SCREW ELEMENT AND METHOD FOR ADDITIVE MANUFACTURING

Description

State of the art

[0001] Various osteosynthesis devices, such as screw elements for fixing bones or bone fragments, are known in the current state of the art. These bone screws are traditionally manufactured using CNC milling and turning machines. Special threaded plates are required for the specific bone thread geometries and, in particular, for the different diameters of the screw elements. This leads to longer delivery times and higher costs. 3D printing offers a potential alternative, as all geometries can be produced without special tools, thus eliminating the waiting time for such tools. Significantly greater flexibility in geometry design is also possible. Furthermore, well over one hundred screw elements can be produced simultaneously using 3D printing, resulting in a considerable cost advantage compared to traditional CNC manufacturing methods.

[0002] A significant disadvantage of the 3D printing manufacturing process is that the surfaces of the printed parts exhibit a natural surface roughness. While this is optimal for bone cell growth, it also creates numerous micro-grooves. These micro-grooves negatively impact the fatigue strength of the printed parts. Furthermore, 3D-printed components exhibit pronounced brittleness, which is why various heat treatments are proposed to counteract this material behavior.

[0003] Based on the current state of the art for implants, intervertebral disc replacement implants (cages) are being mass-produced using 3D printing. This is because the printed geometries are mechanically over-engineered to such an extent that, despite the micro-notches, the minimum fatigue strength criteria are met, and these 3D-printed cage implants can be considered clinically safe. However, if bone screws are to be manufactured using 3D printing, significantly higher fatigue strength requirements must be met. Bone screws are subjected to continuous and recurring high bending stress. Therefore, suitable process steps must be carried out in a strictly defined sequence to prevent the material from becoming brittle and to allow for the removal of the micro-notches.The current state of the art lacks any information on the production of 3d-printed bone screws, in particular on the general manufacturing process, post-processing and especially the sequence of post-processing steps to achieve clinically reliable fatigue strength.

[0004] US Patent 2019 / 0343564 A1 discloses a bone screw with a shaft having a wall, the wall having a small diameter, and at least one thread with an external thread form, wherein the thread form comprises a plurality of threads, at least one of which has a first section having a ridge of the thread form and a second section extending from the first section of one of the threads to the root of an adjacent thread, wherein the first section has a fixed configuration relative to the second section, and the second section extends continuously from the root of one of the threads to the root of the adjacent one of the threads. The wall of the thread may have a lattice structure.

[0005] FR 3 052 659 A1 discloses a method for manufacturing at least one implant abutment for a dental prosthesis, wherein an implant abutment has an insert in a lower part which has a connection configured to connect the abutment to an implant. The method further comprises a body in the upper part configured to support a crown, wherein the method further comprises a step for manufacturing an implant abutment blank, a step for specifically manufacturing the body of the implant abutment, a step for manufacturing the body by additive manufacturing on a build-up plate, starting with the first part of the shaft, beginning with an apex of the body, and a step for manufacturing an insert blank in an extension of the body.comprising a sub-step of manufacturing a connection blank by additive manufacturing on the same additive manufacturing platform, and a step for manufacturing the connection technology, comprising at least one step of electrical discharge machining of the connection part blank by countersinking at least one electrode onto the connector blank, wherein the at least one electrode is embossed into the connector blank (33'), wherein one electrode has a recess which represents a shape which is complementary to the connection technology of the insert to be manufactured.

[0006] US Patent 2013 / 0053901 A1 discloses a cannulated bone anchor assembly comprising a bone anchor, a receiving element for receiving a spinal fixation element that is coupled to the bone anchor, and a locking mechanism for fixing the spinal fixation element relative to the receiving element. The bone anchor comprises a distal shaft with a first threaded section proximal to a proximal head, a second threaded section proximal to and adjacent to the first threaded section, and a third threaded section proximal to and adjacent to the second threaded section. The first threaded section has a constant major and minor diameter. The second threaded section has a tapered major and minor diameter. The third threaded section has a tapered major diameter and a constant minor diameter.

[0007] US Patent 2015 / 0196336 A1 discloses an orthopedic fastener comprising a head and a shank. The shank has a front end section adjacent to a distal tip and a rear end section adjacent to a head. An intermediate section is located between the front and rear end sections. The diameter of the shank increases at the intermediate section. The front end section has a first thread with one or more self-tapping cutting flutes extending alongside the distal tip and through multiple first threads. The intermediate section has a second thread extending from the front end section toward the head. The second threads of the intermediate section have a larger outer diameter than the first threads in the front end section.The intermediate section has one or more cutting grooves, each running along a front transition at the front end section and a rear transition.

