JP2000097218A - Bone joint screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bone joint screw which can be decomposed and absorbed in-vivo, which has a large area effective for transmission of torque of a screwdriver, which can efficiently and uniformly transmits torque without concentration of the torque, and which can firmly be screwed in vivo without damaging cross grooves and a head thereof. SOLUTION: A bone joint screw 1 is made of a polymer which can be decomposed and absorbed in vivo. Cross grooves 5 are formed in the top surface of a screw head 2, and the center parts of the cross grooves 5 are formed in a deep groove parts 6 having deeper bottoms, except the four ends thereof. Due to the provision of the deep groove parts 6, the area effective for transmission of torque of a screwdriver can be increased so that the torque can be efficiently and uniformly transmitted without concentration of the torque, thereby it is possible to screw the bone joint screw into a biological bone without damaging the cross grooves and the screw head 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biodegradable and absorbable osteosynthesis screw which can be firmly screwed into living bone without destroying the cross groove of the screw head.

[0002]

2. Description of the Related Art In the field of surgery such as orthopedic surgery, plastic surgery, thoracic surgery, and oral surgery, a metal or ceramic screw is used as an osteosynthesis device for reducing or fixing a fractured portion. . However, since these screws have a high elastic modulus, there are problems such as a decrease in the strength of the surrounding bone, and in particular, metal screws may harm the living body due to elution of metal ions,
There is a problem that when the fracture is healed, it is necessary to perform a reoperation for removing the fracture from the body at an early stage.

Accordingly, the present applicant has developed an osteosynthesis screw made of polylactic acid which is biodegradable and absorbable. This screw has the same initial strength as living bone, and after healing of the fractured part, it is hydrolyzed and absorbed in the living body, so there is no need for reoperation, especially containing bioceramic powder The screw was excellent in that it had bonding property with living bone.

[0004]

However, the above-mentioned biodegradable and absorptive screw is screwed into a living bone while inserting a plus screwdriver into a cross groove formed in the screw head and applying a large rotating force to the screw. Or, when inserting a hexagon wrench into the hexagonal hole formed in the screw head and screwing it into living bone while applying a large rotational force, the cross groove is missing or the screw head is cracked,
In some cases, the screw could not be screwed completely into living bone.

As a biodegradable and absorptive screw for solving such a problem, a cross-shaped hole 102 is formed in a screw head 101 as shown in FIG. 5, and the four end portions 103 of the cross-shaped hole are adjacent to each other. A screw provided with an “R” on a side surface portion 104 connecting end portions has been proposed (Japanese Patent Laid-Open No. 9-2).
No. 53089). The screw is provided with an “R” to prevent the rotational force from being concentrated on the corners of the cross hole, and to prevent the cross hole 102 and the screw head 101 from being broken.

However, with this screw, the rotational force of the driver acts almost vertically on the side of the cross-shaped hole 102 where the "R" is not provided, and the screw is effectively transmitted.
Since the rotational force does not act vertically on the portion provided with the “R”, particularly on the side portion 104 provided with the large “R”, the effective area for transmitting the rotational force is greatly reduced, and as a result, In addition, there is a problem that the rotational force is concentrated on the side portion where the "R" is not provided, and that portion tends to be chipped.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a large area effective for transmitting the rotational force of a driver, transmitting the rotational force almost uniformly without waste, without concentrating the rotational force. An object of the present invention is to provide a biodegradable and absorbable osteosynthesis screw that can be screwed firmly into a living bone without causing a cross groove or destruction of a screw head.

[0008]

In order to achieve the above object, the screw for osteosynthesis of the present invention is a screw made of a biodegradable and absorbable polymer, wherein a cross groove is formed on the upper surface of the screw head, A central portion of the cross groove excluding four end portions is formed as a deep groove portion in which the groove bottom surface is recessed one step deeper.

The osteosynthesis screw is screwed into a living bone or the like using the following dedicated driver. That is, a dedicated screwdriver is provided in which a cross-shaped projection fitted into the cross groove of the screw head is provided at the tip of the driver, and a small cross-shaped projection fitted into the deep groove is provided at the tip of the cross-shaped projection. The screw for osteosynthesis is screwed into a living bone or the like while the cruciform convex part and the cruciform small protrusion of this dedicated screwdriver are fitted and rotated in the cruciform groove and deep groove part of the screw head.

When the dedicated screwdriver is rotated as described above, one side (one side in the rotation direction) of the cross groove and the deep groove of the screw head exerts the rotational force of the cross-shaped protrusion and the small cross-shaped protrusion at the driver tip. Because it is received substantially vertically and the rotational force is effectively transmitted, it can be applied to a conventional screw in which only a cross groove is formed in the screw head or to the screw in which a cross hole 102 with "R" is formed in the screw head. In comparison, the effective area for transmitting the rotational force is increased, and the rotational force is transmitted to the entire cross-face and the deep groove without being concentrated, and the cross-groove is destroyed. And can be screwed firmly into living bone.

Further, as described above, when the cross-shaped convex portion and the small cross-shaped protrusion at the tip of the dedicated driver are fitted into the cross groove and the deep groove portion of the screw head, the dedicated driver is fitted tightly, and the rotation is performed during the rotation. And it is difficult to remove, so that the screwing work becomes easy.

[0012]

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 front view of an osteosynthesis screw according to an embodiment of the present invention, FIG. 2 is a plan view of the screw, FIG. 3 is a longitudinal sectional view of the screw, and FIG. FIG. 5 is a partial sectional view showing a state where the tip of a dedicated screwdriver is fitted to the head of the screw.

