JP5823752B2 - Bone fixation screws - Google Patents

Description

  The present invention relates to a self-piercing bone fixing screw used in, for example, a craniotomy.

  For example, craniotomy may be performed to treat brain tumors, cerebral thrombi, and the like. In this craniotomy, the scalp of the temporal region is incised, a plurality of holes called bar holes are made in the temporal region of the skull, the bone is cut starting from this, and the cut part (called bone flap) is removed. Then, the skull is opened, and treatment is appropriately performed through the opening, and then the bone flap is returned to the opening and fixed, and the wound on the scalp is sewn.

  As mentioned above, when fixing the bone flap returned to the opening of the skull to the skull, an elongated plate with screw holes formed at both ends, a square frame plate with screw holes formed at the four corners, etc. Is being used. Then, a screw is screwed into each screw hole of the plate arranged between the periphery of the opening of the skull and the periphery of the bone flap, and is fastened and fixed. As the screw used at this time, a self-drilling screw (so-called tapping screw) that does not require the formation of a female screw is generally used. Thus, the plate is screwed and fixed to the periphery of the opening of the skull and the bone flap, so that the bone flap is fixed to the skull via the plate.

  By the way, as a conventional bone fixing screw, for example, those shown in FIGS. The screw 3 includes a head portion 4 and a shaft portion 5, the tip of which is pointed, and a helical thread 5 a is formed from the tip of the shaft portion toward the base side. However, since the tip of the screw 3 is sharp and thin, rigidity may be insufficient, and when the screw 3 is screwed into the bone, the tip portion 5b of the shaft portion 5 may be broken or deformed.

  On the other hand, Patent Document 1 below describes a self-piercing bone screw for preventing the tip portion of the screw shaft from being bent or broken. As for this screw, the thread is formed with the pitch of about 0.7-1.0 mm toward the axial part base end from the front-end | tip of an axial part. And since the front end surface of the shaft portion is a flat surface substantially orthogonal to the center of the shaft portion, and the front end portion of the shaft portion is formed relatively thick, deformation or the like during screwing in the bone is suppressed. It has become. In addition, since a part of the outer periphery of the shaft tip is inclined at an angle of 34 to 43 ° with respect to the flat surface of the shaft tip, the tip of the shaft bites into the bone. .

JP 2005-177473 A

  However, in the screw described in Patent Document 1, although the outer peripheral portion of the shaft portion tip portion is inclined, the shaft portion tip surface is flat and the shaft portion tip portion is formed thick. However, there was a disadvantage that it was difficult to bite into the bone. Therefore, there is a problem in workability because it is necessary to screw a screw while pressing the distal end portion of the shaft portion against the bone with a high pressing load.

  Accordingly, an object of the present invention is to provide a bone fixing screw that can be easily screwed in with a low pressing load without the tip portion of the shaft portion being bent or deformed.

  In order to achieve the above object, the present invention includes a head portion into which a tool can be fitted, and a shaft portion protruding from the center of the back surface of the head portion, the tip of the shaft portion is sharp, In a self-piercing bone fixation screw in which a spiral thread is formed from the tip toward the base, the thread is formed with a predetermined length in the axial direction from the tip of the shaft toward the base. The first screw thread and a length shorter than the first screw thread in the axial direction from the tip end of the shaft portion toward the base side, and at least at the tip portion, between the pitches of the first screw thread And a second thread formed so as to be disposed at the end of the second thread. The terminal of the second thread is formed so as to converge on the first thread.

  In the bone fixing screw of the present invention, it is preferable that the pitch of the second thread is larger than the pitch of the first thread.

  Another aspect of the present invention includes a head portion into which a tool can be fitted, and a shaft portion protruding from the center of the back surface of the head portion, the tip of the shaft portion being sharp, and the base portion from the tip of the shaft portion In a self-piercing bone fixation screw in which a spiral thread is formed toward the side, the thread is a first length formed in the axial direction from the distal end of the shaft toward the base. One screw thread and a length shorter than the first screw thread in the axial direction from the tip end of the shaft portion toward the base side, and at least the tip portion is disposed between the pitches of the first screw thread. And when the shaft portion is viewed in the axial direction, the rotation angle from the start end to the end of the second screw thread is 90 to 720 °. The second screw thread is formed.

