JPH08112291A - Screw fixing system - Google Patents

Abstract

PURPOSE: To obtain a screw fixing system with no projection outside, as well as a tap for cutting an external thread and an internal thread used for the system by making the pitch of the tap longer than the pitch of the external thread, and making the crosssectional shape in the axial direction of each root of the tap in a specified shape. CONSTITUTION: Under a condition where a root of an external thread 1 and a crest 4 of an internal thread formed by a tap are intermeshed, the crosssectional shape of a crest 4 of the internal thread 3 has a space wherein it is movable in the axial direction in the crosssectional shape of a root 2 of the external thread. In addition, the pitch (a) of the internal thread formed by the tap is made to be longer than the pitch (b) of the external screw 1. Furthermore, when the max. width wherein the crosssectional shape of a crest 4 of the internal thread 3 is movable in the axial direction in the crosssectional shape of a root 2 of the external thread 1, is made to be (d) and the difference between the pitch (a) of the crest 4 of the internal thread and the pitch (b) of the root 2 of the external thread 1 is made to be (c), substantial screwing part being larger than the number of pitches of (d/c)+1 can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for fixing a plurality of objects using screws, and particularly for orthopedic surgery and oral surgery, for the internal fixation of fractured bones and the bone fragments of osteotomy. The present invention relates to a screw fixing system used for internal fixing, a male screw used for the screw fixing system, and a tap for cutting a female screw for inserting the male screw.

[0002]

2. Description of the Related Art Conventionally, in orthopedics and oral surgery, when fixing bone fragments during bone fracture treatment and osteotomy of deformed joints, and further when fixing tools such as artificial acetabulum and artificial joints. Internal fixation devices such as bone screws, plates, wires, and intramedullary nails have been commonly used for medical instruments. Treatment methods for fractures are divided into external fixation, which is well known for cast fixation, and internal fixation, which surgically opens the fracture.
The fracture surface is fixed by the fixing tool, and it becomes possible to exercise early after the operation. The shape and usage of such internal fixation tools are described in the Manual of Internal Fixation (M. E. Muller et al., 1991 3rd edition Springer-Fairark issue) and internal fixation of small fractures (U. Heim, K. .M. Pfeiffer, 19
89, Published by Springer Fairark Tokyo Co., Ltd.
And ASTM (F564-85, F543-82, F336
-82, F453-76, etc.).

These generally metallic internal fixation devices must be removed outside the body as much as possible after the fracture has healed. This is because the metal internal fixation device is harder than bone tissue, so the stress transmitted to the bone is absorbed by the internal fixation device,
This is because the bone tissue around the internal fixation device becomes weak. Furthermore, in some cases, inflammation may be caused by metal allergy, or the bone may be detached from the bone and damage the surrounding soft tissue in the long term. The surgical procedure for removing the internal fixation device from the outside of the body is called nailing. However, since the surgical site where the tissue is complicated is reopened, the nerve bundle and the vascular system may be damaged depending on the surgical site. Therefore, the decision as to whether or not to perform nail extraction is made based on the healing disability of the internal fixation device, the patient's discomfort, and the difficulty of nail extraction.
It is always judged by the circumstances.

Of the internal fixing tools, the bone screw is usually made of metal such as stainless alloy or titanium alloy, and like a screw generally used, it has a screw head for transmitting rotational force and exerting a fixing force. , With uniform pitch threads. When pressing and fixing the two bone fragments with this screw, the bone fragment on the side through which the bone screw penetrates is fixed by pressing the bone fragment on the side into which the screw is inserted by the screw head without screwing. It Therefore, unless a recessed portion having substantially the same size as the screw head is newly formed in the bone fragment, the protrusion of the screw head outside the bone cannot be avoided. Further, since the compression force between the bone fragments is concentrated on the contact portion between the screw head and the bone fragment, the screw head inevitably becomes a larger structure than the portion into which the screw is screwed. Therefore, the protrusion of the screw head is liable to cause physical damage to the tissue around the fixing site, and it is difficult to fix the screw head internally, especially near the joint where sliding with tendons or other bones occurs. There was a case.