The osteosynthesis screw 1 is a screw made of a biodegradable and absorbable polymer, and has a screw head 2 and a shaft portion 3.
Is formed. The thread 4 may be formed from the middle to the tip of the shaft 3.

As shown in FIGS. 2 and 3, a cross groove 5 is formed on the upper surface of the screw head 2, and the center of the cross groove 5 excluding the four ends is recessed one step deeper. It is formed in the formed deep groove portion 6. The length of the deep groove portion 6 is
Is desirably set to about 1/2 to 3/4 of the length of the screw, and the depth of the deep groove 6 is set to about 0.5 to 4 mm according to the size (height) of the screw head 2. It is desirable to do. If the length of the deep groove 6 is shorter than 1/2 and the depth is shallower than 0.5 mm, the area of one side surface of the deep groove 6 which receives the rotational force of the dedicated driver substantially vertically becomes small. The advantage of 6 is hardly exhibited. On the other hand, when the length of the deep groove 6 is longer than 3/4 and the depth is more than 4 mm, the thickness from the end of the deep groove 6 to the outer peripheral surface of the screw head 2 becomes thinner. When screw 1 is screwed in, screw head 2 may be broken.

The dedicated screwdriver 7 used for the osteosynthesis screw 1 has a cross-shaped convex portion 7a and a small cross-shaped protrusion 7b at the tip of the driver as shown in FIG. The screw 1 is screwed into a living bone while the projection 7a is fitted into the cross groove 5 of the screw head 2 and the small cross-shaped projection 7b is fitted into the deep groove 6 and rotated.

As described above, when the cruciform convex portion 7a and the cruciform small protrusion 7b of the special driver 7 are fitted into the cross groove 5 and the deep groove portion 6, the tip of the special driver 7 is tightly fitted, and the middle of the rotation. And it is difficult to remove, so that the screwing work becomes easy. In addition, one side surface (one side surface in the rotation direction) of the cross groove 5 and the deep groove portion 6 receives the rotational force of the cross-shaped convex portion 7a and the small cross-shaped protrusion 7b at the tip of the driver substantially vertically, and the rotational force is effectively transmitted. Is done. Thus, the screw 1 of the present invention
Since the one side surface of the cross groove 5 and the one side surface of the deep groove portion 6 are effective surfaces for transmitting the rotational force, the conventional screw in which only the cross groove is formed in the screw head or the "R" in the screw head As compared with the screw having the cross hole 102 with a cross, the area effective for transmitting the rotational force is increased, and the rotational force is not concentrated, so that the whole of one side surface of the cross groove 5 and the deep groove 6 is wasted substantially uniformly. Therefore, the screw can be securely screwed into the living bone without breaking the cross groove 5 and the screw head 2.

The biodegradable and absorbable polymer used as the material of the screw 1 has an initial viscosity average molecular weight of 150,000 to 6
About 100,000, preferably about 200,000 to 550,000 polylactic acid or lactic acid-glycolic acid copolymer is suitable.
Those containing about 60% by weight are more preferably used.

When a bone screw 1 made of a biodegradable and absorbable polymer containing bioceramic powder is screwed into a fractured part in a living body, the bioceramic powder is hydrolyzed from the surface of the screw 1. Deposits or conducts calcium phosphate and bone tissue of the living body on the surface layer of the screw 1, and therefore there is an advantage that the screw 1 is combined with the living bone in a relatively short period of time and loosening does not occur.

The screw for osteosynthesis of the present invention is obtained by melt-molding the above-described biodegradable and absorbable polymer and cutting the molded product, or by further uniaxially stretching the molded product and then cutting the molded product. Alternatively, it is manufactured by further cold forging or compression molding the molded body and then cutting. In particular, when the molded body of the biodegradable and absorbable polymer was cold forged or compression molded before cutting, the polymer molecular chains, their aggregation domains, crystals, etc. were oriented along a number of reference axes different in the axial direction. Since it becomes a compressed multiaxially oriented body or an aggregate of many clusters having reference axes of different orientations, it is dense and has little strength anisotropy, and it can withstand external forces and torsional forces in various directions. On the other hand, there is an advantage that an osteosynthesis screw having a large strength can be manufactured.

[0021]

As is apparent from the above description, the osteosynthesis screw of the present invention transmits the rotational force of the dedicated driver by the depth of the deep groove formed in the center excluding the four ends of the cross groove. The effective area of the screw is increased, and the torque is transmitted to the entire cross-shaped groove and one side of the deep groove without waste, without being concentrated, so that the screw is securely screwed into the living bone without destruction of the cross groove or the screw head. In addition, since the tip of the dedicated screwdriver is tightly fitted in the cross groove and the deep groove and is difficult to come off during the rotation, a remarkable effect that the screwing work becomes easy can be achieved.

[Brief description of the drawings]

FIG. 1 is a front view of an osteosynthesis screw according to an embodiment of the present invention.

FIG. 2 is a plan view of the screw.

FIG. 3 is a longitudinal sectional view of the screw.

FIG. 4 is a partial perspective view of a dedicated driver.

FIG. 5 is a partial cross-sectional view showing a state where the tip of a dedicated driver is fitted to the head of the screw.

FIG. 6 is a plan view of a conventional osteosynthesis screw.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Screw for osteosynthesis 2 Screw head 3 Shaft part 4 Screw thread 5 Cross groove 6 Deep groove part 7 Special driver 7a Cross-shaped convex part 7b Cross-shaped small protrusion

Claims (1)

[Claims] 1. A screw made of a biodegradable and absorbable polymer, wherein a cross-shaped groove is formed on the upper surface of the screw head, and a central portion of the cross-shaped groove excluding four end portions is one step deeper in the groove bottom. An osteosynthesis screw formed in a concave deep groove.