JPH10309297A - Artificial joint plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an artificial joint plug which can prevent a bone cement or biobone pieces from being filled into the depth of a intramedullar, and which can be quickly dissolved when the bone cement is cured. SOLUTION: A plug main body 1 is formed from a biodegradable polymer, and multiple petal-like projections 2 are projected upward-outward from the top circumference of the plug main body 1 to form an artificial joint plug. When this plug is inserted into the intramedullar of a biobone, each of the petal-like projections 2 is pressed internally against the inside wall of the intramedullar, is elastic-deformed, and is fixed in the intramedullar by this repulsion force. When a bone cement or biobone pieces is filled in the intramedullar, it is blocked by the plug main body 1 and the petal-like projections 2 and prevented from being filled into the depth of the intramedullar. Hydro-degradation proceeds, the plug is completely degraded and become extinct in a few years.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial joint plug for inserting and fixing a stem of an artificial joint into a medullary cavity of a living bone.

[0002]

2. Description of the Related Art A hip joint, which is a typical example of an artificial joint, is:
As shown in FIG. 4, a stem 101 made of a titanium alloy or the like bent in a substantially rectangular shape, a substantially spherical bone head 102 made of polyethylene or the like fitted and fixed to the upper end of the stem, and the bone head can be rotated. The inner cup 103 is made up of a substantially hemispherical inner cup 103 made of polyethylene or the like, and an outer cup 104 made of a titanium alloy or the like that covers the inner cup.

In such a hip prosthesis, usually, the outer cup 104 is fixed to the pelvis 106 with bone cement 105, while the stem 101 is inserted into the medullary cavity 108 of the femur 107 from the lower end side to fill the medullary cavity 108. The stem 101 is used with the bone cement 105 fixed.

[0004] However, as described above, bone cement 1
When 05 is filled in the medullary cavity 108 of the femur 107, the bone cement 105 will enter the medullary cavity 108 deeper than the stem 101 and will be filled. For this reason, conventionally, before inserting and filling the stem 101 and the bone cement 105, a small piece of bone (not shown) is filled into the interior of the medullary cavity 108, and the bone cement 105 causes the bone cement 105 to be filled with the small amount of bone.
However, even with this method, bone fragments may not reach a predetermined position of the medullary cavity 108 but reach a deep portion.

Therefore, as shown in FIG. 3, a plug 109 made of polyethylene is inserted into the medullary cavity 108, and this plug 1
At 09, a method of blocking the bone cement 105 so as not to be filled into the medullary cavity 108 was developed.

However, the method using the plug 109 has the following problems.

[0007]

That is, the above plug 1
09 becomes useless after the bone cement 105 is hardened. However, since the plug 109 is made of polyethylene, it is not decomposed and absorbed in the living body and remains permanently in the medullary cavity 108.

[0008] Polyethylene is a biologically inert polymer that does not adversely affect the human body. However, since the plug 109 made of polyethylene is still a foreign substance to the human body, it quickly disappears after performing its role. Ideally.

The present invention has been made in view of the above problems, and has as its object to block and prevent bone cement and living bone fragments from being filled into the medullary cavity and to cure the bone cement. An object of the present invention is to provide an ideal artificial joint plug which is relatively quickly decomposed and absorbed and disappears after fulfilling its role.

[0010]

According to a first aspect of the present invention, there is provided an artificial joint plug according to the first aspect of the present invention, wherein the plug body is formed of a biodegradable and absorbable polymer, and the plug body is formed from a peripheral edge of an upper surface of the plug body. The present invention is characterized in that a plurality of petal-like projections are projected outward and obliquely upward.

The plug for an artificial joint according to claim 2 is
4. The artificial biopolymer according to claim 3, wherein the biodegradable and absorbable polymer is any one of polylactic acid, lactic acid-glycolic acid copolymer, and lactic acid-caprolactone copolymer, or a mixed polymer of two or more thereof. The joint plug is characterized by containing bioceramic powder.

In the plug for an artificial joint according to the first aspect, the plug body is inserted into the medullary cavity of a living bone. When inserted like this,
Each petal-like projection is pressed inward by the inner wall of the medullary cavity and is elastically deformed, and the resilient force fixes the upper end of each petal-like projection in close contact with the inner wall of the medullary cavity.