For the purpose of avoiding such obstacles due to the screw head, the internal fixation is such that it does not have a screw head exposed to the outside of the bone as in the prior art, but has screw threads with different pitches near the leading end and the trailing end. Screws have been invented (Japanese Patent Publication No. 61-
102). In this invention, since the pitch of the screw near the leading end is longer than that of the screw near the trailing end, the bone fragments in which the screw thread of the leading end portion is screwed in as the screw is rotated and advanced. And a compressive force can be generated between the bone fragment into which the screw thread of the trailing end portion is screwed. Therefore, the screw can be inserted also from the joint surface and can be firmly pressed and fixed. However, when the screw is rotated in the direction for retracting the nail for post-healing nail removal, a force is exerted in the direction for separating the bone on the contrary, so that there is a high possibility of re-fracture. Further, in this invention, since the screw pitch at the leading end is different from the screw pitch at the trailing end, it is difficult to insert the posterior bone screw whose tapped thread is cut into a bone fragment. Therefore, at least the screw part at the trailing end has to be structured so as to proceed while cutting the screw thread into bone, which is generally called self-tapping, so it is difficult to make it with a soft absorbent plastic material and eliminate the need for nail extraction. Is clear.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to cut a screw fixing system which does not project to the outside, a male screw used in the screw fixing system, and a female screw for inserting the male screw. To provide a tap.

In particular, a bone fixing system that does not have a portion protruding to the outside of the bone that hinders the tissue around the fixing portion and can be compressed and fixed with easy nailing, and a male screw and a male screw used for the bone fixing system are provided. To provide a tap for cutting a female screw for insertion.

Furthermore, a bone fixing system that does not require nailing,
And a tap for cutting an external thread used for the bone fixing system and an internal thread for inserting the external thread.

[0009]

Means for Solving the Problems The present invention for solving the above problems is as follows. (1) In a screw fixing system including a male screw having a uniform pitch and a tap having a uniform pitch for cutting a female screw into an object into which the male screw is inserted, a pitch of the tap is equal to that of the male screw. Longer than the pitch, and the axial cross-sectional shape of each valley of the tap is a shape that can be moved in the axial direction in the axial cross-sectional shape of each valley of the male screw, and further, each of the taps. The axial cross-sectional shape of the valley is the maximum width that can be moved in the axial direction in the axial cross-sectional shape of each valley of the male screw, and the difference between the tap pitch and the male screw pitch is c. Then, the number of pitches of the value obtained by adding 1 to the value obtained by dividing d by c (d
/ C + 1) with a substantially greater number of pitches, a screw fixing system.

(2) In a male screw having a uniform pitch to be inserted into an object having a threaded hole formed in a female screw,
The pitch of the external thread is shorter than the pitch of the internal thread, and the axial cross-sectional shape of each valley is a shape in which the crests of the internal thread can move in the axial direction, and The maximum width by which the crests of the internal threads can move in the axial direction in the axial sectional shape of the valleys of the external threads is d, and the difference between the pitch of the internal threads and the pitch of the external threads is c. , Then the value obtained by dividing d by 1 is 1.
A male screw having a pitch number substantially smaller than the pitch number (d / c + 1) of the value obtained by adding.

(3) The male screw according to (2) above, which is made of a bioabsorbable material. (4) In a tap having a uniform pitch for cutting a female screw into an object into which a male screw is inserted, the pitch of the tap is longer than the pitch of the male screw, and an axial cross section of each valley of the tap The shape is a shape that can be moved in the axial direction in the axial cross-sectional shape of each valley of the male screw, and further, the axial cross-sectional shape of each valley of the tap is of the valley of each male screw. When the maximum width that can be moved in the axial direction in the axial sectional shape is d and the difference between the tap pitch and the male screw pitch is c, d is c
A tap for cutting an internal thread, which has a pitch number substantially larger than a pitch number (d / c + 1) obtained by adding 1 to the value divided by.

(5) The screw fixing system according to (1), wherein the body into which the male screw is inserted is a living bone. (6) The male screw according to the above (2), which is inserted into a living bone. (7) The tap according to (4) above, wherein the body for cutting the internal thread is a living bone.

