JP3999679B2 - Bone surgery screw set and method of rotating the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to screw set and rotation operating method for Rukotsu surgery used to bone surgery.
[0002]
[Prior art]
In general, in fracture treatment, a fractured portion may be held by fixing the plate with a bone screw that is screwed into the bone while a plate is applied to the outer surface of the bone while the fractured portion is reduced. In some cases, an intramedullary nail is driven into the medullary bone of the fractured bone, and a bone screw is screwed so as to cross the intramedullary nail to hold the fractured portion.
[0003]
When fracture treatment is performed in this manner, the fracture portion is held and fixed by the implant such as the above plate or intramedullary nail until the fracture portion is fused, but once the fracture portion has healed, The plate or intramedullary nail needs to be removed from the body for the purpose of further strengthening or for the purpose of avoiding growth inhibition by the implant when the patient is a young adult in the growth phase. For this reason, in the final stage of fracture treatment, reoperation for removing the bone screw is required.
[0004]
However, the above-mentioned bone screws, bolts, and the like are attached with new adult bone (callus) as the bone regenerates in the process of healing the fractured part, and thereby the implant is fixed to the bone. In many cases, it is difficult to remove the implant with a normal rotary tool such as a screwdriver. For example, when removing a bone screw, since it is often formed so that new bone bites into the screw portion of the bone screw, it is extremely difficult to rotate and loosen the bone screw even if a tool is used. In addition, if the bone screw is forcibly rotated, the head of the bone screw may be crushed or only the head of the bone screw may be broken. When this happens, it becomes more difficult to remove the bone screw.
[0005]
Some bone screws have a recess having a square or hexagonal square hole shape in the head. For a bone screw with such a recess, a rotary tool with an engagement part having a prismatic shape is applied to rotate it, but by applying a strong rotational stress at the time of removal, When the engaging part of the rotary tool or the inner surface of the recess of the bone screw is deformed, the rotary tool and the recess may not be engaged. This is considered to be because the corners provided at the engaging part of the rotary tool and the inner surface of the bone screw recess basically come into a line contact state, and stress concentrates on the line contact part.
[0006]
As a method for avoiding such a situation, for example, when the rotary tool is applied to the recess by forming the inner surface of the square hole-shaped recess in a gentle convex curved shape facing inward, It is known that the inner surface of the recessed portion of the screw abutting against each other and the outer surface of the engaging portion of the rotary tool are elastically deformed to be in a surface contact state, thereby preventing stress concentration (for example, below) Patent Document 1).
[0007]
The head is provided with a plurality of wing-like portions extending radially from the center toward the outside, and one of the side walls of the portion is formed along a line extending spirally from the center toward the outside. A screw provided with a recess is known. This screw uses a rotary tool having a cross-sectional shape corresponding to a plurality of wing-like recesses extending outward (see, for example, Patent Document 2).
[0008]
[Patent Document 1]
Japanese Utility Model Publication No. 53-97261 (refer to FIG. 1 in particular)
[Patent Document 2]
Special Table 2002-525500 gazette (see each figure)
[0009]
[Problems to be solved by the invention]
However, since a screw used for bone surgery is premised on being made of a material having biocompatibility, there are circumstances different from general-purpose screws. Examples of the material having biocompatibility include bioinert metal materials such as titanium and titanium alloys, biodegradable absorbable materials such as polylactic acid, lactic acid-glycolic acid copolymer, and hydroxyapatite. . Since these materials are more brittle than general-purpose screw materials, complicated shape processing is difficult, and breakage is likely to occur during a rotation operation performed during bone surgery. In addition, since it is necessary to avoid the formation of foreign matter (mixing of foreign matter) as a medical device, forging cannot be performed, so in the case of metal materials, it is necessary to perform cutting, so complicated shape processing Is difficult and causes an increase in manufacturing cost.
[0010]
Furthermore, compared to general-purpose screw materials, plastic deformation is likely to occur, so that the recess is likely to be deformed during rotation operation, and rotation operation is often impossible. In particular, when forming a square hole in the head of the screw, the ridge line of the prismatic part of the rotary tool is in line contact with the inner surface of the square hole, so stress concentrates on this line contact part, It is considered that the inner surface of the square hole expands due to plastic deformation, and rotation operation becomes impossible. Further, if the rotary tool is formed of a low hardness material according to the material of the screw, there may be a case where the rotation operation becomes impossible due to the deformation of the corner of the rotary tool.
