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Below Knee Prostheses

There are several designs for below knee prostheses. The style of prosthesis that a patient is fit with will depend on the their activity level, residual limb length and shape, as well as their diagnosis and prognosis. The socket design will be determined. The three major types of socket designs are:

PTB or Patella Tendon Bearing (see below)
S or Silicone Suction Suspension
Suction socket

1. Below Knee Prosthesis- PTB or Patella Tendon Bearing

The patella tendon bearing socket places weight distribution over areas of the residual limb that are tolerant to pressure. This allows the user to put weight on the patella tendon, which is right below the kneecap. The patient is then able to minimize pressure over the residual limb and other boney areas, which are most sensitive. Most below the knee amputees are able to wear a patella bearing prosthesis. The PTB prosthesis is held onto the patient’s residual limb using one of the following common suspension systems.

RSC or Removable Supracondylar
SCSP or Supracondylar Suprapatellar
Suspension Sleeve

Patella Tendon Bearing RSC, or Removable Supracondylar Suspension

RSC, or Removable Supracondylar Suspension, holds the prosthesis on the residual limb by attaching above the bone on the inside of the knee. The user removes the supracondylar wedge to put the prosthesis on then puts it back in once the remnant limb is in the prosthesis. The wedge locks in over the bone of the knee.

Application and Removal

To apply the prosthesis, the patient will first remove the wedge from the prosthesis and insert the residual limb into the socket.
The residual limb is then pushed tightly into the socket.
The removable wedge is then inserted back into the socket to lock in the residual limb.

Care and Maintenance
In order to clean the prosthetic socks, the user should follow the directions of the manufacturer. The prosthetic socket may be wiped out with warm, soapy water, or alcohol if needed. Clean socks should be worn every day.

Tips and Problem Solving
Usually, the most complicated idea for an amputee to master is how to determine the right sock ply to wear in the prosthesis. Wearing the correct amount of socks is important for comfort, as well as proper fit and function of the prosthesis. A good fitting socket can create fit problems if worn with the wrong sock. If a patient is unsure, a prosthetist and physical therapist will provide the patient with information that can help determine the proper sock ply to wear with the prosthesis.

SCSP or Supracondylar Suprapatellar (link)

SCSP or Supracondylar Suspension keeps the prosthesis on the limb by holding on above the inside bone of the knee. A variant of the SC design is SCSP or Supracondylar Suprapatellar. This socket design extends the socket above the kneecap. This particular system is commonly used in individuals with short residual limbs because high trim of the socket improves the control the patient has of the prosthesis.

Patella Tendon Bearing Suspension Sleeve

A suspension sleeve is attached to the prosthesis and held in place by tension and friction of the material. The sleeve is generally rolled up on the thigh and holds the prosthesis on with suction and friction on the patient’s skin. Suspension sleeves are made of silicone, or similar gels, neoprene and elastic fabrics.

Application and Removal
If an insert is used, the prosthesis is applied as follows:

First, a prosthetic sock is pulled on over the insert. The prosthetic sock should be pulled up firmly without any wrinkles. The residual limb is then pushed into the prosthetic socket.

Some socket designs are worn only with socks and no soft liner, this is often referred to as a hard socket. A suspension sleeve may be used with a hard socket where no soft insert is present. In the case of hard sockets the patient is only wearing socks, which can be wool, cotton, acrylic or a blend of the three. Some socks have a silicone gel for improved skin protection and more comfort. With a sock fit and hard socket, the patient first applies the socks, and then pushes into the prosthesis. Once the prosthesis is on, the suspension sleeve must be rolled or pulled up onto the thigh, depending on the manufactures recommendation. In either application, the sleeve must be up on the thigh and wrinkle free. There must be at least 2-3 inches of the sleeve contacting the bare skin of the thigh for good suspension of the prosthesis. In order to achieve good suspension of the sleeve, the sleeve must extend above the socks used with the prosthesis. If the sleeve is applied when sitting, the patient may need to pull the sleeve up when they stand if wrinkles are present.

