Screw, system with screw and plate, and method for manufacturing the screw

Abstract

The present invention relates to a screw (1), preferably a bone screw, comprising a shaft (2) having a tip (3), a head (4), and threads (5). The shaft further comprises a longitudinal axis (A). An array of radial cross sections (Q) of the head (4) extends through the longitudinal axis (A) of the screw (1), the location of each radial cross section (Q) being defined by an azimuthal angle (6) in a plane (E) perpendicular to the longitudinal axis (A). Each radial cross section area (Q) has an area defined by the longitudinal axis (A) and the outer surface of the screw (8). The threads (5) extend into the head (4) such that the surface area of ​​the radial cross section (Q') within a first azimuthal range (9) is constant, and the surface area of ​​the radial cross section (Q'') within a second azimuthal range (10) different from the first azimuthal range (9) has a different, preferably smaller, value than the surface area within the first azimuthal range (9). The first azimuthal angle range (9) is up to 350°, preferably up to 345°.

Description

[Technical field]

[0001] The present invention relates to a screw, a system comprising a screw and a plate, as well as a method for manufacturing the screw, according to the preambles of the independent claims. [Background technology]

[0002] It is known to use screws to connect implants to bone. For example, certain bone fractures are treated by connecting the broken bones with bone plates and fixing them in place with screws. Summary of the Invention [Problem to be solved by the invention]

[0003] Known screws have various drawbacks. For example, conventional screws often cannot be used when the bone to be connected has a thin cortex, since the screw may not adequately engage the bone. Similarly, conventional screws may be aesthetically disadvantageous when used under a thin tissue layer, since a thick plate is required for secure fixation within the bone.

[0004] It is therefore an object of the present invention to provide a screw which overcomes the drawbacks of the prior art and in particular offers greater flexibility of use, for example the screw should also be suitable for use in thin plates and / or for connecting to thin bones, thus allowing a wider range of applications. [Means for solving the problem]

[0005] These and other advantages are achieved by the screw, the system comprising the screw and the plate, and the method for manufacturing the screw according to the features of the independent claims.

[0006] The screw according to the invention is preferably a bone screw and comprises a shaft having a tip, a head and a continuous thread, and a longitudinal axis of the shaft. Furthermore, the screw comprises a set of radial cross-sectional areas of the head bounded by the longitudinal axis of the shaft. The position of each radial cross-section is defined by an azimuth angle in a plane perpendicular to the longitudinal axis. Each radial cross-sectional area has an area defined by the longitudinal axis and the outer surface of the screw. According to the invention, the thread extends into the head such that the area of ​​the radial cross-section is constant within a first azimuth range. The surface area of ​​the radial cross-sectional area in a second azimuth range has a different, preferably smaller, value than the surface area of ​​the first azimuth range. The first azimuth range is different from the second azimuth range. The first azimuth range is up to 350°, preferably up to 345°.

[0007] Preferably, the thread extends substantially from the tip of the screw at least to the head, particularly preferably into the head.

[0008] However, it is also conceivable that the thread does not start at the tip of the screw and / or is interrupted, but extends substantially up to the head, particularly preferably into the head.

[0009] It is conceivable that the thread extends into the head only in an azimuth range, preferably in a second azimuth range. In this case, there is a complementary azimuth range in which the screw according to the invention does not contain a thread at and / or in the head. However, it is also conceivable that the thread extends into the head over the entire circumference of the screw.

[0010] As a result, the threads extend closer to the screw head than conventional screws, particularly into the head, and therefore the screw can also engage bone when using thin plates and / or treating bones with thin cortices.

[0011] The radial cross section of the head is to be understood as the part of the total cross-sectional area of ​​the head on one side of the longitudinal axis and bounded by the longitudinal axis. The cross section of the head therefore by definition has two radial cross sections.

[0012] A continuous thread is designed such that the thread has a start point and an end point, with no non-threaded portion being located between them. In particular, a continuous thread has a constant thread pitch between the start point and the end point. A continuous thread can be a multiple start thread. Particularly preferably, the start point is located substantially at the tip of the screw and / or the end point is located substantially within the area of ​​the screw head.

