JP2000070278A - Screw for fixing artificial joint and joining bone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to fix a hemispherical shell body of an artificial joint in such a manner that the fit of an inner cup is improved by forming the front surfaces of the heads of screws consisting of in-vivo degradable absorptive polymers for fixing this hemispherical shell body to a recessed spherical shape having the same radius as the radius of the inside surface of the hemispherical shell body. SOLUTION: When the hemispherical shell body 4 of the artificial joint is fixed to a pelvis by using the screws 10, the hemispherical shell body 4 and the inner cup 3 come into close contact with each other as the front surfaces 10d of the screw heads 10a are formed to the recessed spherical shape having the same radius as the radius of the inside surface of the hemispherical shell body 4. Then, the fit of the inner cup 3 is good and the friction of the screw heads 10a and the inner cup 3 at the time of walking, or the like, is eliminated and, therefore, the flawing of the inner cup 3 does not occur any more. The hydrolysis of the in-vivo degradable absorptive polymers progresses upon lapse of several months and finally, the screws 10 disappear. More particularly, the screws 10 formed by orienting molecular chains (crystals) diagonally with the central axis have high strength and, therefore, the defect, or the like, may be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biodegradable and absorbable artificial joint fixation and osteosynthesis screw.

[0002]

2. Description of the Related Art As shown in FIG. 10, an artificial hip joint, which is a typical example of an artificial joint, has a stem 1 made of a titanium alloy or stainless steel bent in a substantially "U" shape, and is fitted and fixed to the upper end of the stem. And a substantially hemispherical inner cup 3 made of ultra-high molecular weight polyethylene or a bio-alloy or a bio-alloy or alumina ceramic having the bone head 2 rotatably held. And a substantially hemispherical shell 4 called an outer cup made of a titanium alloy that rotatably surrounds the inner cup.

[0003] In such an artificial hip joint, a substantially hemispherical shell 4 is fixed to a pelvis 7 by a screw 6 made of titanium alloy or stainless steel, while a stem 1 is inserted into a medullary cavity 9 of a femur 8. The stem 1 is used by fixing the stem 1 with the bone cement 5 filled into the base.

[0004] On the other hand, living bone has been joined using a biodegradable and absorbable screw for a fractured part, a bone exfoliated part or the like. The biodegradable and absorptive screw is hydrolyzed by contact with bodily fluids and eventually absorbed by the body and disappears.

[0005]

However, the screw 6 made of a titanium alloy or the like or the biodegradable and absorptive screw is, as shown in FIG.
When the upper surface 6b is flat, the upper surface 6b slightly comes inward from the inner surface of the substantially hemispherical shell 4. Therefore, the inner cup 3 hits the upper surface 6b protruding inward,
A gap is formed between the substantially hemispherical shell 4 and the inner cup 3,
There was a possibility that the inner cup 3 would not fit properly. If the screw 6 is screwed deeper to eliminate this fear, the joint surface with the substantially hemispherical shell 4 is reduced and the fixing force is inferior, or if the thickness of the substantially hemispherical shell 4 is thin, the screw is deeply screwed. There was a fear that he could not even do it.

Further, since the inner cup 3 is pressed against the upper surface 6b of the screw head 6a to generate friction every time walking, there is a problem that the frictional contact portion of the inner cup 3 is damaged. If the screw head 6a protrudes into the substantially hemispherical shell 4 due to "looseness", there is a problem that the inner cup 3 is greatly damaged.

[0007] The above screw 6 keeps the substantially hemispherical shell 4 until the new bone enters the porous portion of the porous coating applied to the outer peripheral surface of the substantially hemispherical shell 4 and is supported and fixed. The screw 6 is made of a titanium alloy or stainless steel, so that it is not necessary to be fixed after the substantially hemispherical shell 4 is fixed. There was a problem that remains.

Further, when the screw 6 is screwed in a narrow space where the substantially hemispherical shell 4 is small, it is difficult for a rotary tool such as a hexagon wrench to fit into the concave hole in the upper surface 6b of the head. The work was hard. Further, if the upper surface 6b of the screw head 6a is flat, the tip of the rotating tool may slide off the upper surface 6b when coming into contact with the upper surface 6b.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to fix a substantially hemispherical shell so that the inner cup can be easily accommodated, and there is a risk of damaging the inner cup. Another object of the present invention is to provide a screw for artificial joint fixation that is substantially decomposed and absorbed after a substantially hemispherical shell is fixed with bone cement and does not remain in a living body. Another object of the present invention is to provide an osteosynthesis screw in which a rotating tool can be easily fitted into a screw head, and the screwing operation is facilitated.

