JPH08299362A - Bone screw assembly body - Google Patents

Abstract

PURPOSE: To prevent dislocation of a junction face due to winding of a bone piece or the like, by making a bone screw body composed of a bone screw which has a consecutive notch part along an axial direction and a screw part in an outer periphery except for the notch part and of a pin body which is inserted into the notch part. CONSTITUTION: A bone screw 2 is rotated toward a specified direction and its screw part 4 is screwed into one bone piece to be tightened by an ordinary method when two bone pieces are fixed by a bone screw composition body 1A. A pin member 7 is inserted along a notch part 6 from a head part 5 side after tightening the screw with adequate strength. An edge part 73 is projected from the screw head 41 and outer circumference of the head part 5 in this condition, thereby a stopper function against the bone piece works by means of this projecting part. Therefore, the bone piece is prevented from winding at the center of the bone screw 2. Furthermore, the bone screw 2 is taken out by making the screw part 4 untightening after taking out the pin member 7 when the constituting materials of the bone screw 2 and the pin member 7 are made of metal.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a bone screw assembly,
Especially in the fields of orthopedics and oral surgery, bone fracture treatment,
The present invention relates to a bone screw assembly used for fixing two bone fragments, fixing a bone fixing material, or fixing a tendon or a ligament, which is performed by bone transplantation, osteotomy, or the like.

[0002]

2. Description of the Related Art Conventionally, a bone screw is used for fixing two bone fragments, fixing a bone fixing material such as a bone plate or an intramedullary nail, and further,
It is used as an instrument for fixing tendons and ligaments.

The fixation of the two bone fragments is performed during fracture treatment, bone transplantation, osteotomy and the like. The most important of these therapies is to secure the bone fragments to the host bone until the bone union occurs.

The principle of fixation by the bone screw is that the tensile force generated between the screw part screwed into the bone fragment on the leading end side and the head of the screw engaging with the bone fragment on the trailing end side is the bone fragment. It acts as a compressive force between and fixes the two bone fragments. Specifically, first, the joint surface of the two bone pieces comes into close contact with each other due to the compressive force, and a frictional force corresponding to the product of the compressive force and the friction coefficient of the joint surface is generated at the closely joined joint surface. This frictional force serves as a force for preventing displacement of the joint surface due to rotation of the bone fragments. That is, the compressive force has a function of bringing the joint surfaces into close contact with each other and a function of generating a frictional force on the joint surfaces to prevent the joint surfaces from being displaced. In order to obtain a sufficient frictional force to prevent the displacement of the joint surfaces, a larger compressive force is required than the compressive force for bringing the joint surfaces into close contact. Therefore, when performing bone fixation with bone screws,
In order to prevent displacement of the joint surface due to rotation of the bone fragments, it is necessary to generate as large a compressive force as possible to secure a large frictional force.

However, in some cases, a sufficient compression force may not be obtained. For example, if there is not enough bone mass or strength to support the screw as in osteoporosis, the screw cannot be tightened strongly and sufficient compression force cannot be obtained. In addition, even if a sufficient compression force is obtained in the initial stage, if excessive stress concentration occurs on the bone surface that engages with the head of the screw, bone resorption occurs after a while after the operation and the compression force becomes weak. It may happen.

As described above, when a sufficient compression force cannot be obtained, the frictional force of the joint surface becomes insufficient, the joint surface is displaced, and bone union failure occurs. Moreover, when fixing a bone fixing material, a tendon, or a ligament using a bone screw, generally, a full screw having a thread formed on the entire shaft except the screw head is used. Of these, when fixing the bone fixing material, all screws are screwed and fixed in the screw holes formed in accordance with the fixing holes of the bone fixing material. Moreover, when fixing a tendon and a ligament, the tip of a tendon and a ligament is inserted in the screw hole formed in the place to fix, and all screws are screwed in and fixed from there. In either case, unlike fixing the two bone pieces, the entire screw thread is used by engaging with the bone.