[0011]
Therefore, the present invention solves the above-mentioned problems, and the problem is that the recess into which the rotary tool is inserted has a shape that can be easily processed and can be prevented from being damaged or seriously deformed. It is to provide a surgical screw.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, a screw set for bone surgery according to the present invention is for bone surgery having a screw portion and a head having a recess that receives a rotary tool having a substantially polygonal cross section and receives the rotational force. screw, and in bone surgical screw sets having a insertable said rotary tool to said recess, said recess of said bone surgical screw is a plurality of arc portions which are curved inwardly is provided around the axis And has a hole cross-sectional shape in which a sharpened portion protruding toward the center side is formed by the adjacent arc portions intersecting each other, the sharpened portion is configured to be plastically deformable , and the rotary tool is And a substantially polygonal cross section having the same number of corners as the arc portion, and the ridge line contacts the arc portion when the center position of the outer surface is rotated by a predetermined angle from the posture arranged opposite to the sharpened portion. Characterized in that said outer surface is provided with an engagement portion configured to abut on the tip portion without.
[0013]
According to the present invention, by applying a rotary tool having a prismatic engaging portion and rotating it, the outer surface of the engaging portion comes into contact with the sharpened portion, and the sharpened portion is plastically deformed and engaged by plastic deformation. Because it is squeezed to follow the outer surface of the part, the engaging part of the rotary tool and the recess of the bone surgery screw come into surface contact with each other. As a result, stress concentration is reduced and normal rotational operation force is ensured. Will be accepted. In particular, since the sharpened portion is formed by intersecting the arc portions on both sides, the width of the tip portion is small, and the width suddenly widens toward the outside. When deformed to some extent, it becomes possible to sufficiently bear the rotational operation force due to the increase in the contact area, and further deformation is suppressed. Therefore, excessive deformation and breakage of the head of the bone surgery screw are prevented, and a situation in which the rotation operation becomes impossible is avoided.
[0014]
Further, since the recess can be processed only by forming a plurality of arc portions around the axis, even a brittle material can be manufactured easily and at low cost. In particular, since it can be formed easily without using forging, it is possible to provide a safe and high-quality bone surgery screw as a medical instrument by avoiding the mixing of foreign substances.
[0015]
Furthermore, since the ridge line of the engaging part of the rotating tool does not contact the inner surface of the recess during the rotating operation, the rotating tool can be prevented from being worn.
[0016]
In the present invention, it is preferable that at least the head of the screw for bone surgery is made of titanium or a titanium alloy. According to this, it is a biocompatible material suitable as a screw for bone surgery, and sufficient plastic deformation can be obtained by a normal rotational operation force (stress given by an operator). In addition, as a material constituting the screw for bone surgery, in addition to the above-mentioned bioinert metal materials such as titanium, titanium alloy, and stainless steel, in vivo such as polylactic acid, lactic acid-glycolic acid copolymer, and hydroxyapatite. A decomposition-absorbing synthetic resin material or a ceramic material can be used. Even in these materials, it is possible to obtain the plastic deformation of the sharp point.
[0017]
In the present invention, when the number of arc portions is m, the predetermined angle is preferably greater than 0 and 120 / m degrees (20 degrees when m = 6). As a result, the stress direction received by the sharpened tool from the rotary tool can be directed closer to the radial direction than the rotational direction. Therefore, the sharpened part of the recess can be reliably deformed by the outer surface of the engaging part, and the sharpened part can be sharpened. Occurrence of a situation such as breakage of the part can be avoided. In particular, the predetermined angle is preferably in the range of 18 / m (3 degrees when m = 6) to 72 / m (12 degrees when m = 6) degrees.
[0018]
Next, in the method for rotating a bone surgical screw according to the present invention, a screw for bone surgery having a screw portion and a head having a recess, and a rotary tool having a substantially polygonal cross section in the recess. In the method of inserting and rotating, the recess has a plurality of inwardly curved arc portions provided around the axis, and the adjacent arc portions intersect each other to the center side. It has a hole cross-sectional shape formed by projecting sharpened portions, and the rotary tool has a substantially polygonal cross section that can be inserted into the recess and has the same number of corners as the arc portion, and the center of the outer surface thereof An engagement portion configured such that the outer surface abuts against the sharpened portion without contacting the arcuate portion when the position is rotated by a predetermined angle from a posture where the position is opposed to the sharpened portion; The rotating tool has an outer surface facing the sharpened portion. It is inserted into the recess so that the position of, and wherein the plastically deforming the sharpened tip by the outer surface by rotating in a predetermined direction.