  According to the present invention, when the tool is fitted to the head, the tip of the shaft is pressed against the bone, and the bone fixing screw is rotated through the tool, the first thread formed on the tip of the shaft is formed. The second screw thread bites into the bone and is screwed by self-tapping, so that the bone fixing screw can be fixed to the bone. As described above, since the two screw threads bite into the bone at the beginning of screwing, the biting on the bone can be improved, and the screw can be easily screwed with a low pushing load, thereby improving workability. In addition, when the distal end of the bone fixing screw is screwed in to some extent, the second screw thread is eliminated and only the first screw thread is obtained. And it can prevent that fixing force falls. Moreover, since the biting to the bone is improved by the two screw threads, the tip portion of the shaft portion can be made relatively thick, and the tip portion of the shaft portion can be prevented from being broken or deformed when screwed. .

1 shows an embodiment of a bone fixation screw according to the present invention, wherein (a) is a perspective view thereof, and (b) is a perspective view when viewed at an angle different from (a). The same bone fixing screw is shown, (a) is a front view, (b) is a right side view. The same bone fixation screw is shown, (a) is a rear view, (b) is a left side view. It is a bottom view of the same bone fixing screw. It is a perspective view which shows the use condition at the time of using the screw for bone fixation for craniotomy. It is explanatory drawing which shows the use condition of the screw for same bone fixation. It is a graph which shows the result of an indentation load measurement test. FIG. 2 is a front view of a conventional bone fixing screw. It is a bottom view of the fixing screw.

  Hereinafter, with reference to FIGS. 1-6, one Embodiment of the screw for bone fixation of this invention is described.

  As shown in FIGS. 1A and 1B, a bone fixing screw 10 (hereinafter simply referred to as “screw 10”) in this embodiment includes a head 20 formed in a substantially disc shape with a predetermined thickness. The shaft portion 30 protrudes from the center of the back surface of the head portion 20.

  As shown in FIG.1 (b), the fitting groove | channel 21 which the front-end | tip part 7a of the tool 7 shown in FIG.5 and FIG.6 fits is formed in the surface side of the said head 20. As shown in FIG. The fitting groove 21 in this embodiment has a cross shape corresponding to the tip 7 a of the tool 7.

  As shown in FIGS. 1 to 3, the shaft portion 30 in this embodiment has a stepped diameter from the base portion 32 toward the tip 31, and the tip 31 has a pointed shape. A spiral thread 35 composed of a first thread 37 and a second thread 39 is formed from the tip 31 of the shaft 30 toward the base 32, and the circumferential direction of each thread 37, 39 is formed. The tip is also pointed. That is, the screw 10 is a self-piercing type (so-called tapping screw) that is fixed by tightening the bone 30 while screwing the shaft portion 30 into the bone such as the skull 1 or the bone flap 2 shown in FIG. is there. In addition, although the screw 10 in this embodiment is a right-hand screw whose clockwise direction is clockwise (clockwise) when the shaft portion 30 is screwed into the bone, it may be a left-hand screw in the opposite direction.

  As shown in FIGS. 1 to 3, the first thread 37 is formed with a predetermined length in the axial direction from the tip 31 of the shaft portion 30 toward the base portion 32. The first thread 37 in this embodiment is formed in a spiral shape from the tip 31 to the base 32 along the circumferential direction of the shaft portion 30.

  As shown in FIG. 2 (a), the distance between adjacent first screw threads 37, that is, the pitch P1 of each first screw thread 37 is preferably 0.5 to 1.0 mm. More preferably, it is 6 to 0.8 mm. When the pitch P1 of the first screw threads 37 is less than 0.5 mm, the screw pitch becomes too short, and it takes time for the screwing operation, and the inner periphery of the bone tends to collapse. On the other hand, when the pitch P1 exceeds 1.0 mm, the indentation load of the screw 10 becomes large and a strong force is required.

