Iceexpress progressive prosthetics
Helping amputees in low income countries and post war zones
Össur Kristinsson
JUNE 2005
A lost leg, below or above the knee, is a severe disability. An artificial leg, or prosthesis, is intended to replace a lost leg with something functional and, preferably, not too uncomfortable, in order to remobilize the amputee.
Prostheses are built from several components. The most critical component of that assembly is the socket. A socket is a rigid container, usually made by resin infusion into a glass or carbon fiber lay-up over a model of the residual limb. (Residual limb is a stump in most people's vocabulary so; hereafter a residual limb is termed as a stump). The socket is the stump's receptacle and hence, has to counteract the load of the body's weight, transferring the ground reaction forces to the skeleton, which is the ultimate receiver of the forces involved.
An integral and very important part of the socket is the interface between stump and socket. It typically consists of stump socks and foam cushioning. Inner sockets, or "liners", made from silicone or similar materials such as polyurethane are also used.
The residual limb is essentially a skin envelope containing the bones and what we simply refer to as soft tissue. Soft tissue is a mix of different components such as blood vessels, fluids, membranes and muscles. The bulk of this soft tissue mass consists of the muscles. After amputation the muscles lose their distal attachment and become non-functional. They have no joint to work, and soon fill with fat to turning into tissue that is soft as well as easily deformed and displaced. Gripping a stump with your hands, manipulating its form and moving the skin up and down, easily demonstrates, that with regards to form, this is a highly unstable mass. The only non deformable part of it is the bones.
For prosthesis to function, the stump has to be enclosed in a receptacle, a socket, of proper volume and form. The socket accepts the loads and counteracts the forces necessary to support the body's weight and to stabilize the moving mass of the body against lateral forces. Prostheses are always custom fitted. A person who fits prosthesis is a prosthetist.
Prosthetists; who are they and what do they do.
A prosthetist is a person that has been certified to fit prostheses to residual limbs of the upper and lower extremities. The fitting of lower extremity prostheses, for example, involves making a socket that fits the stump as a first step. The socket is usually manufactured by glass or carbon fiber infused with acrylic resin or from thermoplastics over a positive model of the stump. The socket is connected to a foot or ankle assembly and in the case of above knee amputation, an artificial knee. The connecting components are usually an aluminum tube with two part pyramid alignment devises one at each end. One of the devises connects to the ankle and the other one to the socket. They allow the foot to be placed in proper position to support the person's weight with the least possible lateral forces acting through the system. Prostheses are aligned with the client walking, while the prosthetist observes the gait and corrects for any deviations from optimized movement when the leg is in the air and for its position at heel strike and toe off.
Above the knee prostheses are several degrees more difficult to make, both in terms of socket design and alignment, than below the knee prosthesis.
The most commonly used methods for fitting sockets to residual limbs start with a hand casting of the stump with plaster of Paris bandages. Important part of the casting procedure is to force form upon the cast by the grip of your hands before the plaster sets. The cast is then filled with plaster of Paris for a positive model and when hardened, the model is further modified by removing and adding material.
The resulting model, hopefully then, is a replica of the stump, moulded to an ideal load bearing form. A socket made over such a model (any socket for the matter of argument) relays on skeletal contact for weight bearing. That weight bearing contact, of course, is transferred to the skeleton via pressure on the skin and underlying tissue in selected areas.
The most common socket concept for below the knee prosthesis is the PTB (Patellar Tendon Bearing) socket, where major weight transfer is supposed to be via the patellar tendon. Patellar Tendon Bar is an indentation in the socket wall over the knee cap tendon. PTB's usually are uncomfortable sockets that have to be rectified and adjusted regularly until they are no longer functional and need to be replaced.
Using conventional fitting and manufacturing methods a BK prosthesis in Europe and in the US carries a price tag of ca. 5.000 US dollars. Time spent on the manufacturing of one BK prosthesis ranges from 25 to 40 hrs.
ICEROSS®
The Iceross silicone liner was introduced in the mid nineties. By rolling a silicone liner onto the stump it becomes a much more stable body than the unsupported stump. This fact has helped tremendously in improving socket design and providing better sockets. The Iceross has a distal (towards the end) locking mechanism which locks the Iceross liner and the socket firmly together. Thus, it solves the problem of suspension and minimizes movement between the stump and the prosthesis. Today most prosthetists use Silicone liners, Iceross or similar, to fit their customers.
ICEX®
A technique called Icex makes it possible to fit prosthetic sockets directly to residual limbs using Iceross as an interface. The Icex technique is an easy fitting method, where the socket is made and alignment performed in one session. The socket is made directly over the stump. The reinforcing material is fitted over the Iceross, infused with odorless polyurethane resin and then pressurized to a select pressure level. The resin sets in fifteen minutes where after the moulded socket can be removed for trimming and assembly. This method is accepted by many prosthetists as being superior to conventional methods and could possibly be a universal solution to the difficult problem of making well fitting sockets. The Icex method is both relatively easy in execution and can be utilized without much technical support.
This method yields a socket that is ready for assembly and alignment in less than an hour.
Össur Kristinsson is an authority on socket design. He is the inventor of the ISNY socket, an above knee socket where the functions of support and containment are separated. This concept allows for sockets to be flexible and to a degree interchangeable without too much effort. He also is the inventor of the Iceross, the Icex and the Icecast.
Össur hf is the owner of the patents and the manufacturer of Iceross, Icex and Icecast.
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