RU2268685C2 - Hip joint's endoprosthesis caput - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: the present innovation deals with predominantly in case of partial articular substitution at keeping natural cotyloid cavity. This innovation enables to save the cartilage of cotyloid cavity against enhanced wearing at coupled work of friction and artificial materials of nonbiological nature. A caput contains a metal cork with a cone-shaped opening for cervix and a sphere for this cork The sphere is designed out of polymeric material, sphere's opening and cork's external surface are designed to have a groove for screwing the cork into the cavity. Surface layer of polymer that forms a threading profile in sphere's cavity is supplied with a system of micropores filled before cork's mounting with liquid component of bony cement. The surface of sphere's threading profile before cork's mounting should be covered with a powder component of bony cement, moreover, during mounting one could observe a shift of components and hardening of bony cement.

EFFECT: higher efficiency.

2 cl, 4 dwg

Description

The invention relates to the field of orthopedic technology and can be used for hip replacement after injuries or diseases.

In many cases, hip replacement surgery is performed using so-called unipolar endoprostheses. They are used if the acetabulum, which is the pelvic component of the joint, is not damaged, and the defects are concentrated in the femoral part of the joint (for example, with fractures of the femoral neck). The problem is that the technical materials used in the friction units of joint endoprostheses wear out the cartilage that covers the acetabulum. The lowest rate of cartilage wear occurs when it is paired with polymeric material. Many designs of unipolar endoprostheses using polymers have been developed.

Endoprosthesis of the femoral head [Application 96.118.782 / 14 of the Russian Federation, A 6 1F 2/36, decl. 1996] consists of the head itself, in the form of a segment of a hollow sphere, and a leg, which has a complex structure in the form of a rod with an opening that is fixed in the cavity of the femur. The head is fixed to the leg with screws and a special flexible element located in the cavity of the rod.

The disadvantage of this design is the difficulty of replacing a worn out or otherwise damaged head during the revision operation.

This disadvantage is overcome in the design of a modular hip joint prosthesis [US Patent No. 5,370,706, A 61 F 2/24, 1994], in which a head provided with a conical hole is mounted on the conical neck of the leg. Used in Sulzer prostheses [MEM (prospectus by PROTEK), Baar: Sulzer Orthopedics Ltd, 1997. - 14p,] the standard eurocone (12/14) on the neck of the leg allows you to quickly and easily install modular heads of any manufacturer on it.

However, the execution of the head from a polymeric material gives rise to problems associated with the weakening of the head on a standard conical neck during operation of such an endoprosthesis. Walking, standing, and other types of loading of the operated limb cause the polymer to be pushed out in the conical hole of the polymer head, which becomes oval in cross section.

Known attempts to solve this problem lead to a significant complication of the design of the endoprosthesis. Thus, an endoprosthesis of the head of the hip joint [Application 96.110.092 / 14 of the Russian Federation, A 61 F 2/36, decl. 1996] involves the implementation of a ball head made of fluoroplastic. In the body of the ball there are channels that connect the friction zone of the head (go out to its spherical surface) and a collector filled with lubricating fluid. Improving the lubrication conditions of the head increases the reliability of its mounting on the leg.

Endoprosthesis of the femoral head [Auth. certificate 1.630.812 USSR, A 61 F 2/36, 1991] in order to ensure rigid fixation of the head on the leg is provided with longitudinal ribs that are made on the surface of the neck.

The complexity of the design of such endoprostheses minimizes the advantages that give them the principle of modular assembly.

Knee Endoprosthesis [Auth. testimonial. 1.061.811 USSR, A 61 F 1/03, 1983] consists of a load-bearing metal substrate, which is coated with a polymer coating of a special structure. In the polymer coating matrix there are pores with a size of 1-3 microns, which are filled with synovial fluid. This structure of the polymer element of the endoprosthesis imitates the structure of the articular cartilage.

Giving such a structure to the surface layer of the head of the hip joint implant will undoubtedly reduce friction in the cartilage-implant pair, but will not solve the problem of the reliability of the fit of the head on the neck with a cone of standard sizes.

The prototype of the invention is a modular joint prosthesis [US Patent 5.858.020, A 61 F 2/36, 2/30, 1999 (prototype)]. It consists of a head containing a metal plug with a conical hole, and a ball provided with a cavity for the plug. In the conical hole of the tube, which corresponds to the standard for conical conjugation of parts of endoprostheses, a neck is planted in a tight fit. It connects the head and leg of the endoprosthesis, which has a special configuration. The latter provides reliable fixation of the legs in the bone marrow canal of the bone entering the endoprosthetics joint.

