JP2002102262A - Artificial joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly prevent dislocation of an inner head by extremely reducing the deformation amount by a dislocation prevention ring effectively withstanding a very large stress even if the very large stress is applied to the inner head in a dislocating direction of the inner head from an outer head. SOLUTION: This artificial joint has the ceramic outer head 2 and inner head 3, and the dislocation prevention ring 6. The ring 6 has an engaging step part 7 with the outer head 2 on the outer circumferential face, and a spherical cutout part 8 corresponding to an outer shape of the inner head 3 in the inner circumferential face. The step part 7 is positioned on the side of an opening edge of the outer head 2 relatively to a minimum diameter ridgeline 9 of the cutout part 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial joint for artificially prosthetic joints of a living body and restoring its function and form. The present invention relates to a bipolar artificial head type artificial joint in which an outer head having a surface is fitted with an inner head made of ceramic provided at a distal end portion of a stem so as to rotate in the outer head.

[0002]

2. Description of the Related Art Injuries due to bone degeneration such as trauma due to traffic accidents, rheumatism, osteoarthritis, etc.
When the joint function is impaired and treatment and recovery are unlikely, replacement surgery is performed in which the joint portion is excised and prosthetic with an artificial joint.

As an artificial joint 60 used at this time, there is a bipolar artificial bone head type shown in FIG. this is,
The acetabular side of the joint maintains the cartilage state and can be used in a case where only the head side is replaced. The bearing insert 4 is provided inside the outer head 30 which abuts and slides on the bone.
0, and the inner head 50 that rotates in the bearing insert 40 is provided at the tip of the stem 4. The outer head 30 and the inner head 50 are decentered by an appropriate amount, so that the outer head 30 and the inner head 50 are eccentric. A mechanical torque is generated between the outer head 30 and the head 50 by a so-called self-centering effect.
And the inner head 50 maintain a stable positional relationship. Therefore, the outer head 3
By sliding between 0 and the inner head 50,
It is possible to complement joint function.

Conventionally, in such a bipolar artificial head type artificial joint 60, an outer head 30 made of metal or ceramic and an inner head 50 made of ceramic are conventionally used.
In general, a bearing insert 40 made of ultra-high molecular weight polyethylene is interposed between the outer head 30 and the inner head 50 so that sliding between the outer head 30 and the inner head 50 is performed by using polyethylene and ceramics. On the other hand, recently, as shown in FIGS. 4 and 5, the artificial joint 10 in which both the outer head 12 and the inner head 13 are made of ceramic and which are brought into contact with each other without using a bearing insert is used. It is starting to be used. Although the artificial joint 10 is shown without the stem in FIG. 4, the inner head 13 is fitted on a pin-shaped stem neck provided at one end of the stem in an actual use form.

An advantage of the artificial joint 10 having such a configuration is that, first, since the sliding between the outer head 12 and the inner head 13 is performed by ceramic-to-ceramic, the wear of polyethylene like the sliding of ceramic-to-polyethylene is attained. There is no need to worry about powder generation. In addition, the size of the inner head 13 can be increased by the absence of the bearing insert, and the strength of the ceramic inner head 13 can be increased by increasing the size of the inner head 13.

Incidentally, the artificial joint 10 is provided with a ring 16 for preventing the inner head 13 from dislocating.
It has. The detachment prevention ring 16 has an inner diameter smaller than the outer diameter of the inner head 13, and can be prevented from dislocating the inner head 13 by being fitted to the opening peripheral portion of the outer head 12.

[0007] As shown in FIG.
6 is provided with a slit 17, and a pair of small holes 18, 18 provided near both sides of the slit 17, respectively.
The ring diameter can be reduced by pinching the removal tool such as tweezers with the tip of the removal tool fitted. Thereby, the detachment prevention ring 16 is released from the state of being fitted to the outer head 12, and as a result, the inner head 13 is released from the state of being fitted to the outer head 12. Therefore, the inner head 13 can be attached to and detached from the outer head 12.

As shown in FIG. 5, in the artificial joint 10, the engagement step 16a provided on the outer peripheral surface of the ring 16 has a smaller diameter ridge line 16c of the spherical cutout 16b provided on the inner peripheral surface thereof. Also, the outer head 12 is located farther from the opening edge of the outer head 12.

[0009]

However, in the above-mentioned conventional technology, when a very large stress is applied in a direction in which the inner head comes off from the outer head, the above-mentioned coming-off prevention ring is deformed, and the inner head is dislocated. There was a fear that it would.

As shown in FIG. 6, the engagement step 16a provided on the outer peripheral surface of the ring 16 is located above the minimum diameter ridge line 16c of the spherical cutout 16b provided on the inner peripheral surface. Therefore, since the cross-sectional shape of the portion (indicated by the symbol P in the drawing) which exerts a resistance to the stress that the inner head 13 tends to come off is a downwardly inwardly inclined portion, the outer head 12 moves from the inner head 13 to the inner head 13. If a very large stress is applied in the direction in which the ring comes off, the ring 16 will not be able to withstand this stress, and the ring 16 will be deformed. As a result, there is a fear that a serious situation of dislocation of the inner head 13 may be caused.

