RU2295320C2 - Articular endoprosthesis manufactured from isotropic pyrolytic carbon - Google Patents

Abstract

FIELD: medical engineering.

SUBSTANCE: device has cup and head members having engageable smooth surfaces. Both cup and head members have bushing manufactured from isotropic pyrolytic carbon and plate manufactured from isotropic pyrolytic carbon rigidly attached to the bushing by means of chemical bonds without foreign material being used. Connection strength is not lower than strength of the material itself.

EFFECT: high reliability of endoprosthesis.

4 dwg

Description

The invention relates to medical equipment and can be used in orthopedics to replace the affected natural joints of a person. Most successfully, the present invention can be used to replace the affected hip joint. However, without violating the essence of the invention, it can be used to replace the knee, elbow and other joints of a person.

Today, the main materials for the manufacture of hip cups are ultra-high molecular weight polyethylene UHMW PE ISO 5834/1 (ASTM F603), and for heads - hot-forged stainless steel FeCrNiMoMn ISO 5832/1 (ASTM F648), CoCrMo alloy ISO 5832/4 (ASTM F75) and Al ₂ O ₃ ceramic ISO 6474 (ASTM F603). Among traditional materials, the combination of polyethylene and Al ₂ O ₃ ceramics is considered the most optimal and most widespread [1]. However, the wear of polyethylene is one of the main problems in the total replacement of the hip joint.

For example, hip arthroplasty is known [2, 3], containing a hinged element in the form of a head and a cup made of ceramics. These joint prostheses have a low coefficient of friction in the joint and high wear resistance. However, there are serious limitations to the use of these endoprostheses. The natural fragility of ceramics does not allow to make the walls of the ceramic liner thinner than 5 mm. A common disadvantage of these prostheses is their low impact resistance. When jumping, running the patient or during surgical procedures, shock loads affect the head and cup of the endoprosthesis, causing microcracks in the ceramics, which grow during operation and cause the hinge element to fail.

Isotropic pyrolytic carbon has higher crack resistance, lower coefficient of friction and higher wear resistance. Comparative tests of the physicomechanical properties of materials for orthopedic implants (silicone rubber, polyethylene, polymethyl methacrylate, titanium, stainless steel, Co-Cr alloy, Al ₂ O ₃ ceramic and pyrolytic carbon) showed that the properties of pyrolytic carbon are closest to cortical bone [4 ]. In terms of biocompatibility, toxicity and corrosion, carbon materials are some of the best for use as implants.

For example, in prosthetic heart valves, widely used in world cardiac surgery, the locking element and the body are made of isotropic pyrolytic carbon. At the same time, there is no wear on friction surfaces, which also experience shock loading, after hundreds of millions of valve opening and closing cycles.

In the first years after the discovery of this unique material, attempts were made to use it in orthopedics. For example, a joint endoprosthesis is known [5], which has at least one element in the form of a head or cup, made in the form of a predominantly rotation body. This element is made of graphite. Moreover, its surface interacting with the counter surface of the second element of the joint is covered with isotropic pyrolytic carbon.

However, endoprostheses with a hinge coated with pyrolytic carbon have not found wide application, since the known technology of coating from isotropic pyrolytic carbon can successfully cover graphite elements of only a simple small shape. The technology predetermines the production of material in the form of coatings with a maximum thickness of about 250 microns, with a greater thickness due to high internal stresses it cracks. In this case, the coating should form a closed stressed surface, and in case of violation of the continuity of the coating, its catastrophic destruction occurs. Therefore, the manufacture of heads and cups of endoprostheses using this technology has significant problems.

Known joint replacement [6], containing at least one element in the form of a head or cup. The head or cup of the endoprosthesis is made of annular segments of monolithic isotropic pyrolytic carbon, the end surfaces of which are perpendicular to the axis of the body of revolution and are motionlessly connected to each other through a layer of polymer material, and the side surfaces that do not interact with the mating surface of the second joint element are motionlessly connected through a layer of polymer material with a frame element made, for example, of metal. The frame element in the joint head is made in the form of a hollow metal sleeve with a shoulder at the base, having a conical hole for connection to the endoprosthesis leg, and a support surface interacting with the end surface of the segment of carbon or ceramic material is made on the shoulder of the sleeve.

However, the manufacture of a head or cup of an endoprosthesis composite and motionlessly interconnected through a layer of polymer material has a number of significant drawbacks that reduce the reliability of the endoprosthesis. Firstly, the strength of the joint is at best equal to the strength of the polymer, which is much less than the strength of isotropic pyrolytic carbon. And there are several such compounds in the design of the endoprosthesis. And the more connections, the lower the reliability of the entire structure. Secondly, any polymers in the environment of the body are prone to swelling, which will also reduce the strength of the joints of the elements of the endoprosthesis. Therefore, it is difficult to talk about the long-term strength and reliability of this design.

This joint prosthesis [6] is selected as a prototype.

The aim of the invention is to increase the reliability of the joint endoprosthesis.