[0013] Particularly preferably, the shape of the thread is substantially the same in all threaded sections, in particular over the entire length along the thread axis along which the thread extends. In particular, the thread pitch and the inner and outer thread diameters may be constant over the entire length. In particular, the envelope of the outer diameter of the thread may extend substantially parallel to the longitudinal axis of the thread.

[0014] Additionally or alternatively, it is contemplated that the thread sections, preferably the end sections of the thread that extend into the screw head, have different thread diameters. Those skilled in the art will appreciate that such end sections having offset thread diameters are not inconsistent with the above-described threads having essentially the same thread form throughout the entire thread length.

[0015] Alternatively, it is also conceivable that the thread has different thread diameters along the longitudinal axis of the thread. In particular, the thread can have a preform region and / or an intermediate region and / or a locking region, as described in WO 2007 / 048267, which is incorporated by reference. The thread can therefore also be self-tapping and / or self-drilling.

[0016] The screw therefore preferably has exactly one continuous thread, which may in particular extend from the tip into the head. The thread section which extends into the head may in particular also be designed only as a stub.

[0017] The screw according to the invention is particularly advantageous when using and fixing bone plates with a thickness of 0.1-1 mm. Such thin plates are particularly advantageous in the treatment of bones with a thin soft tissue coverage. However, even in bones with a thin cortical bone and / or low cancellous bone and / or single cortical fixation, especially in the range of 0.1-2 mm, the screw according to the invention provides a more secure hold compared to the prior art.

[0018] The area content includes only the radial cross-sectional areas on one side of the longitudinal axis, and therefore each cross-sectional area includes two radial cross-sectional areas, each having a surface area whose position is defined by an azimuthal angle that differs by 180°.

[0019] In particular, the azimuth angles defining the position of the respective surface area can be understood as relative indices with respect to an arbitrary zero point. Preferably, the end of the thread is used as the zero point. In this case, the surface area with an azimuth angle of 0° is assigned by definition to a first azimuth angle range, while the directly adjacent surface area (with an azimuth angle greater than 359°) is assigned by definition to a second azimuth angle range. This example serves only for a better understanding of the description of the invention. Similarly, it is possible to choose an arbitrary zero point for the definition of the position of the area contents.

[0020] For the calculation of the surface area, contours that are not related to the thread should be excluded. For example, drives (e.g. Torx, Phillips, slots) can be placed on the screw head, which, due to the lack of rotational symmetry, non-uniformly change the surface area of ​​the radial cross-sectional area. In this case, the drives are not significant for the calculation of the surface area, since they can be filled in imaginatively.

[0021] Preferably, the area in the direction of the longitudinal axis in the direction of the screw head may only be included up to the equator, i.e. up to the widest point of the screw head in a plane perpendicular to the longitudinal axis.

[0022] The head of a screw can be understood in particular as the area of ​​the thread along its longitudinal axis which extends in a plane perpendicular to the longitudinal axis in the radial direction, at least partially over the thread, in particular over the outer radius of the thread. The surface area of ​​the radial cross section can therefore also be calculated in such a way that the area of ​​the thread that does not belong to the head is not included according to the above definition.

[0023] The screw may comprise a material from the group consisting of titanium, titanium alloys and implant steels. However, other biocompatible materials are also contemplated. Preferably, the screw is made of one of the above mentioned materials.

[0024] The screw may preferably have a thread with a thread pitch of 0.4 to 0.6 mm and a thread diameter of 0.9 or 1.2 mm.

[0025] Alternatively, the screw may have a thread pitch of 0.5 to 0.75 mm and a thread diameter of 1.5 or 1.8 mm.

[0026] However, other thread diameters and thread pitches are contemplated, particularly thread diameters between 0.5 and 2.5 mm and thread pitches between 0.1 and 1.5 mm.

[0027] Preferably, the screw has a drive selected from the group including slot, cross, polygon, Torx and Phillips.

[0028] In the case of a double-start, triple-start or multiple-start thread, the first azimuthal region and the second azimuthal region can be divided into at least two, in particular into two or more sections distributed at equal azimuthal intervals.