To remove the prosthesis held on with a suspension sleeve, the sleeve is pulled or rolled down to allow the patient to withdraw the residual limb from the socket.

Care and Maintenance
In order to clean the prosthetic socks, the user should follow the directions of the manufacturer. An insert, if used in the prosthesis, should be cleaned according to the manufactures recommendation or the prosthetist’s suggestion if the insert is a custom made device. The socket should be cleaned with warm, soapy water or alcohol as needed.

Also, follow the manufacturers recommendation on cleaning the suspension sleeves.

A patient’s activity will largely determine the length of time a suspension sleeve will last before being worn out. The average life of a suspension sleeve is two to six months. Over time, the sleeves may become stretched out and develop holes, which both reduce the ability of the sleeve to suspend the prosthesis. If the sleeve is not suspending the prosthesis well, the patient should contact their prosthetist for a replacement suspension sleeve.

2. Below Knee Prosthesis- Silicone Suction Suspension (3S)

Silicone suction suspension employs a roll on silicone liner that creates suction on the patient’s residual limb, and then uses a pin coming out of the bottom of the liner to lock into the prosthetic socket. It can be used with a patella tendon bearing (PTB), total surface bearing, or hydrostatic socket designs. Total surface bearing sockets which load all parts of the patient’s residual limb are often used with the 3S system. Prosthetic socks must still be worn over the silicone insert to compensate for swelling and general fluid changes in the residual limb.

Application

The liner is turned inside out. The liner should be clean and free of any dirt or debris that could irritate the residual limb.
With the liner inside out, press firmly up against the residual limb making sure there is no air pocket on the end of the liner as it is rolled up.With gentle pressure the liner is rolled up onto the residual limb.
Roll the liner up the limb. Do not over pull the liner when rolling it. Take care not to damage the liner with rings or jewelry.
When the liner is rolled up on the residual limb, attempt to get the pin straight off of the end. Take care not to puncture the liner with the pin.
If the liner does not have a fabric cover, a lubricant may be needed on the outer surface in order to get the liner to roll up the limb. Baby powder or a mixture of water and rubbing alcohol used in a spray bottle may be needed to lubricate the outside of the liner. Apply the lubricant onto the outer surface of the liner, turn the liner inside out, apply the lubricant and roll onto the limb. Check with a prosthetist to decide the best lubricant to use with the liner.
Apply the correct thickness of prosthetic socks for an appropriate fit. Be careful to insure the pin is out through the prosthetic socks for proper connection to the lock. A sock over the pin can result in the pin getting stuck in the lock. If this occurs consult a prosthetist.
Once the liner is on the residual limb, insert it into the socket. The pin will insert into the lock and click in as the residual limb goes into the socket. It should not be too easy to get the prosthesis to click on. If the application is too easy a thicker prosthetic sock may be required for a correct fit.

Removal

Depress the release button on the side of the prosthesis at the bottom of the socket and hold it down while removing the remnant limb out of the prosthesis.
The liner can be rolled down once the prosthetic sock is removed. (See figure 6). If the liner does not have a cloth cover, a lubricant may be required to remove the liner.

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 dishtowel, 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 as needed.

Tips and Problem Solving
If the pin-locking device is sticking, spray the lock with WD-40 or spray silicone.

3. Below Knee Prosthesis - Suction socket

A suction socket employs a roll on silicone liner that is rolled onto the patient’s residual limb, and then uses a suspension sleeve or a Seal-end liner and a valve in the end of the socket. The suction socket can be used with a patella tendon bearing (PTB), total surface bearing, or hydrostatic socket designs. Total surface bearing sockets, which load all parts of the patient’s residual limb are often used with below the knee suction socket system. This system creates a positive suspension, and very little movement is allowed between the prosthesis and the residual limb. Prosthetic socks must still be worn over the silicone insert to compensate for swelling and general fluid changes in the residual limb.