[0008] Patent 2005 / 0234561 A1 discloses a wear-resistant orthopedic device made of a titanium alloy. It also discloses a method for manufacturing a wear-resistant orthopedic device made of a titanium alloy by deep diffusion of oxygen into the device. Furthermore, it discloses a method for hardening a titanium device by deep diffusion of oxygen into the device. Description of the invention

[0009] The problem is solved using the screw element according to the invention presented here and its manufacturing method according to claims 1 and 9.

[0010] An additive manufacturing process will be used for production. Additive manufacturing of metallic alloys, also known as 3D printing, utilizes laser or electron beam melting. Suitable materials include all metallic alloys known and accepted as orthopedic implant materials. These include, for example, titanium, cobalt-chromium, and stainless steel alloys. The titanium alloy Ti6Al4V will be used preferentially. For 3D printing, raw material particles or powders with a defined grain size are used. The grain size determines the component accuracy and the layer spacing during production.

[0011] Manufacturers of 3D printing machines suggest an angled placement within the 3D printing build chamber for optimal surface quality and accuracy. Such an angled placement would require the screw element (1) according to the invention to be mounted at an angle within the 3D printer, necessitating the use of numerous lateral support elements or cantilever elements to achieve an optimal printing result. While this produces the highest quality, it is cost-inefficient. Firstly, significantly fewer screw elements fit within the printable build chamber, and secondly, laterally attached support elements can only be removed manually, making them cost-inefficient in high-volume production. Thus, the superior printing results are offset by corresponding cost inefficiency in mass production.

[0012] To effectively utilize the build space and thus maximize the number of producible screw elements (1), it is advantageous if the screw elements (1) could be produced in a vertical position. However, this entails limitations regarding the producible features and printable accuracies. To enable the vertical and cost-effective printing of screw elements (1), various geometric features must be maintained and specified.

[0013] For the screw element (1) according to the invention, spatially assigning coordinate references are defined, such as the proximal direction (101) and the distal direction (102), which extend along a central axis (103). Extending outwards from the central axis (103) is the radial propagation (104) ( Fig. 1 and Fig. 2The screw element (1) according to the invention is suitable for fixing bone components and bone fragments and consists of a shaft (11) with a bone thread (12) and a longitudinal central axis (103) extending along the shaft (11), and the screw element (1) additionally has a head (10), a neck region (20) and a tool attachment point (90) which is provided in the head (10) ( Fig. 4 ).

[0014] In the preferred embodiment, at least three cantilever elements (13) are attached to the proximal end of the head (10, 109), and these cantilever elements (13) project beyond the proximal end of the head (10, 109) in a proximal direction (101). They are arranged mainly along the longitudinal central axis (103). The cantilever elements (13) are preferably integrally connected to the proximal end of the head (10, 109). The cantilever elements (13) can have any shape or geometry. For example, they can consist of plate, wire, beam, or column elements, or a combination thereof. The cantilever elements can at least partially create an additional radial distance from the screw element. The cantilever elements can have further connections to one another to form the cantilever elements as a composite.Furthermore, a ring-like or polygonal arrangement of one or more formations is also conceivable. The function of the cantilever elements is to distance and simultaneously hold the screw element (1) from a base plate of the 3D printer during the 3D printing process. The free ends (17) of the cantilever elements (13) describe a plane (108), so that the screw elements (1) are stabilized against tilting during additive manufacturing by means of this plane (108). For the screw element (1) according to the invention, a build direction (105) for 3D printing is defined, which corresponds approximately to the direction of the central axis (103) and runs from proximal (101) to distal (102), and the build direction (105) corresponds to the surface normal of the plane (108). Only in this combination of these features is upright manufacturing even possible.

[0015] To avoid having to provide the entire outer surface of the head region (10) with cantilever elements (13), it is advantageous if the tool attachment point (90) is open in the proximal direction (101) and terminates in a concentric, cone-shaped recess (94) with an approximately right-angled cone angle. Therefore, it is sufficient if the cantilever elements (13) are provided on a proximal ring structure (95, 109) along the diameter of the tool attachment point.