[0029] This means that the full azimuth angle range is divided into a corresponding number of sections, where the first azimuth angle range and the second azimuth angle range alternate, for example, if the first azimuth angle and the second azimuth angle are divided into two sections, each of the two sections of the first azimuth angle range is bounded by a section of the second azimuth angle range.

[0030] In particular, the azimuthal distance may be measured from the centre of each section, in which case it is preferably 180° or 120°.

[0031] The first azimuth angle range may also be up to 330°, preferably up to 305°.

[0032] The specified azimuth angle ranges should be understood as the sum of the individual sections of each azimuth angle range.

[0033] The thread of the screw may be a multiple start thread, preferably a double or triple start thread. The first azimuthal range can also be at most 340°, 320°, 315° or 300°, in particular for multiple threads. In the case of multiple threads with n threads, the second azimuthal range is particularly preferably at least n×15°. In this case, the first azimuthal range is therefore at most the difference between 360° and n×15°.

[0034] If the threads are multiple start threads, the azimuthal range may be divided into as many sections as there are threads.

[0035] Preferably, in the second azimuthal range, the head has at least one notch formed by a continuation of the threads.

[0036] In particular, the notches may be made by a whirling knife used to make the threads. The notches may, for example, allow the screw to penetrate deeper into the bone, especially into the hard cortical bone just below the plate, before the screw head is placed on the bone plate. This may make the procedure more stable, since the threaded portion just below the head may still be fixed in the bone, reducing damage to the bone. The head may have a number of such notches equal to the number of segments.

[0037] Preferably, each portion of the second azimuthal range has at least one notch formed by a thread continuation.

[0038] In particular, the notch can be shaped like a stump and can also have at least partially elliptical regions. Particularly preferably, the notch has a different width in the circumferential direction, the thickness of which initially increases in the direction in which the thread extends and decreases again in the terminal section. In this case, the maximum width of the notch can be located in the region where the thread terminates in the shaft.

[0039] At least one notch formed by the continuation of the threads may be located under the head in the region of the thread termination.

[0040] The underside of the head can in particular be understood as the area of ​​the surface of the head whose normal direction is at least partially oriented in the direction of the tip of the threaded shaft, in particular with respect to a plane perpendicular to the longitudinal axis. The underside of the head includes the area of ​​the surface of the head that is located on the side of the tip of the shaft, as viewed from the equator of the head.

[0041] The radial cross sections have a geometric center. The geometric center should be understood according to a common definition. The geometric centers of the radial cross sections within the first azimuthal range can each have the same distance to the longitudinal axis. Preferably, the geometric centers of the radial cross sections within the first azimuthal range have the same position relative to the longitudinal axis.

[0042] Particularly preferably, the radial cross-sectional areas in the first azimuthal range also have the same shape. Particularly preferably, the radial cross-sectional areas in the second azimuthal range have at least partially different shapes. However, it is conceivable that the radial cross-sections in the second azimuthal range also have the same shape. However, even in this case, the area of ​​the radial cross-section in the second azimuthal range will be smaller than the area of ​​the radial cross-section in the first azimuthal range.

[0043] If the second azimuthal range is divided into sections, it is particularly preferred that the radial cross-sectional area of ​​one section has the same shape as the radial cross-sectional area of ​​at least one other section, preferably all other sections, where it is possible for the radial cross-sections within a section to have the same or different shapes.

[0044] The thread may be shaped, in particular formed, such that the respective radial cross-sectional areas are connected, in particular a path connection or a simple connection.

[0045] A surface is path-connected if any two points on the surface can be connected by a path within the surface.

[0046] A surface is simply connected if it is connected and any closed line can be reduced to a point.

[0047] In particular, this results in the screw head not comprising a through hole or bore, in particular the screw head preferably not comprising any hole or bore connecting the longitudinal axis to the screw or to the head surface.

[0048] The screw, and in particular the head of the screw, can have a first perpendicular cross-section in a plane perpendicular to the longitudinal axis in the head region of the screw that is non-circular.

[0049] Preferably, the screw, in particular the head of the screw, is circular and has a second vertical section parallel to the first vertical section, whereby the first vertical section is preferably located between the tip of the screw and the second vertical section along the longitudinal axis of the screw.

