JP3469968B2 - Artificial joint - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial joint that artificially prostheses a joint portion of a living body and restores its function and form.

[0002]

2. Description of the Related Art In the case where the joint function is impaired due to the lesion of the joint part due to the lesion of the joint part due to the bone degeneration such as trauma due to a traffic accident, rheumatism, tumor, etc. Replacement surgery is performed in which joints are excised and prostheses are made with artificial joints.

An artificial joint used in this case is called a bipolar type. This is provided with a bearing insert inside a shell that slidably contacts the bone, and between the inner head and the bearing insert that rotate within the bearing insert.
It is designed to move around. In such a bipolar type artificial joint, a stem is generally used by inserting a stem into the femur and then fixing the shell to the inner head at the tip of the stem during surgery.

Japanese Unexamined Patent Publication (Kokai) No. 62-79055 discloses such a bipolar type artificial joint. This artificial joint is provided with a plurality of cuts in the depth direction from the opening of the bearing insert and further has a gap between the shell and the inner wall surface. In the structure, the vicinity of the opening of the bearing insert is made thin so as to form, and the slip-out preventing ring is inserted in the above-mentioned gap.

In such a conventional bipolar type artificial joint, the shell has a center of the diameter of the outer surface, a center of the diameter of the spherical surface constituting the inner surface, and a center of the diameter of the inner head inserted into the bearing insert. Were formed to be concentric.

[0006]

However, in the case of the conventional artificial joint as described above, the center of the diameter of the outer surface of the shell, the center of the diameter of the spherical surface forming the inner surface, and the diameter of the inner head inserted into the bearing insert. Since the center of the bearing is concentric, the wall thickness of the spherical portion of the bearing insert is uniquely determined by the diameter of the inner surface of the shell and the diameter of the inner head. That is, in the spherical portion of the bearing insert, the thickness of the ceiling part that receives the most load and the other parts are the same and the thickness of the ceiling part is small. The amount of deformation is small, the amount of wear is large, and the living tissue may be adversely affected, and the service life is short.

Further, in the conventional bipolar type artificial joint, the strength in the vicinity of the opening of the bearing insert, which is made thin for mounting the pull-out prevention ring, has a small strength, and when the stem comes into contact with this portion, deformation or damage occurs. There was a problem that it was easy.

[0008]

In order to solve the above-mentioned conventional problems, the present invention relates to a bipolar artificial joint in which the center of the diameter of the spherical surface forming the inner surface of the ceramic shell is the diameter of the sphere on the outer surface. Eccentric to the upper side of the center of.

[0009]

In the artificial joint of the present invention having such a structure, the center of the diameter of the spherical surface constituting the inner surface of the shell is eccentric to the upper side of the center of the diameter of the sphere of the outer surface, whereby the ceiling portion of the shell is Since the wall thickness is made small, the wall thickness of the ceiling portion of the bearing insert can be made relatively large, and accordingly, the deformation amount when a load is applied becomes large, so that the wear amount becomes small.

[0010]

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention in a hip joint will be described below with reference to the drawings. As shown in FIGS. 1 and 2, reference numeral 10 denotes a shell having a smooth outer surface 11 having a substantially hemispherical shape that abuts and slides on the acetabulum. This shell 1
Bearing insert 20 to be fitted to the inner surface 12 of 0
Has an outer shape that is in close contact with the entire inner surface of the shell 10 with substantially no gap, and the inner surface 24 has a smooth spherical curved surface so as to slidably contact the inner head 31 formed on the stem 30. , Near the opening of the inner surface 24 2
A narrowest part narrower than the outer circumference of the inner head 31 is formed on the inner surface 4a, and the artificial joint is configured such that the bearing insert 20 alone holds the inner head 31 with a large anti-pulling force.

As described above, the diameter of the narrowest portion of the inner peripheral surface of the bearing insert 20 is made relatively small so that the anti-pulling force of the inner head 31 from the bearing insert 20 becomes large, so that the inner ring 31 does not have a slip-out preventing ring. The head 31 can be restrained, the vicinity of the opening of the bearing insert 20 is thick and strong, and there is no gap, so that micro-movement does not occur and the amount of wear does not increase.