When bone marrow is filled in the medullary cavity after filling with bone fragments as needed, the bone cement is blocked by the plug body and the petal-like projection of the plug for artificial joint. Bone cement can be prevented from being filled into the medullary cavity deeper than the plug.

When the stem is inserted into the filled bone cement, the stem is fixed by hardening of the bone cement, and the plug for the artificial joint becomes useless.
Since the artificial joint plug is made of a biodegradable and absorbable polymer, the plug is brought into contact with body fluid in the medullary cavity and hydrolysis proceeds from the surface of the plug. After several years, the plug is completely decomposed and absorbed and disappears. Therefore, the problem that the plug is permanently left in the medullary cavity as a foreign substance, such as a plug made of polyethylene, is eliminated.

In this case, as in the plug for an artificial joint according to the second aspect, any one of polylactic acid, lactic acid-glycolic acid copolymer, and lactic acid-caprolactone copolymer is used as the biodegradable and absorbable polymer. In the case of using a mixed polymer of more than one kind, the safety (non-toxicity) of the polymer in the living body has already been demonstrated, so there is no risk of adversely affecting the human body, the molecular weight is reduced by hydrolysis, and it is absorbed immediately. Disappeared.

Further, since a polymer such as polylactic acid has an appropriate elasticity, a plug for an artificial joint made of such a polymer is relatively easy to elastically deform each petal-like projection at the time of insertion, so that the plug against the inner wall of the medullary cavity can be easily removed. The contact pressure of each petal is also moderate. Therefore, such a plug is easy to insert, and there is no concern that the inner wall of the medullary cavity is damaged by the petals.

Further, when the bioceramic powder is contained as in the plug for an artificial joint according to the third aspect, the apparent hydrolysis rate is increased, and the plug is decomposed into small pieces at an early stage. Since ceramics induce and form bone cells, bonding with living bone is also possible at an early stage. Moreover,
Since the bioceramics powder is imaged by radiography, the position of the plug in the intrathecal cavity can be confirmed.

[0018]

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

FIG. 1 is a perspective view of an artificial joint plug according to an embodiment of the present invention, FIG. 2 is a plan view of the artificial joint plug, and FIG. 3 is an enlarged sectional view taken along line AA of FIG.

This artificial joint plug is made of a biodegradable and absorbable polymer, and includes a plug body 1 and a plurality of petals 2 as shown in the figure.

The plug body 1 is a short columnar body having a bottom surface formed into a hemispherical surface 1a.
b is formed. The concave hole 1b is used to insert an insertion jig at the time of insertion into the medullary cavity to facilitate insertion. The reason why the bottom surface of the plug body 1 is the hemispherical surface 1a is that the plug body 1 can be smoothly inserted into the medullary cavity of the living bone.

The petals 2 project outward and obliquely upward from the peripheral edge of the upper surface of the plug body 1, and the petals 2 are arranged radially when viewed from above. In this embodiment, six petals 2 are projected, but the number of petals 2 may be more or less.

The thickness D of the petals 2 is 0.5 to 3.0 m.
m, preferably 0.7 to 1.5 mm, and the projection L of the petal-like projection 2 is about 1 to 5 mm, preferably 2 to 5 mm.
3 mm, and the inclination angle θ of the petals 2 is 30 to 80 °.
Degree, preferably 50-70 °. Further, it is desirable that the outer surface of the connection portion 4 between the base portion of the petal-like projection 2 and the plug body 1 be smoothly continuous with a radius of curvature of 5 to 20 mm.

With this arrangement, when the artificial joint plug is inserted into the medullary cavity of the living bone, each petal-shaped projection 2 can be easily elastically deformed inward without being broken, thereby facilitating the insertion operation and its elasticity. The contact pressure with the inner wall of the medullary cavity becomes moderate, and there is no risk of damaging the inner wall of the medullary cavity.

It is desirable to form an outwardly protruding edge 2a as shown in the figure at the upper end of the petal-like projection 2. When such a protruding edge 2a is formed, it is well engaged with the inner wall of the medullary cavity. Therefore, the fixability of the plug in the medullary cavity can be improved.