[0016] For the same reason, it is also important that the tool attachment point (90) is bounded distally (102) by a wall (93) and that this wall (93) extends radially inwards in an increasingly distal direction (102) as a cone, with the cone angle formed by the wall being less than 120°. Preferably, this wall (93) has an approximately right-angled cone angle. This allows this surface (93) to be manufactured using 3D printing, taking into account the defined build direction (105). Thus, cantilever elements for the base of the tool attachment point can also be eliminated here. Removing any cantilever elements from this base surface (93) would be a major challenge, as this base surface (93) is very difficult to access for post-processing. It is also advantageous if the tooth profiles (91) also terminate in this conical surface (93), so that these termination points can be manufactured using the 3D printing process.Such a cone-shaped wall (93) at the base of the tool insertion point (90) could not be produced using CNC manufacturing methods, or only with the highest technical effort.

[0017] In a preferred embodiment, a screw element (1) for fixing bone components and bone fragments is described, consisting of a shaft (11), a neck region (20), and a head (10) located in the proximal direction (101) and a tip (60) located in the distal direction (102). The head (10) is preferably designed as a lens, oblique head, or ball head. However, a combination of different radii and surfaces is also conceivable. The main feature of the head is that the head (10) has a larger outer diameter than the neck region (20). Preferably, the bone anchor has a tool attachment point (90) suitable for applying torque. For minimally invasive procedures, it is advantageous if the bone anchor has a fully penetrating cannulation opening (80) through which a surgical guide wire can be inserted.

[0018] Bone screws, which can be screwed into bone, are preferably used as screw elements (1). However, hooks, clamps, nails, and other types of bone anchors are also suitable. In the example of a screw element (1) presented here, a bone screw with a shaft (11) and a bone thread (12) located on the shaft is shown. The thread (12) can have a finer toothing (30) proximally, at least in some sections, which is better suited for harder cortical bone. A distally tapered thread (60) with a cutting edge (61) at the bone anchor tip (60) is advantageous, so that the screw element (1) can self-tap into the bone when screwed in.

[0019] It is advantageous if the screw element (1) is characterized in that the external thread (12) can be divided into a proximal thread area (30) adjacent to the neck area (20) and extending distally (102), and a distal thread area (50) adjacent thereto, and a distal tip area (60) adjacent thereto, and the distal thread area (50) transitions into the proximal thread area (30) in a transition zone (40), and the proximal thread area (30) forms at least one additional thread turn (31, 32) which forms at least one cutting edge (41) within the transition zone (40).

[0020] This cutting edge (41) achieves a pre-cutting effect without causing space displacement in the bone. This is particularly advantageous in cases of weaker bone, as it can reduce the risk of fractures during implantation.

[0021] It is further advantageous if at least one of the cutting edges (41, 61) is planar and oriented mainly in the radial direction (104). Alternatively, a concave or convex surface is also conceivable for generating the respective cutting edge.

[0022] Various thread tooth profiles and arrangements are conceivable for bone threads. For example, a thread with one tooth in the distal region can transition to a double or triple thread in the proximal region. A double thread in the distal region, transitioning to a quadruple or six-thread pattern in the proximal direction (101), is also possible. To simplify all illustrations, the preferred embodiment with a double thread in the distal region (50) and a quadruple thread in the proximal region (30) is shown.

[0023] In cases of weak bone, such as osteopenia or osteoporosis, it may be necessary to augment the bone anchor. This can be done with bone cement. Bone cement is preferably a polymer made from at least two components and injected in a liquid or paste-like state. The bone cement hardens into a plastic within the bone after a few minutes and bonds with the spongy bone structure. Polymethyl methacrylate cement is most commonly used. Alternatively, other media can be delivered through the bone anchor. It is conceivable that alternative media, such as pharmaceutical agents, media containing cells, nutrients, or media serving as genetic material carriers, or vaccines, could be administered through the bone anchor.

[0024] Optionally, the cannulation (80) has at least one or more laterally extending openings (70) that communicate with the cannulation ( Fig. 3Preferably, the openings are arranged circumferentially in a ring-like formation (71 or 72). If there is more than one circumferentially ring-like opening formation (71 and 72), the openings have different cross-sectional areas (710, 720) in each formation. In the case of bone anchors (1) screwed into a bone, the lateral openings communicate with the surrounding bone tissue from the hollow chamber (80). They are designed to allow the fluid injected into the bone anchor (1) to be released into the surrounding tissue through the lateral openings. Different cross-sectional areas of the opening formations (710, 720) have the advantage that, due to the local pressure difference within the fluid, a similar volume flow is generated through all openings (71, 72).This is achieved by the fact that the openings (72) that are closer to the proximal direction (101) have a smaller cross-sectional area (720) than the openings (710) of the formation (71) that are further distal.

