JPH09103442A - Hip prosthesis - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent cracking of a ceramic head ball. SOLUTION: The head bone B made of ceramic is provided with a tapered hole b having a narrow inner diameter and a hollow space e deeper than the tapered hole b, and corners e1 and e1 of the hollow space e are curved surfaces. . In addition to this, the tip of the stem S is brought into contact with the inside of the tapered hole b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to the replacement of a human hip joint.
The present invention relates to an artificial hip joint to be repaired.

[0002]

2. Description of the Related Art Conventionally used artificial joints, especially artificial hip joints, are made of metal such as stainless steel, cobalt chrome alloy, and titanium alloy, and the head ball and stem are integrated or taper-fitted. The stem is inserted into the femur and the gap between the bone and the stem is fixed with cement. On the other hand, on the acetabular side, a socket made of polyethylene for receiving the head ball is also fixed to the pelvis using cement.

[0003] In recent years, many head caps have a structure that is fixed to the tip of a metal stem by taper fitting, and stainless steel, cobalt chromium alloy, and the like are often used as materials, and the depth and diameter of the tapered hole are changed. This allows the height of the stem to be changed, and this system is becoming mainstream.

On the other hand, as for the material of the head cap, a combination of polyethylene and alumina ceramic, which is a material having low friction and low wear, has been recognized for its excellent performance and has been used in large numbers. However, breakage of the head of the head due to incompatibility with the tapered portion of the metal used when a ceramic head is used tends to be a serious problem. It is said that a maximum load of about 5 times the weight acts on the human head, and about 400 kg for a person weighing 80 kg.
And a very large force acts.

[0005] A high safety factor is also required from the viewpoint of long-term durability. However, in actuality, when the tip of the stem is fitted into a tapered hole formed in a ceramic head ball, there is a serious problem such as inducing a crack in the head head ball even by an incompatibility caused by biting a fine foreign substance.

As a means for solving such a problem, it is necessary to completely match a tapered hole formed in the head ball with a taper formed at the tip of a stem to be fitted into the tapered hole.

However, it is impossible to accurately match the two by machining.

[0008] Then, irregularly arranged irregularities are formed on the circumference of the tapered portion of the metal stem on the circumference (for example, JP-A-51-67693), or the tapered portion of the stem is put in the air or a slit is formed. In addition, a configuration is considered in which the tapered portion of the stem can be deformed so as to conform to the wall shape of the tapered hole formed in the head ball.

However, even with the above-mentioned means, it is not possible to prevent the occurrence of cracking of the ceramic head ball, and therefore the reliability of the function and repair of the human body is incomplete.

[0010]

[Means for Solving the Problems] As a means for solving the above problems, a tapered head ball made of ceramic is provided with a narrow tapered hole and a space deeper than the tapered hole.
By making the corners of the cavity a curved surface, it is possible to prevent cracking of the epiphysis ball.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings. In FIG. 1 and FIG.
B is a head bone made of ceramic such as alumina or zirconia, and is rotatably received in an acetabular socket (not shown). Further, a narrow tapered hole b is bored in the phalange B, and a hollow space e having curved corners e1 and e1 is bored further in the tapered hole b. I am doing it.
S is a stem inserted and fixed to the femur, and this stem S is made of a metal such as titanium alloy, stainless steel,
A tapered portion T is formed at the tip, and the tapered portion T is fitted into the tapered hole b of the head ball B, whereby the head B is attached to the tip of the stem S.

Further, as shown in FIG. 1, when the tapered portion T of the stem S is fitted by forming the reduced diameter portion c at the back of the tapered hole b formed in the epiphyseal ball B, the reduced diameter is Only part c can be abutted and fitted.

Further, as shown in FIG. 2, the stem S is brought into contact with the recessed surface of the tapered hole b formed in the epiphyseal ball B.
However, only the leading end of the tapered portion T may be an enlarged diameter portion d.

