JP3958448B2 - Osteosynthesis screw - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biodegradable and absorbable osteosynthesis screw that can be firmly screwed into a living bone without destroying the cross groove of the screw head.
[0002]
[Prior art]
In surgical fields such as orthopedic surgery, plastic surgery, thoracic surgery, oral surgery, etc., metal or ceramic screws are used as osteosynthesis devices for the purpose of reducing or fixing fractures. However, since these screws have high elastic modulus, there are problems such as lowering the strength of surrounding bones, and in particular, metal screws may cause harm to the living body due to elution of metal ions, so that fractures may occur. When healed, there was a problem that he had to re-operate to remove it from the body as soon as possible.
[0003]
Accordingly, the present applicant has developed an osteosynthesis screw made of polylactic acid that is biodegradable and absorbable. This screw has the same initial strength as a living bone, and after the fracture has healed, it is hydrolyzed and absorbed in the living body, so there is no need for reoperation. The screw was excellent in that it had binding properties with living bones.
[0004]
[Problems to be solved by the invention]
However, the above biodegradable and absorbable screw is formed when a screwdriver is inserted into a cross groove formed in the screw head and screwed into a living bone while applying a large rotational force, or formed on the screw head. If you insert a hexagon wrench into a hexagonal hole and screw it into a living bone while applying a large rotational force, the cross groove may be missing or the screw head may crack, making it impossible to screw the screw into the living bone to the end. It was.
[0005]
As a biodegradable and absorptive screw for coping with such a problem, a cross hole 102 is formed in the screw head 101 as shown in FIG. 5, and the four ends 103 of the cross hole or adjacent ends are formed. There has been proposed a screw provided with "R" on the side surface portion 104 connecting the two (Japanese Patent Laid-Open No. 9-253089). This screw is intended to prevent the rotational force from concentrating on the corners of the cross hole by providing “R”, thereby preventing the cross hole 102 and the screw head 101 from being destroyed.
[0006]
However, in this screw, the rotational force of the driver acts on the side surface portion of the cross hole 102 where the “R” is not provided, and is effectively transmitted, but the portion provided with the “R” is particularly large. Since the rotational force does not act vertically on the side surface portion 104 provided with “R”, the effective area for transmitting the rotational force is greatly reduced. As a result, the side surface portion where “R” is not provided. There was a problem that the rotational force was concentrated and the portion was easily chipped.
[0007]
The present invention has been made in view of the above-described problems, and the object of the present invention is to have a large effective area for transmitting the rotational force of the driver, and transmit the torque almost uniformly without waste, and the cross groove and An object of the present invention is to provide a biodegradable and resorbable osteosynthesis screw that can be firmly screwed into a living bone without causing destruction of the screw head.
[0008]
In order to achieve the above object, an osteosynthesis screw according to the present invention is a screw made of a biodegradable and absorbable polymer , and has a flat cross on the top surface of the screw head and the groove bottom surface extending to the outer peripheral end of the screw head. A groove is formed, and a deep groove portion having a flat bottom surface of the cross shape in which the groove bottom surface is recessed one step deeply in a central portion excluding the four ends of the cross groove is 1/2 to a length of the cross groove. 3/4 of the formed length Rutotomoni, is characterized in that the end face of the square the deep groove portion is formed vertically.
[0009]
This osteosynthesis screw is screwed into a living bone or the like using a dedicated driver as follows. That is, a special screwdriver is provided with a cross-shaped convex part fitted to the cross groove of the screw head at the tip of the driver and a small cross-shaped protrusion fitted to the deep groove part at the tip of the cross-shaped convex part. Using this special screwdriver, screw the osteosynthesis screw into a living bone or the like while fitting and rotating the cruciform protrusion and cruciform small protrusion of the screwdriver into the cruciform groove and deep groove of the screw head.
[0010]
When the dedicated screwdriver is rotated as described above, the cross groove and deep groove on one side (one side in the rotation direction) of the screw head makes the rotational force of the cross-shaped convex part and the cross-shaped small protrusion at the tip of the driver substantially vertical. Since the receiving and rotational force is effectively transmitted, compared to the conventional screw in which only the cross groove is formed in the screw head and the screw in which the cross hole 102 with “R” is formed in the screw head, The effective area for transmitting the rotational force is increased, and the rotational force is not concentrated on the entire side surface of the cruciform groove and deep groove portion without being concentrated. It is possible to screw in securely.
[0011]
Also, as described above, if the cruciform convex part and the cruciform small protrusion at the tip of the dedicated driver are fitted into the cruciform groove and deep groove part of the screw head, the dedicated driver is firmly fitted and is difficult to come off during rotation. Therefore, the screwing operation becomes easy.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
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. FIG. 4 is a partial cross-sectional view showing a position where a tip of a dedicated driver is fitted to the head of the screw.
[0014]
This osteosynthesis screw 1 is a screw made of a biodegradable absorbable polymer, and has a screw head 2 and a shaft portion 3, and a screw thread 4 is formed over the entire length of the shaft portion 3. The thread 4 may be formed from the middle of the shaft portion 3 to the tip.
