Author丨Peking University Third Hospital Li Yang
Reproduction of this article is not allowed without authorization.
When it comes to "joint replacement", I believe many friends will feel very nervous. Some people, when they hear the doctor say they want to "change joints", are particularly worried that their knee joints will be "cut off" and replaced with "iron knees", and their legs will not be able to move from now on.
There are still many people who often ask "Is artificial joint made of iron?" and are worried about "Will I have a rejection reaction to the prosthesis?" and "Can I still have nuclear magnetic resonance after joint replacement?"
Doctors can understand these concerns and questions, mostly because of their lack of understanding of knee arthroplasty . In fact, knee replacement is indeed one of the major orthopedic surgeries, but it is not scary. While today is World Arthritis Day , please Deputy Chief Physician Li Yang, Orthopedic Department of Peking University Third Hospital , talk to you about the knee replacement that you are concerned about.
Knee joint replacement, which part is "replaced"?
Knee arthroplasty is also called knee arthroplasty, is currently the most effective method to treat severe knee osteoarthritis or other severe knee diseases . The surgery has been developed for hundreds of years and is very mature in technology and is widely carried out in various countries around the world. Every year, tens of thousands of patients suffering from knee joint diseases can relieve pain and improve their quality of life through this surgery.
In knee replacement, the doctor will remove the end of the femur (that is, the thigh bone) in the knee joint, the apex of the tibia (that is, the calves bone), the broken cartilage on the surface of the joint on both sides, and the subchondral bone about less than 1 cm; then install a metal component similar to the surface of the original knee joint in situ, which we call the prosthesis, including the femoral side prosthesis, the tibial side prosthesis, and the gasket between the two metal prostheses (see the figure below).
For example, this process is a bit similar to dentures, which is to cut off the broken part and then fill it with metal. During the operation, most major ligaments and tendons are retained in situ and rebalanced; allowing the knee joint to be flexed and extended normally after the operation and to be stable when moving on the left and right sides and anterior and posterior sides.
Usually, knee replacement surgery will last for 1-2 hours, and the patient can move with crutches on the second day after the operation. After that, after 2-3 months of rehabilitation training, most people can return to their normal life, without any problems with walking, doing housework, participating in social activities, and even doing some exercise. It is a very good treatment option for people whose quality of life has declined greatly due to knee disease.
Postoperative rehabilitation training
What is the material for knee replacement prosthesis?
Artificial joints are indeed mostly composed of metal, but they are not metals that are often seen in daily life. The prosthesis for knee replacement is divided into femoral prosthesis, tibial prosthesis, and a gasket between the two prostheses. The installed parts of these three parts are different and the functions they perform are different, so they are also composed of different materials.
tibial side prosthesis (also known as the "tibial platform") is inserted at the apex of the tibia to fill the bone surface and support the weight. It does not directly participate in joint activities. The tibial platform is mainly made of titanium alloy and also contains a small amount of molybdenum, vanadium, chromium and other metals. The main characteristics of titanium alloys are corrosion resistance, high strength and light weight, and are often used in the aerospace industry in life.
In addition, the hardness and elasticity of titanium alloy are similar to the bones of the human body, which allows the tibial platform to have sufficient hardness to support weight and a certain degree of elasticity to disperse the weight into the inside of the tibia. Moreover, titanium alloys have very good biocompatibility and rarely experience allergies or repulsions.
lateral femoral prosthesis (also known as "femoral condyle") is inserted at the distal end of the femoral. In addition to filling the bone surface, it also acts as the articular surface on the femoral side. It constantly rubs and rolls with gasket when the knee joint is active.
Because it has to assume such joint movement function, titanium alloy cannot be used in the femoral condyle, because titanium alloy is relatively soft and cannot withstand repeated friction. The metal used is called cobalt (gǔ), chromium (gè), molybdenum (mù) alloy. In addition to having good biocompatibility, the characteristics of cobalt-chromium molybdenum alloy are also very hard, highly corrosion-resistant and wear-resistant, meeting the characteristics of the femoral condyle requiring repeated friction.
