How Modern Prosthetics Work

Prosthetic limbs have existed since the time of the ancient Egyptians, where a working prosthetic toe of wood with a leather harness allowed the wearer to use the sandals of the time or to go barefoot. Prosthetics may be necessary because of missing body parts due to trauma, congenital conditions, or disease. Prosthetic limbs are designed to restore the missing body part's normal functions. Modern prosthetics are generally created with computer-aided design, but they can also be hand-designed. Of Americans, one in 190 citizens is presently getting along with the loss of a limb. The leading cause is poor circulation due to the disease of the arteries, with more than half of cases occurring in patients with diabetes mellitus.

The Pylon

The pylon, the internal skeleton or frame of a prosthetic limb, is responsible for providing structural support. Traditionally, it has been made of metal rods. More recently, lighter composites of carbon-fiber have been utilized to create the pylons. Sometimes, pylons are enclosed by a foam-like material that serves as a cover that can be colored and shaped to match the skin tone of the recipient to give the prosthetic limb a more lifelike appearance. Pylons transfer weight between the prosthetic ending and the socket. Dynamic pythons are preferred, particularly in lower limb prosthetics, as they reduce the shocks created by the heel striking the ground.

The Socket

A prosthetic limb's effectiveness and comfort are generally governed by the quality of its fit onto the remnant of the patient's actual limb. This is professionally referred to as the residual limb, or more informally, the stump. Some individuals with missing limbs find the term stump offensive, but it is still widely in use in the medical world. Sockets are the connecting parts of the prosthetic limbs. They are painstakingly molded around a cast of plaster taken from the patient's residual limb.

Without a precise fit, sockets of the new limbs may damage the remnant of the residual limbs, causing tissue damage or discomfort and potentially making it too painful to wear the prosthetic limb for an extended period. As the residual limb is generally likely to change in size and shape over time, new sockets are routinely needed. Lasers and 3D printing are now being used to make precise prosthetics.

The Suspension System

The attachment mechanism, known as the suspension system, is an essential part of a well-fitting prosthetic limb. The suspension system can consist of a suction socket, an elastic sleeve, or an old-fashioned arrangement of harnesses and straps. The fitting must be secure and snug, not only because it is vital for comfort, but because it ensures the prosthetic limb can be controlled properly. In many cases, the socket is a part of the suspension system arrangement. In the instance of a prosthetic leg, sockets may come in the form of a large plastic casing that is hollow so the residual limb can be inserted.

Making Prosthetic Limbs

Making prosthetic limbs starts with the design and fabrication procedure and has many steps. It begins with a measurement process that is painstaking in its precision and is later utilized in designing the prosthetic limb. When possible, the prosthetist starts the measurement process even before the patient's limb is amputated. This allows the fabrication procedure to begin well ahead of time. Once the swelling has gone down after the amputation, a plaster mold is made of the residual limb. This serves as a template so a duplicate of the residual limb can be created. This duplicate is then used to continually test the prosthetic limb's fit as it is being fabricated. Newer technologies permit the use of computerized digital measurements to ensure precision.

Controlling The Prosthetic Limb

Some prosthetic limbs are solely cosmetic and designed only with appearance as the goal, rather than controllability. Others are designed with function and usability as a central purpose. One example is a prosthetic hand that may consist of a split hook like a pincer and can be closed or opened to grasp objects and perform similar task types. Controlling the prosthetic limb meant with practicality in mind can occur in several ways. Body-powered limbs are utilized by controlling cables attached elsewhere on the body.

Externally powered limbs, powered by motors, can be controlled by the prosthetic recipient in many ways. One is a switch, which permits the device to be moved by toggling buttons or switches. A more advanced method is to have the limb listen to the remaining muscles in the residual limb that are still capable of contracting. Electrodes placed on the skin's surface are capable of measuring muscle movements when the remaining muscles generate tiny electrical signals upon contraction. These limbs are called myoelectric.