The cut portion 3 between the petals 2 is
It is preferable that the trapezoidal shape or the U-shaped shape as shown in the drawing is used rather than the V-shaped shape. When the cut portion 3 such as the trapezoidal shape is formed, the root portion of each petal-shaped projection 2 can have a certain width. Since each petal-shaped projection 2 is independently deformed, elastic deformation inward is further facilitated, and the insertion work is further facilitated. It is desirable that the width M of the root portion of the petal-like projection 2 is at least 1.0 mm or more, preferably 1.5 to 8 mm, more preferably 3 to 6 mm.

The width N of the split part 3 is 0.5 to 6 m.
m, preferably about 1.0 to 5.0 mm. If it is wider than 6 mm, the bone cement may leak from the split portion 3 and the ratio of the petals 2 to the entire circumference decreases, and the fixing force to the inner wall of the medullary cavity becomes small, so that the bone cement is filled or the stem is filled. When the plug is inserted into the medullary cavity, when the plug is inserted into the medullary cavity, it is difficult for the petal-shaped projections 2 to be sufficiently elastically deformed inward.
Are mutually affected and difficult to deform, making the insertion operation difficult.

When there is a possibility that the bone cement leaks out of the cut portion 3, the bone cement is filled with the small pieces of the living bone on the plug which is inserted and fixed, so that the bone cement is leaked. Can be prevented.

As described above, even when the biodegradable and absorbable polymer is used, the thickness, the protrusion size, the inclination angle θ,
Having the necessary elastic deformation by appropriately selecting the curved shape of the root part, its shape, the shape and dimensions of the split part,
A plug that can be inserted without breakage and has an appropriate contact pressure (fixing force) can be obtained.

The biodegradable and absorbable polymer of the material includes polylactic acid having a viscosity average molecular weight of 50,000 to 400,000,
Thermoplastic polymers such as lactic acid-glycolic acid copolymer and lactic acid-caprolactone copolymer are suitable, and these can be used alone or in combination of two or more.

Since the above polymer has already been demonstrated to be safe (non-toxic) in vivo, a plug for an artificial joint made of the above polymer has no fear of adversely affecting the human body.
Moreover, it is hydrolyzed in the intrathecal cavity to reduce the molecular weight, and is rapidly absorbed and disappears. In addition, since the plug made of a polymer having the above-mentioned molecular weight has appropriate elasticity, the petal-shaped projection 2
Is relatively easy to be elastically deformed inward and easily inserted into the medullary cavity, and the contact pressure between the petal-like projections 2 and the inner wall of the medullary cavity is moderate, so that the plug can be fixed well in the medullary cavity. In addition, there is no risk of damaging the inner wall of the medullary cavity at the time of insertion.

The plug for an artificial joint made of such a biodegradable and absorbable polymer may contain a bioceramic powder uniformly. When bioceramic powder is included, the apparent rate of hydrolysis is increased, and the plug is broken down into small pieces earlier.In addition, the bioceramic powder induces and forms osteocytes, so it can be bonded to living bone. Becomes

The bioceramic powder has a particle size of about 0.1 to 100 μm, preferably several μm to several tens μm.
Surface bioactive sintered hydroxyapatite, bioglass-based or crystallized glass-based biological glass, bioabsorbable wet hydroxyapatite, dicalcium phosphate, tricalcium phosphate, tetracalcium phosphate, octacalcium phosphate, Any one of calcite and diopsite powder or a mixture of two or more powders is preferably used.

The content of the bioceramic powder is 10
It is desirably about 60% by weight. Content rate is 60
If the weight percent is exceeded, the plug becomes harder and more brittle, so that the petal-shaped projection 2 is less likely to be elastically deformed when inserted into the medullary cavity, and the petal-shaped projection 2 may be broken if inserted forcibly. Not preferred.

The plug for an artificial joint having the above configuration is, for example,
It is manufactured by a method in which a biodegradable and absorbable polymer is melt-extruded into a rod shape at a temperature equal to or higher than its melting temperature and lower than the decomposition temperature, and the rod-shaped molded product is cut into the plug shape. In the case of producing an artificial joint plug containing bioceramics powder, the bioceramics powder is uniformly blended with the biodegradable and absorbent polymer of the material so as to have the content, and similarly, After melt extrusion molding, cutting may be performed.