[0050] The invention further relates to a system comprising a bone plate and a bone screw. In particular, the system may comprise a bone screw having the above-mentioned characteristics. The bone plate comprises at least one opening for inserting the bone screw. The bone screw comprises a head, a shaft and a thread therethrough. Preferably, the bone plate has a thickness that is at most equal to the length of the head of the screw along the longitudinal axis of the screw. In particular, the thickness of the plate may have a value between 0.1 and 1 mm. The bone screw is insertable into the opening of the bone plate such that the head is in mechanical contact with the bone plate, in particular rests on the bone plate, and the thread extends at least partially into the opening.

[0051] The invention further relates to a method for manufacturing a screw, in particular a bone screw. Preferably, this method is used to manufacture a screw as described above. The screw is manufactured according to the method of the invention, in particular using a tool selected from the group comprising a whirling knife and a thread cutter. However, other equivalent tools are also conceivable. The method comprises providing a slug material having a substantially cylindrical shape and cutting a thread along the longitudinal axis of the cylindrical shape with the tool. The head is also formed, in particular rotationally molded. The screw is then gripped by a profile collet. The profile collet has a profile that is adapted to the profile of the head or a part of the head and that in the gripped state operably connects with the counter profile of the head or a part of the head. Optionally, it is also possible to at least partially grip the shank, the neck or a part of the thread further.

[0052] This allows the screw to be gripped without damaging the threads that extend into the screw head.

[0053] Preferably, the head is first slug-cut and then the threads are cut. Preferably, the profile of the profile collet is at least partially designed to be essentially complementary to the mating profile of the head or part of the head and the neck or part of the thread of the screw, so that the profile at least partially fits exactly into the mating profile and allows a particularly secure hold.

[0054] Preferably, the threads are cut with a tool very close to the head so that the tool forms a notch on the underside of the head. In particular, this is done when the head is rotationally molded before the threads are cut. However, it is also conceivable to rotationally mold the shape of the head only after the threads have been cut.

[0055] Preferably, a tool with a whirling plate is used, whereby the whirling plate does not enclose the overcutting edge in the cutting direction on the front side, i.e. in the direction of the screw head, away from the already cut thread, and can therefore penetrate deeper into the screw head without leaving a mark of the overcutting edge.

[0056] Preferably, after cutting the threads with a tool, the head is further machined using a CNC lathe. In particular, a screw drive, for example a Torx drive, can be manufactured.

[0057] Preferably, exactly one thread is cut and the entire thread is produced by the same tool. In this way, a thread can be produced which contains exactly one thread, whereby the thread can have the same thread pitch and / or constant inner and outer thread diameters over its entire length.

[0058] Preferably, the thread is cut from the screw tip to the screw head, particularly preferably into the head.

[0059] In the following, the invention will be explained in detail with reference to the attached figures. [Brief description of the drawings]

[0060] [Figure 1] FIG. [Figure 2a] FIG. 2 is a side view of the screw head of the screw. [Figure 2b] FIG. [Figure 2c] FIG. 2 is a bottom view of the screw head. [Figure 3a] FIG. 2c is a cross-sectional view of the screw head in plane E of FIG. 2c. [Figure 3b] FIG. 2c is a cross-sectional view of the screw head in plane E′. [Figure 3c] FIG. 2c is a cross-sectional view of the screw head in plane E″. [Figure 4] FIG. 13 is a bottom view of the head of an alternative embodiment of the screw. [Diagram 5] FIG. 1 is a diagram of a bone plate having screws. [Figure 6] FIG. 13 is a side view of an alternative screw. [Figure 7] FIG. 1 is a schematic diagram of process steps for manufacturing a screw. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] 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 perpendicular to the longitudinal axis A of the screw 1. The plane 52 is positioned along the longitudinal axis A such that in the distal direction of the tip 3 in a cross section perpendicular to the longitudinal axis (to the right of the plane 52 in FIG. 1 ), the shaft 2 of the screw 1 does not project anywhere beyond the radius 51′, 51″ of the male thread. On the other hand, in the other proximal direction (to the left of the plane 52 in the illustration of FIG. 1 ), it projects beyond the radius 51′, 51″ of the male thread and defines the head 4 of the screw. The thread 5 extends beyond the plane 52 into the head and forms a notch 7 on the underside U of the head 4.

