JPH0423540B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an artificial hip joint (a hip joint).
This is related to prothesis.

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 a convex spherical femoral epiphysis on one side and a concave spherical cotyle on the other side. The need for a joint prosthesis may result from deterioration of one of the two aspects, or deterioration of both. Among current hip prostheses, a distinction is made between two types of prostheses: cups and center-diaphysial support prostheses.

Cups are simply intended to replace diseased articular surfaces. The femoral and cotyloidal surfaces can be replaced, or only one of them can be replaced. The cup may be sealed or unsealed. This type of prosthesis is excellent at protecting the epiphyseal tissues and prevents wear and tear and fracture (failure).
When this occurs, a second type of prosthesis can be used. 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 an artificial stem in the femoral shaft. 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 socket. 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 prosthetic joints are responsible for the resection of a considerable bone axis, which is more than that of the cup;
In the event of wear and tear, they can only be replaced by an artificial joint of the same type, which is often a lengthy and difficult operation.

Furthermore, bone is a living tissue that is constantly undergoing repair and alteration.
The densification or, for that matter, absorption of the additive depends on a number of factors, of which mechanical stress is the most important.
Here, fixing the artificial joint in place is
Interacts with the area of stress transmitted within the bone tissue.

Four types of stress are distinguished, simplified as shear, tension, 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 hip 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 To achieve the above objects, the present invention provides a hip prosthesis having two substantially concentric, convex, opposing surfaces.

As a result of this, the direction of the force applied to the artificial hip joint passes through its center and does not disturb the equilibrium of the joint. Furthermore, the transmission of the resultant force at the joint interface acts normal to the convex surface, which roughly follows the direction of the natural line in the bones joined by the joint.

According to a preferred embodiment of the invention, one of the convex surfaces has a larger radius of curvature than the other convex surface. It promotes gliding motion in one part of the joint.

In another preferred embodiment of the invention, the convex surface forms part of a spherical surface. It allows easy sliding movement of the artificial hip joint within the cavity into which it is inserted.

In each of the above embodiments of the invention relating to a hip prosthesis with convex surfaces having different radii of curvature,
The convex surfaces are connected to each other by the side surfaces of a third part, for example a frusto-conical part. It causes maximum flexion of the joint to occur around a convex surface with a minimum radius of curvature.

Furthermore, according to another particular embodiment of the invention, the artificial hip joint is characterized in that the convex surface with the smallest radius of curvature and the third part are connected by an elastic member. This elastic member forms a damper between two bones connected to each other by the artificial hip joint.

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

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

As illustrated, the artificial hip joint according to the present invention includes:
A first convex surface 1 forming part of a spherical surface, which is concentrically arranged oppositely,
The second convex surface 2 forms part of a spherical surface with a radius of curvature greater than the radius of curvature of the truncated cone. In the embodiment shown in FIG. 1, the artificial hip joint is formed from a single piece, for example stainless steel.

FIG. 2 shows an application of the artificial hip joint according to the invention in a cross-section in a plane substantially passing through the axis of the femur. In this embodiment, the first convex surface 1 is the outer surface of a steel ball, indicated at 4, while the opposing second convex surface 2 is connected to the ball 4 by an elastic member 6. The elastic member 6 is formed by the outer surface of the hollow ball part 5 and consists of, for example, polyethylene or an elastomer glued to the ball 4 and the hollow ball part 5. In the embodiment shown, the pelvic bone 7 is slightly concave and the second cup 8 is implanted in the femoral acetabulum. Furthermore, the head 9 is cut along a plane passing through the center of the head 9 and perpendicular to the axis of the lines of force at the neck of the femur. The bone stump is then recessed and fitted snugly to the first femoral cup 10. The diameter of the second convex surface 2 with the largest radius of curvature preferably lies within the second acetabular cup 8, while the first convex surface 1 with a smaller diameter lies within the first cup 10 of the femur. Preferably, they fit snugly. In order to minimize frictional forces, the small diameter first convex surface 1 preferably has a radius as small as possible, while being able to coexist with the compressive stresses imparted by the hip prosthesis. On the other hand, the second convex surface 2 with a larger diameter has a larger diameter than the first femoral cup 10.
the diameter of the femoral head in order to allow the hip prosthesis to deflect into the second acetabular cup 8 in the event that the upper surface comes into contact with the third part, e.g. the side surface 3 of the frustoconical part; Preferably, it is slightly larger than .
We propose that a large diameter of about 50 mm and a small diameter of about 22 mm should be adopted for the human hip joint, which has a diameter of 49 mm. The cups may be made of different materials, the thickness of which depends on the joint in which the artificial hip joint is snugly fitted and the material selected. For the hip joint, a polyethylene cup having a thickness of 6 to 8 mm is preferred.

