JPH05344992A - Joint prothesis device - Google Patents

Abstract

PURPOSE:To prevent the reduction of the pressure receiving area of a bearing by exceedingly reducing the space and gap inside the bearing. CONSTITUTION:An outer ball assembly 2 is constituted of an outer ball 3, first bearing 7 fixed inside the outer ball 3, second bearing 8 arranged so as to contact the first bearing 7, stopper ring 9 which forms a slidable surface for pressing the second bearing 8 by the fitting with the outer ball 3 and supporting an inner ball 1 by the first and second bearings 7 and 8. Accordingly, the space and the gap at the slidable part where the bearing and the inner ball contact can be reduced, and even in the case where the direction of the load changes, the pressure receiving area of the bearing does not reduce, and the generation of the excessive surface pressure, deformation of the slidable surface, increase of abrasion, etc., can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved inner ball support structure suitable for a self-aligning joint prosthesis.

[0002]

2. Description of the Related Art FIG. 7 is a schematic view of a prosthesis for a well-known self-aligning joint used as an artificial joint, especially an artificial hip joint, in which a bearing 4 is fixed inside an outer ball 3 having a hemispherical shell shape. It is supported by the outer ball assembly 2 having the above structure. The inner ball 1 is attached to the tip of a stem 5 fixed to the femur. A portion of the inner surface of the bearing 4 near the opening has a tapered surface 4a that becomes wider at the inner side, and a C ring-shaped tapered ring 6 is fitted into the tapered surface 4a so that the inner diameter is reduced by the C spring 6a. It is energized.

When the inner ball 1 is assembled into the outer ball assembly 2, the taper ring 6 is pushed and moves inward to widen the inner diameter, so that the inner ball 1 is supported by the bearing 4
After that, the inner diameter of the taper ring 6 becomes smaller and the inner ball 1 is prevented from coming off. An area where the bearing 4 and the inner ball 1 are in contact with each other has a size corresponding to a substantially hemispherical portion of the inner ball 1, and a space G is formed inside the bearing 4. This space G is necessary for moving the taper ring 6 as described above. When the inserted inner ball 1 is detached from the outer ball assembly 2, the taper ring 6 is moved inward using a special tool to pull out the inner ball 1 with the inner diameter widened.

By the way, it is most desirable to apply a load to the bearing 4 in the direction A which substantially coincides with the axial center. However, in the case of a self-centering type joint prosthesis, the outer ball assembly 2 is the hip bone of the pelvis. It is fitted in the acetabulum and slides and rotates with walking, etc., and the angle with respect to the acetabulum changes. This is effective in increasing the movable range of the inner ball with respect to the acetabulum, but on the other hand, it causes the load direction to be tilted from the A direction to, for example, the B direction in the figure, and the pressure receiving area of the bearing 4 decreases. The surface pressure becomes excessive, which causes deformation of the sliding surface and increased wear. This problem can be alleviated by providing a bearing on the inlet side as well (see, for example, Japanese Patent Laid-Open No. 4-44756), but even with such a structure, there is a certain degree of space between the inlet-side bearing and the internal bearing. Since the gap is formed, it is inevitable that the pressure receiving area is reduced when the load direction is inclined.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to minimize the space and gap inside the bearing that cause the reduction of the pressure receiving area.

[0006]

In order to achieve the above object, in the joint prosthesis of the present invention, the outer ball assembly supporting the inner ball is fixed to the outer ball having a hemispherical shell shape and inside the outer ball. And a ring-shaped second bearing having a structure capable of changing the inner diameter within a certain range and arranged so as to be in contact with the first bearing. The second bearing is held down, and the stopper ring forms a sliding surface for supporting the inner ball by the first and second bearings.

