JP2002253665A - Screw for fixing artificial hip joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ideal screw for fixing an artificial hip joint having strength and rigidity (elasticity) near to those of a living body bone, keeping high strength until the outer cup of the artificial hip joint is fixed to a femur to be capable of being fixed certainly but subsequently hydrolyzed rapidly to be absorbed by a living body without dispersing decomposed fine pieces or an inorganic filler to the periphery, preventing large bulky decomposed broken pieces from damaging an inner cup, not generating loosening because the screw is bonded to the circumferential bone for 1-2 weeks and conductively forming a bone in a screw hole along with the advance of hydrolysis to fill the screw hole while substituting the screw with the bone. SOLUTION: The screw for fixing the artificial hip joint is a screw 10 comprising a biologically decomposable and absorbable polymer fixing the outer cup of the artificial hip joint and the polymer is characterized in that a viscosity average mol.wt. is 150,000-400,000, compression bending modulus is 7-15 GPa and compression bending strength is not less than 150 MPa and a biologically active inorganic filler is contained in an amount of 20-50 wt.% to be exposed to the surface of the screw.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw for fixing an artificial hip joint which is degradable and absorbable in vivo.

[0002]

2. Description of the Related Art As shown in FIG. 5, an artificial hip joint has a stem 1 made of titanium (alloy) or stainless steel (alloy) bent in a substantially "U" shape and fitted and fixed to the upper end of the stem 1. A substantially spherical inner head 3 made of an ultra-high molecular weight polyethylene or an alumina ceramic, in which the bone head 2 is rotatably held; The outer cup 4 is made of stainless steel (alloy) or titanium (alloy) and rotatably surrounds the inner cup 3.

In such an artificial hip joint, the outer cup 4 is fixed to the pelvis 7 by a screw 6 made of titanium (alloy) or stainless steel (alloy), while the stem 1
Is inserted into the medullary cavity 9 of the femur 8 and the stem 1 is fixed with the bone cement 5 filled in the medullary cavity 9 for use.

[0004] Originally, the screw 6 for fixing the outer cup 4 of the artificial hip joint is used until the new bone enters and is fixed to the porous portion of the porous coating applied to the outer peripheral surface of the outer cup 4. Is fixed so that it does not move, and should be unnecessary after the outer cup 4 is fixed, but since it is actually impossible to remove it, it is left in the body as it is. That is the fact. For this reason, there is a problem that the screw 6 made of titanium (alloy) or stainless steel (alloy) remains permanently as a foreign substance in the body.

In view of such a problem, an invention has been proposed which aims to eliminate the necessity of removal by using a biodegradable and absorbable screw as a screw for fixing the outer cup and decomposing and absorbing in vivo in the living body. (Japanese Patent Publication No. 4-58985).

However, this patent only teaches that the screw is made of a polyester polymer of glycolic acid or lactic acid or the like, and a screw formed of such a polymer alone has a lack of expected mechanical strength, Due to the many problems during disassembly, it has not been put to practical use. In other words, this screw is not homogeneously disassembled, and the screw hole is not observed to be replaced by bone tissue for a long time, and the decomposed pieces fall out of the hole and come into contact with the artificial hip joint to generate wear powder and promote bone resorption. Therefore, there is a possibility that the surrounding bone may be weakened, and there is a serious fear that the screw hole on the acetabular side is not buried with the bone, leading to a reduction in the strength of the acetabular bone.

[0007]

Therefore, the present applicant has
We decided to develop an artificial hip joint fixation screw that can absorb and dissolve in vivo, but found that it was necessary to satisfy the following conditions to obtain a practical screw.

The initial rigidity (elasticity) of the screw is large and close to that of the living bone (pelvis). The initial bending strength of the screw is higher than that of the living bone, and the outer cup 4 of the artificial hip joint is fixed to the femur 7. The high bending strength can be maintained for 3 to 6 months. After the fixation of the artificial hip joint, the disassembly of the screw is performed quickly within a relatively short period of time, and evenly from the surface to the inside. It is absorbed without causing tissue (inflammation) reaction, and the decomposition product of the screw becomes a heterogeneous, large and small mixed bulk debris as seen in conventional bioabsorbable implants. Do not fall into the gap etc. of the inner cup and damage the inner cup 3. In parallel with the decomposition and absorption of the screw, the surrounding bone cells enter the screw hole, and finally It has a strong osteogenic ability to completely fill substituted with over screw within the after implantation 1-2 weeks be certain fixing force combined with the surrounding bone can be obtained.

