Abstract
The invention relates to a screw (1), preferably a bone screw, comprising a shaft (2) with a tip (3), a head (4) and a thread (5). The shaft further comprises a longitudinal axis (A). An array of radial cross-sectional surfaces (Q) of the head (4) extend through the longitudinal axis (A) of the screw (1), the location of each radial cross-sectional surface (Q) being defined by an azimuth angle (6) in a plane (E) perpendicular to the longitudinal axis (A). Each radial cross-sectional area (Q) has an area defined by the longitudinal axis (A) and the outer surface of the screw (8). The thread (5) extends into the head (4) in such a way that the surface areas of the radial cross-sectional surfaces (Q′) in a first azimuth angle range (9) are constant and the surface areas of the radial cross-sectional surfaces (Q″) in a second azimuth angle range (10), which is different from the first, have a different, preferably smaller, value than the surface areas in the first azimuth angle range (9). The first azimuth angle range (9) is at most 350°, preferably at most 345°.
Claims
1-18. (canceled)
19. A screw, comprising a shaft with a tip, a head and a thread, as well as a longitudinal axis of the shaft, and a set of radial cross-sectional surfaces of the head passing through the longitudinal axis of the shaft, wherein the position of each radial cross-sectional surface is defined by an azimuth angle in a plane (E) perpendicular to the longitudinal axis, and wherein each radial cross-sectional surface comprises an area defined by the longitudinal axis and the outer surface of the screw, wherein the thread extends into the head in such a way that the surface areas of the radial cross-sectional areas in a first azimuth angle range are constant and the surface areas of the radial cross-sectional areas in a second azimuth angle range which is different from the first have a different value than the surface areas in the first azimuth angle range, the first azimuth angle range being at most 350°.
20. The screw according to claim 19, wherein the first and second azimuth angle ranges are each divided into at least two sections distributed at equal azimuth angle intervals.
21. The screw according to claim 20, wherein the first azimuth angle range is at most 330°.
22. The screw according to claim 19, wherein the thread is multi-threaded.
23. The screw according to claim 19, wherein the head has, in the second azimuth angle region, at least one indentation formed by the continuation of the thread.
24. The screw according to claim 20, wherein the head has, in the second azimuth angle region, at least one indentation formed by the continuation of the thread.
25. The screw according to claim 24, wherein the head has a number of indentations formed by the continuation of the thread corresponding to the number of sections of the azimuth angle region.
26. The screw according to claim 25, wherein each portion of the azimuth angle region comprises a indentation formed by the continuation of the thread.
27. The screw according to claim 23, wherein the at least one indentation, which is formed by the continuation of the thread, is arranged on an underside of the head in the region of the thread finish.
28. The screw according to claim 19, wherein the radial cross-sectional surfaces have a geometric center, and each geometric center of the radial cross-sectional surfaces in the first azimuth angle range has the same distance from the longitudinal axis.
29. The screw according to claim 19, wherein the screw is formed, such that each radial cross-sectional area is connected.
30. The screw according to claim 19, wherein a first normal cross-section in a plane perpendicular to the longitudinal axis in the head region is at least partially non-circular.
31. The screw according to claim 30, wherein a second normal cross-section is circular and is parallel to the first normal cross-section, and the first normal cross-section is arranged along the longitudinal axis of the screw between the tip of the screw and the second normal cross-section.
32. A system comprising a bone plate and a bone screw, wherein the bone plate comprises at least one opening for insertion of the bone screw, and wherein the bone screw comprises a head, a shaft and a through-thread, wherein the bone screw is insertable into the opening of the bone plate such that the head is in contact with the bone plate, and the thread extends at least partially into the opening.
33. A method for producing a screw with a tool, comprising the steps: providing a slug material having a substantially cylindrical shape; cutting a thread along a longitudinal axis of the cylindrical shape with the tool; and forming a head, wherein the slug material is gripped on the head by means of a contour collet, the contour collet having a contour which, in the gripped state, is in operative connection with a mating contour of the head.
34. The method according to claim 33, wherein the contour of the contour collet is at least partially complementary to the mating contour of the head of the screw.
35. The method according to claim 33, wherein the thread is cut by means of the tool at least close enough to the head that the tool forms an indentation on an underside of the head.
36. The method according to claim 33, wherein the tool comprises a whirling plate that does not comprise an overcut in a cutting direction.
37. The method according to claim 33, wherein after cutting the thread with the tool, the head is further machined by means of a CNC lathe.
Description
[0059] The invention is explained in detail below with reference to the following figures, showing:
[0060] FIG. 1: a screw in a side view.
[0061] FIG. 2a-2c: a screw head of a screw in a side view, perspective view, and bottom view.
[0062] FIG. 3a-3c: cross-sections of a screw head in planes E, E′ and E″ of FIG. 2c.
