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A short introduction to prosthetics

Whether due to car accidents, wars, animal attacks, birth defects or bacterial infection, sometimes body parts, including major limbs, are damaged, missing or amputated to save peoples' lives. Classic images of prostheses include Captain Hook from Peter Pan and other pirates with peg legs. The history of replacement body parts, or prostheses, can be traced to the ancient Greeks, Romans and Egyptians; for example, 3000-year-old mummies have been found with prosthetic toes and fingers. Before the 1840s, most people did not survive the amputation process due to the side-effects of shock, infection and blood loss. The medicine and tools at the time were limited, and prosthetic supplies were scavenged from whatever was available. Starting in 1842, anesthesia was used during surgery, which enabled more precise surgeries and resulted in better prosthetic fits. The great number of amputees from the two World Wars in the 20th century increased the demand for more and better prosthetic designs.
What is the purpose of prostheses and why are they important? The purpose of a prosthesis is to restore the functionality and capabilities of the lost limb. A prosthesis enables an amputee to reestablish mobility, independently conduct the activities of daily living, and keep a job.
What design challenges do engineers face in creating prostheses? One consideration is the location of the amputation. Does the replacement device need to include a movable joint, such as a knee or elbow? Will the prosthesis be designed to improve appearance only (cosmetic), such as an eye or ear, or does it need to perform some of the lost functions of the original limb, such as vision and hearing? The location on the body determines the necessary functions of the prosthesis so as to enable the person to resume daily life activities. Another consideration is the strength of the prosthesis compared to its weight. The material needs to be strong enough to perform the necessary functions and hold body weight if necessary but light enough to be moved easily. Another consideration is the attachment. How will the prosthesis be attached to the body? How do we keep it from falling off? Another consideration is cost. What materials are available to use? How much do they cost? Is the cost reasonable so that patients can afford the prostheses? These considerations and requirements become what engineers call the design criteria and constraints.