Whether it is titanium alloy or cobalt-chromium molybdenum alloy, they are nuclear magnetically safe. They are not attracted by magnetic fields or have less attraction, which is not enough to cause movement in the body, so they can be nuclear magnetically.
Articular prosthesis material is safe for nuclear magnetic examination
between two metal prostheses, called shims. The gasket is fixed on the tibial platform, and the upper surface forms an articular surface with the femoral condyle, which participates in the activities of the knee joint and is also the part that withstands the most wear.
gasket is composed of polyethylene , a thermoplastic resin produced by polymerization of ethylene (the feel is similar to a very hard wax block). The polyethylene used in knee prosthesis is a high crosslinked ultra-high molecular weight polyethylene formed after special treatment. This material has super strong wear resistance, self-lubricity, anti-aging properties, as well as small friction coefficient and high mechanical strength.
research shows that the annual wear of high-crosslinked ultra-high molecular weight polyethylene is less than 0.01mm, while the gaskets we often use are above 10mm. That is to say, theoretically, if we only talk about wear, then the gaskets can be used for more than a century.
titanium alloy tibial platform, femoral condyle of cobalt chromium molybdenum alloy, and ultra-high molecular weight polyethylene gasket, each performs its own functions, forming the knee prosthesis we are currently using. Of course, in addition to these three materials, there are also newer materials such as ceramics, zirconium and niobium alloys that have also been used in knee prostheses, but due to price reasons, it has not been widely used.
After understanding these, it will definitely help you solve many questions about knee replacement. Do you feel that you have less worries and fears after reading it? Don’t forget to like or forward it after reading it, and share it with more friends in need!
Expert introduction
Li Yang
Li Yang, associate chief physician of orthopedics, doctor of medicine, associate professor, Peking University Third Hospital young academic backbone.
focuses on basic research and clinical work in artificial joints for 10 years, and its professional direction is adult knee and hip surgery. It can formulate step-by-step and personalized treatment plans for patients from exercise rehabilitation treatment to drug treatment, minimally invasive treatment, and ultimately arthritis, replacement treatment, and proficiently use various new technologies such as robots, computer navigation, and D printing as treatment aid tools in clinical practice. The annual number of surgeries exceeds 300.
has published more than 20 articles in core professional journals at home and abroad, including 5 SCI papers. He has compiled 2 textbooks and translated 6 works. Obtained national utility model patents.
Peking University The first prize of the 18th Young Teachers Teaching Basic Skills Competition (Medical Category); The second prize of the 11th Young Teachers Teaching Basic Skills Competition (Medical Category); The 2019 Peking University Teaching Excellence Award.
Social Jobs:
American Association of Knee and Hip Surgeons (AAHKS) International member
Member and secretary of the Orthopedic Youth Physician Alliance of Wu Jieping Medical Foundation
Member of the Knee Protection Expert Committee of the Orthopedic Branch of the Chinese Society of Integrated Traditional Chinese and Western Medicine
Editorial board member of the Chinese Journal of Joint Surgery (Electronic Edition)
" Chinese Journal of Medical Sciences ", " Journal of Chinese Academy of Medical Sciences ", etc. Reviewer of domestic core journals and magazines
Professional expertise:
. Arthritis: Degenerative knee and hip osteoarthritis in the elderly, surgical treatment of rheumatoid arthritis in the knee and hip joints, congenital acetabular dysplasia, traumatic arthritis , etc.
2. Osteonecrosis : Alcoholic, hormonal or idiopathic ischemic necrosis .
3. Bone Tumor : Primary or metastatic bone tumors of adult limbs.
clinic information:
every Wednesday afternoon and Thursday morning Beijing Medical Third Hospital Our orthopedic expert clinic.
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