[0019]
In here, it predetermined angle is within the above range and preferably not more than (20 ° in the case of m = 6) likewise greater than 0 120 / m degrees, 18 / m~72 / m degree Is desirable. Further, it is preferable that at least the head of the bone surgery screw is made of titanium or a titanium alloy.
[0020]
In the bone surgery screw of each of the above means, it is desirable that the plurality of arc portions have the same diameter and are coaxially arranged, and are arranged at equiangular intervals around the axis. Moreover, in the said rotary tool, it is desirable for the engaging part to have a regular polygon cross section.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a screw for bone surgery according to the present invention will be described in detail. 1 (a) and 1 (b) are an enlarged plan view and an enlarged partial sectional view of the vicinity of the head of the screw 10 for bone surgery, and FIG. 4 shows the screw 10 for bone surgery and for rotating it. 2 is a schematic perspective view showing an overall shape of a rotary tool 20. FIG.
[0022]
As shown in FIG. 4, the bone surgery screw 10 includes a screw portion 11 having a male screw formed on the distal end side and a head portion 12 formed on the proximal end side. The bone surgical screw 10 has a shaft hole 10a formed at the center. The shaft hole 10a is for inserting a guide pin pierced by a bone, and is screwed into a bone, an implant or the like in a state where the screw 10 for bone surgery is guided by the guide pin. Further, a recess 12 a is formed in the head 12.
[0023]
On the other hand, the rotary tool 20 has a substantially polygonal column-shaped engaging portion 21 formed at the distal end and a gripping portion 22 provided on the proximal end side. The grip portion 22 can be directly gripped and used, but may be used in a state where the grip portion 22 is gripped and fixed by another tool. A shaft hole 20 a is formed at the center of the rotary tool 20. The shaft hole 20a is for inserting the guide pin. The engaging portion 21 of the rotary tool 20 is provided with a plurality of ridge lines 21a and a substantially planar outer surface 21b formed between the ridge lines 21a. The engaging portion 21 in the illustrated example has a regular hexagonal prism shape.
[0024]
As shown in FIG. 1, the hole cross-sectional shape of the recess 12 a formed in the head 12 of the bone surgery screw 10 has a plurality of curvatures that are curved inward and have a radius of curvature smaller than the average inner diameter of the entire recess. An arcuate portion 12b is provided around the axis, and a sharpened portion 12c that protrudes toward the center is formed by the adjacent arc portions 12b intersecting each other. In the recess 12a in the illustrated example, the plurality of arc portions 12b have the same diameter and are arranged at the same coaxial position. Further, six arc portions 12b are formed at equiangular intervals around the axis.
[0025]
2A and 2B are cross-sectional views showing a state where the engaging portion 21 of the rotary tool 20 is inserted into the recess 12a. Here, the outer surface 21b of the engaging portion 21 is opposed to the sharpened portion 12c of the recess 12a, and the ridge line 21a of the engaging portion 21 is inserted in a posture facing the arc portion 12b of the recessed portion 12a. At this time, as shown in FIG. 2 (a), the radial position of the central portion of the arc portion 12b in the recess 12a is Ra, the radial position of the sharpened portion 12c is Rb, and the radial position of the ridge line 21a of the engaging portion 21 is If the radial position of Ta and the central portion of the outer surface 21b is Tb, the engaging portion 21 can be inserted into the recess 12a without any problem if there is a relationship of Ra ≧ Ta and Rb ≧ Tb. However, Ta> Rb must be satisfied in order to perform the rotation operation with the rotary tool 20.
[0026]
When the engaging portion 21 is rotated in a state where the engaging portion 21 is inserted into the recess 12a in the above posture, as shown in FIG. 2B, the ridge line 21a is formed when rotated by a predetermined angle θa. The outer surface 21b comes into contact with the sharpened portion 12c without contacting the inner surface of the arc portion 12b. This condition is determined by the relationship between the center position and the radius of curvature of the arc portion 12b and the radius of the circumscribed circle of the engaging portion 21. The predetermined angle θa is preferably greater than 0 and 20 degrees or less. That is, generally, when the number of arc portions is m (m = 6 in the illustrated example), the predetermined angle θa is greater than 0 and 120 / m or less. This is because if the predetermined angle θa becomes too large, the direction of stress applied to the sharpened portion 12c is greatly inclined from the radial direction toward the rotational direction, so that the possibility of the sharpened portion 12c breaking is increased. From this point of view, the angle θa is more preferably in the range of 3 to 12 degrees (generally in the range of 18 / m to 72 / m degrees). In the illustrated example, it is designed to be 7 degrees (42 / m degrees).
