Modern endoprostheses are constructed from strong, bioinert parts that are identical in form to articular structures. The correct choice of implant and the skill of the surgeon is the key to a quick return of the patient to an active lifestyle. Currently, it is possible to replace even small joints of the fingers and toes. But endoprosthetics of the knee and hip joints are especially common. Indications for surgical treatment are the ineffectiveness of conservative therapy due to severe bone deformation, irreversible damage to the cartilage pad.
When choosing an implant, the doctor takes into account many factors. And this is not only a type of pathology diagnosed in a patient, but also the characteristics of an artificial joint:
- the number of components – two-component, three-component;
- method of connecting components – connected, semi-connected, unrelated;
- congruence – block-shaped, bispherical, concave-convex, biconvex, spherical, spheroidal, cylindrical, truncated-cylindrical, conical;
- the shape of the parts is anatomical, nonanatomical.
The success of the operation is also due to the correct choice by the surgeon of the method for fixing the endoprosthesis. For cement fastening, a special high-strength polymer is used, also called “bone cement”. And with cementless fixation, special hollow structures are used, which are subsequently filled with bone tissues. The latter method is usually practiced when replacing joints in young and physically active people. For elderly patients, cement fixation is considered the most reliable due to the slowed flow of bone tissue repair processes in them.
Shishkevich Vladimir, orthopedic and traumatologist, project editor-in-chief ExpertNews.
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Artificial hip joint
The hip implant consists of a bowl repeating the shape of the acetabulum, fixed inside the liner, legs and head. Dentures made of the following materials are used:
- metal to metal. The design is characterized by increased wear resistance, therefore it is often installed for patients who lead an active lifestyle. Modern endoprostheses are made of titanium or cobalt-chrome alloys. Their disadvantages include an increased likelihood of soft tissue metallosis, a manifestation of the systemic toxic effect of metal ions that enter the bloodstream;
- metal-polyethylene. A relatively budget option, but short-lived. The metal head wears out pretty quickly, but the complex polymer of the acetabular liner reduces friction well;
- ceramics-ceramics. These are the highest quality implants: resistant to friction, with a complete absence of toxicity and a long service life. They have only one “minus” – a relatively high cost;
- ceramic-polyethylene. The ceramic femoral head is made of ceramic, so it will last a long time. And the polymer liner of the acetabulum is made of a complex polymer that is practically resistant to abrasion.
Hip arthroplasty is bipolar and unipolar. In the latter case, during the operation, only the femoral head is replaced with a plastic, metal or ceramic implant. Currently, this method of surgical intervention is rarely practiced. The reason is a high risk of protrusion (failure) of the prosthesis into the pelvic cavity. Even with the destruction of the femoral head only, a total hip endoprosthesis is installed.
The natural knee joint consists of three compartments – the medial, located on the inner side, the external lateral and femoral, located under the patella. An artificial joint has a significantly more complex design. It is represented by the following components:
- tibial. This is a metal platform equipped with a plastic insert and attached to the lower leg in its upper part. Typically, manufacturers of this part use titanium alloys;
- femoral. A large, curved component that is fixed to the femur and is exposed to severe stress during use. Therefore, ceramics and metal, for example cobalt-chrome alloy, are used for its production;
- knee. The part of the domed shape that replaces the damaged patella. It withstands high friction when walking, bending and flexing the joint, as it is made of high-strength polyethylene;
- plastic gasket. Located between the tibial and femoral components, it is designed for smooth displacement of other parts relative to each other. Made of durable and at the same time elastic, flexible plastic.
Previously, fixed-support artificial joints were commonly used. This is a traditional type of endoprosthesis with a polyethylene tibial part and a soft femoral component. Recently, such products are used only for prosthetics of elderly patients due to the low range of available movements (about 40%).
Bearing endoprostheses of the knee joint are now in demand. They provide excellent mobility to the knee, including due to additional degrees of rotation. The bearing prosthesis becomes like a natural part of the leg, and its functionality directly depends on the state of the ligamentous-muscular apparatus.
The lifespan of modern joint prostheses
The life of an artificial joint often becomes a determining factor in its selection. The longer it is, the less frequent is the revision endoprosthesis replacement, that is, the planned replacement of a worn joint. When reinstalled, the surgeon cuts off part of the patient’s own bone. With each subsequent replacement, the amount of bone tissue is reduced. Therefore, it is theoretically possible that the next time you install an implant, the remaining bone will simply not be enough. The following factors affect the life of the endoprosthesis:
- competent surgical intervention;
- the quality of the prosthesis used;
- implementation by the patient of all medical recommendations during the rehabilitation period.
A good endoprosthesis will last 25 years or more if it is not exposed to increased loads. The average life of an implant made of polyethylene and metal is from 15 to 20 years. It can be reduced due to the excess weight of the patient, the presence of chronic pathologies, especially autoimmune, endocrine, metabolic.
The cost of modern endoprostheses
Thanks to quotas for endoprosthetics, many Russian clinics are engaged in the installation of artificial hip and knee joints. But the production of domestic implants is not put on a wide stream. Therefore, when performing operations, imported prostheses are usually used, most often American or European. Chinese models are less in demand. Their cost is significantly lower, but the quality often leaves much to be desired.
When choosing an endoprosthesis, it’s not always worthwhile to focus on its price, but it is it that often determines the quality and becomes the key to a long and trouble-free operation. In the vast majority of cases, orthopedic surgeons prefer artificial hip joints from such manufacturers:
- Zimmer. An international corporation that has been developing and improving endoprostheses for several decades. Zimmer products are of high quality, which determines its price. A prosthesis for a unipolar prosthesis will cost the patient 80-85 thousand rubles, for a bipolar prosthesis – up to 230 thousand rubles;
- Johnson-Johnson. This is a well-known manufacturer of external and internal prostheses, but in our country his products are not too much in demand. The cost of a quality implant from Johnson-Johnson varies in the range of 150-200 thousand rubles;
- Biomet. The company manufacturing medical devices produces high quality endoprostheses with a long service life. But their price is quite high. A ceramic implant costs from 270 thousand rubles and above;
- Stryker. This is an international corporation specializing in the production of orthopedic products. The endoprostheses made by her are reliable, durable, with good technical characteristics. The average cost of an endoprosthesis is 250 thousand rubles.
The prices of artificial knee joints are slightly lower, but not by much. They depend on both the manufacturer and the design. Implants for total arthroplasty cost from 50 to 200 thousand rubles. Partial replacement will cost the patient a little cheaper (20-40%).