The present invention will be described with reference to FIG. 1, which is a schematic diagram. FIG. 1 is a partial cross section of a male screw 1 having a uniform pitch and a female screw 2 cut by a tap. The present invention
The following three basic settings were made as the shapes of the tap and the male screw.

(A) First, with the valley 2 of the male screw 1 and the ridge 4 of the female screw 3 formed by the taps engaged,
One thread 4 of the female screw 3 formed on the object by the tap
The cross-sectional shape of 1 is a shape having a space capable of moving in the axial direction in the cross-sectional shape of one valley 2 of the male screw 1. (B) Next, the pitch of the tap and the male screw 1 is set so that the pitch a of the female screw 3 formed by the tap becomes longer than the pitch b of the male screw 1.

(C) Further, the cross-sectional shape of one crest 4 of the female screw 3 formed by the tap is the maximum width that can be axially moved in the cross-sectional shape of one trough 2 of the male screw 1.
And c is the difference between the pitch a of the crests 4 of the female screw 3 formed by the tap and the pitch b of the male screw 1, d is c
The length of the tap and the male screw 1 is such that a substantial threaded portion can be formed in the component more than the number of pitches obtained by adding 1 to the value divided by (d / c + 1).

Next, the present invention will be described with reference to FIGS. 2 and 3 are partial cross-sectional schematic views showing the relationship between the pitch of the male screw and the pitch of the female screw cut by the tap according to the screw fixing system of the present invention in which d / c is set to 9 in FIG. It is a figure.

In FIG. 2, the male screw 11 is attached to the object 21 and the object 31.
It shows a state in which the internal thread cut in a straight line to the inside is screwed into the internal thread without applying any constant strain.
The thread 12 at the leading end of No. 1 contacts the thread 34 of the female thread formed on the object 31 on the trailing end side of the thread 12, and does not contact the thread 33 of the female thread formed further in the back. Further, the thread 13 of the male screw 11 at the 10th pitch counted from the thread 34 contacts the thread 22 formed on the object 21 on the side surface.

This is because the distance between the trailing end side of the thread 12 at the leading end of the male screw 11 and the leading end side of the thread 13 of the male screw 11 at the 10th pitch counted from the thread 12 is 9
b + f, and the distance between the leading end side of the female thread 34 and the trailing end side of the female thread 22 at the ninth pitch counted from the thread 34 is 9a + e. Since the setting d / c is 9, d / c = (f-
This is because e) / (ab) = 9, that is, 9a + e = 9b + f.

FIG. 3 shows a state in which the male screw is screwed in several pitches. The thread 12 at the leading end of the male screw 11 is
The pitch of the female screw, which is in contact with the female screw thread 32 formed on the object 31 on the trailing end side of the screw thread 12 and is linearly communicated with the object 21 and the object 31, is the pitch of the male screw 11. Since it is longer, the distance between the side surface on the leading end side of the screw thread 14 at the trailing end of the screw thread 13 and the side surface on the trailing end side of the screw thread 23 is just the female screw formed on the object 21 and the object 31. The length c (c shown in FIG. 1), which is the difference between the pitch of the crest and the pitch of the male screw 11, must overlap. This overlap has a width of nc at the screw thread at the trailing end of n pitches from the screw thread 13. The male screw 11 is extended so as to eliminate this overlap, while the object 21 and the object 31 are crimped as a reaction force thereof.

Generally speaking, the male screw 11 is deeper by n pitches than the pitch number h defined by d / c + 1 = h.
When the object to be crimped and fixed is hard and not distorted, the extension of the male screw 11 is nd / (bh +
f + na), and this value increases as n increases. That is, the more the male screw 11 is screwed in,
A pulling force parallel to the axis is applied to the male screw 11, and as a reaction force thereof, the objects can be strongly pressed and fixed to each other. Needless to say, this effect has nothing to do with the hardness of the object to be crimped and fixed or the male screw 11. This indicates that the crimping force can be controlled by the length of the male screw 11 instead of controlling the crimping force by the torque for rotating the screw as in the conventional case.

