Total hip replacement, or hip arthroplasty, can be a desirable option for many people who may be experiencing chronic pain or immobility in this area. These problems can be caused by injury or loss of bone mass because of disease or advanced age. The technology and design of hip prostheses have improved since the original procedure was established, yet the reality of having man-made materials inserted into the body might raise the issue of rejection of the prosthesis.
There are currently two types of metallic hip prostheses. The first type to be developed was a small metal ball that was inserted into the femoral bone, which coupled with a metal cup that replaced the original socket. A plastic spacer was placed between these two metal surfaces. Because of the more rapid degeneration of plastic as opposed to metal, the cup had a tendency to wear away from continual contact with the metal ball. The accumulation of plastic residue in the area would cause a loosening of the prosthesis over time.
Other Inherent Causes
The other type of metallic hip prosthesis has no plastic components. The femoral ball is much larger, thereby creating a better fit with the metal socket. The metal that is used in this prosthesis is made of a cobalt-chrome alloy known as Vitallium. This is a very durable alloy, yet there is still a wearing away of the material over time. However, this type of metal-on-metal prosthesis has been reported to have shown better endurance than the metal-on-plastic type, according to the American Academy of Orthopedic Surgeons.
When any type of hip prosthesis begins to exhibit signs of wear or dislocation, the most common symptoms will be pain and increased limitation of movement in the area. These are caused by a breakdown of the prosthesis function and/or the wearing down of the metal components, according to the Hip and Knee Institute. As these parts wear down, they lose the tight fit that is required for optimum efficiency. The ball and socket junction will loosen, causing the joint to be displaced. Immobility will set in, and pain will be caused by the misalignment of the components of the prosthesis.
Research has been done into the possibility of adverse reactions either from the prosthesis itself or from the residue caused by normal wear of the components. Dermatitis and reactions to the ionisation of metal, primarily of cobalt, are two of the more serious side effects that have been studied. While the statistics vary as to the severity of the accumulation of residue, available data suggest that the severity of adverse reaction is considered to be minimal.
The procedures to correct metal hip-replacement rejection can be serious. Effects of rejection symptoms can include a wearing away of the femur, as well as the pelvis, causing an increased dislocation of the prosthesis, and severe pain and immobility. The surgical procedure to correct any of these requires either replacing one or more components or removing and replacing the entire prosthesis. These are called hip-replacement revisions. Medical reports about this surgical approach indicate that these revisions tend to have success despite the continued invasiveness of surgery on the femur and pelvis, and that they often require longer rehabilitation periods.
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