  In relation to the first thread 37, the outer diameter of the distal end portion 33 of the shaft portion 30 is preferably set to the following dimensions. That is, as shown in FIG. 2 (a), at the tip portion 33 of the shaft portion 30, the first screw thread 37 that is 180 ° opposite to the first screw thread 37 starts to appear. The distance from the portion is defined as the outer diameter D of the distal end portion 33 of the shaft portion 30. The outer diameter D of the tip portion 33 of the shaft portion 30 is preferably 0.1 to 0.4 mm, and more preferably 0.2 to 0.3 mm. If the outer diameter D of the tip portion 33 of the shaft portion 30 is less than 0.1 mm, it is difficult to ensure the rigidity of the tip portion 33 of the shaft portion 30, which is not preferable. On the other hand, when the outer diameter D exceeds 0.4 mm, the insertion resistance of the shaft portion 30 to the bone tends to increase, which is not preferable.

  On the other hand, the second thread 39 has a length shorter than the first thread 37 in the axial direction from the tip 31 of the shaft part 30 toward the base 32 side, and at least at the tip part 33 of the shaft part 30. The first screw thread 37 is formed between the pitches P. In this embodiment, the second thread 39 is formed from the first thread 37 of the first thread 37 provided at the tip 33 of the shaft 30 and the first winding 31 counted from the tip 31 of the shaft 30. It is formed between the two peaks counted (see FIGS. 1, 2A, and 3).

  Further, the second thread 39 is formed from the tip 31 of the shaft portion 30, similarly to the first thread 37. However, as shown in FIG. 4, the start end 37 a of the first thread 37 and the start end 39 a of the second thread 39 join at a position slightly shifted in the circumferential direction at the tip 31 of the shaft portion 30. Yes. The second thread 39 extends in a spiral shape along the circumferential direction of the shaft portion 30, and its end 39b is formed to converge on the first thread 39 (FIGS. 1 and 4). reference).

  Further, as shown in FIG. 4, when the shaft portion 30 is viewed from the front end 31 side in the axial direction, the rotation angle θ3 from the start end 39a to the end end 39b of the second thread 39, that is, the axis C of the shaft portion 30 An angle θ3 between a line S1 connecting the start end 39a of the second thread 39 and a line S2 connecting the axis of the shaft portion 30 and the end 39b of the second thread 39 is 90 to 720 °. The second thread 39 is preferably formed. Furthermore, it is more preferable that the second thread 39 is formed so that the rotation angle θ3 is 180 to 450 °.

  When the rotation angle θ3 of the second thread 39 is less than 90 °, it is not preferable because stable processing of the thread becomes difficult and the biting effect of the second thread 39 on the bone tends to be insufficient. . On the other hand, when the rotation angle θ3 exceeds 720 °, the length in which the first screw thread 37 and the second screw thread 39 are formed becomes long, and a screw groove having a small pitch is formed in the inner circumference of the bone. As a result, there is a possibility that the bone is liable to collapse, and as a result, the fixing force of the screw 10 to the bone may be reduced, which is not preferable.

  As shown in FIG. 2A, when it is assumed that the second thread 39 is formed 360 ° or more along the circumferential direction of the shaft portion 5, that is, one or more turns, the adjacent second screw 39. The distance between the mountains 39 and 39 is defined as the pitch P2. At this time, the pitch P2 of the second thread 39 is preferably formed larger than the pitch P2 of the first thread 37. Further, the pitch P2 of the second thread 39 is preferably 0.7 to 1.5 mm, and more preferably 0.9 to 1.2 mm. When the pitch P2 of the second screw threads 39 is less than 0.7 mm, the screw pitch is short, it takes time for the screwing operation, and the inner circumference of the bone tends to collapse, which is not preferable. On the other hand, when the pitch P2 exceeds 1.5 mm, the biting effect on the bone by the second thread 39 is reduced, which is not preferable.

  The material of the screw 10 is not particularly limited, and examples thereof include Ti, Ti—Al—V, Ti—Al—Nb—Ta, Ti—Zr—Nb—Ta, Ti—Mo—Zr—Al, and the like. Metal materials such as Ti-based alloys, stainless steel, Ni-Ti-based alloys, Co-Cr-based alloys, so-called biodegradable polymers made of lactide, glycolide, caprolactone, etc., fluororesins, polyethylene, polypropylene, polyimide, etc. It can be formed from a synthetic resin or the like, and it is particularly preferable to use Ti or a Ti-based alloy from the viewpoint of biocompatibility and corrosion resistance. In addition, as a manufacturing method of the said screw 10, the 1st thread 37 and the 2nd thread 39 can be formed in the axial part 30 by rolling, cutting, etc., for example.

