JPH01175846A - Artificial joint - Google Patents

Abstract

PURPOSE: To provide an artificial articulation convenient for transmitting force along the inborn line and protecting or recomposing the axis of a bone, by equipping a protruding surface part constituted of two substantially concentric protruding surface parts facing to each other, of which one has a protruding surface part with a radius of curvature larger than that of the other. CONSTITUTION: This artificial articulation is equipped with a first protruding surface part 1, for instance a spherical surface part, engaged with a second spherical part concentrically placed facing to the first surface part, for instance with a radius of curvature larger than that of the first spherical surface part 1, via a surface part 3 of a cone bed. The first protruding surface 1 is formed by the outside surface 4 of a steel ball and the second protruding surface 2 facing to the first one by the outside surface of a hollow ball combined with the ball 4 by an elastic member 6, and, for instance, the elastic member 6 is a polyethylene or elastomer part adhered to the ball 4 and the hollow ball part 5. This artificial articulation can be bent at the position of a border face of transplanting of an artificial fitting without generating tensile stress and remarkably promote recomposing of bone tissue at the position of a border face with a cup.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an artificial joint (a joint prosthesis).
is), particularly, but not exclusively, related to hip prostheses (a hip prosthesis).

BACKGROUND OF THE INVENTION Joints are joined by at least two articular surfaces that are movable relative to each other. For example, the hip joint is formed by the anterior end of a convex spherical femur on one side and a concave spherical cotyle on the other side. The need for a prosthesis may result from deterioration of one or both of the two aspects. Among current hip prostheses, a distinction is made between two types of prostheses: cups and center-diaphyseal supports.
It is a prosthesis with an upport.

The cup is intended solely to replace the pathological articular surface. Femoral surface and white (cotyloida)
l) Faces can be replaced, or only one of them can be replaced. The cup may be sealed or unsealed. This type of prosthesis provides excellent dorsal tissue protection and can be replaced by a second type of prosthesis in the event of wear or failure.

This prosthesis has a sufficient diameter so that it is stable, but on the other hand it is subject to a greater amount of wear and tear.

A second type of prosthesis includes a prosthetic stem in the shaft of the femur. This shaft is supported by the cortical portion of the diaphysis. This articulation part is a ball that can be directly articulated with a natural or artificial mortar. In the latter case, it is possible and an interesting proposal to reduce the diameter of the sphere in order to reduce the amount of wear and tear on the prosthesis, but then there is a risk of instability and dislocation. . Additionally, these prostheses undergo more resection of the bone axis than do cups, so that in the event of wear or fracture, they are often longer and more difficult to operate than the same type of prosthesis. Replacement is possible only with a brace.

Additionally, bones are constantly undergoing repair and change.
It is a living tissue undergoing terat 1on). impregnation with additives (densificati)
on) or on the other hand its absorption depends on a number of actors, among which mechanical stress is the most important. Here, fixing the prosthesis in place interferes with the area of stress transmitted within the bone tissue.

Four types of stress are distinguished: simply shear;
There is tension 8 bending and compression. Compressive stresses, if kept close to physiological values, best enable quality bone motion to be achieved.

OBJECTS OF THE INVENTION The object of the invention is to provide an artificial joint that is convenient for transmitting forces along the natural line and for protecting or reconstructing the bone axis.

(Structure and Effects of the Invention) In order to achieve the above object, the present invention provides an artificial joint having two substantially concentric convex surfaces facing each other on the surface portion.
This is what we provide.

As a result of this, the direction of the force applied to the prosthesis passes through its center and does not disturb the equilibrium of the joint. Furthermore, the interface of the joint
The transmission of the resultant force at position e) acts normal to the convex calendar surface portion, which approximately follows the direction of the natural line in the bones connected by the joint.

In a preferred embodiment of the invention, the convex calendar surface portion is a spherical portion. It causes a simple sliding movement of the prosthesis within the cavity into which it is inserted.

According to another preferred embodiment of the invention, one of the convex ephemeris surface portions has a larger radius of curvature than the other.

It facilitates gliding motion in one part of the joint.

In the above embodiment of the invention, which concerns a prosthesis with convex ephemeris surfaces having different radii of curvature, the convex ephemeris surface portions are connected to each other by frustoconical portions. It causes maximum flexion of the joint to occur around the convex surface portion with the minimum radius of curvature. Furthermore, according to another particular embodiment of the invention, the prosthesis consists of two rigid elements connected by an elastic member. This elastic member thus forms a damper between the two bones connected to each other by the prosthesis.

Other features and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings.

(Example) Next, one embodiment of the present invention will be described with reference to the drawings.