[0062] FIG. 2a shows in a side view the head 4 of a screw 1 according to the invention. For better understanding, a part of the shaft 2 with the thread 5 is also shown. A plane 52 separates the head 4 from the shaft 2. The thread 5 extends beyond the plane 52 into the head and forms a notch on the underside of the head. The screw head 4 therefore comprises a first vertical section 12 and a second vertical section 13. The first vertical section 12 intersects with the notch 7 and is therefore non-circular. The second vertical section 13 is further away from the screw tip 3 along the longitudinal axis than the first vertical section 12. The first vertical section 12 will therefore be located along the longitudinal axis A between the second vertical section 13 and the tip 3. The second vertical section 13 is above the notch 7, so that the second vertical section has a circular shape. A plane E, which is coplanar with the longitudinal axis A, is adjacent to the notch 7.

[0063] Figure 2b shows the screw head 4 of figure 2a in a perspective view. The azimuth angle 6 is plotted in the following figure in a counterclockwise direction around the longitudinal axis A, with plane E as the zero point. As explained above, any other zero point can be chosen. It is also possible to measure the azimuth angle 6 in a clockwise direction.

[0064] FIG. 2c shows the screw head 4 of FIGS. 2a and 2b in a bottom view. The longitudinal axis A, not shown here, extends perpendicular to the image plane, so that the azimuth angle 6 lies correspondingly in the image plane. The first azimuth angle region 9 does not have the notches 7 and extends over an azimuth angle of 195°. The notches 7 therefore extend over an azimuth angle of 165° and define a second azimuth angle range 10. The second azimuth angle range 10 therefore has a value of 165°. Due to the notches 7, a cross section of the screw head 4 in a plane through the longitudinal axis, which is at least partially in the second azimuth angle range 10, is not mirror-symmetrical with respect to the longitudinal axis A. The radial cross section bounded by the longitudinal axis A on the one hand and the outer surface of the head 4 on the other hand has a smaller area in the second azimuth angle region 10 than in the first azimuth angle region 9. This feature is explained below by the cross-sectional views in 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 here marked with a dot on one side, which should facilitate understanding of the orientation of the planes in the following figures.

[0065] FIG. 3a shows a cross-sectional view of the screw head of FIGS. 2a-2c in a plane E. The head 4 is bounded by a plane 52, so that only the area within the boundary of the head 4 and the plane 52 is included in the following description of the surface area. The two radial cross sections Q' are each bounded by the contour of the head 4, the longitudinal axis A, and the plane 52, and have a surface area Q'. The plane E does not intersect with the notch 7 (not shown here). Both surface areas Q' are therefore identical and are located within a first azimuthal range 9. The cross sections are mirror symmetrical with respect to the longitudinal axis A. The two radial cross sections Q' therefore have the same shape. Finally, the radial cross-sectional area Q' includes a geometric center 11 that has a constant distance and position relative to the longitudinal axis A. Both the position and the distance of the geometric center 11 are the same for all surface areas Q' that are located within the first azimuthal range 9. The screw head may include a drive, for example a Torx drive (not shown), which is not included in the present calculation of the surface area. Instead, the drive was imaginarily filled and its area counted as part of the head 4. From Fig. 3a and the following Fig. 3b and 3c, it is clear that the radial sections Q', Q'' are path-continuous and also simply continuous. This means that all points in a surface can be connected by paths that belong to the surface. Furthermore, each closed path in a surface can be reduced to one point. This may not be possible with screw heads that contain holes.

[0066] FIG. 3b shows a cross-sectional view of the screw head 4 of FIG. 2a-c in the plane E'. Two radial cross sections Q', Q'' are each bounded by the contour of the head 4, the longitudinal axis A and the plane 51 and have a surface area. The radial cross sections Q', Q'' differ in shape and surface area. The radial cross section Q'' is located in the second azimuthal region 10 and thus in the head region having the notches 7. The radial cross section Q'' therefore has a smaller surface area than the radial cross section Q'. On the other hand, the radial cross section Q' has the same surface area and the same shape as the two radial cross sections Q' of FIG. 3a, since they are located in the first azimuthal region 9. Similarly, the geometric center 11 of the radial cross section Q' is located at the same distance and in the same position relative to the longitudinal axis A as the one shown in FIG. 3a.