An object of the present invention is to provide a screw for fixing an artificial hip joint which satisfies these conditions, thereby realizing practical use.

[0010]

In order to achieve the above object, a screw for fixing an artificial hip joint according to claim 1 of the present invention is a screw made of a biodegradable and absorbable polymer for fixing an outer cup of an artificial hip joint. The polymer has a viscosity average molecular weight of 150,000 to 400,000, a compressive flexural modulus of 7 GPa to 15 GPa, and a compressive flexural strength of 150 MPa.
As described above, the bioactive inorganic filler is contained at 20 to 50% by weight and is exposed on the screw surface.

[0011] The artificial hip joint fixing screw according to claim 2 of the present invention is characterized in that the biodegradable and absorbable polymer is partially crystallized poly-L-lactic acid or poly-D-lactic acid. The screw for fixing an artificial hip joint according to claim 3 of the present invention is characterized in that the constituent monomer or oligomer of the biodegradable and absorbable polymer is contained in an amount of 0.05 to 0.5% by weight. The artificial hip joint fixing screw according to the present invention, wherein the bioactive inorganic filler is osteoconductive bioceramics or bioceramics containing an alkaline inorganic compound. The fixing screw is compression-molded, and the molecular chains or crystals of the biodegradable and absorbable polymer are oriented, and according to claim 6 of the present invention. Engineering hip securing screw is to, wherein the specific gravity of from 1.410 to 1.735.

The screw for fixing an artificial hip joint according to the first aspect has a compression bending elastic modulus of 7 GPa to 15 GPa, so that it has the same rigidity as a living bone (cortical bone) and a compression bending strength of 150 MPa. As described above, it has strength equal to or higher than that of living bone (cortical bone). Therefore, this screw can be screwed into the femur without breaking, and the outer cup of the artificial hip joint can be firmly fixed,
Since the rigidity is not too high, there is no need to worry about the strength of the surrounding bones being reduced due to the phenomenon of stress protection. When the viscosity average molecular weight of the biodegradable absorbent polymer is smaller than 150,000, it becomes difficult to obtain a screw having a compression bending elastic modulus or a compression bending strength in the above range, and conversely, the viscosity average molecular weight is larger than 400,000. In this case, it takes a long time to completely disassemble, and inevitably increases the disadvantages.

[0013] As the biodegradable and absorbable polymer, the partially crystallized poly-L used for the screw according to claim 2 is used.
Homopolymers such as -lactic acid and poly-D-lactic acid are particularly preferred from the viewpoint of strength and elasticity.

Further, in the screw according to the first aspect of the present invention, the bioactive inorganic filler containing 20 to 50% by weight is exposed on the screw surface by a molding process such as cutting. Due to osteoconductivity, it binds to the surrounding bone about 1-2 weeks after implantation. Therefore, there is no need to worry about loosening of the screw and the like, and a reliable fixing force can be obtained.

When a bioactive inorganic filler is contained, the screw is finely and extremely homogeneously hydrolyzed in fine particles of the inorganic filler by penetration of body fluid into the cleavage of these particles and the matrix polymer. Fragments are formed and become quickly absorbed, with little bulky debris. In particular, since the screw molded under pressure as in claim 5 is dense to the theoretical level, the polymer is surprisingly decomposed to a viscosity average molecular weight of about tens of thousands, Even after losing the strength, the decomposed flakes and filler particles are not seen to break apart and disperse to the surroundings, and are simply decomposed and absorbed in a thin and thin state like wet chalk You. This has been confirmed in the animal experiments described below, which we have been conducting for over 4 years. Therefore, there is almost no fear that the fragments fall into the gap between the inner cup and the outer cup without generating bulk fragments and damage the inner cup. Then, bone tissue is conductively formed in the screw hole by the osteoconductive ability of the bioactive inorganic filler (this fact has also been confirmed), and the screw hole is filled by replacing the screw to be hydrolyzed. There is no danger of affecting the strength of the femur as if it were left forever.