[0007]

The second bearing is arranged so as to be in contact with the first bearing. By further pressing the second bearing with the stopper ring, there is no gap between the first and second bearings, and the load direction is inclined. However, the inner ball is supported by the bearing whose structure does not reduce the pressure receiving area.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in FIGS. 1 to 6 will be described below. 1 and 2 are an overall sectional view and an exploded perspective view showing an inner ball, an outer ball assembly, and
The outer ball and stem are designated by the same reference numerals 1 to 3 and 5 as in FIG. 7, respectively. In this embodiment, the bearing is composed of a first bearing 7 and a second bearing 8 and is provided with a stopper ring 9, and the outer ball assembly 2 is constituted by the outer ball 3, the bearings 7, 8 and the stopper ring 9. Has been done.
As the material of the outer ball 3, for example, cobalt chrome alloy or ceramic is used.
As the material of the stopper ring 9, for example, ultra high molecular weight polyethylene is used.

3 to 6 show the outer ball assembly 2
It is the figure which each showed the detail of each member which comprises. As shown in FIG. 3, the outer ball 3 has a slightly deep hemispherical shell shape, and a seat 3a having a plurality of minute projections 3c on the inner circumference is formed inside, and a ring shape is formed on the inner side of the edge. A locking portion 3d is provided. The small protrusions 3c prevent the first bearing 7 from rotating and prevent the first bearing 7 from slipping off in the axial direction, and have a triangular cross-section and a shape with a higher depth at the back.

As shown in FIG. 4, the first bearing 7 has a hemispherical shell shape having an outer surface having a shape corresponding to the inner surface of the outer ball 3 and an inner surface having a diameter corresponding to the inner ball 1. The dovetail projections 7a for forming the dovetail joint are formed at positions separated by 180 °, and the inner surface is a sliding surface 7b with the inner ball 1. This first
The shape and size of each part of the bearing 7 are selected so that when the bearing 7 is inserted into the seat 3a of the outer ball 3, the bearing 7 is fixed to the outer ball 3 in a stationary state by the minute protrusions 3c.

As shown in FIG. 5, the second bearing 8 is provided with a tapered or spherical sliding surface 8a following the sliding surface 7b of the first bearing 7, and a notch portion 8b is formed at one position C. It has a ring shape, and the inner diameter of the minimum portion of the sliding surface 8a is selected to be slightly smaller than the diameter of the inner ball 1. A groove 8c corresponding to the dovetail projection 7a is provided on the end surface on the side in contact with the first bearing 7, and the outer peripheral surface is a tapered surface 8d. The dovetail groove 8c and the dovetail protrusion 7a of the bearing 7 are loosely connected between the bearings 7 and 8 by combining them, and are formed with sufficient dimensions so as not to be fixed.

The stopper ring 9 has a ring shape as shown in FIG. 6, and the inner diameter thereof is selected so that the inner ball 1 can freely pass therethrough.
Is formed, a flange 9b is formed on the other end surface, and the inner peripheral surface further has a tapered surface 8 of the second bearing 8.
A tapered surface 9c corresponding to d is provided, and a plurality of minute convex portions 9d are provided at equal intervals on the outer peripheral surface. It should be noted that the minute convex portion 9d is not shown in FIG. The locking projection 9a is for locking the stopper ring 9 when the stopper ring 9 is inserted into the outer ball 3 and temporarily assembled to prevent the stopper ring 9 from coming off.
Is for fixing the stopper ring 9 to the outer ball 3 after the inner ball 1 is inserted, and the shapes and dimensions of relevant parts are selected so that such a function can be exerted without trouble. A plurality of notches 9e are formed on the outer periphery of the flange 9b, and when the inner ball 1 inserted into the outer ball assembly 2 is removed, a surgical tool is inserted to release the fixing of the stopper ring 9 to the outer ball 3. Used for.

This embodiment is constructed as described above, and when assembled, first the first bearing 7 and the second bearing 8 are inserted into the outer ball 3 in a state in which the dovetail projection 7a and the dovetail groove 8c are combined. Then, the stopper ring 9 is inserted into the outer ball 3 to a position where the locking projection 9a can be locked to the locking portion 3d. With this, the outer ball assembly 2 is temporarily assembled. The second bearing 8 is free because it is not pushed by the stopper ring 9, and the inner ball 1 is ready for insertion. Next, the stopper ring 9 is separated from the outer ball 3 as shown by the chain line in FIG.
When the inner ball 1 is inserted into the second bearing 8, the inner ball 1 passes through this while widening the inner diameter of the second bearing 8, and is inserted deeper than the bearing 8.