A problem with such use is loosening of the bone screws. When looseness occurs, sufficient fixation cannot be obtained,
Failure of fusion occurs. Further, when the degree of slackness is large, the bone screw may come off and stray.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a bone screw assembly capable of preventing displacement of a joint surface due to rotation of bone fragments when fixing two bone fragments. Also, another object of the invention is, for example, a bone anchoring material or a tendon,
(EN) A bone screw assembly capable of preventing loosening of a bone screw when fixing a ligament.

[0009]

These objects are achieved by the present invention described in (1) to (5) below.

(1) The bone screw main body is provided with at least one notch portion which is continuous along the axial direction and a screw portion on the outer periphery excluding the notch portion, and is inserted into the bone screw and the notch portion. Bone screw assembly comprising:

(2) The pin member has a protrusion, and when at least a part of the pin member is inserted into the notch, the protrusion is in the radial direction of the bone screw, the bone screw main body. The bone screw assembly according to (1) above, which has a shape projecting outward from the screw thread.

(3) The bone screw assembly according to (1), wherein the bone screw has a head portion at a base end portion thereof, and the notch portion is also formed in the head portion.

(4) The pin member has a protrusion, and when at least a part of the pin member is inserted into the notch, the protrusion is in the radial direction of the bone screw, the bone screw main body. The bone screw assembly according to (3) above, which has a shape projecting outward from the outer periphery of the head.

(5) The bone screw and / or the pin member is made of a bioabsorbable material.
The bone screw assembly according to any one of (4) to (4).

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The bone screw assembly of the present invention will be described below in detail with reference to the preferred embodiments shown in the accompanying drawings.

1A and 1B are views showing a first embodiment of a bone screw assembly of the present invention, wherein FIG. 1A is a top view and FIG. 1B is a front view. As shown in FIG. 1, a bone screw assembly 1A of the present invention includes a bone screw 2 and a pin member (peg) 7. Hereinafter, each of these components will be sequentially described.

The bone screw 2 is composed of a bone screw body 3 and a head 5 formed at the base end portion (upper side in FIG. 1) of the bone screw body 3. On the outer periphery of the bone screw body 3, a screw portion 4 in which a spiral screw is engraved in a portion excluding a notch portion 6 described later.
Are formed. In addition, the tip of the bone screw body 3 (see FIG.
The outer diameter of the (middle and lower side) decreases toward the tip and becomes thinner.

The dimensions of the screw portion 4 are not particularly limited,
Usually, it is preferable that the thread diameter of the screw thread 41 is about 1.5 to 6.5 mm and the root diameter of the screw root 42 is about 1.0 to 4.5 mm.

The head 5 has a diameter larger than that of the bone screw body 3, and its upper surface has a rounded shape. Head 5
On the upper surface of the, a letter-shaped groove 51 for rotating the bone screw 2 is formed.

Further, the bone screw 2 has a notch 6 which is continuous from the head 5 to the tip of the bone screw main body 3 along the axial direction thereof.
Are formed. As shown in FIG. 1A, the notch portion 6 is located substantially at the center of the bone screw 2 and has a hole portion 61 having a circular cross section and a hole portion 61 communicating with the hole portion 61 and the bone screw 2.
And a slit portion 62 opened to the outer periphery of the.
The slit portion 62 extends substantially in the radial direction of the bone screw 2, and its width is smaller than the inner diameter of the hole portion 61. The total length of such a bone screw 2 is not particularly limited, but is 10 to 120.
It is preferably about mm.

On the other hand, the pin member 7 is a member to be inserted into the cutout portion 6, and has a shaft portion 71 having a shape corresponding to the hole portion 61 of the cutout portion 6 and a slit portion 62 of the cutout portion 6. The blade portion 72 to be inserted into the blade is integrally formed. The outer diameter of the shaft portion 71 is set to a value substantially equal to or slightly smaller than the inner diameter of the hole portion 61.
The thickness of 2 is substantially equal to or slightly smaller than the width of the slit portion 62.