In the formation of conduction of bone tissue in the screw hole, a bioceramic having osteoconductivity as an inorganic filler as in the screw of claim 4, particularly, a wet hydroxyapatite described later which is excellent in osteoconductivity is selectively used. Then it becomes remarkable.

Further, when the constituent monomer or oligomer of the biodegradable and absorbable polymer is contained in an amount of 0.05 to 0.5% by weight as in the screw according to the third aspect, strength suitable for an artificial hip joint fixing screw is obtained. The maintenance period and the speed of complete decomposition and absorption after achieving the objective are given. That is,
While maintaining the high bending strength for a period of 3 to 6 months until the outer cup of the hip joint is fixed to the femur, it is quickly decomposed and absorbed. Further, when a bioceramic having osteoconductivity is contained as a bioactive inorganic filler as in the screw of claim 4, since the pH of the bioceramic is a factor that affects the rate of hydrolysis, the bioceramic is also used in the living body. It is preferable to use a material close to neutral without any adverse effect, but in some cases, one method is to use bioceramics containing an alkaline inorganic compound that promotes decomposition.

Further, when the molecular chain or the crystal of the biodegradable and absorbable polymer is oriented by compression molding as in the screw of claim 5, it becomes dense and uniformly and finely hydrolyzed as described above. The decomposed flakes are absorbed without being dispersed in the surroundings, and the strength is improved by the molecular chain or crystal orientation, and the compression bending elastic modulus is 7 GPa to 1
A screw having 5 GPa, a compressive bending strength of 200 MPa or more and a high torsional strength can be easily obtained. In the screw containing the inorganic filler in an amount of 20 to 50% by weight, the internal voids are almost completely eliminated by the compression and the specific gravity is increased, and as described in claim 6, the level is equivalent to the theoretical calculation value. It is in the range of 1.410 to 1.735.

[0019]

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

FIG. 1 shows an embodiment of the screw for an artificial hip joint according to the present invention, wherein (a) is a plan view of the screw, (b) is a front view of the screw, and (c) is a view of the screw. It is a bottom view. FIG. 2 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a longitudinal section of the screw,
FIG. 3 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a cross section of the screw.

The artificial hip joint screw 10 is made of a biodegradable and absorbable polymer and has a screw head 10a and a shaft 10b as shown in FIG. 1, and the screw 10 extends over the entire length of the shaft 10b. A peak 10c is formed.
A hexagonal hole 10d for inserting a rotating tool such as a hexagon wrench is formed on the upper surface of the screw head 10a, and a peripheral edge 10e of the screw head 10a avoids buffering with the inner cup 3. It is rounded so that it is not chipped in vivo.

As the biodegradable and absorbable polymer of the material, L-form, D-form or D / L-form polylactic acid, lactic acid-glycolic acid copolymer, lactic acid-caprolactone copolymer and the like are used. Among them, partially crystallized poly-L-
Homopolymers such as lactic acid and poly-D-lactic acid having a crystallinity of 20 to 60%, preferably 30 to 50%, are particularly preferably used. The polymer having such a degree of crystallinity has a good balance between the ratio of the crystal phase and the amorphous phase, and the improvement in strength and hardness by the crystal phase and the flexibility by the amorphous phase are coordinated. There is no brittleness, and there is no weak property without strength as in the case of only an amorphous phase. Therefore, it becomes possible to obtain a screw for artificial hip joint fixation which is tough and has a sufficiently high overall strength.

