JP2009201882A - Tapping screw for bone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tapping screw for a bone, enabling the timing of the completion of tightening of the screw to be easily judged. <P>SOLUTION: The tapping screw for a bone to be used for fixing a bone with a plate in a surgical operation is provided, wherein the pitches of screw threads in a distal end screw part 13 and a straight threaded part 12 are 0.6-0.75 mm, the root diameter D of the straight threaded part 12 is 0.85-1.4 mm, and the thickness S of the shortest part in an unthreaded part 14 is ≤0.12 mm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a bone tapping screw used to fix a bone with a plate in a surgical operation.

  Bone tapping screws used to fix bones, including skulls, with a plate are intended for use on the body and must be particularly safe. For example, as a material, a titanium alloy which is excellent in corrosion resistance and is light and strong is often used. Titanium alloys also have features such as being less likely to cause metal allergies and less likely to transmit heat, and can reduce the influence on the human body.

  Attention is paid not only to the material but also to the shape. For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-177473), it is possible to easily and rapidly screw into a bone or bone fragment by limiting the shape of the thread pitch and the tip, and the like. Provided is a screw that has an effect of preventing the screw tip from being bent or broken.

These shapes are determined in consideration of safety, ease of work and quickness, but there is little mention of screw torque management. If torque management is not performed correctly, it may overtighten and cause the screw to slip or damage the bone. On the other hand, if the tightening is too weak, there may be a problem that the plate cannot be fixed securely. Therefore, it is considered that torque management of the bone tapping screw in the operation is one of important matters.
JP 2005-177473 A

  In view of the above, an object of the present invention is to provide a bone tapping screw that can easily determine the timing of tightening end when the torque suddenly increases when approaching the end of tightening.

  The present invention relates to a bone tapping screw used to fix a bone with a plate, a screw head to which torque is applied for screwing, and a general cone located near the screw tip and provided with a screw thread. A tip screw portion having a shape, a linear screw portion having a thread extending from the tip screw portion to a cylindrical shaft portion, and located between the screw head and the linear screw portion, and An unthreaded portion having a diameter larger than the valley diameter and not provided with a thread, and the length of the shortest portion of the axial length of the unthreaded portion is 0.12 mm or less. Yes.

  The bone tapping screw has a mountain diameter of 1.4 to 2.0 mm, a difference between the mountain diameter and the valley diameter is 0.45 to 0.85 mm in diameter, The angle between the axial direction of the screw and the screw thread can be set to 55 to 65 °, or the countersunk bottom surface of the screw head can be formed into a convex curved surface with a curvature radius of 1.0 to 2.0 mm.

  According to the bone tapping screw of the present invention, by providing almost no unthreaded portion, it is possible to increase the torque abruptly almost simultaneously with the end of the thread and to easily determine the end of tightening. An excellent effect can be achieved.

  Moreover, the screwing torque can be reduced by making the valley diameter of the straight thread portion as thin as possible. And by limiting the angle of the screw thread, it prevents the screw thread from bending when screwing, or by making the shape of the bottom surface of the pan a convex curved surface, it is provided on the plate from point contact to surface contact when screwing Therefore, it is easy to sense the completion of tightening, and even if the screw is obliquely screwed in, it can be easily adapted to the concave portion of the plate.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a diagram of a bone tapping screw 10 according to the present invention, where (a) is a top view and (b) is a front view.

  Since the bone tapping screw 10 of the present invention is self-drilling, when a torque is applied to the screw head 11, the screw is screwed while making a hole in the bone. That is, since the tip screw portion 13 has a substantially conical shape with a thread, it is screwed into the bone while gradually forming a hole. When the screw is screwed up to a certain extent, the straight screw portion 12 has a constant screw diameter, so that the hole does not become any larger.

  Further, the bone tapping screw 10 includes a screwless portion 14 having a diameter larger than the root diameter D of the linear screw portion 12 and not provided with a screw thread between the screw head 11 and the linear screw portion 12. ing. The unthreaded portion 14 is a portion from the end of the screw thread to the lower end of the head 11 and is formed along the spiral of the screw. In the present invention, the length S of the shortest portion of the axial length of the unthreaded portion 14 is determined. Was made 0.12 mm or less. Within this range, the thread is not gradually lowered, but suddenly there is no thread. Therefore, it is considered that the tightening torque suddenly increases and the end of tightening can be easily determined. Here, it is considered that the effect becomes clearer as the length S of the shortest portion of the screwless portion 14 is thinner. Therefore, it is most effective not to provide the unthreaded portion 14 (S = 0 mm). However, considering productivity and the like, 0 mm is difficult, and if it is 0.12 mm or less, the tightening torque can be increased rapidly, and if it exceeds 0.12 mm, the change in tightening torque decreases. I found out.