An edge portion (projection) 73 in which the thickness of the blade portion 72 is gradually reduced is formed at the end portion of the blade portion 72 opposite to the shaft portion 71 along the longitudinal direction of the pin member 7. In the present invention, the position of the edge portion 73 (projection length)
It is characterized in that it will be described below.

FIG. 2 is a sectional view taken along the line II-II in the assembled state of the bone screw assembly shown in FIG. As shown in the figure, when the pin member 7 is inserted into the cutout portion 6 of the bone screw 2, the edge portion 73 causes the screw thread 41 of the screw portion 4 and the outer periphery of the head portion 5 in the radial direction of the bone screw 2. Project more outward than. The protruding portion functions as a stopper for the bone fragment and prevents the bone fragment from rotating.

The protruding length of the edge portion 73 from the screw thread 41 is not particularly limited, but is preferably about 0.5 to 3 times the screw thread height which is the difference between the screw thread radius and the screw root radius. If the protruding length is too short, if the turning force of the bone fragment described later is large, the effect of preventing it will be insufficient,
Further, if the protruding length is too long, it becomes difficult to insert the pin member 7.

The present invention is not limited to the case where the entire area of the edge portion 73 in the longitudinal direction satisfies the above condition, but a part of the edge portion 73 may satisfy the above condition. The total length of the pin member 7 is equal to or shorter than the total length of the bone screw 2.

The constituent materials of the bone screw 2 and the pin member 7 are, for example, various metals such as stainless steel, titanium, titanium alloys, polymethylmethacrylate, high density polyethylene, acrylic resin, polyester, polytetrafluoroethylene, Polyglycolic acid, polylactic acid,
Various resins such as polydioxanone and polyhydroxybutyric acid,
Various ceramics such as calcium phosphate ceramics (hydroxyapatite, TCP), alumina, carbon ceramics, zirconia, titania and the like can be mentioned. In particular, at least one of the bone screw 2 and the pin member 7 is preferably made of a bioabsorbable material such as polyglycolic acid, polylactic acid, polydioxanone, polyhydroxybutyric acid, TCP and the like. The constituent materials of the bone screw 2 and the pin member 7 may be the same or different.

Next, the operation of the bone screw assembly 1A will be described. When the two bone fragments are fixed using the bone screw assembly 1A, the bone screw 2 is rotated in a predetermined direction and the screw portion 4 is screwed into one bone and fastened in accordance with a conventional method. After tightening with an appropriate strength, the pin member 7 is inserted from the head portion 5 side along the cutout portion 6. The method of inserting the pin member 7 into the notch 6 includes a method of directly driving the pin member 7 without opening a pilot hole in the bone and a method of drilling a small pilot hole in the bone using a thin rasp or a drill. After that, there is a method of driving the pin member 7.

When the pin member 7 is inserted into the cutout portion 6, the edge portion 73 has the thread 41 of the screw portion 4 and the head portion 5.
Since it protrudes to the outside of the outer circumference of the bone fragment, this protruding portion functions as a stopper for the bone fragment and prevents rotation of the bone fragment around the bone screw 2.

When the constituent material of the bone screw 2 and the pin member 7 is metal, nailing may be performed. To remove the nail, the pin member 7 is removed and then the screw portion 4 of the bone screw 2 is loosened.

When the constituent material of the bone screw 2 and the pin member 7 is a bioabsorbable material, particularly bioabsorbable plastic, it is not necessary to carry out the nail extraction, so that the labor is saved and the burden on the patient is reduced. It

When it is considered that the turning force of the bone fragment is large, the number of notches 6 is increased or the edge 7 is formed.
By increasing the protrusion length of 3, it is possible to enhance the anti-rotation force, and it is possible to more reliably prevent the displacement of the bone fragments due to the rotation. When a plurality of cutouts are provided, it is preferable to form each cutout radially from the central axis of the bone screw 2 as in the embodiment described later.