It is necessary for these polymers to have a viscosity average molecular weight of 150,000 to 400,000 in a screw after melt-molding. Having a viscosity average molecular weight of 20
It is necessary to use about 800,000. When the viscosity average molecular weight of the polymer in the screw after melt molding is smaller than 150,000, the desired 7 GPa to 15 GPa
It becomes difficult to obtain a screw having a compressive bending elastic modulus of GPa and a compressive bending strength of 150 MPa or more. Conversely, if it is more than 400,000, a material polymer having a high viscosity average molecular weight of 400,000 or more is subjected to severe molding conditions. There are disadvantages, such as the need to melt-mold underneath, and the fact that it takes a long time to completely disassemble the screw. More preferable viscosity average molecular weight (molecular weight after molding) of the biodegradable and absorbable polymer constituting the screw is 200,000 to 30
It is ten thousand.

In the biodegradable and absorbable polymer described above, its constituent monomers and oligomers (for example, L-form or D-form lactic acid, its cyclic dimer, glycolic acid, caprolactone, etc.) are 0.05 to 0. It is desirable that the content be 0.5% by weight. When such a monomer or oligomer is contained, a suitable strength maintaining period as a screw for fixing an artificial hip joint and an early complete decomposition absorption rate after achieving the object are given, and the outer cup of the artificial hip joint is fixed to the femur. Although the high bending strength is maintained for a period of 3 to 6 months until it is released, it is decomposed and absorbed quite rapidly thereafter.

The screw 10 contains 20 to 50% by weight of a bioactive inorganic filler (not shown).
0 is exposed on the surface. As the inorganic filler, an osteoconductive bioceramic powder is preferable. , Tricalcium phosphate, tetracalcium phosphate, octacalcium phosphate, calcite, ceravital, diopsite and the like are used. Among these, bioabsorbable bite ceramics are preferably used, and in particular, unfired hydroxyapatite which is the most active, has excellent osteoconductivity, and has low harm is preferably used.

These bioceramic powders are:
Those having an average particle size of 0.2 to 50 μm, preferably 2 to 20 μm are used. Bioceramics having an average particle size smaller than 0.2 μm are not easily dispersed uniformly in a matrix polymer, while blending bioceramics larger than 50 μm tends to produce relatively large degraded pieces. Is also not preferred.

When the above-mentioned bioceramics are contained, the pH is one of the factors which influence the rate of hydrolysis. Therefore, alkaline inorganic compounds which promote the hydrolysis (for example, calcium hydroxide, magnesium hydroxide, hydroxide, etc.) Bioceramics containing potassium, calcium chloride, magnesium chloride, potassium chloride, zinc chloride, etc.) may be blended as the inorganic filler.

When the above inorganic filler is contained,
The body fluid penetrates into the boundary with the inorganic filler matrix polymer, and the screw is finely and homogeneously hydrolyzed in the unit of fine particles of the inorganic filler and quickly absorbed, so that large bulk fragments are hardly generated. Therefore, there is almost no fear that the bulk fragments fall into the gap between the inner cup and the outer cup and damage the inner cup and the like. And, bone tissue is conductively formed in the screw hole by the osteoconductivity of this inorganic filler, to replace the screw to be hydrolyzed and fill the screw hole,
It does not adversely affect the strength of the femur.

The content of the inorganic filler is 2 as described above.
It is necessary to be in the range of 0 to 50% by weight, and if it is less than 20% by weight, the bondability with living bone, osteoconductivity, promotion of hydrolysis, prevention of generation of bulk-like debris and the like become insufficient.
On the other hand, if the content is larger than 50% by weight, on the contrary, the inherent toughness of the biodegradable and absorbable polymer is impaired and the polymer becomes brittle, so that the screw 1 is easily broken or chipped.
0 indicates that the molecular chain (crystal) M of the biodegradable and absorbable polymer is compression-molded and the central axis C
As shown in FIG. 3, the molecular chains (crystals) M are radially oriented around the central axis CL in the cross section as shown in FIG. Therefore, the strength, surface hardness, density (specific gravity), and the like are improved as compared with the non-oriented one, and in particular, the molecular chain (crystal) orientation between the direction of the central axis CL and the direction perpendicular thereto is improved. Since the anisotropy is small, the strength against external forces in various directions is generally increased in combination with the denseness. Moreover, since the screw 10 has a remarkably improved twisting strength due to the radial arrangement of the molecular chains (crystals), even if a large rotational force or twisting force acts upon screwing, the screw 10 can be broken. Will not occur. In addition, when the polymer is compacted in this way, the decomposed flakes and filler particles are dispersed even after the polymer is decomposed to a viscosity average molecular weight of about tens of thousands and loses the strength of the screw. It does not collapse and disperse to the surroundings. This is a surprising fact.