[0027]
When the engaging portion 21 is further rotated, the outer surface 21b crushes the sharpened portion 12c and plastically deforms it. Then, usually, when the ridgeline 21a is rotated by the limit angle θb and the ridgeline 21a comes into contact with the inner surface of the arc portion 12b, further plastic deformation hardly occurs. The limit angle θb is preferably in the range of 5 to 30 degrees (generally in the range of 30 / m to 180 / m degrees). However, θb> θa must always be satisfied. In particular, θb is desirably in the range of 10 to 20 degrees (generally in the range of 60 / m to 120 / m degrees). In the illustrated example, θb = 16 degrees (96 / m degrees). Here, in FIG. 2B, the engaging portion 21 in the above posture is indicated by a broken line, the state where the outer surface 21b is in contact with the sharpened portion 12c is indicated by a solid line, and the ridge line 21a is in contact with the inner surface of the circular arc portion 12b. Each of these states is indicated by a one-dot chain line.
[0028]
FIG. 3 is an enlarged partial sectional view showing the relationship between the arc portion 12b and the sharpened portion 12c, the ridge line 21a, and the outer surface 21b when the rotary tool 20 is rotated as shown in FIG. As shown in this figure, the initial state (when in the above posture) is indicated by a broken line S1, the state in which the outer surface 21b is in contact with the sharpened portion 12c is indicated by a one-dot chain line S2, and the sharpened portion 12c is being plastically deformed. Is indicated by a two-dot chain line S3, and a state in which the ridge line 21a is in contact with the circular arc part 12b is indicated by a solid line S4. With a normal rotational operation force, the rotation of the engaging portion 21 is stopped between S2 and S4, and the bone surgery screw 10 is rotated. In this case, the relative relationship between the recess 12a and the engagement portion 21 approaches S4 as the rotational resistance of the bone surgery screw 10 increases.
[0029]
In the present embodiment, the engaging portion 21 and the recess 12a are brought into surface contact by plastic deformation of the sharpened portion 12c, and the contact area increases as the rotational operation force increases, so that the recess 12a and the engaging portion 21 are damaged. Is prevented. Here, since the sharpened portion 12c is formed by intersecting adjacent circular arc portions 12b, it has a shape in which the width rapidly increases as it proceeds from the tip to the outer peripheral side, so that plastic deformation tends to occur at the beginning. When the rotational operation force is increased, the contact area increases rapidly, making it difficult for plastic deformation to occur. Therefore, there is a remarkable effect that damage is surely prevented.
[0030]
Further, since the recess 12a is formed by intersecting a plurality of arc portions 12b to form a sharpened portion 12c, the recess portion 12a can be formed only by sequentially forming the arc portion 12b around the axis by cutting or the like. Even brittle materials can be manufactured easily and at low cost.
[0031]
Lastly, the experimental results of the bone surgery screw will be shown. The bone surgery screw 10 was formed of a titanium alloy Ti-6Al-4V (Ti: 90 wt%, Al: 6 wt%, V: 4 wt%). The recess 12a has six arc portions 12b and has a shape with rotational symmetry of sixfold symmetry, and Rb = about 1.25 mm (facing width 2Rb = about 2.5 mm). The rotary tool 20 was made of stainless steel and provided with a regular hexagonal engagement portion, and Tb = about 1.25 mm (facing width 2Tb = about 2.5 mm). For the rotary tool 20, a solid type without the shaft hole 20a and a hollow type having the shaft hole 20a were manufactured and used. In addition, as a comparative example of a conventional bone surgery screw, prepared with the same material as described above and provided with a regular hexagonal recess having a facing width of about 2.5 mm and a width of about 3 mm, and corresponding face-to-face Experiments were performed using a solid type rotary tool having an engagement portion with a width of about 2.5 mm and a hollow type rotary tool having an engagement portion of about 3 mm. The configurations of these bone surgical screws and rotary tools are shown in Table 1 below, and the experimental results are shown in Table 2 below.
