there is no interface between the residual limb and limb.
· Provides excellent stability, as the entire residual limb is retained securely inside the socket.
· Can be difficult in donning.
· Does not accommodate for volume change of the residual limb.
· Does not require replacement of soft goods, such as liners, or socks.
Gel liner -pin locking suspension involves the use of a silicone gel liner as the interface between the residual limb and the socket. The user rolls the gel liner onto the residual limb. The gel liner has a pin sticking out of the distal (bottom) end. This pin locks into a locking mechanism inside the socket. This type of suspension system:
· Provides easier donning/doffing, which can be done even in the sitting position.
· Cushions the residual limb.
· Allows for volume fluctuations, as prosthetic socks can be used in addition to the liner.
· Is sometimes associated with a distal end pulling sensation of the residual limb.
· Requires liner replacement, which can be expected every six to twelve months.
Gel liner – Lanyard suspension involves the use of a silicone gel liner as the interface between the residual limb and the socket. The user rolls the gel liner onto the residual limb. The gel liner has a cord or strap attached to the distal (bottom) end, which is fed through an opening in the distal end of the rigid frame of the socket. Once this is done, the residual limb can then be pulled in securely, and the cord or strap is then secured to the outside of the socket.
Gel liner -suction liner suspension involves a gel liner, which services as the interface between the residual limb and the socket. This liner is similar to the pin locking liner; however, this liner includes a suction rim that eliminated air from the distal end of the socket interior. This type of suspension system:
· Provides easier donning/doffing, which can be done even in the sitting position.
· Cushions the residual limb.
· Allows for volume fluctuations, as prosthetic socks can be used in addition to the liner.
· Is sometimes associated with a distal end pulling sensation of the residual limb.
· Requires liner replacement, which can be expected every six to twelve months.
A suspension belt can be used to supplement any of the suspension systems above. The suspension belt is rarely used today as the main source of suspension, due to instability and pistoning of the residual limb inside the prosthetic socket. There are several types are suspension belts, including Silesian belts made of leather, or silicone, and TES belts, which are commonly used for a user’s initial prosthesis. Higher level amputees may also benefit from a pelvic/hip band belt design. Many users today have developed a preference against the use of belts; however, a suspension belt can provide a subtle and effective form of suspension security.