The screw 10 for an artificial hip joint as described above
Can be manufactured, for example, by the following method.

First, a biodegradable and absorbable polymer having a viscosity average molecular weight of 200,000 to 800,000 (preferably containing 0.05 to 0.5% by weight of a constituent monomer or oligomer) is mixed with 20% of a bioactive inorganic filler. 〜50% by weight and molding by means such as melt molding or pressure molding to produce a cylindrical billet made of a polymer having a viscosity average molecular weight of 150,000 to 400,000.

Next, a molding die 12 as shown in FIG. 4, that is, a large-diameter cylindrical housing cavity 12a having a large cross-sectional opening area, and a small-diameter cylindrical bottomed molding cavity having a small cross-sectional opening area. A molding die 12 having a constricted portion 12b whose inner peripheral surface is a tapered surface of a downward constriction is provided between the molding die 12 and the inner peripheral surface of the molding die 12 as shown in FIG. The billet 13 is housed in the housing cavity 12a. Then, at the temperature at which the biodegradable and absorbable polymer can be crystallized (above the glass transition temperature and below the melting temperature) by the male mold 12d for pressurization, as shown in FIG. And continuously or intermittently.

With such press-fitting, when the billet 13 passes through the constricted portion 12b, a large shearing force is generated between the billet 13 and the tapered surface due to frictional resistance, which is a molecular chain (crystal).
Direction (MD) and transverse direction (TD)
Acts as an external force, so that the molecular chains (crystals)
2 is compressed while being oriented obliquely downward from the periphery toward the central axis L (in other words, the central axis of the billet 13), and crystallization proceeds. After being filled in the molding cavity 12c, the inner surface and the bottom surface of the molding cavity 12c receive a back pressure, and are fixed while maintaining the molecular chain (crystal) orientation and the compressed state. Molded body 1
30 is obtained. The compression-oriented molded body 130 has a compression bending elastic modulus in a range of 7 GPa to 15 GPa and a compression bending strength of 150 MPa or more (usually 200 MPa or more).
And the specific gravity is 1.410 to 1.735 which is equivalent to the theoretical value.
Range (Polymer is polylactic acid and crystallinity is 20-60%
And 20 to 50% by weight of unfired hydroxyapatite as an inorganic filler).

Then, the compression oriented molded body 130 is removed from the mold 12 and cut to form a screw head 10a and a shaft 10b.
Is screwed to form a screw thread 10c, and a hexagonal hole 10d is formed in the upper surface of the screw head 10a, so that the molecular chains (crystals) M are oriented obliquely from the periphery toward the central axis CL. Flexural modulus of 7 GPa to 15 G
The artificial hip joint screw 10 having a dense compression bending strength of 150 MPa or more at Pa and an inorganic filler exposed on the surface.
Is obtained.

In the above-mentioned manufacturing method, as the deformation ratio R (the cross-sectional area of the billet 13 / the cross-sectional area of the compression-oriented molded body 130) increases, the denser compression-oriented molded body 130 can be obtained. If it is too large, an excessive shearing force is applied to the compression-oriented molded body 130, so that molding failure occurs, and only a material having a low strength is obtained. On the other hand, if the deformation ratio is too small, the required strength cannot be obtained. Therefore, the opening area between the housing cavity 12a and the molding cavity 12c is set so that the deformation ratio R is substantially in the range of 1.5 to 3.0. It is desirable to change the ratio. The crystallinity of the compression-oriented molded body 130 can be controlled to 20 to 60 as described above by controlling the opening area ratio between the housing cavity 12a and the molding cavity 12c, the press-in temperature, the pressure, and the press-in speed of the billet 13. % Is desirably adjusted.

