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Above knee prostheses consist of five main components which allow the knee to bend, transmit weight and provide the individual with the potential to walk and include:
- The Socket
- Knee Systems
- Suspension Systems
- Shank
- The Foot-Ankle System
The Socket
The socket for an above knee amputee has two basic designs:
Ischial Containment Sockets- normally have a rigid frame with a flexible inner socket designed to contain the pelvis inside the socket. This rigid frame increases stability and optimises control when walking.
Quadrilateral Socket - provides a shelf for the pelvis to sit on, maintaining contact with the pelvis on the brim of the socket. In comparison to the ischial containment the socket is narrower at the front and back and wider in width.
Knee Systems
Knee systems are designed to stabilise the individual during standing by transmitting weight through the prosthesis. The knee system should also enable the prosthesis to bend, operating similar to a normal knee and allowing the person to walk at will.
A single-axis knee system can only bend and straighten in one direction. This knee system has reduced stability during standing, requiring the individual to use their own muscle strength.
Polycentric knees allow the knee to bend in slightly different directions. This can allow individuals to walk on uneven surfaces and run but will depend on the individual’s aims and capabilities.
Suspension Systems
Suspension systems are designed to hold the socket on the stump. There are various designs including; a silesion bandage, a pelvic band with joint, a suspension sleeve silicone liner with a locking mechanism in the socket or a true suction socket with a valve. Each system has its own criteria and advantages and disadvantages. Individual preference will also be considered when choosing a particular suspension system for the prosthesis.
Shank
The shank makes up the lower leg and connects the socket to the ankle-foot assembly. There are two main designs:
Endoskeletal design has a soft foam cover to look and feel like skin. This prosthetic is lightweight, easily adjustable and compatible with the advancing technology in knee systems. However, the foam cover is fragile and can be easily damaged.
Exoskeletal design has a rigid and durable shell made of laminated combined material and does not allow adjustments once it is finished. This design is more durable than the exoskeleton and is able to transfer weight over the entire design, so it is more suitable for people who require prosthesis to carry out heavy duties.
Foot-Ankle System
The foot-ankle system is vital to provide support while the individual stands on the prosthesis. There are several designs of prosthetic feet which include:
SACH (Solid Ankle Cushion Heel) which produces only a single motion. The advantages of this design it that it is lightweight, durable and relatively inexpensive.
Single-axis foot this design allows ankle motion and assists in making the knee more stable.
Dynamic response feet are designed to allow the prosthesis to “bounce” off their heel being more energy efficient to walk with.
If you would like more information on above knee prostheses or to book an appointment please call Physio.co.uk on 0330 088 7800 Alternatively, book online today!