  Next, an example of how to use the screw 10 according to the present invention will be described. The screw 10 is fixed by being screwed into the bone, and its use is not particularly limited. Here, the case where the screw 10 is used for plate fixation at the time of craniotomy will be described.

  As shown in FIG. 5, when performing a craniotomy for treatment of a brain tumor, a cerebral thrombus, etc., it is performed as follows, for example. That is, the scalp is incised to open a plurality of bar holes (not shown), a part of the skull 1 is excised using these as base points, and the bone flap 2 is removed. Then, after opening the skull 1, treatment of the above-described brain tumor, cerebral thrombus, and the like is appropriately performed through the opening 1 b. After the treatment, the bone flap 2 is returned to the opening 1b and the bone flap 2 and the skull 1 are fixed. At this time, the bone fixing plate 6 is used. In the case of this embodiment, the plate 6 has a rectangular frame shape, and screw insertion holes 6a are formed at the four corners. However, the plate may be an elongated plate having screw insertion holes formed at both ends, and is not particularly limited.

  Then, one side of the plate 6 is arranged on the peripheral side of the opening 1b of the skull 1, and the other side of the plate 6 is arranged on the bone flap 2 side. In this state, the screw 10 is disposed in each screw insertion hole 6a, the tip portion 7a of the tool 7 is fitted into the fitting groove 21 of the head 20, and the sharp tip 31 of the shaft portion 30 is set to the skull 1 or bone flap. 2 (hereinafter simply referred to as “bone”), the screw 10 is rotated clockwise through the tool 7 (see FIG. 6).

  Then, the first screw thread 37 and the second screw thread 39 formed at the distal end portion 33 of the shaft portion 30 bite into the bone and are screwed by self-tapping.

  At this time, in the screw 10, the tip portion 33 of the shaft portion 30 has not only the first screw thread 37 but also a length shorter than the first screw thread 37 and a pitch P between the first screw threads 37. Since the second screw thread 39 is formed so as to be disposed at the same time, as shown in FIG. 6, when the screw 10 is screwed in, both the two screw threads 37 and 39 bite into the bone. As a result, it is possible to improve the biting of the tip 33 of the shaft 30 of the screw 10 to the bone, so that it is necessary to screw in while pushing strongly against the bone as in the screw described in Patent Document 1. Therefore, the screw 10 can be easily screwed with a low indentation load, and the workability of fixing the screw 10 to the bone can be improved.

  Further, in this embodiment, the pitch P2 of the second thread 39 is formed larger than the pitch P1 of the first thread 37 (see FIG. 2 (a)). The biting can be made better, and the end 39b of the second thread 39 can be gradually converged to the first thread 37.

  When the distal end portion 33 of the screw 10 is screwed to some extent, the second screw thread 39 disappears and only the first screw thread 37 is obtained. Therefore, the screw pitch is made long to some extent, and the inner periphery of the bone is broken by the screw thread 35. Therefore, it is possible to effectively prevent a reduction in the fixing force of the screw 10 to the bone.

  Furthermore, since the bite of the tip portion 33 of the shaft portion 30 of the screw 10 to the bone is improved by the two screw threads 37 and 39, the tip portion 33 of the shaft portion 30 can be made relatively thick. It is possible to prevent the distal end portion 33 of the shaft portion 30 from being bent or deformed during screwing. In particular, in the present embodiment, the outer diameter D of the distal end portion 33 of the shaft portion 30 is 0.1 to 0.4 mm, so that the rigidity of the distal end portion 33 can be increased while suppressing insertion resistance.

  Further, in this embodiment, as shown in FIGS. 1 and 4, the end 39 b of the second thread 39 is formed so as to converge on the first thread 37. 39b and the first screw thread 37 can be prevented from being stepped, and the second screw thread 39 and the first screw thread 37 can be smoothly connected to each other. It is possible to prevent the torque from fluctuating rapidly and to perform the screwing operation smoothly.