[0025] For 3D printing, it is particularly advantageous if these lateral openings (70, 71, 72) are designed as polygons (700). Conventionally, such lateral openings (70) are drilled concentrically. In 3D printing, concentric openings would create small overhangs, resulting in so-called dross formations (i.e., miniature stalactite-like formations). This would necessitate costly manual post-processing in mass production. Polygons offer an alternative, and thus the preferred embodiment. The sloping surface elements of a polygon form a roof-like structure. Slopes with a cone angle of approximately 90° to each other can be easily produced in the printing process without cantilever elements or dross formations.

[0026] 3D printing also makes it possible to provide different surface roughnesses on the surface of the screw element (1). According to the invention, the thread surfaces (121) of the thread flanks (12) facing proximally are provided with a greater surface roughness than the thread surfaces (122) of the same thread flanks facing distally. Fig. 3 A higher roughness on the thread surfaces (121) in the proximal projection direction has the advantage of generating higher friction between the bone and the screw element in the pull-out direction, resulting in a significantly higher pull-out strength for the screw element. Smoother thread surfaces (122) in the distal projection direction have the advantage that the screw element (1) can still be easily screwed into the bone.

[0027] Method for manufacturing a screw element (1) according to one of the preceding claims, comprising the following steps: a. Providing raw material particles of a Ti6A14V alloy. b. Additively building up the screw element (1) according to the invention using a 3D printing process, which assembles the raw material particles three-dimensionally, such that at least three cantilever elements are attached to the proximal end of the head, the free ends of which describe a plane, and such that the external thread of the screw element has at least one thread surface facing away from the plane and at least one thread surface facing this plane, and the thread surface facing the plane has a greater roughness than the thread surface facing away from the plane. c. Stress-relieving the screw element (1) at a temperature of at least 500°C, but not higher than 840°C, with a holding time of at least one hour, but less than 6 hours. d. Removing the cantilever elements (13) from the proximal head region (109) ( Fig. 5 ). e. Second heat treatment of the screw element (1). f. Removal of incompletely joined raw material particles.

[0028] For stress-relief annealing, it is advantageous if, during the stress-relief annealing of the screw element (1), a temperature of preferably between 550°C and 800°C, preferably between 550°C and 750°C, preferably between 600°C and 720°C, is set for the duration of the holding time.

[0029] The removal of the cantilever elements (13) can be carried out manually or mechanically. Any machining or cutting processes are suitable for this purpose, such as grinding, milling, turning, or die-sinking and wire EDM.

[0030] Three different methods are suitable for the second heat treatment of the screw element (1). This second heat treatment optimizes the material structure with respect to its initially brittle behavior, achieving a certain material toughness. Different temperature ranges and environmental conditions exist for this purpose, yielding the best material properties. One option for the second heat treatment of the screw element (1) is to create an argon atmosphere at a temperature between 900°C and 940°C, preferably between 910°C and 930°C, and to subject the screw element (1) to a pressure of at least 900 bar, preferably at least 950 bar, maintaining these temperature and pressure conditions for a holding time of at least one hour but less than four hours.Another option for the second heat treatment of the screw element (1) is to generate an argon atmosphere at a temperature of at least 920°C but less than 1050°C, for a holding time of at least one hour but less than four hours. Another option for the second heat treatment of the screw element (1) is to generate a temperature of at least 820°C but less than 920°C, and to maintain this temperature for a holding time of at least one hour but less than four hours.

[0031] Heat treatments alone (stress-relief annealing and the second heat treatment for optimizing the material structure) are insufficient to increase fatigue strength. A corresponding fatigue strength is only achieved if the material exhibits the correct properties and the surfaces are free of micro-notches. Therefore, the process for manufacturing the screw element includes the step of "removing incompletely bonded raw material particles." It is advantageous to employ two different, complementary material removal processes. The removal of incompletely bonded raw material particles should therefore comprise the following: g. Removal of incompletely joined raw material particles using a mechanical-abrasive process, and h. Removal of incompletely joined raw material particles using a chemical abrasive process.