[0032]
[Table 1]
Screw for bone surgery Rotary tool Example 1 Face width 2.5mm Face width 2.5mm (solid type)
Example 2 Face width 2.5 mm Face width 2.5 mm (hollow type)
Comparative Example 1 Face width 2.5mm Face width 2.5mm (solid type)
Comparative Example 2 Face width 3.0 mm Face width 3.0 mm (hollow type)
[0033]
[Table 2]
Maximum applied torque [N · m] Final state Example 1 5.81 Rotating tool breaks Example 2 4.33 Rotating tool breaks Comparative example 1 5.06 Recess is deformed Comparative example 2 4.55 Engagement with recess Both joints are deformed. [0034]
As shown in Table 2, in all the comparative examples, the recess of the screw is deformed and cannot be rotated, whereas in Example 1, the recess is deformed up to 5.81 [N · m]. Finally, the rotary tool broke. Also in Example 2, the rotary tool broke at 4.33 [N · m]. In either case, in the example, the rotation operation was not disabled due to the deformation of the recess (the rotating tool did not slurp the recess).
[0035]
In the above embodiment, a titanium alloy is used as the material for the bone surgery screw. However, examples of the material of the present invention include bioinert materials such as pure titanium, stainless steel, synthetic resin, and ceramics, various synthetic resins and ceramics. A biodegradable and absorbable material such as can be used.
[0036]
Moreover, in the said embodiment, what provided the six circular arc part as a recess shape was illustrated, and what has a regular hexagon-shaped engaging part as a rotary tool was illustrated, but this invention is 3 or more arbitrary arbitrary A recess provided with a natural number of arc portions can be provided, and the rotary tool can also be provided with a square engagement portion of an arbitrary natural number of 3 or more correspondingly.
[Brief description of the drawings]
1A and 1B are a plan view and a partial cross-sectional view, respectively, of a bone surgery screw head according to an embodiment.
FIGS. 2A and 2B are cross-sectional views showing an engaged state of a screw and a tool.
FIG. 3 is an enlarged partial cross-sectional view showing an enlarged engagement state between a screw and a tool.
FIG. 4 is a perspective view of a screw and a tool.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Screw for bone surgery, 10a ... Shaft hole, 11 ... Screw part, 12 ... Head, 12a ... Recess, 12b ... Arc part, 12c ... Sharp part, 20 ... Rotary tool, 20a ... Shaft hole, 21 ... Engagement Joint part, 21a ... Ridge line, 21b ... External surface

Claims (5)

A screw for bone surgery having a screw portion and a head having a recess that receives a rotary tool that receives a rotary tool having a substantially polygonal cross section , and the rotary tool that can be inserted into the recess. In the bone surgery screw set ,
The concave portion of the bone surgery screw has a plurality of arc portions curved inwardly around the axis, and a sharpened portion protruding toward the center by the adjacent arc portions intersecting each other. It has a hole cross-sectional shape formed, and the sharpened portion is configured to be plastically deformable ,
The rotary tool has a substantially polygonal cross section having the same number of corners as the arc part, and the ridge line of the arcuate line is rotated when the center position of the outer surface is rotated by a predetermined angle from the posture arranged opposite to the sharpened part. A screw set for bone surgery comprising an engaging portion configured such that the outer surface abuts against the sharpened portion without contacting the portion . The screw set for bone surgery according to claim 1, wherein at least the head of the screw for bone surgery is made of titanium or a titanium alloy. The screw set for bone surgery according to claim 1 or 2, wherein the predetermined angle is greater than 0 and 120 / m degrees or less, where m is the number of arc portions. A method for rotating a bone surgical screw having a screw portion and a head with a recess by rotating a rotary tool having a substantially polygonal cross section into the recess,
The recess includes a plurality of arc portions curved inwardly around the axis, and a hole cross section formed by a sharpened portion projecting toward the center when the arc portions adjacent to each other intersect each other. Has a shape,
The rotary tool can be inserted into the recess, has a substantially polygonal cross section having the same number of corners as the arc portion, and is rotated by a predetermined angle from a posture in which the center position of the outer surface is opposed to the sharpened portion. The ridge line is provided with an engaging portion configured so that the outer surface abuts on the sharpened portion without contacting the arc portion,
Bone surgery, wherein the rotary tool is inserted into the recess so that the outer surface thereof is in a posture facing the sharpened portion, and the sharpened portion is plastically deformed by the outer surface by rotating in a predetermined direction. Screw rotation method.   5. The method for rotating a bone surgical screw according to claim 4, wherein at least the head of the bone surgical screw is made of titanium or a titanium alloy.

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