In addition, since the length of the tapered portion 16d disposed above the engaging step 16a on the outer peripheral surface of the slip-off preventing ring 16 is short, the radial thickness of the outer head 12 at this portion must be increased. Could not. Therefore, the strength of this portion was not always large.

In view of the above-mentioned problems of the prior art, the present invention provides a structure in which the detachment prevention ring effectively resists stress even when a very large stress is applied in the direction in which the inner head comes off from the outer head. It is another object of the present invention to reliably prevent the dislocation of the inner head by minimizing the amount of deformation, and to increase the strength near the opening of the outer head.

[0013]

In order to achieve the above object, an artificial joint according to claim 1 is an artificial joint having a ceramic outer head, an inner head, and a slip-off prevention ring. The outer peripheral surface is provided with an engaging step with the outer head, and the inner peripheral surface is provided with a spherical notch corresponding to the outer shape of the inner head, and the engaging step is below the minimum diameter ridge line of the spherical notch. It is characterized by being located in.

According to this configuration, the engaging step provided on the outer peripheral surface of the slip-off preventing ring is located closer to the opening edge of the outer head than the minimum diameter ridge of the spherical cutout provided on the inner peripheral surface. In the slip-off prevention ring, the cross-sectional shape of the portion that exerts a resistance to the stress that the inner head tends to slip out is a shape portion that is inclined upward and inward. As a result, even if a very large stress is applied in the direction in which the inner head comes off from the outer head, the come-off prevention ring effectively resists the stress and minimizes the amount of deformation to ensure the dislocation of the inner head. Can be prevented.

In the artificial joint according to a second aspect of the present invention, in the artificial joint according to the first aspect, the engaging step provided on the slip-off prevention ring is more than two-thirds the axial length of the outer head from above the slip-off prevention ring. It is characterized by being arranged on the side of the opening.

According to this configuration, the length of the tapered portion normally provided on the outer circumference of the slip-off preventing ring is increased, and as a result, the thickness of the outer head near the opening of the outer head can be increased. Therefore,
The mechanical strength of this part can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a fragmentary cutaway view showing an artificial joint 1 according to the present invention. In the drawing, reference numeral 2 denotes an outer head having a smooth, substantially hemispherical outer surface 2a which abuts and slides on a bone, and 3 denotes a substantially hemispherical fitting hole 2 provided in the outer head 2.
Reference numeral 4 denotes a stem, which is fitted and rotated in the inner portion b. The inner head 3 is fitted to the tip of a pin-shaped stem neck 4a at the tip. Reference numeral 5 denotes a ring fitting recess provided on an opening edge facing the fitting hole 2b of the outer head 2, and 6 denotes a ring fitting recess.
And a stopper ring for preventing the inner head 3 from coming off by engaging with the inner head 3.

The ring fitting recess 5 has a stepped recess 5a on the side surface.
The step-recessed ring 6 is fixed in the ring fitting recess 5 of the outer head 2 by fitting the stepped recess 5a with a tapered step-shaped protrusion 6c provided on the outer surface of the ring 6. Is done.

The artificial joint 1 is of a bipolar artificial head type, in which the stem 4 is fixedly mounted in a long tubular bone such as a femur. The artificial joint 1 can be used in a case where the acetabular side of the joint is maintained in a cartilage state and only the side of the head is replaced, and the center 21 of the outer head 2 and the center 31 of the inner head 3 are decentered by an appropriate distance. By setting the distance d, a mechanical torque is generated between the outer head 2 and the inner head 3, so that the outer head 2 and the inner head 3 maintain a stable positional relationship by a so-called self-centering effect. I have. Therefore, the joint function is complemented mainly by sliding between the outer head 2 and the inner head 3.

The material of each member constituting the artificial joint 1 is such that both the outer head 2 and the inner head 3 are made of a safe ceramic material such as alumina, zirconia or the like which is not harmful to the living body, and the stem 4 is made of pure titanium or titanium. alloy,
It is made of a safe metallic material that is not harmful to living organisms such as a cobalt-molybdenum alloy. Further, the ring 6 is made of a polymer material having no harm to the living body such as ultra-high molecular weight polyethylene.

Preferably, high-purity alumina is used as the ceramic material. By forming the sliding surface with high-purity alumina, a sliding member having high strength and high abrasion resistance (without generation of abrasion powder) can be obtained.

The outer surface 2a of the outer head 2 and the inner wall surface 2c of the fitting hole 2b, which constitute the sliding surface, and
The outer surface 3a of the inner head 3 is mirror-finished by polishing.