FIG. 3 is a cross sectional view showing a second embodiment of the bone screw assembly of the present invention. Bone screw assembly 1B shown in FIG.
Is the same as the bone screw assembly 1A except that the length of the blade portion 72 of the pin member 7 is different.

In this bone screw assembly 1B, the blade portion 7
2 has a shorter length than the above, and the pin member 7 is attached to the bone screw 2
When inserted in the notch 6 of the edge portion 73 (protrusion)
In the radial direction of the bone screw 2.
It is located outside the outer circumference of the screw thread 41 and the head portion 5 and projects outward from the outer circumference of the head thread 5. Under such a condition, not only the case where the entire area of the edge portion 73 in the longitudinal direction is satisfied, but a part of the edge portion 73 may be satisfied.

Next, the operation of the bone screw assembly 1B will be described. When fixing a bone fixing material, a tendon, or a ligament using the bone screw assembly 1B, the bone screw 2 is rotated in a predetermined direction and the screw portion 4 is screwed into the bone and fastened in accordance with a conventional method. After tightening with an appropriate strength, the pin member 7 is inserted from the head portion 5 side along the notch portion 6 by the same method as described above.

When the pin member 7 is inserted into the cutout portion 6, the edge portion 73 has the thread trough 42 and the thread ridge 41 of the threaded portion 4.
It is located between and. Accordingly, in the case of fixing the bone fixing material, the rotation (loosening) of the bone screw 2 can be prevented without the pin member 7 hitting the inner wall of the fixing hole of the bone fixing material, and the tendon and the ligament are fixed. In this case, the rotation (loosening) of the bone screw 2 can be prevented without damaging the tendon or the ligament fixed around the screw portion 4.

FIG. 4 is a top view (a) and a front view (b) showing a third embodiment of the bone screw assembly of the present invention, and FIG. 5 is a view of FIG. 4 in a state where the bone screw assembly is assembled. It is a VV line sectional view.

The bone screw assembly 1C shown in these figures comprises a bone screw 2 and a pair of pin members 9. The bone screw 2 has a pair of notches 8 having a rectangular cross section. They are formed symmetrically with respect to the central axis of the screw 2. Also, bone screw 2
A hexagon wrench fitting hole 52, which is a tool for rotating the bone screw 2, is formed in the center of the upper surface of the head 5.

Each of the pin members 9 has a cross-sectional shape substantially equal to that of the cutout portion 8, and a curved convex surface (projection portion) 91 is formed on one side thereof so as to project outward in the radial direction of the bone screw 2. ing. As shown in FIG. 5, when each pin member 9 is inserted into the cutout portion 8, the curved convex surface 91 projects outward from the screw thread 41 of the screw portion 4. As a result, the same effect as described above can be obtained.

FIG. 6 is a top view (a) and a front view (b) showing a fourth embodiment of the bone screw assembly of the present invention, and FIG. 7 is a sectional view of FIG. 6 in the assembled state of the bone screw assembly. VII-V
It is a II sectional view.

A bone screw assembly 1D shown in these figures comprises a bone screw 2 and a pair of pin members 11. The bone screw 2 has a pair of notches 10 having a V-shaped cross section. Are formed symmetrically about the central axis of the bone screw 2. In addition, a one-character groove 51 for rotating the bone screw 2 is formed on the upper surface of the head 5 of the bone screw 2.

Each pin member 11 has a substantially rhombic cross-sectional shape, and a mountain-shaped protrusion (projection) 12 protruding outward in the radial direction of the bone screw 2 is formed at one end thereof. There is. As shown in FIG. 7, when each pin member 11 is inserted into each notch 10, the protrusion 12 protrudes outward from the screw thread 41 of the screw portion 4. As a result, the same effect as described above can be obtained.

FIG. 8 is a top view (a) and a front view (b) showing a fifth embodiment of the bone screw assembly of the present invention, and FIG. 9 is a view of FIG. 8 in a state where the bone screw assembly is assembled. FIG. 9 is a sectional view taken along line IX-IX.