[0010]

In order to achieve the above object, an artificial joint fixing screw according to a first aspect of the present invention is a screw made of a biodegradable and absorbable polymer for fixing a substantially hemispherical shell of an artificial joint. Wherein the upper surface of the screw head is formed as a concave spherical surface having substantially the same radius as the radius of the inner surface of the substantially hemispherical shell.

When the substantially hemispherical shell of the artificial joint is fixed using the artificial joint fixing screw, the upper surface of the screw head becomes a concave spherical surface having substantially the same radius as the radius of the inner surface of the substantially hemispherical shell. Since it is formed, the upper surface does not protrude inward from the inner surface of the substantially hemispherical shell. Therefore, the substantially hemispherical shell body and the inner cup are in contact with no gap, so that the inner cup fits well, and the friction between the screw head and the inner cup during walking or the like is eliminated, so that the inner cup is not damaged. . Then, several months after the substantially hemispherical shell is fixed, the biodegradable and absorptive polymer is hydrolyzed by contact with the body fluid, and is eventually completely decomposed, absorbed and disappears.

Next, the osteosynthesis screw according to claim 2 of the present invention is a screw made of a biodegradable and absorbable polymer, wherein the upper surface of the screw head is formed in a concave spherical surface. Is what you do.

This screw has a concave top surface on its head, so that even if a rotary tool such as a hexagon wrench hits the concave spherical surface, it does not slip off from the upper surface, and the rotary tool has a concave hole provided in the concave spherical surface. Therefore, even if the screw is small or the screwing operation is performed in a narrow place, the rotating tool can be quickly fitted into the concave hole.

Next, the screw for artificial joint fixation and osteosynthesis according to claim 3 of the present invention is compressed, and the molecular chains or crystals of the biodegradable and absorbable polymer are slanted from the periphery toward the central axis of the screw. It is characterized by being oriented.

This screw has a high strength because the molecular chains (crystals) of the biodegradable and absorbable polymer are oriented by being compressed. In particular, the molecular chain between the direction of the central axis and the direction perpendicular to the direction of the central axis. Since the anisotropy of the (crystal) orientation is small, the strength against external forces in various directions is greatly improved as a whole, in combination with the denseness. Moreover, in this screw, in a cross section perpendicular to the central axis, the molecular chains (crystals) take a radial arrangement around the central axis, so that the torsional strength is remarkably improved. Therefore, even if a large rotational force or twisting force acts when screwing the screw, the screw does not cause torsional breakage.

Further, a screw for artificial joint fixation and osteosynthesis according to a fourth aspect of the present invention is characterized in that the screw according to any one of the first to third aspects further comprises a bioceramic powder. Things.

When this screw is screwed into the pelvis or the like to fix a substantially hemispherical shell, the bioceramics powder induces bone tissue to form on the surface of the screw with hydrolysis of the biodegradable and absorbable polymer. Within a short period of time, the screw is connected to the pelvis and fixed. When the screw is connected to the pelvis, etc. in this way, there is no "looseness", so the screw head protrudes to the inside of the substantially hemispherical shell body due to "looseness" like a conventional screw, and the inner cup is severely damaged Can be eliminated.

When a fractured bone or the like is joined with this screw, the fractured part is healed and the bone tissue is guided and formed on the surface of the screw, so that the fractured part is joined early and an unexpected force is applied. Never leave.

[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 artificial joint fixing screw according to an embodiment of the present invention. FIG. 1A is a plan view of the screw, FIG. 1B is a front view of the screw, and FIG. It is a bottom view of a screw. And FIG. 2 is FIG.
(A) an enlarged cross-sectional view of the screw head along AA,
FIG. 3 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a longitudinal section of the screw, FIG. 4 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a transverse section of the screw, and FIG. It is sectional drawing which shows one use example.

This artificial joint fixing screw 10 is made of a biodegradable and absorbable polymer, and has a screw head 10a and a shaft 10b as shown in FIG.
The thread 10c is formed over the entire length of 0b. The diameter of the screw head 10a is 5 to 15 mm,
0b thread 10c has a diameter of 3 to 10 mm and an axial length of 20
５０50 mm.

As shown in FIG. 2, the upper surface of the screw head 10a has a concave spherical surface 10d having a radius R substantially the same as the radius of the inner surface of the substantially hemispherical shell 4 of the artificial joint.
A concave hole 10e for inserting a rotating tool such as a hexagon wrench is formed in the center of the hole. The concave spherical surface 1
As the radius R of 0d, a radius in the range of 5 to 30 mm is used. Also, the peripheral portion 1 of the screw head 10a
0f is cut into a round shape, and when screwed into a living bone, the peripheral edge 1
0f is not missing.