  Furthermore, in the present embodiment, when the shaft portion 30 is viewed from the front end 31 side in the axial direction, the second rotation angle θ3 from the start end 39a to the end end 39b of the second thread 39 is 90 to 720 °. Since the screw thread 39 is formed, it is possible to improve the biting to the bone at the beginning of screwing and to shorten the length in which the first screw thread 37 and the second screw thread 39 are formed. As a result, a screw groove with a small pitch is formed long on the inner periphery of the bone, and the bone is easily broken, so that the fixing force of the screw 10 to the bone can be prevented from being reduced.

  As described above, the shaft portion 30 of the screw 10 is screwed into the bone, and the head portion 20 of the screw 10 is engaged with the inner periphery of the screw insertion hole 6a of the plate 6 through the screw 10. The plate 6 can be fixed to both the skull 1 and the bone flap 2, and the bone valve 2 can be held in a state of being fitted to the opening 1 b of the skull 1. The screw 10 can be used not only for fixing the skull and bone flap during craniotomy as described above, but also for fixing bones during fractures of arms and legs, and is particularly limited. It is not a thing.

  The indentation load on the bone was measured.

(Example)
As an example, the same screw as that shown in FIGS. The outer diameter D (see FIG. 2A) of the distal end portion 33 of the shaft portion 30 is 0.23 mm.

(Comparative example)
As a comparative example, a screw having the same form as the conventional screw 3 shown in FIGS. That is, the second screw thread is not formed on the screw of the embodiment. In addition, the outer diameter of the front-end | tip part of an axial part is 0.20 mm.

(Test method)
The pseudo bone is placed on a test apparatus having a mechanism capable of applying a rotational torque while applying a pushing load. Next, the screws of the example and the comparative example are screwed into the pseudo bone at a rotation speed of 30 rpm while gradually applying the pushing load by the above mechanism. Then, when the rotational torque value reached 5 mN · m, the screwing operation was stopped and the indentation load (N) at that time was measured. This was measured for each of the screws of the examples and comparative examples, and the average was obtained. The results are shown in Table 1 below. FIG. 7 shows a chart comparing the average values.

As can be seen from Table 1 and FIG. 7, the indentation load of the example screw can be reduced by about 17.3% compared to the comparative example screw although the tip part has a larger outer diameter. I understood. That is, according to the screw of the present invention, it was confirmed that the pushing load was low and the fixing workability was excellent while ensuring the rigidity of the tip of the shaft portion to prevent breakage and deformation.

10 Bone fixing screws (screws)
20 Head 30 Shaft 31 Tip 32 Base 33 Tip 35 Thread 37 First Thread 39 Second Thread 39a Start End 39b End

Claims (3)

A head having a head into which a tool can be fitted and a shaft protruding from the center of the back surface of the head, the tip of the shaft being sharp, and a spiral screw from the tip of the shaft toward the base In the self-drilling bone fixation screw with a mountain,
The thread includes a first thread formed with a predetermined length in the axial direction from the tip of the shaft toward the base, and the first thread in the axial direction from the tip of the shaft toward the base. A second screw thread having a length shorter than that of the screw thread, and at least a tip portion formed so as to be disposed between the pitches of the first screw thread,
The bone fixation screw is characterized in that an end of the second screw thread is formed so as to converge to the first screw thread.   The bone fixing screw according to claim 1, wherein a pitch of the second screw thread is larger than a pitch of the first screw thread. A head having a head into which a tool can be fitted and a shaft protruding from the center of the back surface of the head, the tip of the shaft being sharp, and a spiral screw from the tip of the shaft toward the base In the self-drilling bone fixation screw with a mountain,
The thread includes a first thread formed with a predetermined length in the axial direction from the tip of the shaft toward the base, and the first thread in the axial direction from the tip of the shaft toward the base. A second screw thread having a length shorter than that of the screw thread, and at least a tip portion formed so as to be disposed between the pitches of the first screw thread,
Bone fixation, wherein the second thread is formed such that a rotation angle from the start end to the end of the second thread is 90 to 720 ° when the shaft portion is viewed in the axial direction. Screws.