  In addition, even if the dimension of the length S of the shortest portion of the screwless portion 14 is 0 mm, the entire screwless portion 14 is not lost. Since the unthreaded portion 14 is formed along the spiral of the screw, even if the length of the shortest portion of the unthreaded portion 14 becomes 0, the length opposite to 180 ° is ½ of the thread pitch. The non-threaded portion is formed.

  In the present invention, the thread pitch P is in the range of 0.6 to 0.75 mm. When the bone tapping screw 10 was prototyped while changing the parameters, when the thread pitch P was 0.6 mm, the number of rotations until the torque reached a peak was about 6 revolutions, but the thread pitch P was 0.75 mm. If it becomes, it reaches a peak at about 4.5 rotations. If the thread pitch P is increased in this way, the number of rotations can be reduced, so that the screwing operation can be performed quickly. However, if the thread pitch P is increased to 0.75 mm or more, the force for pushing the screw has to be increased. Therefore, the value of the thread pitch P is preferably 0.75 mm or less.

  In the present invention, the valley diameter D of the straight threaded portion 12 is in the range of 0.85 to 1.4 mm, the peak diameter is 1.4 to 2.0 mm, and the difference between the peak diameter and the valley diameter D is 0.1. It was made to enter the range of 45-0.85 mm. When the valley diameter D is made as small as possible, the friction surface between the bone and the bone tapping screw 10 becomes smaller, so the tightening torque is reduced and the work is good. However, the difference between the peak diameter and the valley diameter D is reduced. If it is larger than 0.85 mm, there is a high risk that the trough will be sheared when screwed. In addition, if the valley diameter D is thicker than 1.4 mm, the screwing torque increases due to friction, so the maximum diameter is set to 1.4 mm in the present invention. On the other hand, if the difference between the crest diameter and the trough diameter D is smaller than 0.45 mm, the difference in tightening torque becomes small, so that it is difficult to determine the end of tightening. The head 11 has a mountain diameter of 2.5 to 3.5 mm, which is within the range of the size of a conventional bone tapping screw.

  In the present invention, the angle α between the axial direction of the screw and the thread is in the range of 55 to 65 °. This is because when the angle α exceeds 65 °, there is a disadvantage that the tip portion of the screw thread is bent. This is because if the angle is less than 55 °, the tightening torque becomes too large.

  FIG. 2 is a cross-sectional view showing a state in which the bone tapping screw 10 of the present invention is fixed to the bone 25 via the plate 20. By making the lower surface 15 of the head 11 a curved surface along the plate portion 21 of the screw through hole of the plate 20, the stability of the plate 20 is improved. Moreover, it is easy to become familiar even when the bone tapping screw 10 is not screwed straight. The radius of curvature R of the lower surface 15 of the head 11 was set to a range of 1.0 to 2.0 mm in consideration of the thickness of the plate 20 and the size of the bone tapping screw 10. By making the lower surface 15 have such a radius of curvature, it is possible to easily detect the completion of tightening.

  FIG. 3 is a graph comparing torque changes during screwing of the conventional tapping screw (Example 4) of the present invention. The number of materials n is 3 each, and the average value of each torque screwed into Trewood (registered trademark) of artificial wood used as a material close to bone is plotted. Trewood is made of polystyrene and has a light foam layer wrapped with a high density and strong skin layer, and has a light and robust property.

  Table 1 is a table showing the parameters of the bone tapping screw 10 of the present invention (Examples 1 to 4 and preferred ranges) and the conventional type. The difference between the present invention used in this test and the conventional bone tapping screw is that the thickness S (the unthreaded portion length) of the shortest axial length of the unthreaded portion 14 is 0 to 0. 0 in the present invention. The difference between the peak diameter and the valley diameter D is 0.45 to 0.85 mm. In Example 1, the difference between the crest diameter and the trough diameter is set to 0.85 mm (crest diameter 2.0 mm), and the unthreaded portion length is set to 0.12 mm. In Example 2, the difference between the crest diameter and the trough diameter is set. In addition to 0.45 mm (crest diameter 1.85 mm), the unthreaded portion length is 0 mm. In Example 3, the difference between the crest diameter and the trough diameter is 0.7 mm (crest diameter 1.9 mm). The screw part length was 0 mm, and in Example 4, the difference between the crest diameter and the trough diameter was 0.55 mm (crest diameter 1.4 mm), and the unthreaded part length was 0 mm. It is considered that the curvature radius R of the lower surface 15 of the head 11 does not particularly affect the test result of this time.

