JP2021052926A - Osteosynthesis screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an osteosynthesis screw which is less likely to loosen and can fix a bone with sufficient strength until the bone regenerates. SOLUTION: The osteosynthesis screw is made of a bioabsorbable material, and the osteosynthesis screw has a head portion and a leg portion having a thread formed on the outer periphery thereof, and the top of the screw thread is formed. Flat osteosynthesis threads. [Selection diagram] Fig. 1

Description

The present invention relates to an osteosynthesis screw that is less likely to loosen and can fix the bone with sufficient strength until the bone regenerates.

Conventionally, wires, plates, screws, pins, screws, staples, clips, rods and the like made of stainless steel, ceramics and the like have been used as osteosynthesis materials for fixing bones until the fracture is healed. However, since the osteosynthesis material made of metal or ceramic is not absorbed by the human body, it remains in the body even after healing, and these osteosynthesis materials are made of SUS-316 stainless steel and are about ^{323 N / mm 2.} It is made of ceramic and has a bending strength of about 245 to 490 N / mm ^2, which is practically sufficient, but it is too rigid compared to human bones. There is a problem that bone melting, decrease in strength of new bone, delay in growth of regenerated bone, etc. may occur.

On the other hand, osteosynthesis materials made of bioabsorbable materials such as poly-L-lactic acid have been developed. For example, in Patent Document 1, a molded product of a bioabsorbable material is extruded hydrostatically at a temperature equal to or higher than the glass transition point of the polymer and lower than the melting point, and the molecules of the bioabsorbable material are oriented in the long axis direction. There is disclosed an osteosynthesis material which is a high-density molded product and has a density of 1.260 g / cm ^{3 or more measured by the floating-sink method.}

Japanese Patent No. 2619760

As an osteosynthesis material made of a bioabsorbable material, a screw-shaped material has also been developed. The screw-shaped material is used for joining bones to each other, joining living tissues such as tendons to bones, joining other bone joining materials such as plates and dumbbells to bones, and the like. However, such a screw-like material has a problem that the bone may be gradually loosened before the bone is regenerated, resulting in insufficient fixation of the bone.

In view of the above situation, it is an object of the present invention to provide an osteosynthesis screw that is less likely to loosen and can fix the bone with sufficient strength until the bone regenerates.

The present invention is an osteosynthesis screw made of a bioabsorbable material, wherein the osteosynthesis screw has a head portion and a leg portion having a thread formed on the outer periphery thereof, and the top of the screw thread is formed. It is a flat osteosynthesis screw.
The present invention will be described in detail below.

As a result of diligent studies, the present inventors have found that in an osteosynthesis screw made of a bioabsorbable material and having a head and a leg having a thread formed on the outer periphery, the screw thread has a flat top. By doing so, it was found that the occurrence of loosening until the bone was regenerated could be suppressed, and the present invention was completed.

The osteosynthesis screw of the present invention is made of a bioabsorbable material.
By constructing the osteosynthesis screw with a bioabsorbable material, the osteosynthesis screw is gradually absorbed into the body over time, so that it does not need to be removed by surgery later.

Examples of the bioabsorbable material include polyglycolide, polylactide, poly-ε-caprolactone, lactide-glycolic acid copolymer, glycolide-ε-caprolactone copolymer, lactide-ε-caprolactone copolymer, polycitrate, and the like. Polyapple acid, poly-α-cyanoacrylate, poly-β-hydroxy acid, polytrimethylene oxalate, polytetramethylene oxalate, polyorthoester, polyorthocarbonate, polyethylene carbonate, poly-γ-benzyl-L-glutamate, Synthetic polymers such as poly-γ-methyl-L-glutamate, poly-L-alanine, and polyglycol sebastic acid, polysaccharides such as starch, alginic acid, hyaluronic acid, chitin, pectinic acid and derivatives thereof, gelatin, Examples thereof include natural polymers such as proteins such as collagen, albumin and fibrin, and bioabsorbable inorganic substances such as magnesium. Of these, a lactide-glycolic acid copolymer is preferable because the decomposition rate in the body is suitable for use as a screw for osteosynthesis. In the present specification, lactide includes any of L-lactide, D-lactide, and D, L-lactide (racemic), but L-lactide is preferable. These bioabsorbable materials may be used alone or in combination of two or more.