In the artificial hip joint of this embodiment constructed as described above, the distal end of the stem S is a tapered hole b of the epiphyseal ball B.
Since it is configured so as to contact only the tapered wall surface that is at least ½ of the wall length of the head, the head head ball is prevented from cracking from the vicinity of the opening of the taper hole b of the head head ball and is deeper than the tapered hole b Since the space e is formed in the portion, the load stress applied to the contact surface between the head ball B and the stem S can be reduced by the space e.
Since it can be dispersed in the surrounding area, the compressive strength of the head ball B can be improved.

Incidentally, a corner portion e of the void e having a curved surface shape.
For 1 and e1, the radius of curvature r is 1.0 to 3.0 m
m is preferable. On the other hand, when the radius of curvature is less than 1.0 mm or more than 3.0 mm, the mechanical strength of this portion may be insufficient.

Further, regarding the above-mentioned vacant space e, FIG.
As shown in the explanatory diagrams of (A) to (B), the wall of the tapered hole b is used to make the rotary diamond tip t1
At the time of precision grinding with, the tip t1 is first acted from the opening of the tapered hole b toward the back [FIG. 3 (A)], but the tip t1 is allowed to escape into the void e [FIG. 3 (B)], Even if the side shape of the tip t1 has some irregularities, it is not transferred to the inner wall surface of the tapered hole b, and it is possible to perform precision grinding by folding back from the space e toward the opening of the tapered hole b. It has the effect of increasing efficiency.

[0017]

As described above, according to the present invention, when the ceramic head ball and the metal stem are connected, a cavity is formed further deep in the tapered hole.
Since the load stress applied to the contact surface between the headcap and the stem can be dispersed around the cavity, the compressive strength of the headcap is improved. When the wall surface of the tapered hole of the head ball is precision ground with a rotary diamond chip, the chip can be released into the void, so that the uneven shape of the chip is not transferred to the wall surface at the back of the tapered hole. In addition, precision grinding can be performed by folding back from the void toward the opening of the tapered hole, thereby increasing the processing efficiency.

In addition, when the tapered portion at the tip of the stem is fitted into the tapered hole formed in the epiphyseal ball, the tapered portion abuts on the tapered surface at a depth of about half or more of the depth of the tapered hole, and When worn, the strength of the epiphyseal ball can be significantly increased. Since it is not necessary to target the entire area of the tapered surface, the manufacturing control becomes very easy. It is not necessary to provide groove-shaped irregularities or slits on the tapered peripheral surface of the stem tip, or to make it pipe-shaped, which facilitates manufacturing. Since a small diameter headcap can be made, the thickness of the high-density polyethylene or the like forming the sliding surface of the acetabular socket can be made sufficiently thick, and the useful life (life) of the joint can be increased. Since the sections of both tapered surfaces that contact each other are short, it is only necessary to process the short surface with high precision only in that portion, so that the processing is easy and the production cost can be reduced.

Therefore, an artificial hip joint having high productivity, high strength, long life, and high reliability can be provided, which can greatly contribute to human welfare.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an artificial hip joint according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of an artificial hip joint according to another embodiment of the present invention.

3 (A) and 3 (B) are explanatory views for explaining the action of the void, and are cross-sectional views of the main parts of the epiphyseal ball of the artificial hip joint.

[Explanation of symbols]

 B: Head ball S: Stem

Claims (3)

[Claims] 1. An artificial hip joint characterized in that a ceramic head ball is provided with a taper hole having a narrow inner diameter and a cavity deeper than the taper hole, and a corner of the cavity is curved. . 2. The artificial hip joint according to claim 1, wherein a reduced diameter portion is formed at the inner side of the tapered hole so that the tip of the stem abuts at the inner side of the tapered hole. 3. The artificial hip joint according to claim 1, wherein an enlarged diameter portion is formed at the stem tip portion so that the stem tip portion abuts at the inner side of the tapered hole.