JP3786532B2 - Artificial joint - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an artificial joint that artificially prosthetics a joint portion of a living body and restores its function and form, and in particular, an outer having a smooth, substantially hemispherical outer surface that contacts and slides on a bone. The present invention relates to a bipolar artificial bone head type artificial joint formed by fitting a ceramic inner head provided at the distal end of a stem so as to rotate within the outer head.
[0002]
[Prior art]
If the joint function is impaired due to trauma due to traffic accidents, rheumatism, osteoarthritis, etc., and the joint function is impaired and the chances of treatment and recovery are low, the joint is removed and the artificial joint is removed. Replacement surgery to prosthesis is performed.
[0003]
As an artificial joint used at this time, there is a bipolar artificial head type. This can be used in cases where the acetabular side of the joint is maintained in the state of cartilage and only the side of the bone head is replaced. The bearing insert is integrated inside the outer head that slides against the bone. And comprising a stem having an inner head that rotates within the bearing insert, and by decentering the outer head and the inner head by an appropriate amount, the outer head within the acetabulum can be utilized by utilizing the principle of Jagiro Bay. While maintaining the position substantially constant, the joint function can be supplemented mainly by sliding between the anter head and the inner head.
[0004]
Such a bipolar artificial head artificial joint is generally used by first inserting and fixing a stem to the femur during an operation, and then attaching an outer head to the inner head at the end of the stem. Must be structured so that they cannot be easily detached (dislocated) after being combined.
[0005]
The invention of Japanese Patent Laid-Open No. 62-79055 relates to such a bipolar artificial bone head type artificial joint, and forms a plurality of cuts in the depth direction from the opening of the bearing insert, and further thins the vicinity of the opening. This makes it possible to enlarge the opening, making it easy to attach and detach the bearing insert and inner head, and after mounting the inner head, after mounting the bearing insert, between the thin portion near the opening of the bearing insert and the inner wall of the outer head. The inner head supported the inner head only by the inner wall surface of the bearing insert by inserting a drop prevention ring into the gap.
[0006]
[Problems to be solved by the invention]
According to the present invention, a reliable coupling mechanism can be provided by the above-described configuration, and the inner head abuts and slides against the smooth surface of the inner wall of the bearing insert, so there is no uneven wear or partial wear, and durability. As a result, the effect was very large.
[0007]
However, since the bearing insert is interposed between the outer head and the inner head, the structure is slightly complicated and the inner thickness is secured to ensure the thickness of the ultra-high molecular polyethylene constituting the bearing insert. The head diameter must be reduced, the inner head strength is limited, and the bearing insert is overhanging beyond the equator line of the inner head, so the range of motion is not so wide ( The small diameter of the inner head is also a cause of narrowing the range of motion), and the friction between the polyethylene of the bearing insert and the ceramic of the inner head causes a lot of wear powder. It was.
[0008]
Therefore, an object of the present invention is to solve such problems.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a ceramic outer head having a smooth, substantially hemispherical outer surface that abuts and slides on a bone, and a stem tip that rotates within the outer head. In the artificial joint formed by fitting the provided ceramic inner head with a clearance of 35 μm or less between the two, the fitting hole of the outer head sliding with the inner head has a hemispherical portion, and the fitting hole A tapered wall that opens outward at the opening edge facing the surface, and a cylindrical portion is formed in the fitting hole between the hemispherical portion and the tapered wall, and the height of the cylindrical portion is 1 to 6 mm. Features.
[0010]
[Action]
The artificial joint of the present invention is of a bipolar artificial head type, and can be used in cases where the acetabular side of the joint is maintained in the state of cartilage and only the side of the head is replaced. It consists of a stem with an inner head that rotates in the outer head.By decentering the outer head and inner head by an appropriate distance, the position of the outer head in the acetabulum can be adjusted using the principle of Yajiro Bay. The joint function is complemented mainly by sliding between the anter head and the inner head while maintaining almost constant.
