Above Knee Prostheses
Above knee prostheses are available in several designs, usually depending on the patient’s age, activity level, residual limb size and shape, as well as their diagnosis and prognosis. The above knee amputee will support their body weight on the ischial tuberosity (seat bone), with the soft tissue of the residual limb bearing only a minimal amount of weight. The above knee amputee will always feel some pressure on the ischial tuberosity because they are essentially sitting on the socket. The above knee prosthesis is held onto the patient’s residual limb using one of the following suspension methods.
Above Knee Prosthesis - Suction Suspension
Suction suspension refers to the negative pressure or suction that is created between the residual limb and the smaller prosthetic socket when a person pulls his or her remnant limb into the prosthesis with a sock or a donning sleeve through a hole in the bottom of the socket. Once a person is down in the socket, a valve is then inserted into the hole and vacuum is achieved. Suction suspension helps the prosthesis feel lighter to the wearer because it is a positive suspension and little movement occurs between the residual and the socket. Persons using suction suspension must have stable volumes of their residual limb. If the person swells or gains weight he will no longer be able to get into the prosthesis. If the person loses weight, suction will be lost and the prosthesis can fall off. A person using suction suspension must also have sufficient arm and hand strength and the steadiness to pull their remnant limb into the prosthesis.
Application of a Suction Socket
The three traditional ways to apply or don a suction socket are a pull sock, ace bandage, or a donning sleeve.
- Pull sock: Use a cotton or nylon tubular pull sock that is two to three times the length of the residual limb. Pull the sock over the remnant limb all the way up to the groin area. Push the long excess remainder of the sock through the valve opening at the bottom of the prosthetic socket. Begin pulling the end of the sock through the valve hole while pushing the remnant leg into the prosthetic socket. The wearer must alternate between lifting up and pushing down while gently pulling the sock through the valve hole. Progressively, the pull sock will have pulled all the way out of the valve hole and the remnant limb will be all the way into the socket. There should be no air pocket between the remnant and the bottom of the socket. While keeping the weight on the prosthesis, the valve is then inserted into the valve housing creating an airtight suction seal.
- Ace Bandage: Use a 4”x 5’ ace bandage. Begin wrapping the bandage from the top of the remnant limb using modest force and overlapping roughly half of the previous wrap. After wrapping the whole remnant limb, a length of ace bandage will be remaining at the bottom of the remnant limb. Push what’s left of the bandage through the valve hole at the bottom of the prosthetic socket. Begin pulling the end of the bandage through the valve hole while pushing the remnant limb into the socket. The wearer must alternate between lifting up and pushing down while gently pulling the bandage through the valve hole. Progressively, the bandage will have pulled all the way through the valve hole and the remnant limb will be all the way into the socket. While keeping weight on the prosthesis, the valve is then inserted into the valve housing creating an airtight suction seal.
- Donning Sleeve: This is a cone fashioned sleeve made out of a slick material that is like parachute fabric. Introduce the remnant limb into the sleeve up to the groin area. Begin pulling the tail of the sleeve out through the valve hole in the bottom of the socket while pushing the remnant limb into the socket. Start pulling the end of the tail through the valve hole. The wearer must alternate between lifting up and pushing down while gently pulling the sleeve through the valve hole. Progressively, the sleeve will pull totally through the valve hole and the remnant limb will be all the way into the socket. While keeping weight on the prosthesis, the valve is then inserted into the valve housing creating an airtight seal.
To remove the prosthesis, the wearer should either depress the button on the suction valve or unscrew the valve fully to remove it, this then releases the vacuum. Now the prosthesis can be pushed and gently worked off of the remnant limb.
Care and Maintenance
The prosthetic socket ought to be washed daily with mild soap (no perfumes, lotions, or deodorants) and water. Depending on the skin sensitivity of the wearer, alcohol or moist towlettes may also be used. The valve may also need intermittent cleaning. Ask a prosthetist how to take apart and clean the suction valve or see a prosthetist for periodic valve cleaning.
Tips and Problem Solving
If the prosthesis looses its suction:
- There may be a leak in the valve. See a prosthetist for an assessment.
- A weight loss may have resulted a decrease in remnant limb volume. The prosthetist should be seen for possible filling of the socket.
If the bottom of the residual limb is purplish in color or swollen:
- Weight increase or volume fluctuation may be preventing the remnant limb from going all of the way into the socket. See a prosthetist for a socket assessment.
Above Knee Prosthesis - Silicone Suction Suspension
A silicone suction suspension user rolls a silicone suspension liner onto the remnant limb creating a seal between the liner and the person’s skin. The suspension liner has a pin with a pull string or a rubber seal on the end that locks into the bottom of the socket. A prosthetic sock is worn on the silicone insert in order to allow for volume fluctuation.
Application and Removal
To apply the silicone suction liner prosthesis, the liner insert must first be turned inside out and gently rolled onto the remnant limb. Do not us any lotions or creams on the remnant limb before rolling on the silicone insert. When rolling on the liner be certain there is not an air pocket between distal liner and the remnant limb. As the liner is rolled up on the remnant limb be sure the top of the liner is not stretched up on the thigh. Over pulling the top of the liner can cause blisters and skin irritation. Socks are then worn over the liner for an appropriate fit of the prosthesis and to adjust the fit of the prosthesis for size changes of the remnant limb. At the bottom of the silicone liner there is either a pin with a string or a rubber seal.
The string is put down in the socket and pushed into the center of the lock located in the bottom of the socket. As the string is pushed into the lock it will come out the front of the prosthesis and will be pulled down towards the foot which will pull the remnant limb into the prosthesis. A clicking will be heard as the string is pulled down which indicates the prosthesis is locked on. To remove the prosthesis press in and hold the release button which is generally located near the bottom of the socket on the outside of the prosthesis. With the release button pushed in you can generally push the prosthesis off your remnant limb.
The Seal-end liner is rolled on the remnant limb the same as the pin type liner. Before the remnant limb and liner are inserted into the socket a 50 /50 mixture of water and rubbing alcohol are lightly sprayed in the socket from a spray bottle. The person then pushes the remnant limb and liner into the socket and the trapped air is pushed out a valve at the end of the socket. The rubber seal then creates a suction seal between the silicone liner and the socket which holds the prosthesis in place. Special Seal-end socks can be used to compensate for shrinkage of the remnant limb. This sock is placed under the rubber seal of the silicone liner and them fits on the upper part of the remnant limb and the liner. If the sock is pulled over the rubber seal no suction suspension will be created. To remove the prosthesis with a Seal-end liner, air must enter the bottom of the socket by removing the suction valve or pushing and holding it in as the prostheses is pushed off.
The gel insert is removed by unrolling the insert off of the limb.
Care and Maintenance
- The gel insert must have the inside washed by hand every day with mild soap such as Soft Soap and water. DO NOT USE AN ABRASIVE DEVICE WHEN CLEANING THE LINER, scrubbing with your hand works best. Avoid soaps with perfumes or deodorants and rinse well several times to remove all soap. Dry by blotting with a lint free towel such as a dish towel and store the insert right side out away from direct heat.
- Clean prosthetic socks should be used every day.
- The socket can be wiped out with mild soap and water or with rubbing alcohol weekly, or as needed.
Tips and Problem Solving
- If the pin locking device is sticking, spray the lock with WD-40 or spray silicone.