Here, the stopper ring 9 is attached to the outer ball 3
When the second bearing 8 is strongly pushed in, the tapered surface 8d on the outer periphery of the second bearing 8 is pressed by the tapered surface 9c of the stopper ring 9 and the inner diameter is reduced. The inner ring 1 is brought into sliding contact with the inner ball 1, and the stopper ring 9 is fixed by the minute convex portion 9d and the locking portion 3d of the outer ball 3 to prevent the stopper ring 9 from coming off. The bearing 8 is connected to the bearing 7 by a dovetail joint, but since it is not fixed at this portion, the inner diameter can be changed.

Although the insertion of the inner ball 1 into the outer ball assembly 2 is completed by the above operation, when the stopper ring 9 is unfixed by utilizing the notch 9e in this state, the bearing 8 has the groove 8c. Since it is separated from the stopper ring 9 in combination with the protrusion 7a, the inner ball 1 can be removed from the outer ball assembly 2 by the operation reverse to the above. Such attachment / detachment operation can be easily performed even when the prosthesis is actually used for the hip joint of the patient.

In this embodiment, the second bearing 8 is arranged so as to be in contact with the first bearing 7 as described above, and is pressed by the stopper ring 9 after the inner ball 1 is inserted. A large space, as in the conventional example, of course is almost eliminated between 8 and 8. Therefore, even if the direction of the load is inclined, the pressure receiving area does not decrease, and it is prevented that the surface pressure becomes excessive and the sliding surface is deformed and wear is increased. Therefore, the joint prosthesis suitable for the self-aligning type in which the direction of the load on the assembly is likely to change can be obtained. The present invention can be applied not only to the hip joint shown in FIG. 1 but also to a shoulder joint prosthesis.

[0017]

As is apparent from the above description, according to the present invention, an outer ball assembly for supporting an inner ball, a hemispherical shell-shaped outer ball, a first bearing fixed inside the outer ball, and A ring-shaped second bearing, which is arranged so as to be in contact with the first bearing and has a structure capable of changing the inner diameter within a certain range, and presses the second bearing by fitting the outer ball, And a stopper ring that forms a sliding surface for supporting the inner ball by the second bearing.

Therefore, a relatively large space is not formed in the sliding portion where the bearing and the inner ball are in contact with each other, and a gap is not formed between the bearing provided on the inlet side and the inner bearing. The bearing surface does not decrease even if the direction of the load on the outer ball assembly changes, preventing excessive bearing pressure from causing deformation and increased wear on the sliding surface. Therefore, it becomes easy to prolong the life of the joint prosthesis and prevent the adverse effects of the abrasion powder on the bone tissue and the pain due to loosening.

[Brief description of drawings]

FIG. 1 is an overall sectional view of an embodiment of the present invention.

FIG. 2 is an exploded perspective view of the same.

FIG. 3 is a front view, an AA line cross-sectional view, and an enlarged cross-sectional view of a main part of the outer ball of the same embodiment.

FIG. 4 is a front view, a vertical sectional view and a plan view of a first bearing of the same embodiment.

FIG. 5 is a front view, a vertical sectional view and a plan view of a second bearing of the same embodiment.

FIG. 6 is a front view, a partial vertical cross-sectional view, and an enlarged front view of a main part of a stopper ring of the same embodiment.

FIG. 7 is a sectional view of a conventional example.

[Explanation of symbols]

 1 Inner Ball 2 Outer Ball Assembly 3 Outer Ball 7 First Bearing 7b Sliding Surface 8 Second Bearing 8a Sliding Surface 8b Notch 8d Tapered Surface 9 Stopper Ring 9c Tapered Surface

Claims (1)

[Claims] 1. A joint prosthesis comprising an inner ball and an outer ball assembly supporting the inner ball, comprising:
The outer ball assembly includes a hemispherical shell-shaped outer ball, a first bearing fixed inside the outer ball, a structure arranged to be in contact with the first bearing, and a structure capable of changing the inner diameter within a certain range. A ring-shaped second bearing provided, and a stopper ring that presses the second bearing by fitting it to the outer ball and forms a sliding surface that supports the inner ball by the first and second bearings. A joint prosthesis characterized by being performed.