[0067] Figure 3c shows a cross-sectional view of the screw head 4 of figures 2a-c in the plane E''. This view essentially corresponds to the view of figure 3b, but the radial sections Q' and Q'' are inverted. In this view, the geometric centre 11 of the radial section Q'' is depicted. Said geometric centre is variable in a second azimuthal range 10, i.e. it can have different positions and different distances relative to the longitudinal axis A depending on the azimuthal angle.

[0068] FIG. 4 shows the head 4 of an alternative embodiment of the screw 1 in a bottom view. The screw head 4 has two notches 7 on its bottom surface U. Such a screw head is particularly suitable for use with screws with multiple threads, in particular with screws with double threads. The head region with the notches 7 is located in the second azimuthal region 10. The first azimuthal region 9 does not have the notches 7 and is therefore mirror-symmetrical with respect to the longitudinal axis A perpendicular to the image plane. The first azimuthal region 9 and the second azimuthal region 10 are each divided into two sections B1, B2, B3, B4, which are bounded by the respective other azimuthal regions 9, 10 and are arranged at equal azimuthal intervals. The bisector 14 of the boundary of the sections is preferably used as a reference point for determining the angular separation. The angular distance between the sections is therefore 90°. The total value of the first azimuthal range 9 is 90° and is distributed in two intervals of 45°. Furthermore, when the illustrated screw head 4 is used with a screw having a double thread, the head 4 has as many segments as the screw has threads. Furthermore, each segment of the second azimuthal region 10 has exactly one notch 7.

[0069] Figure 5 shows the screw 1 in threaded engagement with a bone plate 15 in a thin cortical layer 16. The screw 1 essentially corresponds to the screw 1 shown in Figure 1. A flat surface 52 is also shown separating the head 4 from the shaft 2. Due to the notches 7 and threads 5 extending in the head 4, the threads 5, despite being thin, engage at least part of the thickness of the bone 16. The threads 5 penetrate an opening in the bone plate 15 and extend forward.

[0070] Figure 6 shows an alternative embodiment of a thread 1 produced with a modified whirling knife without overcutting. The notches 7 are therefore smaller than in the thread 1 of Figure 1, but the thread 5 essentially corresponds to the thread 5 of Figure 1. The first azimuthal region 9 does not have the notches 7. The second azimuthal range 10 in which the notches 7 are located has a value of, for example, 45°. The first azimuthal range 9 has a value of 315°.

[0071] FIG. 7 shows process steps diagrammatically for the production of a screw 1. In this case, a whirling knife (not shown) was used to cut the thread 5 of a bar-shaped ingot material. In the process steps shown, the screw 1 is held on the head 4 by a profile collet 30 after the insertion of the thread 5. Furthermore, a guide sleeve 33 prevents the screw 1 from tilting when the profile collet 30 is opened. The profile collet 30 has a profile 31 for this purpose, which is designed to form a counter profile for the head 4 of the screw 1. It is therefore suitable for gripping the head 4 of the screw 1 and holding it firmly. However, it is also conceivable to use other profiles, which grip, for example, the head or parts of the head and also the screw shank or parts of the thread. In particular, it is also possible to hold only a section of the head 4. By gripping the screw 1 on the head as shown here, it is possible to further process the head 4 to produce, for example, a screw drive, here a Torx drive 32. In this case, the process steps are carried out with a screw 1 as shown in FIG. 1 or FIG. 6, the thread extending into the head. Gripping with a conventional collet is therefore not possible, as holding the thread 5 would damage it. The process steps shown are therefore particularly suitable for producing a screw according to the invention. However, it will be clear to a person skilled in the art that the process steps shown are also suitable for producing conventional screws.

