Knee prosthesis is a partial or total replacement of the knee joint. It is used in cases of injury or severe wear and tear of the knee.
What is a knee replacement?
A partial or total replacement of the knee joint is called a knee prosthesis. A knee prosthesis is an implanted prosthesis that either partially or completely replaces the human knee joint. The knee endoprosthesis or knee joint prosthesis is implanted during surgery and is used to restore joint stability. In addition, the patient can move again without pain. Knee prosthesis is used in case of injuries of the knee joint or its wear and tear. After the hip prosthesis, the knee prosthesis is the second most frequently used joint endoprosthesis in Germany. Approximately 175,000 initial surgeries are performed in this country each year. In most cases, people over the age of 70 receive a knee prosthesis. Implanting a knee prosthesis is usually done only when conservative treatments such as drug therapy or physical therapy do not show the hoped-for success.
Forms, types, and styles
The first knee prostheses came into use in the early 1970s. Meanwhile time there are three different types of prosthesis. These are the unilateral surface replacement, also called a sled prosthesis, the total surface replacement, and the total joint replacement with axial guidance. Each type of prosthesis includes numerous different models. Their selection is based on the patient’s individual specifications, such as the circumference and shape of the knee, physical activities and body weight. In order to insert the correct type of prosthesis, the surgeon performs an X-ray examination in advance. In addition, a comparison with trial prostheses is possible during the operation. A sled prosthesis is a unilateral surface replacement. It is used to replace the inner or outer surface of the knee joint. The remaining components of the knee are still intact. The sled prosthesis is placed on either the outer or inner femoral condyle. A metal base and a plastic block are attached to the other side of the knee joint at the plateau of the tibia. When the knee moves, the desired back and forth sliding of the knee prosthesis then occurs on the block. A total surface replacement is a knee prosthesis that serves as a replacement for several knee joint structures. However, the ligaments that are responsible for the axial guidance of the knee remain intact. This form of prosthesis is one of the most commonly used types. If not only cartilage and bone structures but also the ligaments have been affected by the knee damage, a complete joint replacement with axial guidance is used. In this case, the knee prosthesis also provides axial guidance, which stabilizes the knee in the longitudinal axis, thus counteracting displacement in the lateral direction. To prevent the lower leg bone from moving laterally relative to the femur, this type of prosthesis is equipped with a support in the center of the joint.
Structure and mode of operation
The structure of a knee prosthesis consists of three components, the replacement of which must take place during knee implantation. These are the tibial component (tibial portion), the femoral component (femoral portion), and a plastic support located on the tibial portion. In most cases, the femoral component is made of a cobalt-chromium alloy. It serves as a replacement for the worn surface of the cartilage of the femoral condyle. The tibial component is mostly made of titanium. Its function is to replace the worn joint sections on the tibial head. On the tibial component there is an inlay made of plastic, which is polyethylene. This material has the property of being abrasion resistant and acting as a sliding surface. To ensure that the knee prosthesis remains stable for as long as possible, certain criteria are required for the materials. These include, first and foremost, corrosion resistance and load-bearing capacity. For example, abrasion must not occur when the prosthesis sliding pairs rub against each other. In addition, incompatibility reactions caused by the foreign substances must be prevented. For this reason, special plastics, metals and ceramics are used as materials for knee prostheses.
Medical and health benefits
The health benefits of a knee prosthesis are considered high. It makes sense to use an artificial knee joint when joint functions are impaired or affected individuals suffer from severe pain. The most common indications for a knee endoprosthesis are osteoarthritis, inflammation of the knee joint such as rheumatism, injuries, overloading and malpositions. Depending on the extent of the disease, the doctor decides which type of prosthesis is best suited for the individual patient. However, the insertion of a knee prosthesis is not without risks. For example, unexpected complications occur in around 5.5 percent of all patients. These include, above all, bacterial infections, the occurrence of thrombosis (blood clots) or the dislocation of individual parts of the prosthesis. Sometimes the knee prosthesis also loosens prematurely, which can result in pain, leg malposition or instability. However, these complications occur only in rare cases. In principle, the prognosis after insertion of a knee prosthesis is positive. The patient regains mobility and experiences significantly less pain, which considerably improves his or her quality of life. The durability of a knee prosthesis is on average 10 to 15 years. To prevent the knee prosthesis from loosening, the patient should avoid joint-shaking sports, lifting heavy loads and being overweight.
