FI3927264T3

FI3927264T3 - Corticalis screw consisting of bioresorbable material

Info

Publication number: FI3927264T3
Application number: FIEP20706697.8T
Authority: FI
Inventors: Oliver Bielenstein; Frank Witte; Romano Matthys; Tadic Drazen Dr
Original assignee: botiss biomaterials GmbH
Priority date: 2019-02-22
Filing date: 2020-02-20
Publication date: 2023-05-29
Also published as: DE102019104545A1; EP3927264B1; WO2020169735A1; EP3927264A1

Description

1 EP3 927 264

CORTICALIS SCREW CONSISTING OF BIORESORBABLE MATERIAL

Description Field of the invention

The invention relates to a corticalis screw made of a bioresorbable material, and a to set having a corticalis screw.

Background of the invention

Corticalis screws are known from practice in a wide variety of embodiments.

These are in particular designed for fixing ligaments, bone fragments and for fastening implants, in particular bone plates.

Generally, a corticalis screw comprises a screw thread for screwing into the cortical bone, and a head having a drive.

Bioresorbable screws are also known from practice.

These can in particular consist of a bioresorbable metal. In particular, the use of magnesium as the bioresorbable material has long been known.

Since pure magnesium does not have very high strength and generally corrodes very guickly, magnesium alloys are usually used in practice. In particular, yttrium- containing magnesium alloys are known, which have a higher strength than pure magnesium, and whereby the corrosion of the implant is reduced, above all due to the yttrium.

Bone screws made of a magnesium alloy known from practice comprise a head having a drive which is designed, for example, as a hexalobular internal socket.

The problem is that the magnesium alloys used still have a significantly lower strength than conventionally used titanium or stainless steel alloys. In particular in the case of smaller implants having a diameter of less than 5 mm, there is therefore the risk of the drive being damaged when the implant is screwed in.

2 EP3 927 264

Another problem that is long known from practice is that of hydrogen formation during breakdown. Gas bubble formations may impair the healing process.

It is therefore desirable to form such implants from as little material as possible.

Hollow structures in the case of a screw, in particular a porous configuration of the material, however, are in turn accompanied by a reduced strength in such a way that the screw may in some circumstances break during screwing in, within the thread region.

Medical screws are known from the following documents: - EP 1234 637 A2 - US 5659497 A - FR 2 803 739 A1 - US 6 283 973 B1 - FR 2 879 915 A1 - US 2001/041937 A1 - US 2012/179163 A1 - EP 3 315 085 A1 - US 2005/177243 A1 - EP 3 072 540 A1

Object of the invention

In comparison, the object of the invention is that of providing a corticalis screw in which the mentioned disadvantages are at least reduced.

An object of the invention is in particular that of providing a corticalis screw which, at a low weight, has a low risk of breakage during the screwing-in operation.

Summary of the invention

3 EP3 927 264

The object of the invention is already achieved by a corticalis screw according to claim 1.

Preferred embodiments and developments of the invention can be found in the subject matter of the dependent claims, the description and the drawings.

The invention relates to a corticalis screw made of a bioresorbable material.

According to the invention, the corticalis screw consists of magnesium or a magnesium alloy.

The corticalis screw comprises a screw thread for screwing into the cortical bone, and a head having a drive.

The drive is thus accessible via the head of the corticalis screw, by a handling tool.

In particular, the drive can comprise a positive-locking element which extends axially through the head.

According to the invention, the drive extends through the screw thread, at least in portions.

Preferably, the drive extends over at least half of the screw thread, very particularly preferably through the entire screw thread.

The invention is based on the effect that, by providing a continuous channel, preferably the entire length of the implant can be used for torque transmission. At the same time, the channel in turn reduces the weight of the corticalis screw, which reduces the formation of gas during breakdown, when the corticalis screw is made of magnesium or a magnesium alloy.

The handling tool, the cross section of which preferably substantially corresponds to the cross section of the channel, stabilizes the corticalis screw during screwing in, such that, despite an implant which is lighter compared to a screw without a channel, the risk of breaking during the screwing-in operation is reduced.

Preferably, the drive is formed as a channel which is continuous from a rear end to a front end, and which forms a positive-locking element for a handling tool.

4 EP3 927 264

According to one embodiment, the screw thread of the corticalis screw has passages to the channel.