The bone screw assembly 1D shown in these figures comprises a bone screw 2 and a pin member 16, and the bone screw 2 is provided with a notch 13 having a cross section of approximately Ω. ing. The notch 13 has a hole 14 having a circular cross section,
The bone screw 2 is formed with a defective portion 15 (shown by a chain line in FIG. 8A) such that the outer peripheral surface of the bone screw 2 is cut into a circular arc shape so as to communicate with the hole portion 14. Further, a fitting hole 52 similar to the above is formed in the center of the upper surface of the head 5 of the bone screw 2.

The pin member 16 has a hole 14 in the notch 13.
And a pair of blade portions 18 joined to the outer peripheral surface of the shaft portion 17 and protruding in mutually opposite directions.
And are integrally formed. Both blade parts 1
Edge portions (projections) 19 in which the thickness of the blade portion 18 is gradually reduced are formed at the ends of the pin member 8 along the longitudinal direction of the pin member 16.

As shown in FIG. 9, the shaft portion 1 of the pin member 16
In the state where 7 is inserted into the hole 14 of the cutout portion 10, both edge portions 19 project outward from the screw thread 41 of the screw portion 4. As a result, the same effect as described above can be obtained.

Although the bone screw assembly of the present invention has been described with reference to the illustrated embodiments, the present invention is not limited to these. For example, the bone screw may not have a head screw 5. Further, the shape of the cutout portion and the shape of the pin member can be arbitrary.

Hereinafter, the present invention will be described in more detail with reference to specific examples. (Example 1) A bone screw assembly including a bone screw and a pin member was manufactured. The conditions are as follows.

[Bone screw] Type: Bone screw for cancellous bone (with screw head) Total length: 40 mm Total length of screw part: 32 mm Screw thread diameter: 4.5 mm Screw root diameter: 3.2 mm Screw pitch: 1.75 mm Notch formation Position: Axial direction from the base side of the bone screw to the tip Number of notches: 1 Notch cross-sectional shape: Shape shown in Fig. 1 and 2 Bone screw constituent material: Stainless steel

[Pin member] Overall length of the pin member: 40 mm Cross-sectional shape of the pin member: Shape shown in 70 of FIG. 1 (a) Blade thickness: 0.75 mm Edge position: screw thread and screw head during assembly Approximately 1.2mm outwardly protruding Pin member material: Stainless steel

Using the conventional bone screw and the bone screw assembly of the first embodiment, an experiment was conducted on the assumption that two bone fragments were fixed with the bone screw. A cancellous bone fragment was prepared from the distal end of the sheep femur and used as a bone fragment for fixation. The bonded surface was polished to form a flat surface.

First, two bone fragments were fixed by using a conventional cancellous bone screw having no notch portion by a method in which the screw is screwed only into the bone at the leading end side so that a compressive force is applied. . At that time, the screw head was tightened by applying a torque of 3 kgf · cm.
Next, in this state, fix the leading end side bone fragment to the torque meter, gradually apply torque to the trailing end side bone fragment counterclockwise around the screw part, and adjust the torque value that the joint surface shifts. It was measured.

In the same manner as described above, the bone screw in Example 1 was fastened to the bone on the leading end side, and then the pin member was inserted into the cutout portion of the bone screw. Next, in this state, fix the bone fragments on the leading end side to the torque meter, gradually apply torque to the bone fragments on the trailing end side counterclockwise around the screw part, and measure the torque value at which the joint surface shifts. did.

As a result of the measurement, the joint surface of the conventional bone screw was displaced by 3.2 kgf · cm, whereas the joint surface of the bone screw assembly of Example 1 was displaced by 4.8 kgf · cm. This allows
It was confirmed that the bone screw assembly of the present invention has a high effect of preventing rotation of the bone.