[0011]
According to the artificial joint of the present invention, the clearance between the outer head and the inner head is made extremely thin at 35 μm or less, so that in the in-vivo environment, the biological fluid is interposed between the two in a substantially film shape. Thereby, a mutual suction force is generated between the outer head and the inner head. Further, the inner wall surface of the outer head beyond the equator plane with respect to the inner head is a substantially vertical surface that does not squeeze inward, but mutual suction force is also generated in this portion. The mutual suction force of this part assists the mutual suction force in the hemispherical dome-like part provided in the inner part of the fitting hole of the outer head, and the mutual suction force in the inner part is eliminated by a large pulling force etc. Even in such a case, the mutual suction force at the back portion is prevented from being eliminated by the mutual suction force of the substantially vertical surface portion resisting the pulling-out force. Thus, the inner head does not dislocate from the outer head by the action of the suction force.
[0012]
According to the structure of the artificial joint of the present invention, the outer head is overhanged (wrapped) so as to squeeze the outer head inward at the opening side portion beyond the equator plane of the inner head, as in the conventional structure. There is no need to increase the height. And since the height of an outer head is low, the movable range of a joint can be enlarged very much.
[0013]
Further, conventionally, a bearing made of a deformable elastic material as a sliding member on the outer head side with respect to the inner head in order to overhang the outer head so as to squeeze the outer head inward in the opening side portion beyond the equator plane of the inner head. Although the insert is provided, in the present invention, the ceramic inner head is configured to slide directly with the ceramic outer head without interposing the bearing insert. As an advantage of such a configuration, first, in the ceramic-to-ceramic sliding, there is no fear of generation of polyethylene abrasion powder, unlike the ceramic-to-polyethylene sliding. Moreover, the size of the inner head can be increased by the amount that the bearing insert is not provided. By increasing the size of the inner head, it is possible to increase the strength of the ceramic inner head and to improve the anti-dislocation force.
[0014]
Finally, the artificial joint has a tapered wall at the fitting hole wall surface of the outer head that slides with the inner head, and when the stem neck and the outer head come into contact, it makes line contact instead of point contact The structure is such that excessive stress concentration is unlikely to occur.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
FIG. 1 is a fragmentary cutaway view showing an artificial joint 1 of the present invention, wherein 2 is an outer head having an outer surface 2a having a smooth, substantially hemispherical shape that contacts and slides on a bone, and 3 indicates the outer head 2 4 is a stem formed by fitting the inner head 3 to the tip of a pin-shaped neck portion 4a.
[0017]
The artificial joint 1 is of a bipolar artificial bone head type, and the stem 4 is mounted in the long bone marrow cavity. The acetabular side of the joint can be maintained in the state of cartilage, and can be used in cases where only the head side is replaced. The outer head 2 and the inner head 3 are decentered by an appropriate distance (distance d). The joint function is supplemented mainly by sliding between the anter head 2 and the inner head 3 while keeping the position of the outer head 2 within the acetabulum substantially constant.
[0018]
The material of each member constituting the artificial joint 1 is such that the outer head 2 and the inner head 3 are made of a safe ceramic material having no biological harm such as alumina, and the stem 4 is pure titanium, titanium alloy, cobalt-molybdenum. It consists of a safe metal material that is not harmful to living organisms, such as an alloy. In addition, it is preferable to use high-purity alumina as the ceramic material, and a sliding member having high strength and high wear resistance (hard to generate wear powder) by constituting the sliding surface with high-purity alumina. It can be.
[0019]
Further, the outer surface 2a of the outer head 2 constituting the sliding surface, the inner wall surface 2c of the fitting hole 2b, and the outer surface 3a of the inner head 3 are mirror-finished by polishing.
[0020]
Next, in FIG. 2 as an enlarged view of the region A in FIG. 1, CL is a clearance between the outer head 2 and the inner head 3, and the artificial joint 1 is characterized in that the clearance CL is set to 35 μm or less. . Further, the inner wall surface 2c of the outer head 2 beyond the equator plane P with respect to the inner head 3 is provided with a substantially vertical surface 2d having a height h that is not restricted inward.
[0021]
In this way, by setting the clearance CL between the outer head 2 and the inner head 3 to be as thin as 35 μm or less, in the in vivo environment, the biological fluid is interposed between the two in a substantially film shape. Thereby, a mutual suction force is generated between the outer head 2 and the inner head 3.
[0022]
Although 35 μm does not necessarily mean a critical value, it was confirmed that a mutual attractive force was surely generated if the value was less than this value.