[0015]
As shown in FIGS. 2 and 3, the upper surface of the screw head 2 is formed with a flat cross groove 5 having a groove bottom surface extending to the outer peripheral end of the screw head 2, and the four end portions of the cross groove 5 are formed. central portion excluding the 2, as is apparent from FIG. 3, Rutotomoni formed on the bottom surface is flat deep groove portion 6 of the cross that one step deeper recessed groove bottom, the end face of the square the deep groove portion 6 Are formed vertically . The length of the deep groove 6 is preferably set to about ½ to ¾ of the length of the cross groove 5, and the depth of the deep groove 6 is the size (height) of the screw head 2. It is desirable to set to about 0.5 to 4 mm depending on. If the length of the deep groove portion 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 portion 6 that receives the rotational force of the dedicated driver substantially perpendicularly becomes small. The merit of 6 is hardly exhibited. On the other hand, if the length of the deep groove 6 is longer than 3/4 and the depth is deeper than 4 mm, the thickness from the end of the deep groove 6 to the outer peripheral end of the screw head 2 is reduced. The screw head 2 may be destroyed when the screw 1 is screwed.
[0016]
As shown in FIG. 4, the dedicated screwdriver 7 used for the osteosynthesis screw 1 is provided with a cruciform convex portion 7a and a cruciform small protrusion 7b at the tip of the driver. As shown in FIG. 5, the cruciform convex portion 7a. Is fitted into the cross groove 5 of the screw head 2 and the screw 1 is screwed into the living bone while the small cross-shaped projection 7b is fitted into the deep groove portion 6 and rotated.
[0017]
When the cruciform protrusion 7a and the cruciform small protrusion 7b of the dedicated driver 7 are fitted into the cruciform groove 5 and the deep groove portion 6 as described above, the tip of the dedicated driver 7 is firmly fitted and is difficult to come off during rotation. Therefore, the screwing operation becomes easy. In addition, one side surface (one side surface in the rotational 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 projection 7b at the tip of the driver substantially vertically, and the rotational force is effectively transmitted. Is done. Thus, in the screw 1 of the present invention, since one side surface of the cross groove 5 and 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. Compared with the screw having the cross hole 102 with “R” on the screw head, the effective area for transmitting the rotational force is increased, and the cross groove 5 and the deep groove portion 6 do not concentrate the rotational force. Therefore, it can be firmly screwed into the living bone without causing the destruction of the cross groove 5 and the screw head 2.
[0018]
The biodegradable absorbable polymer that is the material of the screw 1 is preferably a polylactic acid or lactic acid-glycolic acid copolymer having an initial viscosity average molecular weight of about 150,000 to 600,000, preferably about 200,000 to 550,000. In particular, those containing about 10 to 60% by weight of bioceramic powder such as hydroxyapatite are more preferably used.
[0019]
When the osteosynthesis screw 1 made of biodegradable absorbable polymer containing bioceramic powder is screwed into a fractured part in the living body, the bioceramics powder becomes living body with hydrolysis from the surface of the screw 1. Since calcium phosphate and bone tissue are deposited or conductively formed on the surface layer of the screw 1, there is an advantage that the screw 1 is combined with the living bone within a relatively short period of time and does not loosen.
[0020]
The screw for osteosynthesis according to the present invention is obtained by melt-molding the above-mentioned biodegradable absorbable polymer and cutting the molded body, or by further uniaxially stretching the molded body, or cutting it. Is manufactured by further forging or compression-molding the molded body and then cutting. In particular, when a molded body of biodegradable absorbable polymer is cold forged or compression-molded before cutting, the polymer molecular chains, their aggregate domains, crystals, etc. are oriented along a number of reference axes with different axial directions. Since it becomes a compressed multiaxially oriented body or a cluster of many clusters having different orientation reference axes, it is dense and has little strength anisotropy, and can be applied to external forces and twisting forces in various directions. On the other hand, there is an advantage that an osteosynthesis screw having a large strength can be manufactured.
[0021]
【The invention's effect】
As is clear from the above description, the osteosynthesis screw of the present invention has an area effective for transmitting the rotational force of the dedicated driver by the amount of the deep groove formed in the center portion excluding the four ends of the cross groove. It increases and the rotation force is not concentrated, and it is transmitted almost uniformly and without waste to the entire side surface of the cross groove and deep groove part, so that it can be firmly screwed into the living bone without breaking the cross groove and screw head, Since the tip of the dedicated screwdriver is firmly fitted in the cross groove and the deep groove and is difficult to come off during the rotation, the screwdriver can be easily screwed.
[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 a 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 Bone screw 2 Screw head 3 Shaft part 4 Screw thread 5 Cross groove 6 Deep groove part 7 Dedicated driver 7a Cross-shaped convex part 7b Cross-shaped small protrusion

Claims (1)

A screw made of a biodegradable absorbable polymer , wherein a flat cross groove on the bottom surface of the groove extending to the outer peripheral end of the screw head is formed on the upper surface of the screw head , excluding the four ends of the cross groove and the central portion, the deep groove portion flat one step deeper recessed the cruciform bottom groove bottom is formed in a length of 1 / 2-3 / 4 of the length of the cross groove Rutotomoni, the deep grooves An osteosynthesis screw, characterized in that the four end faces of the are vertically formed .

Images