In the screw fixing system of the present invention, as described above, the pressing force can be controlled by the pitch of the taps, the pitch of the male threads, and the mountain shape of both. However, making many types of taps and screws can cope with various situations and at the same time easily cause confusion to the operator. Preferably, the shape of the tap is fixed, and the fixing force is set by the pitch and mountain shape of the male screw and the length of the male screw, which is possible in the present invention. That is, when fixing a relatively small object or when it is impossible to take a deep screw hole in the object, the above d / c + 1 = (fe) / (ab) + 1 =
By using a male screw having a small pitch number h defined by h, the male screw can be fixed with a short male screw. Further, when the bone is used to fix a bone when a fracture occurs, a male screw having a large pitch number h may be used when the fracture surface is deep from the opening of the screw hole.

Further, the thread shape of the male screw and tap of the present invention, that is, the cross-sectional shape of each thread is not limited at all, and in addition to the shape shown in the drawing, it may be a trapezoid or a triangle. Or even if there is a curved line. That is, it is sufficient that one mountain shape of the female screw in one valley shape of the male screw has a space capable of relatively moving in the axial direction of the screw.

For example, when used for a living bone, if the portion of the male screw which transmits the compressive force to the object is inclined in the direction of expanding the bone tissue, the bone screw is deformed by compression or the screw is deformed by pulling. It is easy to not only increase the contact area of bone tissue, but also suppress shear fracture in the direction parallel to the bone tissue of the fixed part and the axis of the screw thread, and suppress the loosening of the screw due to the increase in rotation resistance. Expected.

When the screw fixing system of the present invention is used for living bone in particular, even if the trailing end of the bone screw is not exposed to the outer surface of the bone,
Since the compression force between the bone fragments can be exerted between the advancing end and the trailing end of the bone screw, physical obstacles due to the screw head around the fixing part can be avoided, and a fixing approach from the joint sliding part such as cartilage surface is also possible Is. Further, since the pitch of the bone screws is uniform, the force for separating the fractured surface does not work during nailing, and the risk of re-fracture is low.

Further, if the male screw of the present invention is made of a plastic material that can be decomposed and absorbed in the body, it becomes an unprecedented absorbable bone fixing tool capable of compression fixing without a screw head protruding to the outside. That is, Japanese Patent Publication No. Sho 61-10
A compression-fixable screw without a metallic screw head, as reported in No. 2, has at least one screw part
In general, it is difficult to fabricate a soft absorbent plastic material because it has a structure called self-tapping that advances while cutting a screw thread into bone.

In the screw fixing system of the present invention, since the tap pitch and the bone screw pitch are both constant,
Bone screw threads do not need to be hard enough to tap into the bone. Therefore, the bone screw of the present invention made of a disassemblable and absorbable plastic can be compressed and fixed without protruding to the outside, and nails can be eliminated.

Further, when the screw fixing system of the present invention is used for a living bone in particular, even when the posterior end of the male screw is exposed on the outer surface of the bone, basically the advancing end of the screw and the bone near the outer surface of the bone It is possible to exert a compression force in the vicinity of one side. That is, when the posterior end of the bone screw is left over due to the surgical procedure, or when the screw head for connecting the screwdriver or wrench for rotating the bone screw is exposed, the portion exposed from the bone may cause compression fixation. As it is, you can separate it as an unnecessary part with a cutting tool such as nippers.

In the screw fixing system of the present invention, the male screw and the tap for cutting the female screw into the object into which the male screw is inserted need to give a rotational force, and a tool such as a wrench or a screwdriver for that purpose. It is clear that it is preferable to have a portion that joins The part to which the tool is joined may have any shape as long as it has a structure capable of giving a necessary rotational force. For example, a hexagonal shape that is conventionally generally formed at the end of a screw or tap. Alternatively, it may be a quadrangular convex portion or a concave portion, or a minus or plus driver fitting portion.

In the screw fixing system of the present invention, when a female screw is formed on an object with a tap, a desired hole is opened with a small diameter drill, and the tap is inserted into the hole while rotating.
Make a pile of female threads. The crest shape of the tap forms at least part of a thread trough formed on the object by the tap, and the trough shape of the tap is substantially the same as the thread crest formed on the object by the tap. Therefore, if the tap of the present invention is set from a general tap shape, a male thread having a thread shape similar to the shape and pitch of the thread troughs formed in the object piece can be used as a sharp part in the axial direction. It may be one prepared. Of course, it is obvious that it is not necessary to stick to the existing tap shape as long as the female screw as described above can be manufactured on the object. For example, it is possible to form a wood screw shape without a scratched portion.

