SCREW ELEMENT OPTIMIZED FOR 3D PRINTING

Description

State of the art

[0001] Various osteosynthesis devices, such as screw elements for the fixation of bones or bone fragments, are known in the state of the art. Such bone screws are traditionally manufactured using CNC milling and turning machines. For the specific bone thread geometries and, above all, for the different diameters of the screw elements, special thread plates must be provided if they are to be manufactured in series production. This leads to longer delivery times and higher costs. 3D printing offers a possible alternative, as all geometries can be manufactured without special tools, and thus without waiting for special tools. Significantly greater flexibility in geometric design is possible.

[0002] Pedicle screws, for example, are used as screw elements in spinal treatment. They are characterized by the fact that they have two different thread areas. Distal is a bone thread with coarse teeth and proximal is a finer toothing. Coarse teeth offer the best hold in cancellous bone, while finer teeth offer greater hold on the cortical bone. Such screw elements, with fine and coarse teeth, are considered state of the art because they combine the best holding conditions on the spine. Between the distal and proximal threads there is a thread transition area. In this thread transition area, another thread tooth is provided from the distal end between the threads of the distal thread, which then extends into the proximal area. This creates finer teeth in the proximal area.If such screw elements are conventionally manufactured using CNC lathes and milling machines, the manufacturing process results in a spiral start to the additional thread profile, which increases radially along the circumferential direction. When the pedicle screw is screwed in, this spiral start of the thread transition area presses into the bone to create space for the subsequent additional thread. In some cases, particularly in weaker bones, this space-occupying process of the additional thread can lead to the pedicle being inadvertently ruptured and a fracture being created. This is due to the lack of thread pre-tapping. It would therefore be desirable to provide a cutting edge for the additional thread. This is very difficult to achieve with conventional CNC manufacturing methods. 3D printing offers a very good alternative.

[0003] If bone screws are to be manufactured using 3D printing, further challenges are to be expected. With a view to cost-effective production, the post-processing of the parts after 3D printing must be optimized. A key optimization step is the reduction of all support structures required for construction, as these are complex and often have to be removed manually. Once the construction direction has been determined, there should be no straight surfaces or overhangs in the construction direction in order to eliminate precisely these support structures. This has implications for openings and other features, such as lateral fenestration openings and the tool attachment point. The state of the art lacks appropriate features for how these must be geometrically designed in order to use as few support structures as possible.

[0004] A screw element having the features of the preamble of claim 1 is known from US 2012 / 197311 A1. Description of the invention

[0005] The solution according to the invention lies in the features of independent claim 1. Advantageous developments of the invention are the subject of the dependent claims.

[0006] A method for manufacturing a screw element according to the invention is also described, which does not form part of the claimed invention. It serves merely to facilitate understanding of the invention.

[0007] Conventional CNC manufacturing of the screw element (1) with a cutting edge at the thread transition area is currently not possible or only possible with extreme technological effort. Therefore, additive manufacturing is the method of choice. Additive manufacturing of metallic alloys, also known as 3D printing, uses laser or electron beam melting processes. All metallic alloys known and accepted as orthopedic implant materials are suitable. These include, for example, titanium, cobalt-chromium, and stainless steel alloys.

[0008] The long-term success of a 3D-printed implant depends heavily on its post-treatment. Targeted heat treatment and surface treatment are extremely important. Relevant literature is available that explains the interrelationships between the post-treatments. Preferably, the 3D-printed parts are first stress-relieved between 500°C and a maximum of 850°C and then subjected to a hot isostatic pressing (HIP) process. The parts are then corundum blasted to remove loose particles from the surface. Another part of the surface treatment involves smoothing the microstructures. Here, a corresponding reduction in surface roughness can be achieved with the help of chemical etching, which can optionally be supported by galvanic voltage and / or mechanical stimulation.The goal is to remove the incompletely welded particles, as tensile stresses and micro-notches caused by the incompletely welded particles can weaken the fatigue strength. Following this process, a shot peening process is suitable for creating residual compressive stresses on the implant surface. This further increases the fatigue strength.

[0009] When manufacturing using a 3D printing process, several design parameters must be considered. Firstly, a minimum wall thickness of at least 0.1 mm, or even better, 0.3 mm, must be maintained for all structures. Secondly, gaps or slits must have a gap thickness of at least 0.1 mm, or even better, 0.3 mm, to ensure that the gap remains open during additive manufacturing and does not accidentally close.