[0032] For the automation of series production, the mechanical-abrasive process can be carried out using an abrasive, at a minimum application pressure of 2 bar and a minimum application duration of 5 minutes, whereby a sharp-edged abrasive, such as corundum, is used, and the abrasive has a grain size between 0.05 mm and 0.25 mm, but preferably between 0.07 mm and 0.15 mm. Alternatively, the mechanical-abrasive process can also be carried out using a coarse vibratory finishing or vibration grinding process.

[0033] The chemical-abrasive process is carried out using a chemical pickling or etching process. A chemical process has the advantage that contours and geometric features that are not externally accessible can still be reworked or ablated. Thus, for example, the inner contour of the cannulation (80) can be freed from incompletely joined particles. The chemical-abrasive process can be supported by electro-galvanic and / or mechanically induced vibrations.

[0034] The fatigue strength of components subjected to bending stress can be further increased by generating compressive residual stresses on the surfaces. This can be achieved using a suitable blasting medium. Therefore, it is advantageous if, at the end of the process, the surfaces of the screw element (1) are hardened using a blasting medium, maintaining a minimum application pressure of 2 bar and a minimum application duration of 5 minutes, using a spherical blasting medium such as ceramic spheres, with a grain size between 0.05 mm and 0.25 mm, preferably between 0.07 mm and 0.15 mm. A brief description of the drawings shows

[0035] Fig. 1 an oblique view of the screw element according to the invention in a standing orientation, Fig. 2 an oblique view from the distal side. Fig. 3a side view of the screw element according to the invention, as well as a detailed representation of the side openings and thread flanks. Fig. 4 Side view and corresponding sectional view through the bone anchor according to the invention, Fig. 5 a step during the manufacturing process. Fig. 6 Two screw elements according to the invention are mounted in conjunction with U-shaped clevises and a connecting rod. Description of preferred embodiments

[0036] The Fig. 1 It can be seen that the assembly direction (105) of the screw element (1) according to the invention corresponds approximately to the direction of the central axis (103) and runs from proximal (101) to distal (102). Furthermore, the assembly direction (105) corresponds to a surface normal (108). The advantages have already been described at the outset.

[0037] Fig. 2Figure 1 shows an embodiment of a screw element (1) consisting of a head region (10), a neck region (20), and a shaft region (11) with a bone thread (12). It is further shown that the external thread (12) can be divided into a proximal thread region (30) adjacent to the neck region (20) and extending distally (102), and a distal thread region (50) adjacent thereto, and a distal tip region (60) adjacent thereto, and that the distal thread region (50) transitions into the proximal thread region (30) in a transition zone (40), and that the proximal thread region (30) forms at least one additional thread turn (31, 32) which forms at least one cutting edge (41) within the transition zone (40).

[0038] Another cutting edge (61) is formed at the distal tip region (60). Ideally, the respective cutting edge (41, 61) runs primarily planar in the radial direction. Other surface geometries with convex or concave areas are also conceivable. Alternatively, circumferentially recurring patterns that have a pre-cutting effect, such as serrations or teeth, are also conceivable.

[0039] Fig. 2Figure 1 illustrates an embodiment of a screw element (1) which forms two separate thread teeth (51 and 52) in the distal region (50). This is a so-called double thread, whereby a larger pitch is achieved compared to a single thread with the same number of thread teeth. This reduces the number of turns required to implant such a screw element (1). The thread root or thread valleys (53) are located between the threads. In the proximal region (30), an additional thread tooth (31, 32) is provided between each of the distal threads (51, 52). The proximal threads (31, 32) have the same pitch as the distal threads (51 and 52). In the transition region (40), two cutting edges (41, 42) are formed, although the second cutting edge (42) is not visible in this view. It is the (not visible here) start for the second proximal thread (32).The cutting edges (41, 42) offer the significant clinical advantage that such screw elements (1) can prevent fractures during implantation in the future. If a different thread is used, the number of cutting edges is increased or decreased accordingly.

[0040] In Fig. 3 A preferred embodiment of a screw element (1) is shown, in which the lateral fenestration openings (70) are configured as polygons. It is also shown that the lateral openings (70) are arranged circumferentially in a ring-like formation (71 and / or 72), and if there is more than one circumferential ring-like formation (71 and 72), the openings (70) have different cross-sectional areas (710, 720) in each formation. Optimally, the cross-sectional area (710) of the distal formation (71) is larger than the cross-sectional area (720) of the proximal formation (72).