The channel is thus open laterally at at least one, preferably at a plurality of, locations. The passages are used for pressure compensation. For example, a gas exchange can take place, in particular since gases that may form inside the channel escape easily.

Furthermore, the passages can also compensate osmotic pressures, due to the formation of metal salts during breakdown, in an improved manner.

According to a preferred embodiment of the invention, the passages are formed as overlappings of the channel with the tooth base of a thread.

For example, the passages can be provided in a very simple manner, by providing a semi-finished product comprising the channel having the thread. The tooth base of the thread overlaps with the channel, such that passages result in the tooth base.

In particular when a central cross-shaped channel is present, four passages, distributed about 90° in each case, are formed in each thread turn.

Preferably, in particular as described above, the channel is simultaneously formed as a drive for the corticalis screw.

According to the invention, the screw thread merges in a transition-free manner into a conical head having a head thread. Transition-free merging is understood to mean that the last thread flight of the screw thread merges into a thread flight of the head thread.

This embodiment allows the head to become jammed. The corticalis screw is therefore particularly suitable for fastening ligaments or bone fragments.

According to the invention, the screw thread of the corticalis screw has a larger pitch than the head thread. At the end of the screwing-in process, the corticalis screw is thus jammed not only due to the conical head, but also due to the different thread pitches.

EP3 927 264

The corticalis screw can consist of a magnesium alloy which comprises 0.5 to % by weight yttrium.

The corticalis screw preferably comprises a channel having a non-circular cross section, such that a torque can be exerted on the screw via a handling tool. 5 The channel preferably has a uniform cross section at least in the region of a thread, particularly preferably over its entire length.

Preferably, the channel extends concentrically with respect to the central axis of the corticalis screw.

The channel is preferably open at the front, that is to say at the tip of the corticalis 10 screw.

According to another embodiment of the invention, however, it is also conceivable to provide a continuous channel which ends at a tip which is designed, for example, as a drill having cutting edges. However, the continuous channel preferably extends at least as a blind hole as far as the tip, and extends in particular along a thread of the implant.

However, a channel that is open at the front in particular has the advantage that the corticalis screw can be produced in an efficient manner from an extruded magnesium alloy in which the channel used as a positive-locking element has been introduced during the extrusion process.

According to a preferred embodiment of the invention, the channel is cross- shaped. In particular, the channel, when viewed in cross section, consists of two intersecting rectangles, which are preferably identical to one another and where preferably the center points of the rectangles line on one another.

Such a cross-shaped cross section can be produced in a simple manner, even in the case of smaller diameters, by an extrusion method, and preferably provides radially extending side surfaces which are offset only with respect to the central axis and are used as radially oriented engagement surfaces for the handling tool.

In a development of the invention, the corticalis screw comprises a coating.

6 EP3 927 264

In particular, the corticalis screw comprises a magnesium fluoride coating. Such a layer can be provided in a simple manner by immersing the corticalis screw in hydrofluoric acid.

Furthermore, the corticalis screw, in particular in order to slow down corrosion immediately after the insertion, can comprise a polymer coating.

It is provided in particular to provide the corticalis screw with a combination of magnesium fluoride coating and polymer coating. The magnesium fluoride coating is used inter alia as an adhesion promoter layer.

The coating, in particular the polymer coating, preferably has a thickness of less than 5 um, preferably less than 1 um, in particular a thickness of 0.2 to 0.8 um.

Such a thin coating minimizes the risk of the layer cracking during insertion.

Preferably, the corticalis screw has a length of 6 to 20 mm and/or a diameter of 2 to 5 mm.

According to a further embodiment, the corticalis screw has a self-tapping tip.

Such a self-tapping tip can also be provided in the case of a corticalis screw having a channel open at the front by at least one bevel at least of the first front thread turn.

The self-tapping tip can in particular be formed by a recess which, in plan view of the tip of the corticalis screw, is substantially in the shape of a circular segment.

The recess preferably runs outwardly in the first thread turn or after the first thread turn.

The corticalis screw can consist of a magnesium alloy having a tensile strength

Rm (according to DIN EN ISO 6892-1, version 2017-02) of above 250 MPa, in particular above 350 MPa, and/or below 500 MPa, in particular below 450 MPa.

The channel of the corticalis screw is in particular designed as a cross which is formed in cross section from two identical rectangles which overlap perpendicularly.