[0063] FIG. 4: a bottom view of a head of an alternative embodiment of a screw.
[0064] FIG. 5: a bone plate with a screw.
[0065] FIG. 6: a side view of an alternative screw.
[0066] FIG. 7: schematic of a process step for manufacturing a screw.
[0067] FIG. 1 shows a screw 1 according to the invention in a side view. The screw 1 comprises a shaft 2 with a tip 3, a thread 5, and a head 4. In the present case, the head 4 is bounded by a plane 52 which is perpendicular to the longitudinal axis A of the screw 1. The plane 52 is positioned along the longitudinal axis A in such a way that the shaft 2 of the screw 1 in the distal direction of the tip 3 (to the right of the plane 52 in FIG. 1) in cross-section perpendicular to the longitudinal axis does not project anywhere beyond the radius of the external thread 51′,51″. A section in the other proximal direction (to the left of plane 52 in the illustration of FIG. 1), on the other hand, projects beyond the radius of the external thread 51′,51″ and defines the head 4 of the screw. The thread 5 extends beyond the plane 52 into the head and forms an indentation 7 on the lower side U of the head 4.
[0068] FIG. 2a shows the head 4 of the screw 1 according to the invention in a side view. For better understanding, a part of the shaft 2 with the thread 5 is also shown. The plane 52 separates the head 4 from the shaft 2. The thread 5 extends beyond the plane 52 into the head and forms an indentation on the underside of the head. The screw head 4 therefore comprises a first normal cross-section 12 and a second normal cross-section 13. The first normal cross-section 12 intersects the indentation 7 and is therefore non-circular. The second normal cross-section 13 is further away from the screw tip 3 along the longitudinal axis than the first normal cross-section 12. It therefore follows that the first normal cross-section 12 is arranged along the longitudinal axis A between the second normal cross-section 13 and the tip 3. Since the second normal cross-section 13 lies above the indentation 7, the second normal cross-section has a circular shape. A plane E, which is coplanar with the longitudinal axis A, is adjacent to the indentation 7.
[0069] FIG. 2b shows the screw head 4 from FIG. 2a in a perspective view. An azimuth angle 6 is drawn in a counterclockwise direction around the longitudinal axis A, with the plane E serving as the zero point for the following figures. As explained above, any other zero point could be selected. It would also be possible to measure the azimuth angle 6 in a clockwise direction. FIG. 2c shows the screw head 4 from FIGS. 2a and 2b in a bottom view. The longitudinal axis A, not shown here, runs perpendicular to the image plane, so that the azimuth angle 6 lies correspondingly in the image plane. A first azimuth angle region 9 has no indentation 7 and extends over an azimuth angle of 195°. The indentation 7 accordingly extends over an azimuth angle of 165° and defines a second azimuth angle range 10. The second azimuth angle range 10 therefore has a value of 165°. Due to the indentation 7, the cross-sections of the screw head 4 in planes through the longitudinal axis, which lie at least partially in the second azimuth angle range 10, are not mirror-symmetrical with respect to the longitudinal axis A. The radial cross-sections bounded by the longitudinal axis A on one side and by the outer surface of the head 4 on the other side have a smaller area in the second azimuth angle region 10 than in the first azimuth angle region 9. This feature is described below by means of cross-section figures in the planes E, E′ and E″ shown here. As mentioned above, plane E is at an azimuth angle 6 of 0°, plane E′ is at an azimuth angle 6 of 135° and plane E″ is at an azimuth angle 6 of 300°. All planes are marked here on one side with a dot, which should facilitate the understanding of the plane orientation in the following figures.
[0070] FIG. 3a shows a cross-sectional view of the screw head of FIGS. 2a-2c in the plane E. The head 4 is bounded by the plane 52, so that only the area within the boundary of the head 4 and the plane 52 is included for the following discussion of surface areas. Two radial cross sections Q′ are each bounded by the outline of the head 4, the longitudinal axis A and the plane 52 and have surface areas Q′. The plane E does not intersect the indentation 7 (not shown here). Therefore, both surface areas Q′ are identical and are located in the first azimuth angle area 9. The cross section is mirror symmetrical with respect to the longitudinal axis A. Therefore, the two radial cross sections Q′ have the same shape. Finally, the radial cross-sectional area Q′ comprises a geometric center 11, which has a distance and a position with respect to the longitudinal axis A. Both position and distance of the geometric center 11 are the same for all surface areas Q′ located in the first azimuth angle range 9. The screw head can contain a drive, for example a Torx drive (not shown). This has not been included in the present calculation of the surface areas. Instead, the drive was filled in mentally and its area counted as part of the head 4. It is also evident from FIG. 3a, as well as from the following FIGS. 3b and 3c, that the radial cross-sections Q′,Q″ are path-contiguous and simply contiguous. This means that all points within the surface can be connected by a path belonging to the surface. In addition, each closed path within the surface can be contracted to one point. This might not be possible with a screw head that contained a hole.