  “Inclination (N / cm / rad)” shown in Table 1 is a value indicating the gradient of the straight lines a and b indicating the torque change tendency at the completion of tightening in the torque change curve in FIG. A larger value indicates that the tightening torque increases rapidly. When the torque rises rapidly, it is possible to clearly recognize that the tightening has been completed. The slope of this straight line was 1.5 for the straight line b of the conventional product, but 2.6 for the straight line a (Example 4) of the present invention, which was a significant improvement. As a result of investigating the doctor's feeling about tightening the screws of the conventional product and each example, it was difficult to determine that the tightening of the conventional product was completed, but the tightening of all of Examples 1 to 4 was completed. I was able to recognize this clearly. In the example, since the inclination is 2.1 or more, it is considered that the inclination (N / cm / rad) is preferably about 2.0 or more.

  Further, from the graph of FIG. 3, the number of rotations up to the peak of the torque is about 5 rotations in the conventional type, but about 6 rotations in the bone tapping screw of the present invention, and a difference of about 1 rotation is seen. . Since the thread pitch P is the same at 0.6 mm, this is caused by an increase in the number of threads because the bone tapping screw of the present invention used in the test did not have the unthreaded portion 14. It is a difference.

  When the torque is compared, there is almost no difference until around the first rotation, but after that, the torque of the bone tapping screw of the present invention is slightly smaller and remains unchanged. Until the first rotation, the shaft of the tip screw portion 13 is conical, so there is no difference due to the difference in the valley diameter D of the straight screw portion 12, but after that, there is a difference in torque resistance due to the difference in the valley diameter D. It is thought that there is.

  Further, it can be seen that the torque of the conventional type gradually increases toward the peak, whereas in the bone tapping screw of the present invention, the torque suddenly increases after the fifth rotation. Furthermore, since the peak value of the torque is about 1.5 times that of the conventional type, the difference between the conventional type and the present invention when the screwing operation is performed is clear. The cause of such a difference in torque fluctuation is that the influence of the size of S of the screwless portion 14 is large by comparing various parameters of the conventional tapping screw 10 of the present invention and the bone tapping screw 10 of the present invention shown in Table 1. Conceivable. Since S is 0 or very small, it is considered that the threading ends suddenly and the torque suddenly increases.

  In the curve showing the change in torque in FIG. 3, the torque decreases after exceeding the peak, but this is a state where a so-called screw has become stupid, and when used for bone, the bone is damaged. It becomes a state. Therefore, actually, the tightening of the bone tapping screw is completed before the peak.

It is a figure of the tapping screw for bones of this invention, (a) is a top view, (b) is a front view. It is sectional drawing which shows the state which fixed the bone tapping screw of this invention to the bone through the plate. It is the graph which compared the change of the fastening torque at the time of screwing in the conventional product and the tapping screw for bones of the present invention.

Explanation of symbols

10 Bone tapping screw 11 Screw head 12 Straight screw portion 13 Tip screw portion 14 Unthreaded portion 15 Lower surface 20 Plate P Screw pitch α Angle between screw axial direction and screw thread D Valley diameter R of straight screw portion Radius of curvature S on the bottom of the plate The axial length of the unthreaded part is the thickness of the shortest part

Claims (4)

A bone tapping screw used to fix the bone with a plate,
A screw head to which torque is applied for screwing;
A substantially conical tip threaded portion with a thread located near the screw tip;
A linear threaded portion having a thread extending from the tip threaded portion to a cylindrical shaft portion;
A non-threaded portion that is located between the screw head and the straight threaded portion and has a diameter larger than the root diameter of the straight threaded portion and is not provided with a thread;
The bone tapping screw, wherein the length of the shortest axial length of the screwless portion is 0.12 mm or less.   The bone tapping screw according to claim 1, wherein a crest diameter of the bone tapping screw is 1.4 to 2.0 mm, and a difference between a crest diameter and a trough diameter is 0.45 to 0.85 mm.   The bone tapping screw according to claim 1 or 2, wherein an angle between an axial direction of the bone tapping screw and a screw thread is 55 to 65 °.   The bone tapping screw according to any one of claims 1 to 3, wherein the countersunk bottom surface of the screw head has a curved surface shape having a curvature radius of 1.0 to 2.0 mm.

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