Such an artificial joint fixing screw 10
Is replaced with the conventional metal screw 6 shown in FIG.
When the outer cup 4 is fixed to the pelvis 7 by screwing from the hole of the outer cup 4 of the artificial hip joint into the screw hole formed in the pelvis 7, the screw is formed by the action of an inorganic filler such as bioactive bioceramics exposed on the surface of the screw 10. 10 bind to surrounding bone within 1-2 weeks after implantation. Therefore, loosening of the screw 10 does not occur, and the outer cup 4 can be firmly fixed to the femur 7. Moreover, this screw 1
0 indicates that the compression bending elastic modulus is 7 GPa to 15 GPa and has the same rigidity as that of a living bone (cortical bone), and the compression bending strength is 150 MPa or more (preferably 200 MPa or more).
It has strength equal to or greater than that of living bone (cortical bone)
Further, since the strength and torsional strength against external force in various directions are enhanced by the compression orientation of the polymer molecular chains (crystals), the screw 10 is screwed into the screw hole of the femur 7.
The outer cup 4 can be securely fixed without breaking the screw 10 or breaking when a load is applied, and there is no danger that the surrounding bone is weakened by stress protection after implantation.

The screw 10 maintains a compressive bending strength of 150 MPa or more (preferably 200 MPa or more) for a period of 3 to 6 months until the outer cup 4 is fixed to the femur 7 and stabilized. As described above, since the constituent monomers or oligomers and the alkaline inorganic compound are contained, after a period of 3 to 6 months has elapsed, hydrolysis is rapidly performed to the extent that inflammation does not occur, and
Because it contains an inorganic filler, it is finely and uniformly hydrolyzed and does not produce large bulk decomposed debris, and because it is densified by compression, even if hydrolysis proceeds, decomposed debris and inorganic filler are It does not break apart and disperse to the surroundings. Therefore, the hydrolysis is slow like a screw made of only the biodegradable and absorbable polymer, and large bulk fragments are generated during the hydrolysis, and the bulk fragments are formed in the gap between the outer cup 4 and the inner cup 3 of the artificial hip joint. There is no need to worry about falling down and damaging the inner cup 3.

When the hydrolysis of the screw 10 further proceeds, the bone tissue is conductively formed in the screw hole by the osteoconductivity of the bioactive inorganic filler such as bioceramics, and the screw is replaced by the screw to be hydrolyzed. Since the hole is filled, there is no fear that the strength of the femur is adversely affected as in the case where the screw hole remains forever.

In the screw 10 of this embodiment, the molecular chains (crystals) of the polymer are obliquely orientated from the periphery toward the central axis by compression, thereby increasing the strength against external forces and torsional strength in various directions. Alternatively, the molecular chains may be uniaxially oriented by means of uniaxial stretching while heating or so-called isostatic extrusion.
However, in this case, since the screw is not dense, it is difficult to suppress the dispersion of the hydrolyzed decomposed debris and the inorganic filler around, and the molecular orientation in the stretching direction and the direction perpendicular to the stretching direction. Since the anisotropy of the chain orientation is large, it is also difficult to improve the strength against external forces in various directions and to improve the torsional strength.

Next, an experiment of hydrolysis by animals will be described.

Unmelted hydroxyapatite (u-HA) was mixed with poly-L-lactic acid (PLLA) having a viscosity-average molecular weight of 400,000 before melting and 30% by weight, and a cylindrical billet was prepared by melt molding. did. This billet was forged into a compression-oriented molded body at a deformation ratio of R = 2.8 using the above-described molding die, and this was cut to obtain a rod having a diameter of 3.2 mm and a length of 30 mm. The compression bending elastic modulus of the rod was 7.5 GPa, the compression bending strength was 270 MPa, the viscosity average molecular weight of the polymer was 200,000, and the crystallinity was 45%. The specific gravity of the billet was 1.465, whereas the specific gravity of this rod was improved to 1.508, indicating that the rod was a dense rod having substantially no internal voids.

