Prosthetics

Hip replacement surgery goes back to the 1930s. By the 1960s three substantial improvements in hip surgery made this procedure both popular and successful. The materials used for the hip prostheses were made from metals and plastics that were strong enough to support the weight brought on the hip and were also self-lubricating. Cements were developed to adhere well to the bone. Extremely antiseptic operating rooms and clothes worn by the operating personnel reduce the danger of infection that accompanies a hip replacement operation.

The hip is the joint between the pelvis and upper end of the femur (thigh bone). It is an example of a ball-and-socket-joint that is subject to several major disorders. The most common disorder is osteoarthritis. Pain and stiffness accompany the movements of the hip. Other types of arthritic disorders can cause similar malfunction. Fracture of the hip often occurs with the elderly, who may be prone to falls. In the case of extreme trauma there may be a dislocation of the hip, which is rare but may occur in such mishaps as an automobile accident.

Hip replacements are surgical procedures in which either part or all of the hip joint is replaced with artificial parts. In the operation, the hip joint is exposed from around the surrounding fat and muscle tissue. The thigh bone (femur) and pelvis is prepared to accept the two component parts for the replacement to the natural hip joint. The components consist of a metal shaft and ball as one unit replacing the shaft of the thigh bone with its natural ball and a socket that is made either from metal or plastic. The new socket receives the shaft and ball after it is cemented into the pelvis. These parts are bound into place by a special cement into the surrounding bone. After the new ball is attached to the socket, the muscles and tendons are stitched back into place and the incision is closed.

Recently, a robot has been devised that can drill a hole in the femur much more accurately than a surgeon can. The robot's precise hole can hold the prosthesis much better, thus extending the life of the hip replacement. A surgeon can be as much as 30% off in his drilling. When that happens, only twenty percent of the implant comes in contact with the bone, leaving wide gaps around the prosthesis. Use of the surgical robot brings 96% percent of the implant in contact with the bone and gaps were reduced from 0.15-0.02 in (4.0-0.5 mm). This technology is still in an early state of development.