Achieving the goal of improving the reliability of the joint prosthesis containing a cup and a head, made with interacting smooth surfaces of isotropic pyrolytic carbon, is ensured by the fact that:

- both the cup and the endoprosthesis head consist of a sleeve of isotropic pyrolytic carbon and fixedly connected to it by chemical bonding without the use of foreign materials with a bond strength not lower than the strength of the material of the isotropic pyrolytic carbon plate itself.

Known technical solutions with a combination of features similar to those that distinguish the claimed solution from the prototype, not identified.

The proposed technical solution increases the reliability of the joint endoprosthesis.

The joint will have the highest reliability, in which both the head and the cup are made of solid isotropic pyrolytic carbon. However, based on the technological features of obtaining monolithic isotropic pyrolytic carbon, this is impossible. Upon receipt of a monolithic isotropic pyrolytic carbon of such sizes, large internal stresses will inevitably arise in it, which will lead to cracking of the material. Therefore, both the head and the cup of the joint endoprosthesis must be made integral. When performing both the head and the cup of the joint prosthesis from a sleeve made of isotropic pyrolytic carbon and fixedly connected to it by chemical bonding without the use of foreign materials with a bond strength not lower than the strength of the material of the plate made of isotropic pyrolytic carbon, the problem of internal stresses will be eliminated and the possibility of manufacturing and the heads and cups of the joint endoprosthesis are the same as those of a solid monolithic isotropic pyrolytic carbon, since the strength is chemical the connection between the sleeve and the plate is not lower than the strength of the material itself. The absence of foreign materials also increases the reliability of the joint endoprosthesis.

The invention is illustrated by drawings. Figure 1 presents the main view of the endoprosthesis of the hip joint of isotropic pyrolytic carbon, taken as an example implementation of the invention. Figure 2 presents the head of the endoprosthesis in a diametrical section. Figure 3 presents the cup of the endoprosthesis in a diametrical section. Figure 4 presents the scheme for obtaining a chemical compound between the sleeve and the plate.

The endoprosthesis of the hip joint contains a leg 1, a head 2 and a cup 3. The head 2, made of monolithic pyrolytic carbon, for example, in the form of a ball, consists of a sleeve 4 and a plate 5, which in the zone 6 are motionlessly interconnected by chemical bonding without using foreign materials with a bond strength not lower than the strength of the material itself. A cup 3 made of monolithic pyrolytic carbon, for example, with an internal spherical surface, consists of a sleeve 7 and a plate 8, which in the zone 9 are motionlessly interconnected by chemical bonding without the use of foreign materials with a bond strength not lower than the strength of the material itself.

The proposed invention is as follows.

Isotropic pyrolytic carbon is obtained by pyrolysis of hydrocarbons at high temperature by deposition of a special graphite substrate on the inner surface. With a flat form of the substrate, a plate is obtained, with a cylindrical one, a sleeve. Take the sleeve 10 (figure 4) of isotropic pyrolytic carbon obtained by the method described above. A graphite plug 11 is inserted into the sleeve, and the sleeve together with the plug is mounted in a flat graphite substrate 12. The end face of the sleeve 10 becomes part of the surface of the substrate 12. Then, another process for producing isotropic pyrolytic carbon is carried out with this substrate. When isotropic pyrolytic carbon is deposited between the end face of the sleeve 10 and the deposited plate of isotropic pyrolytic carbon 13, a chemical bond is formed with the bond strength not lower than the strength of the material itself. After the process of obtaining a plate of isotropic pyrolytic carbon by mechanical processing, an element of the joint prosthesis in the form of a head or cup is obtained.

An endoprosthesis of a joint containing a cup and a head works as follows.

Using conventional surgical procedures, the hip joint prosthesis is fixed in the patient’s femur and pelvic bones. When the patient’s leg moves, the head of the hip joint endoprosthesis moves inside the cup. In this case, smooth, for example, spherical surfaces interact - the outer one at the head and the inner one at the cup, made of isotropic pyrolytic carbon. Thanks to this, minimal friction forces and minimal wear of rubbing surfaces are achieved.

The proposed joint prosthesis containing a cup and a head, while maintaining such advantages of the prototype as high wear resistance and minimal friction in the hinge, has increased reliability due to the lack of components associated with a foreign polymer material.

Information sources

1. V.A. Fokin. Friction pairs for total hip arthroplasty and wear problems. - Margo Anterior No. 4/2000, p. 3.

2. U.S. Patent No. 5,549,697.

3. US Patent No. 6187049.

4. Kampner S.L., Weinstein A.M. l-st Int. Conf. Eng. and clin. Aspekt Endoprosthetic Fixat. - London, 13-15 June 1984, 111-120.

5. US Patent No. 4,166,292.

6. Patent RU No. 22240081 C1, A61F 2/30, 02/18/2003 (prototype).

Claims (1)

An endoprosthesis of a joint containing a cup and a head made with interacting smooth surfaces, characterized in that both the head and the cup consist of a sleeve of isotropic pyrolytic carbon and fixedly connected to it by chemical bonding without the use of foreign materials with a bond strength not lower than the strength of the material itself plates of isotropic pyrolytic carbon.

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