The screw 10 is compressed, and the molecular chains (crystals) M of the biodegradable and absorbable polymer are oriented obliquely downward from the periphery toward the center axis CL of the screw as shown in FIG. As shown in FIG. 4, in the cross section, the molecular chains (crystals) M are in a radially oriented state around the central axis CL. Therefore, the strength, density, surface hardness, and the like are higher than those of the non-oriented one, and in particular, the anisotropy of the molecular chain (crystal) orientation between the direction of the central axis CL and the direction perpendicular thereto. Is small, and the strength against external forces in various directions is generally increased in combination with the high density. In addition, since the twist strength of the screw 10 is remarkably improved due to the radial arrangement of the molecular chains (crystals), even if a large rotating force or twisting force is applied when the screw 10 is screwed into the screw 10, the screw 10 is not broken. Will not occur.

It is desirable to adjust the orientation angle of the molecular chain (crystal) M with respect to the central axis line CL in the range of 10 to 60 °, and if it is less than 10 °, the improvement of the anisotropy of the molecular chain (crystal) orientation becomes insufficient. If the angle exceeds 60 °, the production is not easy and cracks and the like tend to occur. A more preferred range of the orientation angle is 10 to 35 °.

The artificial joint fixing screw 1 as described above
0 can be produced, for example, by the following method.

First, a cylindrical billet is produced by molding a biodegradable and absorbable polymer of a material by means such as melt molding or pressure molding. As the biodegradable and absorbable polymer of the material, all thermoplastic thermoplastic polymers that are high in molecular weight, have high strength and toughness, are non-toxic and can be absorbed into the body by hydrolysis can be used. Has a viscosity average molecular weight of 100,000 to 700,000, preferably 150,000 to 6
About 100,000 polylactic acid, lactic acid-glycolic acid copolymer, lactic acid-caprolactone copolymer, and the like are particularly suitable, and these are used alone or in combination of two or more.

Next, a molding die 12 as shown in FIG. 9, 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.

When press-fitted in this manner, when the billet 13 passes through the constricted portion 12b, a large shear 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 center axis L (in other words, center axis of billet 13)
Compressed while being oriented obliquely downward from the periphery toward, 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. A molded body 130 is obtained.

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 threaded to form a thread 10c, and the upper surface of the screw head 10a is cut to form a concave spherical surface 10d.
Is formed, the artificial joint fixing screw 10 in which the molecular chains (crystals) M are obliquely oriented from the periphery toward the central axis CL is obtained.

In the above-described manufacturing method, the orientation angle of the molecular chains (crystals) with respect to the center axis L of the molding die 12
Angle θ of the tapered surface and the accommodation cavity 12a
Is determined approximately by the ratio of the opening area of the mold cavity 12c, and the orientation angle of the molecular chains (crystals) is changed by changing the ratio of the inclination angle θ to the opening area.
It is desirable to adjust to a range of 0 °. In that case, the deformation ratio (cross-sectional area of billet 13 / cross-sectional area of compression-oriented molded body 130) is substantially in the range of 1.5 to 6.0.
It is desirable to change the opening area ratio between the housing cavity 12a and the molding cavity 12c within the range of 1.5 to 6.0. If the deformation ratio is less than 1.5, a compression-oriented molded product having insufficient molecular chain (crystal) orientation is obtained, and if it exceeds 6.0, the orientation becomes excessive and a fibrillated compression-oriented molded product is obtained.

The degree of crystallinity of the compression-oriented molded body 130 can be 30 to 60% by controlling the ratio of the opening area between the housing cavity 12a and the molding cavity 12c, the press-in temperature, pressure, press-in speed of the billet 13, and the like. It is desirable to adjust the range. Screw 10 obtained by cutting a compression-oriented molded product having such a crystallinity
Has a good balance of the ratio of the crystalline phase and the amorphous phase, and the improvement of the strength and hardness by the crystalline phase and the flexibility by the amorphous phase are well harmonized, so that there is no brittleness like only the crystalline phase. Also, there is no weak property without strength as in the case of the amorphous phase alone. Therefore, the artificial joint fixing screw 10 which is tough and has sufficiently high strength overall is obtained.

It is to be noted that, instead of the above-described compression-orientation molded product, a stretch-orientation product which is stretched and oriented in the major axis direction may be prepared and cut to obtain the screw of the present invention. However, such a stretch-oriented screw is not dense and has a large anisotropy in the molecular chain orientation between the stretching direction and a direction perpendicular to the stretching direction. However, it is not possible to relatively improve the strength with respect to, or to significantly improve the torsional strength. However, when the twisting strength is not so required, it can be used sufficiently.