The disadvantages of the prototype:

- insufficient reliability of fastening the head on the leg of the endoprosthesis if the ball is made of a polymeric material;

- technological incompatibility of the cork and the unified heads of the endoprostheses of the hip joint, corresponding to the European standard;

- insufficient reliability of the design of the legs, containing a detachable connection of the neck and the rod.

Tasks to be solved by the invention:

1) to develop a simple design of a unipolar hip joint implant with a head made of a polymer material;

2) reduce the likelihood of revision operations due to the instability of the fastening of the elements of the endoprosthesis;

3) apply binders used in the practice of endoprosthetics for fastening the elements of the endoprosthesis.

The problem is solved in that the known design of the head of the hip joint replacement, containing a metal plug with a conical hole for the neck and a ball with a hole for the plug, is supplemented with new elements. The ball is made of polymeric material, and the hole in the ball and the outer surface of the cork are threaded to screw the cork into the cavity. The surface layer of the polymer, forming a threaded profile in the cavity of the ball, is equipped with a system of micropores filled before the installation of the cork with the liquid component of bone cement. The surface of the threaded profile of the ball before installing the cork is covered with a powder component of bone cement. When installing the cork, the components are mixed and the bone cement hardens.

A variant of the proposed design of the head is that in the threaded hole of the ball and / or on the thread of the tube, annular grooves filled with bone cement are made.

The next option is characterized in that in the cork and ball at an angle to their common axis, blind coaxial cylindrical channels are made. They are open from the side of the uniform conical hole in the cork and do not extend to the surface of the ball. Fonts or studs are installed in the tight fit channels, the threaded part of which is located in the cork wall. Canals can be filled with bone cement.

The essence of the invention lies in the fact that the surface layer of the threaded cavity in the ball is transferred to the state of jelly. In the polymer matrix of the latter there are micropores filled with a dispersion liquid. With the help of special technological operations, the jelly fluid was replaced in micropores with the fluid component of bone cement. The surface of the threaded profile of the ball is covered with a layer of the powder component of bone cement. When screwing the cork into the ball, the components are mixed and the cement hardens. The latter is located in the micropores of the threaded profile in the cavity of the ball and forms an adhesive connection with the threaded surface of the metal tube. This increases the reliability of fixing the cork in a polymer ball, and the detachable cone pairing of the metal neck and cork according to the criteria of manufacturability and reliability meets international standards of orthopedics. This makes it possible to replace the endoprosthesis head in accordance with the present invention with another standard head during revision operations, regardless of which manufacturer it was manufactured.

Examples of the proposed head design of a unipolar hip joint endoprosthesis are shown in FIGS. 1-4: FIGS. 1, 3, 4 are cross-sections of the heads; figure 2 - structure of the surface layer of the ball at the border with the cork.

Figure 1 shows the design, consisting of a polymer ball, provided with a blind threaded hole, into which a screw 2 with an external thread is screwed, having a through conical hole 3.

Cork 2 is made of bioinert metal, for example, of a titanium-aluminum-vanadium alloy (Ti-6A1-4V), which is widely used for the manufacture of endoprostheses. The conical opening 3 corresponds to the international standard ISO 7206 - 87 “Implants for surgery”.

Ball 1 is made of ultra-high molecular weight polyethylene (UHMWPE), which is best (compared to other structural polymers) proven in friction pairs of endoprostheses, for example, UHMWPE of the brand Chirulen DIN 5883 C (Hoechst AG, Germany). The threaded hole of the ball is preliminarily subjected to special processing, which included the following operations:

1) vaseline (MB) medical oil (GOST 3164-78) was poured into the hole, after which the ball was thermostatically controlled at T = 125 ° C for a time τ = 1 h;

2) oil removal, washing the hole with hexane (“hch”, TU 6-09-3375-78) for 20 minutes and vacuum drying;

3) processing of the threaded profile in the cavity of the ball with a plasma of a glow high-frequency discharge for 5 minutes;

4) applying to the thread surface the liquid component of bone cement (methyl methacrylate - 97.5%, dimethyltoluene - 2.5 wt.%), Holding for 15 minutes, removing excess fluid;

5) spraying on the thread surface of the powder component of bone cement (polymethylmethacrylate - 98%, benzoyl peroxide - 2 wt.%), After which plug 2 was screwed into ball 1.