As shown, the prosthesis according to the invention comprises a first convex surface portion 11, e.g. It engages with a second spherical portion having a larger radius of curvature via the truncated conical surface portion 3. In the embodiment shown in FIG. 1, the prosthesis is a single piece.
), for example made of stainless steel.

FIG. 2 shows an example of the application of the prosthesis according to the invention to a hip joint in a cross-section in a plane substantially passing through the axis of the femur. In this example, the first convex surface l is the outer surface of a steel pole, indicated at 4, while the second opposing convex surface 2 is a hollow ball portion 5 connected to the ball 4 by an elastic member 6. The elastic member 6 is, for example, a piece of polyethylene or an elastomer glued to the pole 4 and the hollow pole part 5.

In the illustrated embodiment, the pelvic bone 7 is slightly concave;
Cup 8 is implanted in the abutment of the thigh. moreover,
The head 9 is cut along a plane passing through the center of the head and perpendicular to the axis of the lines of force in the neck of the femur. The bone stump is then recessed and snugly aligned with the femoral cup IO.

The diameter of the surface 2 with the largest radius preferably fits within the white cup, while the smaller diameter surface l preferably fits snugly within the femoral cup. In order to minimize frictional forces, it is preferred that the small diameter surface l has as small a radius as possible, while being able to coexist with the compressive stresses imparted by the prosthesis. In contrast, the large diameter surface allows the prosthesis to deflect into the white cup 8 in the event that the upper surface of the femoral cup 10 comes into contact with the truncated conical wall section 3. Preferably, it is slightly larger than the diameter of the femoral head. Diameter 49
For the human hip joint of mm, the large diameter is about 5Qmm and about 2
We recommend that a small diameter of 2 mm be adopted. The cups may be made of different materials, the thickness of which depends on the joint in which the prosthesis is fitted and the material selected. For the hip joint, it is preferred that the cup is made of polyethylene and has a thickness of 6 to 8 mm.

It is noted that in the illustrated embodiment, the concentricity of all elements and the entire surface of the different components makes it possible to eliminate any mechanical torques. Therefore, no bending and tensile stresses occur at the interface of the implantation of the prosthesis, and therefore the reconstruction of the bone tissue at the interface with the cup is very significantly promoted.

Furthermore, all stresses applied to the prosthesis are compressive forces through the center of the prosthesis. Therefore, the static balance of the prosthesis remains unchanged. Joint mobilization (Mobilisa)
tion) naturally occurs on small diameter couplings. The risk of dislocation is limited by the mobility of the large diameter connection. Finally, prosthetic implantation does not damage the bone axis;
This, in turn, allows replacement in the event of wear or fracture by a prosthesis with a diaphyseal central support.

The invention is not limited to the embodiments described above, but various modifications are possible without departing from the scope of protection. In particular, although the particular embodiment shown consists of two spherically convex surfaces, other shapes of convex surfaces, such as paraboloids, may also be used, with the engaging cup also having a complementary shape. This should be understood, for example, as a shape that allows displacement with sliding movement over the working part of the prosthesis. Similarly, while the embodiments described above consist of precisely concentric convex surfaces,
It is also possible to provide a slightly eccentric convex surface, especially for joints such as the shoulder.

Finally, if the condition of the cotyle allows, the prosthesis can be placed directly into the existing cotyle without the provision of a prosthetic cotyle; preferably, the center of the prosthesis is It may coincide with the center of the head of the femur or, in the case of another joint, with the center of the dorsal end to be replaced by the prosthesis.

In short, the exact shape of the prosthesis, its dimensions, the materials used will be applied in each case depending on which joint and taking into account the individual morphology.

[Brief explanation of the drawing]

FIG. 1 is a front view of an embodiment of the prosthesis according to the present invention, FIG.
The figure is a cross-sectional view of a hip joint fitted with a prosthesis according to the invention. 1.2... Convex surface portion. Patent applicant: Leclerc Secu Sylvian and 2 others Agent: Patent attorney Aoyama Aoyama and 2 others

Claims (4)

[Claims] (1) consisting of two substantially concentric opposing convex surface portions (1, 2), one of which (1) is adjacent to the other (2);
) A prosthetic joint characterized in that it has a convex surface portion with a larger radius of curvature. 2. Artificial joint according to claim 1, characterized in that the convex surface portions are connected to each other by a frustoconical portion (3). (3) An artificial joint according to claim 1 or 2, characterized in that the convex surface portion is a spherical portion. (4) Two rigid elements (4, 5) connected by an elastic member (6), each of which displaces one of said convex surface parts. The artificial joint according to any one of Items 1 to 3.