[0010] For the screw element (1) according to the invention, spatial coordinate references are defined, such as the proximal direction (101), the distal direction (102), which extend along a central axis (103). The radial extension (104) is defined outwardly from the central axis (103) ( Fig. 1 ).

[0011] To reduce the number of support structures required during 3D printing, it is advantageous if the construction direction (105) of the screw element (1) roughly corresponds to the direction of the central axis (103) and runs from proximal (101) to distal (102). A different orientation would require the screw element (1) to be constructed at an angle in the 3D printer and a large number of lateral support structures would have to be provided. This would make production less cost-efficient. Ideally, the head area (10) is manufactured first. This way, only the head needs to be lined with support structures, and the diameter of the head (10) offers sufficient lateral support, especially for longer screw elements. With a larger support diameter, longer components do not need to be additionally supported in the distal direction during 3D printing.

[0012] To avoid having to provide the entire surface of the head region (10) with support structures, it is advantageous if the tool attachment point (90) is open in the proximal direction (101) and opens into a concentric, conical recess (94) with an approximately right-angled cone angle. Thus, the support structures can be reduced to a support structure ring (95) along the diameter of the tool attachment point.

[0013] For the same reason, it is also important that the tool attachment point (90) is delimited in the distal direction (102) by a wall (93), and that this wall (93) runs as a bevel in an increasing distal direction (102) radially inward, and that the cone angle formed by the wall is less than 120°. This wall (93) preferably has an approximately rectangular cone angle. This also eliminates the need for support structures for the base of the tool attachment point. Removing any support structures from this base surface (93) would be a major challenge, since this base surface (93) is very difficult to access for post-processing.

[0014] In a first embodiment, a screw element (1) for the fixation of bone components and bone fragments is described, which consists of a shaft (11), a neck region (20), and a head (10) located in the proximal direction (101), as well as a tip (60) located in the distal direction (102). The head (10) is preferably designed as a lens, an inclined head, or a spherical head. However, a combination of different curves 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). The bone anchor preferably has a tool attachment point (90) suitable for introducing a torque. For minimally invasive treatment, it is advantageous if the bone anchor has a cannulation opening (80) that runs completely through it, through which a surgical guide wire can be guided.

[0015] Bone screws that can be screwed into a bone are preferably used as the screw element (1). However, hooks, clamps, nails and other types of bone anchors can also be used. The example of a screw element (1) presented here shows a bone screw with a shaft (11) and a bone thread (12) on the shaft. The thread (12) can have, at least in some sections proximally, a finer serration (30), which is better suited for harder cortical bone. A thread (60) that tapers to a point towards the distal end and has a cutting edge (61) at the bone anchor tip (60) is advantageous so that the screw element (1) can self-tappingly pull itself into the bone when screwed in.

[0016] It is advantageous if the screw element (1) is characterized in that the external thread (12) can be divided into a proximal thread region (30) adjacent to the neck region (20) and extending in the distal direction (102), and a distal thread region (50) adjacent thereto, and in turn adjacent thereto a distal tip region (60), and the distal thread region (50) merges into the proximal thread region (30) in a transition zone (40), and 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).

[0017] This cutting edge (41) provides a pre-cutting effect and prevents space displacement in the bone. This is particularly beneficial in weaker bone.

[0018] It is further advantageous if at least one of the cutting edges (41, 61) is planar and oriented primarily in the radial direction (104). Alternatively, a concave or convex surface is also conceivable for creating the respective cutting edge.

[0019] Different thread tooth patterns 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 can also be provided, which transitions to a quadruple or sextuple thread in the proximal direction (101). To simplify all illustrations, the preferred embodiment has been shown with a double thread in the distal region (50) and a quadruple thread in the proximal region (30) ( Fig. 1-4 ).

[0020] In the case of weak bones, such as in cases of osteopenia or osteoporosis, it may be necessary to further augment the bone anchor. This can be done with bone cement. Bone cement is preferably a polymer made up of at least two components and injected in a liquid or paste-like state. After a few minutes, the bone cement hardens into a plastic in the bone and bonds with the spongy bone structure. Polymethyl methacrylate cement is usually used. Alternatively, other media for delivery through the bone anchor are also conceivable. It is conceivable that alternative media, such as pharmaceutically active media, media containing cells, nutrients, media that serve as genetic information carriers, or vaccines, could be administered through the bone anchor.

