Artificial limb and joint

Almost four million Americans use artificial limbs, the majority necessitatedby amputation resulting from poor circulation caused by diabetes or atheroscleroses. Crude artificial limbs have been used since the earliest loss of anextremity; Greek historian Herodotus mentioned a wooden foot in 500 b.c.; a Roman mosaic depicts a peg-leg; and medieval knights had artificial limbs to improve their appearance. Today, prostheses rival natural limbsboth in function and appearance.

The modern era of artificial limbs began with the famous French surgeon Ambroise Paré (1517-1590), a barber-surgeon who, in 1536, became a battlefield surgeon. After devising safer, more effective methods of amputation, Paré turned his attention to the design of artificial limbs, exercising great ingenuity and striving to simulate some degree of natural movement. An artificial leg pictured in Paré's Works of 1575 featured a movable knee joint controlled by a string, a flexible foot operated with a strong spring, and an artificial hand with fingers that moved individually by means of tiny internal cogs and levers. As the many nineteenth-century wars createda larger demand, more sophisticated devices were invented. The most significant impetus for improvement in prosthetic design was the birth in the early 1960s of babies with vestiges of arms, a birth defect caused by a drug called thalidomide often prescribed to pregnant women. Artificial arms poweredby carbon dioxide were developed for these children. Modern limbs include electric arms which use a small battery, others controlled by a tiny switch, and the myoelectric prostheses which uses electrical impulses detected by small electrodes placed on the skin over the remaining arm muscles. Artificial legs can be fitted with spring-loaded feet, artificial feet constructed with toes, synthetic coverings made to match skin tone and hair patterns, andelectrodes in the artificial limb leading to the natural skin which allows the brain to register "feeling" in the prosthesis. Artificial limbs take advantage of plastics and fiberglass for enhanced strength and comfort.

Joints are the movable points where two bones come together--as at theknee or shoulder. Surgical joint replacement- -joint arthroplasty--began in the 1950s. Today, more than 500,000 joint repairs and replacements areperformed in the U.S. each year, including 20,000 new cases of hip osteonecrosis (bone death). The first total knee arthroplasty was performed in1951; 10 years later the first total hip replacement occurred, and shoulder replacements began in the 1960s. Artificial joints are secured either by cement or "bone ingrowth," a process in which the natural bone grows into the porous surface of the a prosthesis. In 1998, Dr. Jay Lieberman, of the Universityof California, Los Angeles began clinical trials to treat osteonecrosis of the hip by inserting a capsule containing bone-morphogenetic protein (BMP) into an allograft (implant of purified human bone). Total hip replacements are metal and have a limited life span--BMP, which occurs naturally in small quantities in the bone matrix, imitates the bone development process whichoccurs during fetal development. Researchers believe BMP may reducing the need for total hip replacement. John M. Wozney with Genetics Institute in Massachusetts, first cloned BMP in 1988--in early 1998, more than 30 BMPs were cloned. 1998 also saw results of a seven-year study in which cells from a patient's healthy cartilage are transplanted into the damaged portion of the knee joint, regenerating cartilage and reducing the need for knee replacement. Researchers look ahead to tissue-engineered implants and cell-based therapies fordegenerative diseases such as osteoarthritis and osteoporosis. Research is ongoing to improve prosthetic materials, surgical techniques, ways of securingjoints, and postoperative mobility.

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