[0023]
Further, since the cylindrical portion 20 provided with the substantially vertical wall 2d of the outer head 2 beyond the equatorial plane P following the inner hemispherical portion 10 has a small gap, mutual suction force is generated. The mutual suction force of the substantially vertical wall 2d part assists the mutual suction force in the hemispherical dome-like part provided in the back part of the fitting hole 2b of the outer head 2, and at the back part by a large pulling force or the like. Even when the mutual suction force is about to be eliminated, the mutual suction force resists the pulling force, thereby preventing the mutual suction force at the inner part from being eliminated. From dislocation.
[0024]
According to the configuration of the present invention as described above, the inner head 3 restraining ring member or the like does not have to be inserted, so that the height t of the outer head 2 can be kept low. Therefore, the range of motion of the joint is very large. Further, the size of the inner head 3 can be increased by the amount that the bearing insert is not provided. Increasing the size of the inner head 3 has the advantage that the strength of the ceramic inner head 3 can be increased and the anti-dislocation force is improved.
[0025]
The height h of the substantially vertical surface 2d is preferably in the range of 1 to 6 mm. When the height h is less than 1, the inner head 3 may be easily dislocated. On the other hand, when the height h is greater than 6, the height t of the outer head 4 may be increased, and the movable range may be decreased.
[0026]
As shown in FIG. 2, the inner wall surface 2c of the outer head 4 has a tapered wall 2e that opens outwardly from the substantially vertical wall 2d. The tapered wall 2e constitutes the surface of the annular elastic member 6 made of polyethylene or the like fitted into the annular groove 5.
[0027]
With this configuration, direct contact between the metal (stem 4) and the ceramic (outer head 2) is avoided, and when the neck 4a of the stem 4 and the annular elastic member 6 are in contact, the line is not in point contact but in line. The structure is such that it does not contact and excessive stress concentration is unlikely to occur.
[0028]
The annular elastic member 6 is preferably made of γ-irradiated polyethylene. This is because γ-irradiated polyethylene is excellent in wear resistance, so that the amount of abrasion powder generated by sliding contact with the neck portion of the stem 4 is very small.
[0029]
Moreover, about the ceiling thickness w of the said outer head 4 shown in FIG. 1, it is preferable that it is the range of 3.5 mm-15 mm. When the ceiling thickness w is less than 3.5 mm, the strength of the ceiling portion is insufficient. On the other hand, when it exceeds 15 mm, the amount of eccentricity becomes very small, and the desired operation as a bipolar artificial joint may not be achieved. is there.
[0030]
【The invention's effect】
As described above, according to the present invention, since the clearance between the outer head and the inner head is made extremely thin as 35 μm or less, mutual suction force is generated between the outer head and the inner head, Since the inner wall surface of the outer head beyond the equator plane is provided with a substantially vertical surface that does not squeeze inward, mutual suction force is generated even in this part, and the inner head is mounted inside the outer head by the action of these suction forces Therefore, the height of the outer head can be reduced. As a result, the range of motion of the joint can be greatly increased, and the ceramic inner head slides directly against the ceramic outer head without any bearing inserts. There is no worry. In addition, the size of the inner head can be increased by the amount not provided with the bearing insert, the strength of the ceramic inner head can be increased, and the anti-dislocation force is 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.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Artificial joint 2 Outer head 2a, 3a Outer surface 2b Fitting hole 2c Inner wall surface 2d Substantially vertical surface 2e Tapered wall 3 Inner head 4 Stem 4a Neck part 5 Groove 6 Annular elastic member 10 Hemispherical part 20 Columnar part d Distance h Height P Equatorial plane CL Clearance

Claims (2)

A ceramic outer head having a smooth, substantially hemispherical outer surface that abuts and slides against the bone, and a ceramic inner head provided at the distal end of the stem so as to rotate within the outer head. An artificial joint that is fitted with a clearance of 35 μm or less, and has a hemispherical portion in the fitting hole of the outer head that slides with the inner head and opens outwardly at the opening edge facing the fitting hole An artificial joint comprising a wall, a cylindrical portion formed in a fitting hole between the hemispherical portion and the tapered wall , wherein the cylindrical portion has a height of 1 to 6 mm . The artificial joint according to claim 1, wherein the tapered surface is made of γ-irradiated polyethylene.

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