Further, the above artificial joint fixing screw 1
It is desirable that 0 contains a bioceramic powder. When the screw containing bioceramic powder is screwed into living bone as described above, the bioceramic powder induces bone tissue to form on the surface of the screw along with the hydrolysis, and the screw is formed in a relatively short time. Screws are "loose" because they are fixed by bonding with living bone
Does not occur.

Examples of the bioceramics powder include sintered bioapatite having surface bioactivity, bioglass or crystallized glass for living body, bioabsorbable wet hydroxyapatite, dicalcium phosphate, tricalcium phosphate and tetracalcium phosphate. Examples include powders of calcium phosphate, octacalcium phosphate, calcite, diopsite, and the like, and these may be used alone or as a mixture of two or more. In particular, a powder of wet hydroxyapatite having a high ability to induce and form bone tissue is preferably used. These bioceramic powders preferably have a particle size of about 0.2 to 50 μm, and more preferably those having a particle diameter of several μm to several tens μm.

The concentration of the bioceramic powder is 10
It is desirable to set the range to 60% by weight, and if it is less than 10% by weight, the ability of the bioceramics powder to form and induce bone tissue is insufficient, so that it is difficult to bond with living bone in a short period of time. On the other hand, when the content is more than 60% by weight, the hardness of the screw 10 is improved, but the inherent toughness of the biodegradable and absorbable polymer is impaired and the polymer becomes brittle, so that it is easily broken or chipped.

When the substantially hemispherical shell 4 of the artificial joint is fixed to the pelvis 7 as shown in FIG. 5 using the artificial joint fixing screw 10 having the above structure, the upper surface 10d of the screw head 10a is substantially fixed. Since the upper surface 10d is formed as a concave spherical surface having a radius substantially the same as the radius of the inner surface of the hemispherical shell 4, the upper surface 10d does not protrude inward from the inner surface of the substantially hemispherical shell 4, and the substantially hemispherical shell 4 And the inner cup 3 are in contact with no gap, so that the inner cup 3 fits better,
When walking, etc., the screw head 10a and the inner cup 3
, The inner cup 3 is not damaged. When the screw 10 is fixed, even if a rotating tool such as a hexagon wrench hits the concave spherical surface of the upper surface 10d of the screw head 10a, the screw 10 slides on the concave spherical surface and is guided to the concave hole 10e, so that the fixing can be easily performed. And a substantially hemispherical shell 4
A few months after being fixed to the pelvis 7, the contact with the body fluid promotes the hydrolysis of the biodegradable and absorbable polymer, and eventually the screw 10 is completely decomposed and absorbed to disappear.

In particular, a screw 1 in which molecular chains (crystals) are obliquely oriented from the periphery with respect to the central axis of the screw.
0 has a large strength against external forces in various directions as described above, and particularly has a large torsional strength, so that there is no fear of cracking or chipping when screwing into the pelvis 7. Further, since the screw 10 containing the ceramic powder is not combined with the pelvis 7 in a short period of time and does not cause “loosening” as described above, the screw head is not loosened as in the conventional screw 6. The drawback that 6a protrudes into the substantially hemispherical shell 4 and significantly damages the inner cup 3 can be reliably eliminated.

FIGS. 6A and 6B show an artificial joint fixing screw according to another embodiment of the present invention. FIG. 6A is a plan view of the screw, FIG. 6B is a front view of the screw, and FIG. It is a longitudinal section of a screw.

This artificial joint fixing screw 11 has exactly the same configuration as the screw 10 of the above embodiment except that a screw thread 10c is formed from the middle to the tip of the shaft portion 10b. Therefore, in FIG. 6, the same members will be denoted by the same reference numerals, and the description thereof will be omitted. It is apparent that such a screw 11 is used for fixing the substantially hemispherical shell 4 of the artificial joint similarly to the screw 10 described above, and has the same function and effect.

FIG. 7 is a sectional view showing a use state when the screw 10 shown in FIG. 1 is used as an osteosynthesis screw. The screw 10 is screwed into the fractured living bones 70a and 70b and joined. It is fixed. Since this screw 10 is the same as that of the embodiment shown in FIG.
Here, the description is omitted.