[0021] Optionally, the cannulation (80) has at least one or more openings (70) leading laterally and communicating with the cannulation. The openings are preferably arranged in a ring-like formation (71 or 72) in the circumferential direction. If there is more than one ring-like opening formation (71 and 72) in the circumferential direction, the openings for each formation have different opening cross-sectional areas (710, 720). In the case of a bone anchor (1) screwed into a bone, the lateral openings communicate from the hollow chamber (80) with the surrounding bone tissue. They are suitable for discharging the fluid injected into the bone anchor (1) through the lateral openings into the surrounding tissue. A different cross-sectional area of the opening formations (710, 720) has 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 more distal.

[0022] It is particularly advantageous for 3D printing if these lateral openings (70, 71, 72) are provided as a polygon (700). Conventionally, such lateral openings (70) are drilled out concentrically. In 3D printing, concentric openings would create small overhangs and result in so-called dross formations (i.e. miniature stalactite-like formations). This would require costly manual post-processing in series production. Polygons offer an alternative and therefore preferred embodiment. The sloping surface elements of a polygon form a roof-like structure. Slopes with an angle of approximately 45° can be easily produced using the printing process without support structures or dross formations.

[0023] Therefore, it is advantageous for the preferred embodiment that the lateral openings (70) are provided as a polygon (700). It is advantageous if the polygon (700) has at least one surface element (701, 702) that is formed primarily along the central axis (103). Furthermore, it is optimal if the distance between the surface elements (701 and 702) running parallel to the central axis (103) is smaller than the cannulation diameter D82 at the opening point (83). Furthermore, the polygon (700) should have at least two surface elements (e.g. 703, 704, 705, 706) which, in a side view, are each aligned at an angle of 25° to 65°, preferably of 35° to 55°, in particular of 40° to 50° with respect to the central axis (103), so that they can be produced along the defined construction direction (105) using a 3D printing process.

[0024] In the preferred embodiment, at least two surface elements (703, 704 or 705, 706) are oriented symmetrically relative to the central axis (103). Alternative embodiments are also conceivable, in which the polygon (700) is provided, for example, as a rhombus, a parallelogram, or with significantly more surface elements.

[0025] With 3D printing it is also possible to provide different roughnesses on the surface of the screw element (1) ( Fig. 2). For example, it is possible to have a greater surface roughness on the surfaces of the thread flanks (12) facing in the proximal direction (121) than on the surfaces of the same thread flanks facing distally (122). A greater roughness on the thread flanks in the proximal projection direction (121) has the advantage that higher friction is generated between the bone and the screw element in the pull-out direction and the screw element has a significantly higher pull-out strength. Smoother thread flanks in the distal projection direction (122) have the advantage that the screw element (1) can still be easily screwed into the bone.

[0026] An alternative screw element (1) according to the invention for the fixation of bone components and bone fragments consists of a shaft (11) with an external thread (12) and a longitudinal central axis (103) extending along the shaft (11), thereby defining a distal (102) and a proximal (101) direction. The screw element (1) has a continuous cannulation (80). The cannulation (80) has at least two openings (70) extending laterally and communicating with the cannulation (80, 83). The openings (70) are provided as a polygon (700) in a side view. The external thread (12) can be divided into a proximal threaded region (30) adjacent to the neck region (20) and extending in the distal direction (102), and a distal threaded region (50) adjacent thereto, and in turn, a distal tip region (60) adjacent thereto.The distal threaded portion (50) merges into the proximal threaded portion (30) in a transition zone (40). The proximal threaded portion (30) forms at least one additional thread pitch (31, 32), which forms at least one cutting edge (41) within the transition zone (40).