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 hip prosthesis, and therefore the remodeling of the bone tissue at the interface with the cup is very significantly promoted.

Furthermore, all stresses applied to the hip prosthesis are compressive forces through the center of the hip prosthesis. Therefore, the static balance of the artificial hip joint remains unchanged.
Joint mobilization occurs naturally over small diameter couplings. The risk of dislocation is limited by the mobility of the large diameter connection. lastly,
The implantation of a hip prosthesis does not compromise the bone axis, and this allows replacement in the event of wear or fracture by a hip prosthesis with 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 cups also being complementary. For example, the shape should be understood as a shape that allows rolling with sliding movement over the active parts of a hip prosthesis. Similarly, although the embodiments described above consist of precisely concentric convex surfaces, it is also possible to provide slightly eccentric convex surfaces. Finally, if the condition of the buttocks allows, the prosthetic hip joint can be replaced with a prosthesis.
It is possible to install it directly into the existing abutment without providing a cotyle.

Preferably, the center of the artificial hip joint coincides with the center of the head of the femur.

[Brief explanation of drawings]

FIG. 1 is a front view of an embodiment of the artificial hip joint according to the present invention, and FIG. 2 is a sectional view of the hip joint to which the artificial hip joint according to the present invention is tightly attached. 1, 2...Convex surface portion.

Claims (1)

[Scope of Claims] 1. A hip prosthesis for placement between a pelvic bone and a femoral head of a hip joint, comprising: a first convex surface rotatably disposed within a cavity formed within the femoral head; a second convex surface portion rotatably disposed within a cavity formed in the bone of the pelvis and convex in a direction opposite to the convex direction of the first convex surface portion; a third portion located between the two convex surfaces and fixedly provided with respect to these surfaces, the radius of curvature of the first convex surface being equal to the radius of curvature of the second convex surface; An artificial hip joint characterized by being smaller than the radius. 2. The artificial hip joint according to claim 1, wherein the first and second convex surfaces form part of a spherical surface. 3. The artificial hip joint according to claim 2, wherein the third portion has a truncated cone shape. 4. The artificial hip joint according to claim 3, characterized in that the bottom of the truncated cone is fixed to the second convex surface. 5. A hip prosthesis for placement between a pelvic bone and a femoral head of a hip joint, comprising: a first convex surface rotatably disposed within a cavity formed in the femoral head; a second convex surface portion rotatably disposed within a cavity formed therein and convex in a direction opposite to the convex direction of the first convex surface portion; and between the first and second convex surface portions. and a third portion fixedly disposed relative to these surfaces, wherein the radius of curvature of the first convex surface is smaller than the radius of curvature of the second convex surface; one convex surface is disposed within the cavity by being positioned within the first cup means;
The first cup means is shaped on one surface to fit into a cavity formed in the femoral head and has an opposite surface shaped in the shape of the first convex surface. An artificial hip joint characterized by: 6. A hip prosthesis for placement between a pelvic bone and a femoral head of a hip joint, comprising: a first convex surface rotatably disposed within a cavity formed within the femoral head; a second convex surface portion rotatably disposed within a cavity formed therein and convex in a direction opposite to the convex direction of the first convex surface portion; and between the first and second convex surface portions. and a third portion fixedly disposed relative to these surfaces, wherein the radius of curvature of the first convex surface is smaller than the radius of curvature of the second convex surface; two convex surfaces are disposed within the cavity by being positioned within the second cup means;
An artificial hip joint characterized in that one surface of the second cup means is configured to fit into a cavity formed within the bone of the pelvis. 7. A hip prosthesis for placement between a pelvic bone and a femoral head of a hip joint, comprising: a first convex surface rotatably disposed within a cavity formed within the femoral head; a second convex surface portion rotatably disposed within a cavity formed therein and convex in a direction opposite to the convex direction of the first convex surface portion; and between the first and second convex surface portions. and a third portion fixedly disposed relative to these surfaces, the radius of curvature of the first convex surface being smaller than the radius of curvature of the second convex surface, and an elastic member. is disposed between the first convex surface portion and the third portion, and the first convex surface portion and the third portion are disposed between the first convex surface portion and the third portion.
An artificial hip joint characterized in that a portion is fixed to the elastic member.