[0071] FIG. 3b shows a cross-sectional view of the screw head 4 of FIGS. 2a-2c in the plane E′. Two radial cross sections Q′,Q″ are each bounded by the outline of the head 4, the longitudinal axis A and the plane 51 and have surface areas. The radial cross sections Q′,Q″ differ in shape and surface area. The radial cross section Q″ is located in the second azimuth angle area 10 and is therefore located in a head area that has an indentation 7. The radial cross section Q″ therefore has a smaller surface area than the radial cross section Q′. The radial cross section Q′, on the other hand, has the same surface area as well as the same shape as the two radial cross sections Q′ from FIG. 3a, since they are located in the first azimuth angle area 9. Likewise, the geometric center 11 of the radial cross section Q′ is arranged at the same distance and in the same position relative to the longitudinal axis A as shown in FIG. 3a.
[0072] FIG. 3c shows a cross-sectional view of the screw head 4 of FIGS. 2a-2c in the plane E″. The representation corresponds essentially to that of FIG. 3b, but the radial cross sections Q′ and Q″ are oriented in reverse. In the present figure, the geometric center 11 of the radial cross section Q″ is drawn. Said geometric center is variable in the second azimuth angle range 10, i.e. it can have a different position and a different distance to the longitudinal axis A depending on the azimuth angle. FIG. 4 shows a head 4 of an alternative embodiment of a screw 1 in a bottom view. The screw head 4 has two indentations 7 on its bottom side U. Such a screw head is particularly suitable for use with multi-threaded, in particular double-threaded, screws. The head areas that have an indentation 7 are located in the second azimuth angle area 10. The first azimuth angle area 9 does not have any indentations 7 and is therefore mirror-symmetrical relative to the longitudinal axis A, which is perpendicular to the image plane. The first azimuth angle region 9 and the second azimuth angle region 10 are each divided into two sections B1,B2,B3,B4, which are bounded by the respective other azimuth angle region 9,10 and are arranged at equal azimuth angle intervals. The bisecting line 14 of the boundaries of the sections is preferably used as the reference point for determining the angular separation. Therefore, the angular distance between the sections is 90°. The first azimuth angle range 9 has a total value of 90°, which is distributed over two sections of 45° each. Furthermore, when the screw head 4 shown is used with a screw with a double thread, the head 4 has the same number of sections as the thread has threads. Furthermore, each section of the second azimuth angle area 10 then has exactly one indentation 7.
[0073] FIG. 5 shows a screw 1 in the screwed-in state with a bone plate 15 in a thin cortical layer 16. The screw 1 corresponds essentially to the screw 1 shown in FIG. 1. Also shown is the plane 52 separating the head 4 from the shaft 2. Due to the indentation 7 and the thread 5 extending into the head 4, the thread 5 engages over at least part of the thickness of the bone 16, even though it is thin. The thread 5 extends forward into the opening of the bone plate 15.
[0074] FIG. 6 shows an alternative embodiment of a screw 1 produced with a modified whirling knife without an overcut. The indentation 7 is therefore smaller than in the screw 1 of FIG. 1, although the thread 5 corresponds essentially to the thread 5 of FIG. 1. The first azimuth angle region 9 has no indentation 7. The second azimuth angle range 10, in which the indentation 7 is located, has a value of 45°, for example. The first azimuth angle range 9 then has a value of 315°.
[0075] FIG. 7 schematically shows a process step for the manufacture of a screw 1. In this case, a whirling knife (not shown) was used to cut a thread 5 in a rod-shaped ingot material. In the process step shown, the screw 1 is held on the head 4 by means of a contour collet 30 after insertion of the thread 5. In addition, a guide sleeve 33 prevents the screw 1 from tilting when the contour collet 30 is opened. The contour collet 30 has a contour 31 for this purpose, which is designed in such a way that it forms a counter-contour to the head 4 of the screw 1. It is therefore suitable for gripping the head 4 of the screw 1 and holding it securely. However, it would also be conceivable to use other contours that grip, for example, on the head or parts of the head as well as parts of the screw shank or thread. In particular, only a section of the head 4 could also be held. By gripping the screw 1 on the head, as shown here, it is possible to further process the head 4, for example to manufacture a screw drive, here a Torx drive 32. In the present case, the process step is performed with a screw 1 as shown in FIG. 1 or FIG. 6, in which the thread extends into the head. Therefore, gripping by a conventional collet would not be possible, since holding on to the thread 5 would damage the thread 5. The process step shown is therefore particularly suitable for producing a screw according to the invention. However, it is obvious to the person skilled in the art that the process step shown is also suitable for manufacturing a conventional screw.