During this processing, the following transformations of the surface layer of the threaded profile occurred:

1) a colloidal solution of UHMWPE and MB was formed in the surface layer with a thickness h = 140-150 μm; upon cooling, the solution disintegrated into phases and acquired the structure of a jelly consisting of a polymer matrix, in the pores of which (diameter 1-10 μm) there is MB;

2) as a result of washing with hexane and vacuum drying of the ball, MB was extracted from the pores of the UHMWPE matrix;

3) in the process of plasma treatment, the surface microporous layer of the ball acquired a polarizing charge and increased wetting ability;

4) the liquid component of bone cement moistened the surface of the thread and entered the pores of the UHMWPE matrix;

5) the powder component of bone cement was evenly distributed over the surface of the threaded profile of the ball, during the installation of the cork, components were mixed (at the interface and in the pores of the matrix) and the cement hardened.

Figure 2 shows the structure of the modified surface layer 4 of the material of the ball 1 at the boundary with the plug 2. Layer 4 of thickness h has the structure of a polymer gel: communicating pores of 5 micron sizes filled with bone cement are located in the UHMWPE matrix. The hardening of the cement in the gap of the threaded connection provides an adhesive connection of the tube and head. Thus, the probability of spontaneous unscrewing of the plug from the head is further reduced.

Figure 3 shows an example of strengthening the adhesive connection of the tube and ball. Annular grooves are made on their threaded parts: 6 — on the ball 1 and / or 7 — on the plug 2. The grooves are filled with bone cement before screwing the plugs.

Figure 4 shows examples of designs that provide high reliability of the connection of the ball and cork. In these parts, blind coaxial channels 8 are drilled at an angle to their common axis. They have a pin 9 or a pin 10 in a tight fit, the threaded part of which is located in the tube wall. Channel 8 may be filled with cement “plug” 11.

The proposed head design ensures the achievement of the following technical results:

the head is made of bioinert materials, many years of experience in the use of which in endoprostheses served as the basis for their inclusion in ISO standards for orthopedics, and therefore is biocompatible;

- fixing the cement “glue” in the micropores of the UHMWPE-matrix allows solving the problem of “poor” adhesion of bone cement to polymer materials, which ensures rigidity and high reliability of the unipolar endoprosthesis;

- the first operations of the technology for creating a microporous layer simulating cartilage on the friction surface of the head are similar to the first three operations of the technology for modifying the surface layer of thread described above; their essence consists in translating the surface layer into a jelly state and removing the jelly dispersion liquid; this gives the claimed design manufacturability;

- head elements providing additional fastening of a metal plug in a polymer ball (cement rings in grooves 6 and 7, pin 9, hairpin 10, cement "plug" 11), are in blind channels blocked by the neck of the endoprosthesis; this eliminates the ingress of fastening elements and products of their wear into the operated joint;

- the ball made of a polymeric material is equipped with a unified, world-class standard fastening element on the endoprosthesis leg, which ensures interchangeability of the heads.

The proposed design of the head of a unipolar hip joint prosthesis can be used in practical orthopedics as a means of preserving the cartilage of the acetabulum from increased wear by artificial materials of a non-biological nature.

Claims (3)

1. The hip endoprosthesis head containing a metal plug with a conical hole for the neck and a ball with a hole for the plug, characterized in that the ball is made of polymer material, the hole in the ball and the outer surface of the plug are threaded to screw the plug into the cavity, the surface layer polymer, forming a threaded profile in the cavity of the ball, is equipped with a system of micropores filled before the installation of the cork with a liquid component of bone cement, the surface of the threaded profile of the ball before installation of the cork is covered and the powder component of bone cement, while installing the cork, the components mix and solidify the bone cement. 2. The endoprosthesis head according to claim 1, characterized in that the annular grooves filled with bone cement are made in the threaded hole of the ball and / or on the thread of the plug. 3. The endoprosthesis head according to claim 1 or 2, characterized in that in the cork and ball at an angle to their common axis, blind coaxial cylindrical channels are made, open from the side of the conical hole and not protruding onto the surface of the ball, in which pins are mounted snugly or studs with a threaded part in the cork wall, or the channels are filled with bone cement.

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