Using this screw 10, living bone 70
a, a rotary tool 7 such as a hexagon wrench to join the 70b
As shown in FIG. 8, when the screw 1 is fitted into the concave hole 10e of the screw head 10a,
e, but does not directly fit into the concave spherical surface 10d of the screw head 10b.
Since f is higher than the center, the rotating tool 71 does not slip on the concave spherical surface 10d and does not come off the screw head 10a. Conversely, the rotating tool 71 is guided along the concave spherical surface 10d to the concave hole 10e. . Therefore, not only when the joining operation is performed in a wide place as shown in FIG. 7, but also when the joining operation is performed in a narrow place or the screw is small, the rotating tool 7 can be used.
1 can be smoothly fitted into the concave hole 10e, and osteosynthesis can be easily performed. In particular, it is preferable that the living bone to be joined has a concave spherical surface, since the concave spherical surface of the living bone and the concave spherical surface of the screw 10 substantially match.

The screw 1 of the embodiment shown in FIG.
The same operation is performed for the osteosynthesis using No. 1, and the osteosynthesis can be easily performed.

[0043]

As is apparent from the above description, the screw for artificial joint fixation of the present invention has the upper surface of the screw head which does not come out from the inner surface of the substantially hemispherical shell of the artificial joint.
After the gap between the substantially hemispherical shell and the inner cup no longer occurs, the inner cup fits better, the fear of the inner cup being damaged by the pressure contact friction with the screw head is eliminated, and after the substantially hemispherical shell is fixed Since it is gradually decomposed and absorbed, it has a remarkable effect that it does not remain in a living body as a foreign substance.

Further, in the osteosynthesis screw of the present invention, since the upper surface of the screw head has a concave spherical surface, even if the rotating tool hits the concave spherical surface, it does not slip off from the screw head, but follows the concave spherical surface. Since the rotating tool is guided and fitted into the concave hole, a remarkable effect such as easy osteosynthesis can be achieved.

In particular, a screw in which molecular chains (crystals) are compressed and oriented obliquely from the periphery toward the center axis of the screw is high in torsional strength and strength against external forces in various directions. Screws that contain ceramic powder do not loosen due to bonding with living bone in a short period of time and do not loosen. Can protrude into the inside of the substantially hemispherical shell body and damage the inner cup significantly,
The living bones can be joined together at an early stage.

[Brief description of the drawings]

FIG. 1 shows an artificial joint fixing screw according to an embodiment of the present invention, wherein (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 an enlarged vertical sectional view of a screw head taken along line AA of FIG.

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

FIG. 4 shows a molecular chain (crystal) in a cross section of the screw.
FIG. 3 is a conceptual diagram showing an orientation state of the liquid crystal.

FIG. 5 is a sectional view showing an example of use of the screw.

6A and 6B show an artificial joint fixing screw according to another embodiment of the present invention, wherein FIG. 6A is a plan view of the screw, FIG. 6B is a front view of the screw, and FIG. FIG.

FIG. 7 is a sectional view showing a use state when the screw shown in FIG. 1 is used as an osteosynthesis screw.

8 is a partially enlarged cross-sectional view for explaining the action of the concave spherical surface of the screw head of the screw shown in FIG.

FIG. 9 is a view for explaining one method of manufacturing the screw for fixing an artificial joint according to the present invention. FIG. 4 is a cross-sectional view showing a state where the molding cavity is press-fitted and filled.

FIG. 10 is a sectional view illustrating an artificial hip joint.

FIG. 11 is a partially enlarged view of the hip prosthesis shown in FIG. 10;

[Explanation of symbols]

 Reference Signs List 1 stem 2 bone head 3 inner cup 4 substantially hemispherical shell (outer cup) 5 bone cement 6 titanium alloy screw 6 7 pelvis 8 femur 9 medullary cavity 10, 11 artificial joint fixing screw 10a screw head 10b shaft 10c Thread 10d Upper surface formed in concave spherical surface 70a, 70b Fractured living bone R Radius of upper surface

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kunihiro Hata 2-3-1 Azuchicho, Chuo-ku, Osaka-shi F-term (reference) in Takiron Co., Ltd. 4C060 LL15 4C097 AA01 AA03 AA04 BB04 BB09 CC06 CC20 DD06 DD07 EE20 FF20 SC10 TA10

Claims (4)

[Claims] 1. A screw made of a biodegradable and absorbable polymer for fixing a substantially hemispherical shell of an artificial joint, wherein the upper surface of the screw head has a radius substantially the same as the radius of the inner surface of the substantially hemispherical shell. An artificial joint fixation screw formed on a concave spherical surface having: 2. A screw for osteosynthesis, comprising a biodegradable and absorbable polymer, wherein the upper surface of the screw head is formed into a concave spherical surface. 3. The method according to claim 1, wherein the molecular chains or crystals of the biodegradable and absorbable polymer that is compressed are oriented obliquely from the periphery toward the central axis of the screw. screw. 4. The screw according to claim 1, further comprising a bioceramic powder.