[0027] Another alternative screw element (1) according to the invention for the fixation of bone components and bone fragments consists of a shaft (11) with an external thread (12) and a longitudinal central axis (103) extending along the shaft (11), thereby defining a distal (102) and a proximal (101) direction. The external thread (12) can be divided into a proximal threaded region (30) adjacent to the neck region (20) and extending in the distal direction (102), and a distal threaded region (50) adjacent thereto, and in turn a distal tip region (60) adjacent thereto. The distal threaded region (50) merges into the proximal threaded region (30) in a transition zone (40). 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). Show brief description of the drawings

[0028] Fig. 1 an oblique view of the screw element according to the invention, Fig. 2 a side view of the screw element according to the invention and a detailed view of the polygon-shaped side openings. Fig. 3 Side view and corresponding sectional view through the bone anchor according to the invention, Fig. 4 two screw elements according to the invention in combination with U-shaped fork heads mounted with a connecting rod. Description of the preferred embodiments

[0029] Fig. 1shows the screw element (1) consisting of a head region (10), a neck region (20), and a shaft region (11) with a bone thread (12). Furthermore, it can be seen that the external thread (12) can be divided into a proximal thread region (30) adjacent to the neck region (20) and extending in the distal direction (102), and a distal thread region (50) adjacent thereto, and in turn, a distal tip region (60) adjacent thereto. The distal thread region (50) merges into the proximal thread region (30) in a transition zone (40), and 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).

[0030] A further cutting edge (61) is formed at the distal tip region (60). Ideally, the respective cutting edge (41, 61) is primarily planar in the radial direction. Other surface geometries with convex or concave regions are also conceivable. Alternatively, recurring patterns in the circumferential direction that have a pre-cutting effect, such as serrations or teeth, are also conceivable.

[0031] Fig. 1illustrates, in a preferred embodiment, 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, wherein a greater 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 core or the 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). Two cutting edges (41, 42) are formed in the transition region (40), wherein the second cutting edge (42) cannot be shown due to the view.It is the starting point (not visible here) for the second proximal thread (32). The cutting edges (41, 42) have the significant clinical advantage that such screw elements (1) can prevent future fractures during implantation. If a different thread is provided, the number of cutting edges can be increased or decreased accordingly.

[0032] The Fig. 1 It can also be seen that the construction direction (105) of the screw element (1) corresponds approximately to the direction of the central axis (103) and runs from proximal (101) to distal (102). The advantages have already been described above.

[0033] In Fig. 2a preferred embodiment of a screw element (1) is shown, in which the lateral fenestration openings (70) are designed as a polygon (700). The polygon (700) has at least one surface element (701, 702) which is formed mainly along the central axis (103). The distance between the surface elements (701 and 702) running parallel to the central axis (103) is smaller than the cannulation diameter D82 at the mouth point (83). Furthermore, the polygon (700) has at least two surface elements (e.g. 703, 704, 705, 706) which, in a side view, are each aligned at an angle of 25° to 65°, preferably of 35° to 55°, in particular of 40° to 50° with respect to the central axis (103). It is advantageous if at least two of the surface elements (703, 704 or 705, 706) are oriented symmetrically to one another with respect to the central axis (103).It is also conceivable that the surface elements (701-706) merge into one another with the help of curves (707).

[0034] In Fig. 2 It is further shown that the lateral openings (70) are arranged in a ring-like formation (71 and / or 72) in the circumferential direction, and if there is more than one ring-like formation (71 and 72) in the circumferential direction, the openings (70) have different opening cross-sectional areas (710, 720) for each formation. Optimally, the opening cross-sectional area (710) of the distal formation (71) is larger than the opening cross-sectional area (720) of the proximal formation (72).

[0035] Fig. 3discloses a sectional view of the screw element (1). The interior of the head region (10) and the continuous cannulation (80) can be seen. The main feature of the head is that the head (10) has a larger outer diameter than the neck region (20). The bone anchor preferably has a tool attachment point (90) which is suitable for introducing a torque. The torque for screwing in the bone anchor can thus be introduced directly via the tool attachment point. This tool attachment point can have any profile (91, 92), such as a multi-tooth round head, hexagon socket, Phillips recess, a simple slot or a differently designed toothing. In the preferred embodiment, the tool attachment point (90) is located at the proximal end (101) and is delimited in the distal direction (102) by a wall (93).This wall (93) is formed as a slope that runs radially inward in the distal direction (102), and the cone angle formed by the wall is less than 120°. Ideally, the cone angle is approximately rectangular. Furthermore, it can be seen that the

[0036] The tool attachment point (90) is open in the proximal direction (101) and opens into a concentric conical recess (94) and has an approximately right-angled cone angle. The outer proximal ring functions as the support structure ring (95) described above.