The outer surface 2 of the bearing insert 20
2, a slit 21 in the shape of a spherical surface is provided in the vicinity of the equator along the circumferential direction. As shown in FIG. 3, when the shell 10 bites into the bearing insert 20 by the claws 14 provided on the inner surface 12 of the shell 10, the slit 21 becomes a play so that the inner surface 24 of the bearing insert 20 has a true shape. It is effective for fixing without impairing the sphericity.

Further, in the shell 10, the center N of the diameter of the spherical surface forming the inner surface 12 is eccentric to the upper side of the center M of the diameter of the sphere of the outer surface 11. This makes shell 10
The wall thickness w of the ceiling portion is small, and the wall thickness of the ceiling portion of the bearing insert 20 is relatively large.

Thus, the wall thickness w of the ceiling portion of the shell 10
And the wall thickness of the ceiling portion of the bearing insert is increased, the amount of deformation when a load is applied also increases, and the amount of wear decreases.

The size of the artificial joint will be described below. As for the wall thickness y of the equatorial portion and the wall thickness w of the ceiling portion of the shell 10, it is preferable that the wall thickness w of the ceiling portion is 0.5 to 0.8 times the wall thickness y of the equatorial portion. . That is, when the wall thickness is less than 0.5, the shell 10
The strength of the ceiling of the
Bearing insert 20 when larger than 0.8 times
There is a problem that the wall thickness of the ceiling part cannot be made large enough.

The thickness of the equator portion y of the shell 10 is preferably 2 to 4 mm. That is, when the thickness y of the equator is smaller than 2 mm, the strength of the shell 10 may be low, and especially the strength of the ceiling may be significantly low. On the other hand, when it is larger than 4 mm, the thickness of the bearing insert 20 should be small. Therefore, the amount of wear may increase.

[0018]

The width of the slit 21 provided on the outer surface of the bearing insert 20 is 1 mm-2.
It is preferably 5 mm. That is, the slit 21
If the width is less than 1 mm, the force holding the bearing insert 20 in the shell 10 may be insufficient, while if the width is greater than 2.5 mm, the wall thickness of this part of the bearing insert may be There is a risk that the stress received from the claws 14 may adversely affect the shape of the inner surface 24 of the bearing insert and the slidability between the inner surface 24 and the inner head 31.

[0020]

As described above, according to the present invention, the center of the diameter of the spherical surface forming the inner surface of the shell is eccentric to the upper side of the center of the diameter of the sphere of the outer surface, whereby the ceiling portion of the shell is formed. Since the wall thickness of the bearing insert is reduced, the wall thickness of the ceiling portion of the bearing insert can be relatively increased, and accordingly, the deformation amount when a load is applied also increases, so that the wear amount decreases.

[0021]

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an artificial joint according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a head portion of the artificial joint shown in FIG.

FIG. 3 is an enlarged view showing a region A of FIG.

[Explanation of symbols]

10 shell 11 outer surface 12 Inner surface 20 bearing inserts 21 slits 22 outer surface 24 Inner surface 24a near the opening 30 stems 31 Inner head Center of M, N sphere w Thickness of the ceiling y Equatorial thickness

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Claims (3)

(57) [Claims] 1. A bearing insert is fitted and fixed to a ceramic shell having a smooth, substantially hemispherical outer surface that abuts and slides on a bone, and is provided at the tip of the stem so as to rotate in the bearing insert. An artificial joint having an inner head inserted therein, wherein the center of the diameter of the spherical surface forming the inner surface of the shell is eccentric to the upper side of the center of the diameter of the sphere of the outer surface. . 2. The artificial joint according to claim 1, wherein the shell has a ceiling thickness 0.5 to 0.8 times that of the equator. 3. The shell has an equatorial wall thickness of 2 to 4 mm.
The artificial joint according to claim 1, wherein