[0041] Fig. 4Figure 1 reveals a sectional view of the screw element (1). The interior of the head region (10) and the continuous cannulation (80) are visible. The main feature of the head is that the head (10) has a larger outer diameter than the neck region (20). Preferably, the bone anchor has a tool engagement point (90) suitable for applying torque. The torque for screwing in the bone anchor can thus be applied directly via the tool engagement point. This tool engagement point can have any profile (91, 92), such as a multi-tooth round, internal hexagon, cross recess, a simple slot, or a toothed design of a different type. In the preferred embodiment, the tool engagement point (90) is located at the proximal end (101) and is bounded distally (102) by a wall (93). This wall (93) is shaped as a chamfer or...A cone is formed that extends radially inwards in an increasingly distal direction (102), and the cone angle formed by the wall is less than 120°. Ideally, the cone angle is approximately perpendicular. Furthermore, it can be seen that the tool insertion point (90) is open in the proximal direction (101) and terminates in a concentric, cone-shaped recess (94) with an approximately perpendicular cone angle.

[0042] In Fig. 4Also shown is the course of the cannulation opening (80). It is advantageous if a proximal section (81) with a slightly larger diameter is provided, into which an application cannula can be inserted. Adjacent to this is the central part of the cannulation (82) with a diameter of [missing information]. The lateral openings (70) open into the cannulation (82) through corresponding opening points (83). It is advantageous if distally (102) the cannulation diameter is reduced in a distal cannulation section (84). The transitions (812, 834) between the different cannulation diameters ideally have a cone angle of less than 120°; preferably, they are approximately perpendicular so that they, too, can be optimally manufactured for 3D printing.

[0043] Fig. 5 represents a step in the manufacturing process in which the cantilever elements (13) are removed.

[0044] Fig. 6Figure 1 illustrates two screw elements (1) according to the invention, mounted with U-shaped clevises (2) and a connecting rod (4). The screw elements (1) have a proximal head region (10) which at least partially comprises a spherical segment suitable for providing a polyaxially pivotable connection with a U-shaped clevis (2) as seen in a side view. After the connecting rod (4) is inserted and the adjusting element (3) is fixed, the screw elements (1) are angularly stable and connected to each other. They form a rigid fixation, such as is used, for example, in spinal surgery.

Claims

1. A screw element (1) for the fixation of bone components and bone fragments consisting of a shaft (11) with a bone thread (12) and a longitudinal central axis (103) extending along the shaft (11) and thereby defining a distal (102) and a proximal (101) direction, and the screw element (1) further comprises a head (10), and a neck area (20) and a tool attachment point (90) is provided in the head (10), wherein the screw element comprises a Ti6Al4V alloy, characterized in that at least three cantilever elements (13) are attached to the proximal end of the head (10, 109) and said cantilever elements (13) extend in proximal direction (101) beyond the proximal end of the head (10, 109) and are positioned mainly along the longitudinal central axis (103), wherein the free ends (17) of the cantilever elements (13) describe a plane (108) and the outer thread (12) of the screw element (1) has at least one thread surface (122) which is directed away from the plane (108) and at least one thread surface (121) that faces this plane (108), and the surface (121) facing the plane has a greater roughness than the thread surface (122) directed away.

2. The screw element (1) according to the preceding claim, characterized in that for 3D printing a building direction (105) of the screw element (1) is defined which corresponds approximately to the direction of the central axis (103) and runs from proximal (101) to distal (102) and the building direction (105) corresponds to a surface normal of the plane (108).

3. The screw element (1) according to any of the preceding claims, characterized in that the tool attachment point (90) is bounded in the distal direction (102) by a bottom wall (93) and said bottom wall (93) runs as a cone from radially outside to radially inside in increasing distal direction (102) and said bottom wall (93) is defined by an approximately right-angled cone angle.

4. The screw element (1) according to any of the preceding claims, characterized in that the tool attachment point (90) is open in the proximal direction (101) and opens into a concentric cone-like recess (94) and this recess (94) has an approximately right-angled cone angle.

5. The screw element (1) according to any of the preceding claims, characterized in that the head area (10) comprises, at least in sections, a ball segment or lens segment, said head area is configured to provide a polyaxially pivotable connection with a fork head (2) that is u-shaped in a side view.