The present invention is preferably made of a plastic capable of decomposing and absorbing a male screw (bone screw) in a living body, particularly when it is used for a living bone in orthopedic surgery or oral surgery. The plastic that is decomposed and absorbed in the present invention is
Various existing resins can be used as long as they are hard materials. For example, polylactic acid, polydioxanone, degradable and absorbable polyesters such as polyhydroxybutyric acid, polysaccharides such as chitin and chitosan, and those containing bone-replaceable phosphates such as hydroxyapatite in these resins Available.

The type of resin used can be changed depending on the period during which stress is required. For example, polylactic acid and polyhydroxybutyric acid are expected to be capable of retaining stress in the body for 6 months to 1 year, depending on the shape and molecular weight of each polymer before transplantation. In addition, polydioxanone may be for 1 to 3 months, and polyglycolic acid and polyglycolic acid-polylactic acid copolymer used in absorbable sutures may be around 1 week. These differ depending on the fixing site, and should be appropriately set depending on the period during which the stress of the internal fixing tool is required to be retained and the time for performing the nail removal operation when using a metal screw.

[0032]

The present invention will be described in more detail with reference to the following examples. The male screw and tap used in the screw fixing system of the present invention can be produced by the existing molding method without any problem.
Also, the sizes of the male screw and the tap can be adjusted according to the size of the object to be fixed.

(Example 1) A male rod and a tap having three types of thread shapes shown in Table 1 were cut and produced from a SUS round bar.

[0034]

[Table 1]

In Example 1a, the cross-sectional shape of the screw thread is trapezoidal for both the tap and the male screw, the angle of the slope of the male screw thread and the angle of the slope of the tap screw thread are set to be the same, and the contact between the female screw and the male screw thread is made. Is a surface. In Example 1b, the cross-sectional shape of the thread of the male screw is a bell shape having a curved surface,
By making the cross section of the tap ridges trapezoidal, the contact between the ridges of the female and male threads is made linear.

In Example 1c, the thread heights of the screws are set lower and the pitch is set narrower than in Examples 1a and 1b, so that the contact between the threads of the male screw and the female screw becomes a surface. In addition, for each tap, after cutting the same male thread of the mountain shape, a part of the thread is cut in the axial direction, and the joint part of the tool for rotating is made at the trailing end, Shaped.
In addition, each male screw had a linear concave portion cut into the end face at the trailing end that could be fitted with a flat head screwdriver.

The following tests were carried out using the obtained male screws and taps having three thread shapes. Drill a hole with a diameter of 2.7 mm so as to penetrate the two plates in the sample sandwiched by a vise with a thickness of 2 cm made of PVC so as not to shift.
After cutting the female screw with various taps, the corresponding male screw was screwed in with a screwdriver. As a result, each male screw
The rotational resistance increased within 1 pitch before and after the specified pitch that the compression force could achieve, and the two plates could be firmly joined even after the plates were removed from the vise.

(Example 2) From a polylactic acid round bar, as shown in FIG.
A male screw shown in the external view of FIG. In this embodiment,
Since it was made of plastic that is softer than metal, the fitting part of the driver penetrated to the leading end. Further, a tap for cutting the female screw into which the male screw is inserted was also created. The cross-sectional shapes of the threads of the male screw and the tap are the same as in Example 1a of Table 1, but the height of the threads of the tap and the male screw is 0.6 mm, the diameter of the mountain is 4.5 mm, and the total length of the male screw is 4 mm.
It was set to 0 mm.

A screwing experiment was conducted using the above male screw and tap. In the screw-in experiment, cancellous bone near the trochanter of the humerus was cut approximately perpendicular to the bone axis, and osteotomy was performed with osteopathic forceps. 3.
A 4 mm drill was used to make a pilot hole, and a female screw was cut with a tap. After that, the male screw was screwed into the female screw using a plate-shaped driver that can be inserted into the screw beyond the leading end of the male screw. After screwing in several times from the specified pitch to achieve compression force, the driver was removed and the part exposed from the bone was cut off with a nipper.
Even after removing the osteopathic forceps, the bone fragments could be sufficiently fixed.

