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Yanke Bionics - For patients with a trans-femoral amputation

Your Definitive Prosthesis

There are two primary types of design for a definitive prosthesis:

Exoskeletal

Exoskeletal designs include a hard shell often made of acrylic plastic. This shell or "skin" is rigid and durable. This type of prosthesis is not readily adjustable after it has been finished. The primary advantage of an exoskeletal design is durability and its ability to transfer the weight from the socket to the foot. The acrylic lamination often used for the prosthetic shell allows a high-impact surface with excellent load bearing capabilities. When an amputee requires great durability in a prosthesis, such as that needed for farming, or other element-involv-ing or heavy-duty occupations, an exoskeletal design may be a good choice.

Endoskeletal/Modular

Endoskeletal/Modular designs include an anatomically shaped, soft foam cover designed to look and feel like skin. This soft material covers the internal structure of the prosthesis and is removable to allow the prosthetist to make adjustments and changes to the prosthetic system when necessary. Connectors with an aluminum, titanium, or carbon pylon (tube) connect the socket with the foot. The soft covering on an endoskeletal prosthesis is some-what fragile and requires careful attention to prevent damage. The primary advantages of this design are that it is adjustable and lightweight. In addition, most of the technologically advanced knees are compatible with endoskeletal designs.

Components

There are four main parts to any above knee prosthesis: socket, suspension system, knee and foot.

Socket

As mentioned earlier, the socket is the part of the prosthesis into which your residual limb fits. It is the interface between the residual limb and the prosthesis. Each socket designed by your prosthetist represents a particular amputee's needs and the prosthetist's efforts to treat those needs.

Your prosthetist knows from experience that you will be more likely to wear a prosthesis that fits comfortably and he/she will carefully design the socket with your comfort in mind. Sockets may be hard or soft and can be made from one of many different materials. In addition, the socket may include a liner of foam, leather, silicone, or other materials.

Sockets must fit intimately to be comfortable and your prosthetist may use a check socket made from clear material to evaluate the socket fit before actually producing the socket for your definitive prosthesis.

There are two basic socket designs for above knee amputees:

Ischial Containment Sockets may be rigid or flexible and can be made in a variety of shapes. They are designed to contain the pelvis inside the socket. In general, ischial containment sockets have a larger dimension front to back and a narrower dimension from side to side than the quadrilateral socket.

Quadrilateral Sockets have four sides and are designed to maintain the pelvis on the brim. Quadrilateral sockets have a larger dimension side to side and a narrower dimension from front to back than the ischial containment sockets. With the quadrilateral socket, there is a shelf for the pelvis to sit on.

Suspension System

A suspension system holds the socket on your residual limb and may include a Silesian bandage, a pelvic band with hip joint, suspension sleeve, suction suspension sleeve, or suction valve. Sometimes a prosthesis will use more than one suspension method. There are certain criteria for the use of specific systems, and patient preference can also play a role. In general the use of a belt is not necessary when fitting a prosthesis to a long residual limb.

Suction is the most desired suspension system because of the intimate fit and is typically suited to a longer residual limb. Sleeker suspension options, such as silicone sleeves with pins, are available for residual limbs which have healed and for which most of the changes in shape and volume have occurred.

Each suspension system has advantages and disadvantages that your prosthetist will consider when choosing the right suspension for you.

Knee

The knee allows the prosthesis to bend while you are standing on the foot and when taking a step forward. Prosthetic knees are designed to avoid buckling when standing and to allow the artificial leg to be advanced normally at will. Special designs can allow you to walk on uneven ground or to run and change speed. Typically younger and more active amputees wear these knees. Your prosthetist will discuss your activity level with you to allow special options to be included in the design of your prosthesis.

If you have a relatively short residual limb, you will not have as much hip extension muscle control and will require a “safer” design. Your physician may prescribe a weight activated locking knee (safety knee) which will lock when you step on your foot and then release to allow the knee to swing when advancing the prosthesis forward.

Advanced systems are available for amputees who wish to run. Swing phase control systems can include either pneumatic or hydraulic control systems to enable the wearer to run or vary walking speeds. Newer "high tech" knees include those with microprocessors which are adjustable throughout the life of the prosthesis, often using a laptop computer to alter them. Other lightweight knee frames include those made of graphite, which house small adjustable knee control units.

Foot

The prosthetic foot provides the necessary support to keep the knee stable while you stand on the prosthesis. There are a variety of types of prosthetic feet.

For many years the standard foot was the Sach foot, pronounced "SATCH" which stands for Solid Ankle Cushion Heel. As the name implies, the Sach foot is solid, produces only simulated motion, and is lightweight, durable, relatively inexpensive, and provides nice smooth foot action when walking.

Another option is the single axis foot. This articulated foot allows ankle motion which assists in making the knee stable.

Recently a great deal of research has produced feet with flexible keels, which allow amputees to “spring” on and off the foot as they walk. These feet bend when walking and because of their design, the materials store and release energy like a spring. These feet sometimes referred to as "energy storing" or dynamic response feet. Some of the “energy storing” feet have been shown to actually save energy for the amputee as he/she walks.

Your prosthetist will detail the many foot options and will further explain any special considerations in dealing with your individual situation.

Request an online evaluation

Use our evaluation form to request a no-obligation consultation from our clinicians. We will contact you to discuss your pre-surgery or prosthetic-related questions.

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