Claims

1. A screw (1) comprising a shaft (2) having a tip (3), a head (4) and threads (5), a longitudinal axis (A) of the shaft (2) and a set of radial cross sections (Q) of the head (4) bounded by the longitudinal axis (A) of the shaft (2), the position of each radial cross section (Q) being defined by an azimuth angle (6) in a plane (E) perpendicular to the longitudinal axis (A), each radial cross section (Q) having an area defined by the longitudinal axis (A) and an outer surface of the screw (1); The set of radial cross sections (Q) includes a first radial cross section (Q') defined by a first azimuthal range (9) and a second radial cross section (Q'') defined by a second azimuthal range (10); The thread (5) extends at least from the tip (3) to the head (4) of the screw (1); 1. A screw (1), characterized in that the thread (5) extends into the head (4) in such a way that the area of ​​the first radial cross section (Q') is constant within the first azimuthal range (9), and the area of ​​the second radial cross section (Q'') in the second azimuthal range (10) different from the first azimuthal range has a smaller value than the area of ​​the first azimuthal range (9), the first azimuthal range (9) being a maximum of 350°.

2. 2. The screw (1) according to claim 1, wherein the first azimuth angle range (9) and the second azimuth angle range (10) are each divided into at least two sections distributed at equal azimuth angle intervals, and sections of the same azimuth angle range are arranged so as not to be adjacent to each other.

3. The screw (1) according to claim 2, wherein said first azimuthal angle range (9) is a maximum of 330°.

4. The screw (1) according to any one of claims 1 to 3, wherein the thread (5) is a multiple start thread.

5. The screw (1) according to any one of the preceding claims, wherein the head has at least one notch (7) formed by a continuation of the threads (5) in the second azimuthal range (10).

6. 3. The screw (1) according to claim 2, wherein said head (4) has a number of notches (7) formed by successions of said threads (5) corresponding to the number of said segments of said second azimuthal range (10).

7. 7. The screw (1) according to claim 6, wherein each portion of the second azimuthal range (10) comprises a notch (7) formed by a continuation of the threads (5).

8. 6. The screw (1) according to claim 5, wherein the at least one notch (7) formed by the continuation of the thread (5) is arranged on the underside (U) of the head (4), in the region of the thread termination.

9. 9. The screw (1) according to any one of the preceding claims, wherein said radial cross-sections (Q) have centres of gravity (11), and each centre of gravity (11) of said first radial cross-sections (Q') in said first azimuthal range (9) has the same distance from said longitudinal axis.

10. The screw (1) according to any one of the preceding claims, wherein the thread is formed such that at least one of the first radial cross section (Q') and the second radial cross section (Q'') are connected in an arc.

11. The screw (1) according to any one of the preceding claims, wherein a first vertical cross section (12) in a plane perpendicular to the longitudinal axis (A) of the head (4) is at least partially non-circular.

12. The screw (1) as described in claim 11, wherein a second vertical cross section (13) in a plane perpendicular to the longitudinal axis (A) of the head (4) is circular and parallel to the first vertical cross section (12), and the first vertical cross section (12) is positioned along the longitudinal axis (A) of the screw (1) between the tip (3) of the screw (1) and the second vertical cross section (13).

13. 13. A system comprising a bone plate and a screw (1) according to any one of claims 1 to 12, characterized in that the bone plate comprises at least one opening for inserting the screw, the head of the screw having a full-threaded screw thread and insertable into the opening of the bone plate such that the head is in contact with the bone plate and the screw thread extends at least partially into the opening.

14. A method for manufacturing a screw (1) according to any one of claims 1 to 12, using a tool, comprising: Providing a slug material having a substantially cylindrical shape; cutting a thread (5) along the longitudinal axis (A) of the cylindrical shape with said tool; forming a head portion (4); Including, 11. The method of claim 10, wherein the slug material is gripped on the head (4) by a profiled collet (30), the profiled collet (30) having a profile (31) that operatively connects with a mating profile of the head (4) in the gripped state.

15. 15. The method according to claim 14, wherein the profile (31) of the profile collet (30) is substantially at least partially complementary to the mating profile of the head (4) of the screw (1).

16. 16. The method of claim 14 or 15, wherein the threads are cut by the tool at least sufficiently close to the head that the tool forms a notch on an underside of the head.

17. The method according to any one of claims 14 to 16, wherein the tool comprises a whirling plate that does not include overcutting in the cutting direction.

18. The method according to any one of claims 14 to 17, wherein after cutting the threads with the tool, the head is further machined by a CNC lathe.

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