When the bioabsorbable material is a lactide-glycolic acid copolymer, the molar ratio of lactide to glycolic acid is preferably 70:30 to 95: 5. By using a lactide-glycolic acid copolymer containing lactide and glycolic acid in such a ratio, it is possible to obtain an osteosynthesis screw having sufficient strength until bone regeneration. The molar ratio of lactide to glycolic acid in the lactide-glycolic acid copolymer is more preferably 75:25 to 90:10, and even more preferably 79:21 to 85:15.

When the bioabsorbable material is a polymer, the weight average molecular weight is preferably 140,000 or more and 320,000 or less. By setting the weight average molecular weight to 140,000 or more, the strength of the osteosynthesis screw can be further increased. By setting the weight average molecular weight to 320,000 or less, the osteosynthesis screws are absorbed into the body at an early stage after the bone is regenerated, so that the foreign body reaction in the body can be suppressed. The weight average molecular weight of the bioabsorbable material is more preferably 180,000 or more, further preferably 200,000 or more, and 30,000 or more, from the viewpoint of further increasing the strength of the osteosynthesis screw and allowing it to be absorbed into the body faster after bone regeneration. 10,000 or less is more preferable, and 280,000 or less is further preferable.
Here, the weight average molecular weight is a standard polystyrene-equivalent weight average molecular weight by GPC (Gel Permeation Chromatography). Specifically, at a column temperature of 40 ° C., chloroform is used as the eluate, the pore-polydispersed organic solvent-based column (for example, SHODEX GPC column LF-80, manufactured by Showa Denko Co., Ltd.) is used as the column, and Hitachi High Technologies America Co., Ltd. is used as the GPC device. It can be determined by polystyrene standard using a LaChrom Elute system.

The osteosynthesis screw of the present invention has a head and a leg having a thread formed on the outer circumference. Usually, the head and the legs are integrated.
The shape of the head is not particularly limited, and examples thereof include conventionally known shapes such as pans, plates, round plates, trusses, binds, and low heads. The head may have a groove on the surface for contacting an instrument such as a medical driver when using the osteosynthesis screw of the present invention. The shape of the groove for contacting the instrument is not particularly limited, and conventionally known shapes can be mentioned.

The legs have threads formed on the outer circumference. The thread is usually formed in a spiral shape along the outer circumference of the leg, and may be formed over the entire leg or only a part of the leg. The direction of the spiral of the screw thread is not particularly limited, and may be right-handed or left-handed.

The thread has a flat top.
Here, the top of the thread means the highest part in the cross-sectional view of the thread, in other words, the outermost part. Further, "flat" means that it is confirmed that the image is flat and not sharp when observed at a magnification of about 1 to 50 using an image size measuring device.
By making the top of the thread flat, the adhesion and affinity between the osteosynthesis screw and the bone can be enhanced, and the occurrence of loosening until the bone regenerates can be suppressed.

The shape and angle of the thread are not particularly limited as long as the top is flat, and may be a conventionally known shape and angle. Specific cross-sectional shapes of the thread include, for example, a trapezoid, a sawtooth shape, a rectangle, a square, and a shape in which the top of a semicircle is flat. Among them, a sawtooth shape that can obtain the maximum resistance to the axial force is preferable because the osteosynthesis screw whose material is resin is fixed to the brittle material (bone). The spacing between the threads (leads, pitches, etc.) is not particularly limited, and may be conventionally known spacings (leads, pitches, etc.).

The thread preferably has a flat valley bottom. Here, the valley bottom of the thread means the lowest part in the cross-sectional view of the thread, in other words, the innermost part. By adding the above thread to the top and making the valley bottom a flat structure, the adhesion and affinity between the osteosynthesis screw and the bone are further enhanced, and the occurrence of loosening until the bone regenerates is further suppressed. it can.

FIG. 2 shows a diagram schematically showing a specific cross-sectional shape of a screw thread in the osteosynthesis screw of the present invention. As shown in FIG. 2, specific cross-sectional shapes of the threads include, for example, a trapezoid or a sawtooth shape (FIGS. 2 (a) to (d)), a rectangle (FIG. 2 (e)), and a square (FIG. 2). (F)), a shape in which the top of the semicircle is flat (FIG. 2 (g)), and the like. In FIGS. 2 (b), (d), (e), (f) and (g), not only the top of the thread but also the bottom of the valley is flat.
The cross-sectional shape of the screw thread can be observed at a magnification of about 1 to 50 using an image size measuring device.