(Example 2) A bone screw assembly similar to that of Example 1 was manufactured except that the positions of the edge portions were set as follows. Position of edge part: Outside of screw root and inside of screw thread and screw head (2.1 mm from bone screw center axis) during assembly

An experiment was conducted on the assumption that the bone fixing material, the tendon, or the ligament was fixed using the conventional bone screw and the bone screw assembly of the second embodiment.

A cancellous bone fragment prepared from the distal end of the sheep femur was fitted with the conventional bone screw for cancellous bone in an amount of 3 kgf.
It was tightened by applying a torque of cm. Next, a torque value for slackening the bone screw was measured using a torque wrench.

After the bone screw in Example 2 was fastened to the cancellous bone fragment by the same method as described above, a pin member was inserted into the cutout portion of the bone screw. Next, the torque value for slackening the bone screw assembly was measured using a torque wrench.

As a result of the measurement, the conventional bone screw is 3.1 kgf ·
The bone screw assembly of Example 2 has a slack in cm.
It slackened at 4.2 kgf · cm. From this, it was confirmed that the bone screw assembly of the present invention has a high effect of preventing loosening of the screw.

[0059]

As described above, according to the bone screw assembly of the present invention, in the case where two bone fragments are fixed by a bone screw, the bone fragments are not rotated even when a sufficient compression force cannot be obtained. It can be applied to prevent the joint surface from shifting. In particular, when the projection of the pin member projects outward in the radial direction of the bone screw beyond the thread of the threaded portion, this effect is further enhanced.

Further, according to the bone screw assembly of the present invention, when fixing the bone fixing material, the tendon, or the ligament with the bone screw, it is possible to prevent loosening due to rotation of the bone screw. As a result, safety is significantly improved. Further, when the bone screw and / or the pin member is made of a bioabsorbable material, it is not necessary to remove the nail, and the burden on the patient can be reduced.

[Brief description of drawings]

FIG. 1 is a top view and a front view showing a first embodiment of a bone screw assembly of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a cross-sectional view showing a second embodiment of the bone screw assembly of the present invention.

FIG. 4 is a top view and a front view showing a third embodiment of the bone screw assembly of the present invention.

5 is a sectional view taken along line VV in FIG.

FIG. 6 is a top view and a front view showing a fourth embodiment of the bone screw assembly of the present invention.

7 is a sectional view taken along line VII-VII in FIG.

FIG. 8 is a top view and a front view showing a fifth embodiment of the bone screw assembly of the present invention.

9 is a sectional view taken along line IX-IX in FIG.

[Explanation of symbols]

 1A-1E Bone screw assembly 2 Bone screw 3 Bone screw main body 4 Screw part 41 Screw ridge 42 Screw trough 5 Head 51 Groove 52 Fitting hole 6 Notch part 61 Hole part 62 Slit part 7 Pin member 71 Shaft part 72 Blade Part 73 Edge part 8 Notch part 9 Pin member 91 Curved convex surface 10 Notch part 11 Pin member 12 Projection part 13 Notch part 14 Hole part 15 Missing part 16 Pin member 17 Shaft part 18 Blade part 19 Edge part

Claims (5)

[Claims] 1. A bone screw in which at least one cutout portion continuous along an axial direction is formed in a bone screw body, and a screw portion is formed on an outer periphery excluding the cutout portion, and the bone screw is inserted into the cutout portion. Bone screw assembly comprising: 2. The pin member has a protrusion, and when at least a part of the pin member is inserted into the notch,
The bone screw assembly according to claim 1, wherein the protrusion has a shape protruding outward from the bone screw main body in a radial direction of the bone screw. 3. The bone screw has a head portion at a base end portion thereof, and the notch portion is also formed in the head portion.
The bone screw assembly according to. 4. The pin member has a protrusion, and when at least a part of the pin member is inserted into the notch,
The bone screw assembly according to claim 3, wherein the protrusion has a shape that protrudes outward from the outer circumferences of the bone screw main body and the head in the radial direction of the bone screw. 5. The bone screw and / or the pin member is made of a bioabsorbable material.
The bone screw assembly according to any one of 1.