6. The screw element (1) according to any of the preceding claims, characterized in that the outer thread (12) can be zoned into a proximal thread area (30) adjacent to the neck area (20) and extending in the distal direction (102), and a distal thread area (50) adjacent thereto, and a distal tip area (60) adjacent thereto, and the distal thread area (50) merges into the proximal thread area (30) in a transition zone (40), and the proximal thread area (30) forms at least one further course of thread (31, 32) forming at least one cutting edge (41) within the transition zone (40).

7. The screw element (1) according to any of the preceding claims, characterized in that the distal tip area (60) forms at least one cutting edge (61).

8. The screw element (1) according to any of the preceding claims, characterized in that the screw element (1) has a continuous cannula(80), the cannula (80) has at least two laterally extending openings (70) being connected with the cannula (80, 83), and the openings (70) are provided as a polygon (700) in a side view.

9. A process for manufacturing and further processing a screw element (1) according to any of the preceding claims, comprising the steps: a. Providing raw material particles of a Ti6Al4V alloy. b. Additive building of the screw element (1) by means of a 3D printing process, which joins the raw material particles together in three dimensions so that at least three cantilever elements (13) are attached to the proximal end of the head (10, 109), the free ends (17) of which describe a plane (108), and so that the external thread (12) of the screw element (1) has at least one thread surface (122) that is directed away from the plane (108), and has at least one thread surface (121) that faces this plane (108), and the surface (121) that faces the plane (108) has a greater roughness than the surface (122) directed away from the plane (108). c. Stress relief heat treatment of the screw element (1) at a temperature of at least 500°C, but not greater than 840°C, with a hold time of at least one hour, but less than 6 hours; d. Removing the cantilever elements (13) from the proximal head area (109); e. Second heat treatment of the screw element (1); and f. Removing incompletely joined raw material particles.

10. The process according to claim 9, characterized in that during the stress relief heat treatment of the screw element (1) a temperature of preferably between 550°C and 800°C, preferably between 550°C and 750°C, preferably between 600°C and 720°C, is set for the duration of the hold time.

11. The process according to claim 9, characterized in that during the second heat treatment of the screw element (1), an argon atmosphere and a temperature between 900°C and 940°C, preferably between 910°C and 930°C, is applied, and the screw element (1) is exposed to a pressure of at least 900 bar, preferably at least 950 bar, and for the temperature and the pressure a hold time of at least one hour but less than 4 hours is applied.

12. The process according to claim 9, characterized in that during the second heat treatment of the screw element (1), an argon atmosphere at a temperature of at least 920°C but less than 1050°C is applied, and a hold time of at least one hour but less than 4 hours is applied.

13. The process according to claim 9, characterized in that during the second heat treatment of the screw element (1) a temperature of at least 820°C but less than 920°C is applied, and a hold time of at least one hour but less than 4 hours is applied.

14. The process of any of the preceding claims 11, 12 or 13, characterized in that removing incompletely joined raw material particles comprises: a. Removing incompletely joined raw material particles by means of a mechanical removal process, and b. Removing incompletely joined raw material particles by means of a chemical removal process.

15. The process according to claim 14, characterized in that the mechanical removal process is conducted by means of blast means at a minimum application pressure of 2 bar and a minimum application duration of 5 min, wherein sharp-edged blast means, such as corundum, is used, and the blast means comprises a particle size between 0.05 mm and 0.25 mm, but preferably a particle size between 0.07 mm and 0.15 mm.

16. The process according to claim 14, characterized in that the mechanical removal process is conducted by means of a coarse vibratory finishing or vibratory finishing process.

17. The process according to claim 14, characterized in that the chemical removal process is conducted by means of a staining or etching treatment.

18. The process according to claim 17, characterized in that the chemical removal process is supported electro-galvanically and / or by mechanically induced vibrations.

19. The process according to any of the preceding claims 9-18, characterized in that, at the end of the process, the surfaces of the screw element (1) are solidified by means of a blasting abrasive, wherein a minimum application pressure of 2 bar and a minimum application duration of 5 min are applied, wherein spherical blasting abrasives are used, such as ceramic balls, and the blasting abrasive has a particle size between 0.05 mm and 0.25 mm, but preferably a particle size between 0.07 mm and 0.15 mm.