In order to examine the change of the rod due to hydrolysis in the living body, a surgical operation was performed in which the femur of a rabbit was cut and the rod was implanted in the medullary cavity. After four years, the femur was cut again, and the change in the rod was examined. As a result, the rod became thin with a diameter of 2.5 to 2.7 mm, a bone tissue was formed around the rod, and the rod was present in the medullary cavity without disintegrating into decomposed pieces. Hydrolysis of the rod taken out of the medullary cavity had progressed to such an extent that it could be easily crushed with a finger. In addition, no serious inflammatory reaction or the like was observed in the medullary cavity, indicating no harm.

From the results of this experiment, it is clear that the artificial hip joint fixing screw of the present invention has strength and elasticity equal to or higher than that of a living bone, is dense and has a high specific gravity, and has a bonding property with a living bone and an osteoinductive property. And that it was quickly and finely and uniformly hydrolyzed, and the decomposed flakes and inorganic filler were absorbed without disintegration and dispersion.

[0044]

As is apparent from the above description, the artificial hip joint fixing screw of the present invention has a rigidity (elasticity) close to that of a living bone and a high bending strength higher than that of a living bone, and the outer cup of the artificial hip joint has a thigh. 3-6 until fixed to bone
The outer cup can be fixed firmly by maintaining its high bending strength for months, but after that it is rapidly and finely and uniformly hydrolyzed to the extent that it does not cause inflammation, and the decomposed chips and inorganic filler are dispersed around It will be absorbed into the living body without doing, there is no fear that large bulk decomposed debris is generated during the hydrolysis and enters between the outer cup and the inner cup and damages the inner cup etc.
1 to 2 weeks after implantation due to the action of bioactive inorganic filler, it binds to the surrounding bone, so the outer cup can be fixed firmly without loosening of the screw, and the bone is conducted to the screw hole as the hydrolysis progresses Since the screw hole is filled and formed to replace the screw, there are many remarkable effects such that there is no fear of adversely affecting the strength of the femur.

[Brief description of the drawings]

FIG. 1 shows a screw for fixing an artificial hip joint according to an embodiment of the present invention, in which (a) is a plan view of the screw, (b) is a front view of the screw, and (c) is a screw of the screw. It is a bottom view.

FIG. 2 is a conceptual diagram showing an orientation state of a molecular chain (crystal) in a longitudinal section of the screw.

FIG. 3 is a conceptual diagram showing an orientation state of a molecular chain (crystal) in a cross section of the screw.

FIG. 4 is a view for explaining one manufacturing method of the screw.
(A) is a cross-sectional view showing a state where a billet is housed in a housing cavity of a mold, and (B) is a cross-sectional view showing that a billet is press-fitted into a mold cavity of the mold.

FIG. 5 is a sectional view of an artificial hip joint.

[Explanation of symbols]

 Reference Signs List 4 outer cup of artificial hip joint 10 screw for fixing artificial hip joint 10a screw head 10b shaft 10c screw thread

Claims (6)

[Claims] 1. A screw made of a biodegradable and absorbable polymer for fixing an outer cup of an artificial hip joint,
The polymer has a viscosity average molecular weight of 150,000 to 400,000, a compression bending elastic modulus of 7 GPa to 15 GPa, and a compression bending strength of 150.
Not less than MPa, and 20 to 5 bioactive inorganic fillers
A screw for fixing an artificial hip joint, which is contained at 0% by weight and is exposed on the screw surface. 2. The biodegradable and absorbable polymer is partially crystallized poly-L-lactic acid or poly-D-lactic acid.
2. The screw for fixing a hip joint according to item 1. 3. The screw for fixing an artificial hip joint according to claim 1, wherein the constituent monomer or oligomer of the biodegradable and absorbable polymer is contained in an amount of 0.05 to 0.5% by weight. 4. The screw for fixing an artificial hip joint according to claim 1, wherein the bioactive inorganic filler is osteoconductive bioceramics or bioceramics containing an alkaline inorganic compound. 5. The screw for fixing an artificial hip joint according to claim 1, wherein the molecular chain or the crystal of the biodegradable and absorbable polymer is oriented by compression molding. 6. The screw for fixing an artificial hip joint according to claim 5, wherein the specific gravity is 1.410 to 1.735.