[0040]

As described above, according to the screw fixing system of the present invention, objects are pressed and fixed to each other by the threads of the male screw and the female screw, so that the male screw can be fixed without providing a screw head. Therefore, when the present invention is used for treatment of a bone fracture of a living body, it is not necessary to provide a screw head protruding outside the bone on the screw by making the male screw from a plastic that is decomposed and absorbed in the living body, and After healing, it is decomposed and absorbed in the body, so there is no need to remove nails.

[Brief description of drawings]

FIG. 1 is a schematic partial cross-sectional view for explaining the relationship between the male and female threads of a screw fixing system of the present invention and the axial widths of crests and troughs of a female thread cut by a tap.

FIG. 2 is a schematic partial cross-sectional view illustrating the relationship between the pitch of the male screw and the female screw when the screw is fixed using the screw fixing system of the present invention, and shows the initial state in which the male screw is inserted. .

FIG. 3 is a schematic partial cross-sectional view illustrating the relationship between the pitch of the male screw and the female screw when fixing the screw using the screw fixing system of the present invention, showing a state where the male screw is inserted all the way to the back. .

FIG. 4 is an external view showing an example of an embodiment of a male screw of the present invention.

[Explanation of symbols]

1, 11 ... Male screw, 2, 12, 13, 14 ... Male screw thread, 3 ... Female screw formed by tap, 21, 31 ... Object, 4, 22, 23 , 24, 3
2, 33, 34 ... Threads of female screw formed by tap, a ... Pitch length of female screw, b ... Pitch length of male screw, e ... Substantially of female screw A wide mountain, f ...
・ Substantial valley width of male screw

Claims (4)

[Claims] 1. A screw fixing system comprising a male screw having a uniform pitch and a tap having a uniform pitch for cutting a female screw into an object into which the male screw is inserted, wherein the pitch of the tap is the male screw. Longer than the pitch of the screw, and the axial cross-sectional shape of each valley of the tap is a shape that can be moved in the axial direction in the axial cross-sectional shape of each valley of the male screw, and further, The axial cross-sectional shape of each trough is the maximum width that can be moved in the axial direction in the axial cross-sectional shape of each trough of the male screw, and the difference between the pitch of the tap and the pitch of the male screw is c. , The pitch number of the value obtained by adding 1 to the value obtained by dividing d by c (d /
A screw fastening system characterized in that it has a substantially higher number of pitches than c + 1). 2. A male screw having a uniform pitch to be inserted into an object having a threaded hole formed in the female screw, wherein the pitch of the male screw is shorter than the pitch of the female screw, and the axis of each trough. The directional cross-sectional shape is a shape in which the crest of the female thread can move in the axial direction in the cross-sectional shape, and the axial cross-sectional shape of each valley of the male thread is the crest of the female thread in the cross-sectional shape. Is the maximum width that can move in the axial direction, and the difference between the pitch of the female screw and the pitch of the male screw is c.
The male screw is characterized in that the number of pitches is substantially smaller than the number of pitches (d / c + 1) obtained by adding 1 to the value obtained by dividing d by c. 3. The male screw according to claim 2, which is made of a bioabsorbable material. 4. A tap having a uniform pitch for cutting an internal thread into an object into which an external thread is inserted, wherein the pitch of the tap is longer than the pitch of the external thread, and the axis of the valley of each of the taps. The directional cross-sectional shape is a shape that can be moved in the axial direction in the axial cross-sectional shape of each valley of the male screw, and further, the axial cross-sectional shape of each valley of the tap is each of the male screw. When the maximum width that can be moved in the axial direction in the axial cross section of the valley is d and the difference between the pitch of the tap and the pitch of the male screw is c, 1 is added to the value obtained by dividing d by c. A tap for cutting an internal thread, characterized in that it has a pitch number substantially greater than the value pitch number (d / c + 1).