The maximum diameter of the leg is not particularly limited, and is usually smaller than the maximum diameter of the head. The preferable lower limit of the maximum diameter of the leg portion is 1.0 mm, and the preferable upper limit is 3.0 mm. By setting the maximum diameter of the leg portion to the above range, the osteosynthesis screw is less likely to loosen, and the bone can be fixed with sufficient strength until the bone regenerates. In addition, since bone is absorbed into the body at an early stage after bone regeneration, it is possible to suppress a foreign body reaction in the body. The more preferable lower limit of the maximum diameter of the leg portion is 1.7 mm, and the more preferable upper limit is 2.2 mm.

The length of the leg is not particularly limited, but the preferred lower limit is 2.5 mm and the preferred upper limit is 20.5 mm. By setting the length of the leg portion in the above range, the osteosynthesis screw is less likely to loosen, and the bone can be fixed with sufficient strength until the bone regenerates. In addition, since bone is absorbed into the body at an early stage after bone regeneration, it is possible to suppress a foreign body reaction in the body. The more preferable lower limit of the length of the leg portion is 3.0 mm, and the more preferable upper limit is 10.0 mm.
The maximum diameter of the head of the osteosynthesis screw, the maximum diameter of the leg, and the length of the leg can be measured using an image dimension measuring device.

FIG. 1 shows a perspective view and a cross-sectional view schematically showing the osteosynthesis screw of the present invention. As shown in FIGS. 1A and 1B, the osteosynthesis screw 1 of the present invention has a head portion 1a and a leg portion 1b having a thread formed on the outer periphery thereof. In the leg portion 1b, the top portion A and the valley bottom portion B of the thread are flat. By forming the screw thread in such a structure, the adhesion and affinity between the osteosynthesis screw 1 and the bone can be enhanced, and the occurrence of loosening until the bone is regenerated can be suppressed.

The method for producing the osteosynthesis screw of the present invention is not particularly limited, and examples thereof include a method of injection molding or cutting so that the top of the thread is flat using a bioabsorbable material.

The use of the osteosynthesis screw of the present invention is not particularly limited, and for example, bone-to-bone bonding, bone-body tissue such as tendons, and bone-bonding, plate-shaped, dumbbell-shaped, and other bone-bonding materials to bone It is preferable that it is used for such purposes. That is, the osteosynthesis screw of the present invention is preferably used for screwing or penetrating into one mass and another mass to fix both.

According to the present invention, it is possible to provide an osteosynthesis screw that is less likely to loosen and can fix the bone with sufficient strength until the bone regenerates.

It is a perspective view and cross-sectional view schematically showing the screw for osteosynthesis of this invention. It is a figure which showed typically the concrete cross-sectional shape of the thread in the thread for osteosynthesis of this invention.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
A lactide (L-form) -glycolic acid copolymer (constituent unit derived from lactide: molar ratio of the structural unit derived from glycolic acid = 82:18, weight average molecular weight: 280,000) was prepared as a raw material for the screw.
By injection molding the above raw materials and forming threads by cutting, osteosynthesis screws (maximum head diameter 3.4 mm, leg maximum diameter 2.2 mm, leg length 10.0 mm) Got When the obtained osteosynthesis screw was observed at a magnification of 5.0 using an image size measuring device, the cross-sectional shape of the thread was sawtooth, and the top and valley bottom of the thread were flat. ..

(Comparative Example 1)
An osteosynthesis screw was obtained in the same manner as in Example 1 except that the cross-sectional shape of the screw thread was triangular and the top and valley bottom of the screw thread were not flat and pointed.

<Evaluation>
The osteosynthesis screws obtained in Examples and Comparative Examples were evaluated by the following methods. The results are shown in Table 1.

(Evaluation of looseness of screws (pull-out test))
Looseness of the screws was evaluated by measuring the force required to pull out the osteosynthesis screws according to ASTM standard F2502-17.

According to the present invention, it is possible to provide an osteosynthesis screw that is less likely to loosen and can fix the bone with sufficient strength until the bone regenerates.

1 Bone joining screw 1a Head 1b Leg A Top B Valley bottom

Claims (3)

An osteosynthesis screw made of a bioabsorbable material.
The osteosynthesis screw has a head and a leg having a thread formed on the outer circumference.
An osteosynthesis screw characterized in that the top of the thread is flat. The osteosynthesis screw according to claim 1, further characterized in that the valley bottom of the thread is flat. The osteosynthesis screw according to claim 1 or 2, wherein the bioabsorbable material is a lactide-glycolic acid copolymer.

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