A prosthetic device is an artificial replacement for a part of the body that has been removed. A prosthetic may be a limb or a joint; the purpose of the prosthetic may be entirely functional, cosmetic, or both. The term prosthetic is derived from a Greek word, meaning to add to or to add on.
Prosthetics have existed throughout history. In earlier times, when a leg or a hand was lost through war or misadventure, the artificial limb was a simple peg leg or a hand hook. The U.S. Civil War (1861–1865) was the first great impetus to prosthetic research; the Union army had over 30,000 amputations in the course of conflict.
A prosthetic is closely related to another common sport device, the orthotic. While a prosthetic is a replacement device for a component of the muscu-loskeletal system, an orthotic is designed to support a weakened area or to correct a structural misalignment. For example, foot orthotics are designed to equalize leg length.
Research has taken modern prosthetic devices far beyond simple peg legs and hooks. The development of effective prosthetic devices for use in sport engages a number of scientific disciplines, including kinesiology (the science of human movement), bio-mechanical engineering (the relationship between the mechanisms and the living function of the body), structural engineering (design and construction principles), materials and fabrication experts (optimal metals and composites), coaching input (regarding the specific demands of the sport), and the athlete. Once operative, a prosthetic used in sport will involve the ongoing support of experts from the sports medicine, orthopedic medicine, physical therapy, and athletic therapy disciplines.
The design and construction of a modern above-the-knee prosthetic device illustrate the science that supports the application. Where the residual limb of the person ends, the prosthesis begins. A socket, with its fit adjustable to the wearer by means of an inflatable pouch, is the component that connects to the leg. Below the socket, encased in a protective lightweight plastic structure, is the artificial knee, constructed of aluminum, titanium, and other metals. The knee is connected to the lower portion of the prosthesis through a device that both reduces shock and suppresses torque, which is the force generated by the turning of the knee during running motion, which would otherwise be absorbed by the person. The prosthetic is supported by an artificial foot constructed from polyurethane, with the foot carefully oriented to ensure that the individual is not misaligned during a running or walking motion so as to direct unequal forces into the opposite leg.
Such prosthetics have benefited from the development of materials that are both lighter and stronger. The artificial leg used by Terry Fox, the cancer patient who endeavored to run across Canada in 1981 before succumbing to his disease, was approximately 50% heavier than modern prosthetics, which also have sophisticated cushioning that the Fox version lacked.
The Paralympic movement has fostered many technological developments in sports prosthetics. The Paralympic competitions each have separate classification rules, with the degree of the disability of the athlete determining the competition class. The lighter and more functional the prosthetic is, the greater the ease of movement experienced by the athlete. Athletes now benefit from prosthetic devices such as the gait-adaptive knee, an artifical limb that can be modified to suit the particular variations and idiosyncrasies of its user.
One testament to technology is found in the results achieved by Paralympic athletes who use prosthetics in the 100-m sprint. In the various classifications based on the degree of limitation, the slowest of the winning times at the 2004 Athens Paralympics in the men's categories was 12.1 seconds, a result that compares favorably to the able-bodied elite time of slightly under 10 seconds.
In addition to the advances made in the material composition of sport prosthetics, significant research has been carried out on the development of devices that are hardwired into the nervous systems of the athlete. The connection between the user and the machine is referred to as the neural linkage. The ability of science to develop the necessary interface between user and machine depends to a considerable degree on the nature of the amputation: the more extensive the loss of limb, the more difficult the proposition to connect the artificial component to the body, as there will be a greater degree of connectivity required. Both direct connections of existing muscle to machine and those of bone and machine have been attempted, with limited success. The best success in achieving a true interface between the prosthesis and the body have been with respect to artificial hands, where very simple muscular commands have successfully been obeyed through the prosthetic.