[0037] In Fig. 3Also 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 D82. The lateral openings (70) open into the cannulation (82) through corresponding openings (83). It is advantageous if the cannulation diameter is reduced distally (102) in a distal cannulation section (84). The transitions (812, 834) between the different cannulation diameters optimally have a cone angle of less than 120°, preferably they are approximately right-angled.

[0038] Fig. 4illustrates two screw elements (1) according to the invention in combination with U-shaped fork heads (2) mounted with a connecting rod (4). The screw elements (1) have a proximal head region (10) which, at least in sections, has a spherical segment which is suitable for providing a polyaxial pivotable connection with a fork head (2) which is U-shaped in a side view. After the connecting rod (4) and fixed adjusting means (3) have been inserted, the screw elements (1) are connected to one another in a stable angle. They form a rigid fixation, as is used, for example, in spinal surgery.

Claims

1. Screw element (1) for the fixation of bone components and bone fragments consisting of a shaft (11) with an external 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) has a continuous cannulation (80), the cannulation (80) has at least two laterally extending openings (70) communicating with the cannulation (80, 83), wherein the openings (70) are provided in a side view as a polygon (700), characterized in that the external thread (12) can be divided into a proximal thread region (30) adjoining the neck region (20) and extending in the distal direction (102), and a distal thread region (50) adjoining the proximal region, and in turn a distal tip region (60) adjoining the distal region, and the distal thread region (50) merges into the proximal thread region (30) in a transition zone (40), and the proximal thread region (30) forms at least one additional thread (31, 32), which forms at least one cutting edge (41) within the transition zone (40).

2. Screw element (1) according to the preceding claim, characterized in that the polygon (700) has at least one surface element (701, 702) which is formed mainly along the central axis (103).

3. Screw element (1) according to one of the preceding claims, characterized in that the distance between the surface elements (701 and 702) running parallel to the central axis (103) is smaller than the cannulation diameter D82 at the mouths (83) of the openings (70).

4. Screw element (1) according to one of the preceding claims, characterized in that the polygon (700) has at least two surface elements (e.g. 703, 704, 705, 706) which are in a side view each aligned at an angle of 25° to °, preferably of 35° to 55°, in particular of 40° to 50° with respect to the central axis (103).

5. Screw element (1) according to one of the preceding claims, characterized in that at least two surface elements (703, 704 or 705, 706) are oriented symmetrically with respect to one another in relation to the central axis (103).

6. Screw element (1) according to one of the preceding claims, characterized in that the surface elements (701-706) merge into one another by means of curves (707).

7. Screw element (1) according to one of the preceding claims, characterized in that the lateral openings (70) are arranged in a ring-like formation (71 and / or 72) in the circumferential direction and, in the case of more than one ring-like formation (71 and 72) in the circumferential direction, the openings (70) have different opening cross-sectional areas (710, 720) for each formation.

8. Screw element (1) according to claim 7, characterized in that the opening cross-sectional area (710) of the distal formation (71) is larger than the opening cross-sectional area (720) of the proximal formation (72).

9. Screw element (1) according to one of the preceding claims, characterized in that the lateral openings (70) are placed in the thread base (53).

10. Screw element (1) according to one of the preceding claims, characterized in that the screw element (1) furthermore has a head (10), a neck region (20) and a shaft region (11) with a bone thread (12) and a tool attachment point (90) is provided in the head (10) and the tool attachment point (90) is limited in the distal direction (102) by a wall (93) and this wall (93) extends radially inwards as a slope in the increasing distal direction (102) and the cone angle formed by the wall is smaller than 120°.

11. Screw element (1) according to claim 10, characterized in that the wall (93) describes an approximately right-angled cone angle.

12. Screw element (1) according to claims 10 or 11, 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 has an approximately right-angled cone angle.

13. Screw element (1) according to one of the preceding claims, characterized in that the distal tip region (60) forms at least one cutting edge (61).

14. Screw element (1) according to claim 13, characterized in that at least one of the cutting edges (41, 61) is planar and is mainly aligned in the radial direction (104).

15. Screw element (1) according to claim 13, characterized in that at least one of the cutting edges (41, 61) has a concave surface which is oriented mainly in the radial direction (104).

16. Screw element (1) according to claim 13, characterized in that at least one of the cutting edges (41, 61) has a convex surface which is oriented mainly in the radial direction (104) .