Next, in FIG. 2, which is an enlarged view of the area A in FIG. 1, reference numeral CL denotes a clearance between the outer head 2 and the inner head 3, and in the artificial joint 1, the clearance CL is very narrow, 35 μm or less. It was set so that a membrane of biological fluid was interposed between them in the in-vivo environment.
This improved the sliding characteristics.

As shown in FIG. 2, the detachment prevention ring 6
The outer peripheral surface is provided with a stepped portion 7 for engaging with the outer head 2, and the upper side of the inner peripheral surface is provided with a spherical cutout 8 corresponding to the outer shape of the inner head 3. Are located closer to the opening edge of the outer head 2 (the lower side in the figure) than the minimum diameter ridge line 9.

As described above, the engaging step 7 provided on the outer peripheral surface of the pull-out preventing ring 6 is replaced with the spherical cutout 8 provided on the inner peripheral surface thereof.
Is located below the minimum diameter ridge line 9, the cross-sectional shape of the portion (indicated by the symbol S in the drawing) of the portion of the slip-prevention ring 6 that exerts a resistance to the stress that the inner head 3 tends to slip out is upward As a result, even if a very large stress is applied in the direction in which the inner head 3 comes off from the outer head 2, the come-off prevention ring 6 effectively resists the stress, and the deformation amount is reduced. Is extremely reduced, the dislocation of the inner head 3 can be reliably prevented.

In the outer peripheral surface of the ring 6, the upper side of the engaging step 7 is a tapered portion 6 a. This is a configuration for enabling the detachment prevention ring 6 to be easily worn by the operator's hand. When the engagement step portion 7 has an axial length of 2 mm from the upper end in FIG.
/ 3, the side closer to the opening edge of the outer head 2 (in the figure,
(Lower side).

Accordingly, the length of the tapered portion 6a of the engagement step 7 on the outer periphery of the slip-off preventing ring 6 is increased, and as a result, the thickness of the outer head 2 near the opening of the outer head 2 is increased. can do. Thereby, the mechanical strength of this portion can be improved.

The embodiment of the present invention has been described above.
The present invention is not limited to the above-described embodiment, and can be in any form without departing from the technical idea of the invention.

[0030]

As described above, according to the present invention, the present invention provides a ceramic outer head and an inner head,
And an artificial joint having a slip-off prevention ring, wherein the slip-out prevention ring has an engagement step with the outer head on the outer peripheral surface, and has a spherical cutout corresponding to the outer shape of the inner head on the inner peripheral surface, Since the engaging step portion is located closer to the opening edge of the outer head than the minimum diameter ridge line of the spherical cutout portion, in the slip-off prevention ring, a portion of the inner head that exerts resistance to the stress that the inner head tends to slip out. The cross-sectional shape is a shape portion inclined upward and inward. This allows
Even if a very large stress is applied in the direction in which the inner head comes off from the outer head, the disengagement prevention ring effectively resists the stress and prevents the dislocation of the inner head by making the amount of deformation extremely favorable. can do.

The present invention also relates to the present invention, when the engaging step provided on the slip-off preventing ring is disposed below the axial length of the slip-off preventing ring, which is less than 2/3. The length of the taper portion normally provided in the joint portion becomes longer, and as a result, the thickness of the outer head in the vicinity of the opening of the outer head can be increased. Therefore, the mechanical strength of this portion can be improved.

[Brief description of the drawings]

FIG. 1 is a fragmentary cutaway view of an artificial joint according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a region A in FIG.

FIG. 3 is an exploded perspective view showing a conventional bipolar artificial joint having a bearing insert.

FIG. 4 is a schematic view showing a conventional bipolar head type artificial joint without a bearing insert, wherein (a) is an exploded perspective view excluding a stem, and (b) is a perspective assembled view.

FIG. 5 is a fragmentary cutaway view showing the configuration of a conventional artificial joint.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Artificial joint 2 Outer head 2a Outer surface 3a Outer surface 2b Fitting hole 3 Inner head 4 Stem 4a Stem neck 5 Ring fitting recess 6 Detachment prevention ring 7 Engagement step 8 Spherical notch 9 Minimum diameter ridge

Claims (2)

[Claims] 1. A ceramic outer head having a smooth substantially hemispherical outer surface which slides against a bone and a substantially hemispherical fitting hole so as to rotate in said fitting hole. An artificial joint in which a ceramic inner head provided at the tip of the stem is fitted, and a stopper ring is attached to a ring fitting recess provided at an opening edge facing the fitting hole of the outer head, The slip-off prevention ring has an outer peripheral surface with an engagement step with the outer head and an inner peripheral surface with a spherical notch corresponding to the outer shape of the inner head, and the engagement step is formed of the spherical notch. An artificial joint, wherein the artificial joint is located closer to an opening edge of the outer head than a minimum diameter ridge line. 2. A step of engaging the outer head provided on the slip-off prevention ring is 2/3 of the axial length of the slip-off prevention ring.
The artificial joint according to claim 1, wherein the artificial joint is disposed closer to an opening edge of the outer head.