The plug for an artificial joint obtained by cutting the melt molded product of the biodegradable and absorbable polymer as described above,
The surface has a rough surface having an appropriate surface roughness by cutting and has a large contact area with a body fluid in the medullary cavity, so that it has good hydrolyzability.

The method of using the plug for an artificial joint is the same as that of the conventional plug, and the plug is connected to the medullary cavity 10 of the living bone 107.
Insert into 8. When inserted in this manner, each petal
Is pressed inward by the inner wall of the medullary cavity 108 to be elastically deformed, and the resilient force fixes the plug with the protruding edge 2a of each petal-like projection 2 closely contacting the inner wall of the medullary cavity. Next, the bone cavity 105 is filled into the medullary cavity 108 after the living bone is filled with small pieces if necessary. Filling like this,
The bone cement 105 is blocked by the plug body 1 and the petal-shaped projection 2 of the plug for an artificial joint, so that the medullary cavity deeper than the plug is not filled. Then, the stem 101 is inserted before the bone cement 105 hardens. After the bone cement 105 is hardened and the stem 101 is fixed and the plug for the artificial joint becomes unnecessary, the plug comes into contact with the body fluid in the medullary cavity 108 and hydrolysis proceeds from the surface. Decomposed and absorbed. Therefore,
The problem of permanently remaining in the medullary canal like a conventional plug is eliminated.

The plug for an artificial joint described above has a state in which the molecular chain of the biodegradable and absorbable polymer is non-oriented.
Orientation of the molecular chains can lead to the strength of the plug, especially the petals 2
And the contact pressure on the inner wall of the medullary cavity 108 can be increased. As the orientation means, the following orientation means and compression orientation means are employed.

In the case of stretching orientation, the above-mentioned melt molded product of the biodegradable and absorbable polymer is heated in the longitudinal direction while heating.
What is necessary is just to extend about 10 to 10 times, and to process this, and to manufacture an artificial joint plug. In such a plug, the molecular chain of the polymer is uniaxially oriented along the central axis of the plug, so that the strength is improved.

In the case of the compression orientation, the melt molded product of the biodegradable and absorbable polymer described above is placed in a cavity of a mold in a cold state (a crystallizable temperature between the glass transition temperature and the melting temperature of the polymer). And press-fitting while plastically deforming, and cutting the obtained compression-oriented molded body to produce an artificial joint plug. In that case, the deformation ratio R = S / s
(S: cross-sectional area of the melt-molded product, s: cross-sectional area of the compression-oriented molded product) is desirably set in the range of 1.5 to 6. In such a plug, since the molecular chains of the polymer are obliquely oriented from the periphery toward the central axis of the plug, there is little anisotropy in the molecular chain orientation between the central axis direction and the direction perpendicular thereto. Combined with the compression, the strength in all directions is greatly improved.

[0041]

The plug for an artificial joint according to the present invention can close the bone cement in the medullary cavity so that the bone cement does not fill the medullary cavity deeper than the stem. After becoming unnecessary, it is hydrolyzed in the medullary cavity and completely disappears, so that it has a remarkable effect that it does not remain as a foreign substance.

[Brief description of the drawings]

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

FIG. 2 is a plan view of the artificial joint plug.

FIG. 3 is an enlarged sectional view taken along line AA of FIG. 1;

FIG. 4 is a cross-sectional view for explaining an artificial hip joint.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plug main body 1a Hemisphere 1b Concave hole 2 Petal-like projection 2a Projecting edge 3 Cut part 101 Stem of artificial joint

Claims (3)

[Claims] 1. An artificial joint plug in which a plug body is formed from a biodegradable and absorbable polymer, and a plurality of petals are projected obliquely upward and outward from an upper peripheral edge of the plug body. 2. The biodegradable and absorbable polymer is polylactic acid,
The artificial joint plug according to claim 1, wherein the plug is a polymer of any one of lactic acid-glycolic acid copolymer and lactic acid-caprolactone copolymer or a mixed polymer of two or more thereof. 3. The plug for an artificial joint according to claim 1, wherein a bioceramic powder is contained.