7 EP3 927 264

Preferably, the inner and/or outer edges of the cross are rounded. The risk of cracking at the edges can thus be reduced. At the same time, the insertion of the handling tool is facilitated by the rounded portions.

The cross in cross section preferably has a height and/or a width of 20-60 %, preferably 30-45 % and/or rounded edges having an edge radius of 5-40 %, preferably 10-30 % of the outer diameter of the thread of the implant.

By means of this dimensioning, optimal stabilization by the drive, with simultaneously little material volume, could be achieved.

The cross section of the cross preferably has a height and/or width of 1.3 to 2.5mm, particularly preferably of 1.5 to 2.1 mm.

The rounded edges preferably have an edge radius of 0.1 to 0.8 mm, particularly preferably of 0.2 to 0.6 mm.

The invention further relates to a set comprising the above-described corticalis screw and a handling tool.

The handling tool is in particular designed as a screwdriver having a handle, or as a motor-driven medical instrument.

The handling tool comprises a shaft which is adapted to a channel of the corticalis screw, which channel is formed as a positive-locking element.

The shaft is in particular the same shape as the channel. With regard to the tolerances, the shaft and channel are preferably matched to one another in such a way that the corticalis screw can be pushed onto the handling tool in a clamping manner such that it is secured against accidental falling during insertion.

Such a clamping can be achieved in particular in a simple manner, since large surfaces are provided via the continuous channel, in contrast to a conventional screw, by means of which surfaces a frictional connection can be established.

The shaft of the handling tool preferably extends up to the front end of the corticalis screw.

8 EP3 927 264

According to a development of the invention, the tip of the shaft is formed as a drill.

This embodiment therefore relates to screws having a channel that is open at the front, the shaft protruding from the corticalis screw at the front by a portion sharpened for drilling for example.

The handling tool can thus be used simultaneously for pre-drilling or expanding an already set pre-bore.

The shaft of the handling tool can have a coupling. A coupling makes it possible for the handling tool to be used in particular in manually or motor-driven instruments.

The coupling is preferably designed as a quick coupling, that is to say a coupling which can be actuated without tools. As couplings, standard couplings used in the medical, in particular dental, field are preferably possible.

The handling tool can be designed, for example, as a bit that can be inserted into an instrument.

Brief description of the drawings

The subject matter of the invention will be explained in more detail below on the basis of an embodiment with reference to the drawings of Fig. 1 to 9.

Fig. 1 is a side view of a corticalis screw according to the invention.

Fig. 2 is an axial sectional view.

Fig. 3 is a plan view of the corticalis screw from the rear.

Fig. 4 shows the corticalis screw from the front.

The design of the corticalis screw will be explained further with reference to Fig. 5, which shows the geometry of the corticalis screw enveloping the thread.

Fig. 6 is a perspective view of the corticalis screw.

9 EP3 927 264

Fig. 7 is a schematic perspective view of a handling tool, by way of example, for a corticalis screw according to the invention.

Fig. 8 is a schematic view of the nozzle of an extrusion machine, as can be used to produce a corticalis screw according to the invention.

Fig. 9 shows an alternative embodiment of a handling tool which is designed as an insert for a handpiece.

Detailed description of the drawings

Fig. 1 is a side view of an embodiment of a corticalis screw 1 according to the invention.

The corticalis screw 1 comprises a screw thread 2 which, in this embodiment, extends from the front to a head 8 having a head thread 5.

The tooth tips 4 of the screw thread 2 are flattened, in particular flat, in order to improve the clamping of the inserted corticalis screw 1 and to reduce damage to soft tissue. The flattened portion formed by the tooth tips 4 can in particular have a length of 0.3 to 2 mm.

The screw thread 2 merges in a transition-free manner, that is to say without a step, into an otherwise conical, in particular frustoconical, head 8.

Both the screw thread 2 and the head thread 5 formed in this way are designed in a single-duct manner in this embodiment.

The screw thread 2 has a larger pitch than the head thread 5.

In particular, the pitch of the screw thread 2 is 5 to 20 %, particularly preferably 8 to 15 %, larger than the pitch of the head thread 5.

The corticalis screw 1 is thus jammed at the end of the screwing-in operation.

The pitch of the screw thread 2 is preferably 2 to 5 mm.

The corticalis screw 1 preferably has a length of 6 to 20 mm, particularly preferably of 8 to 14 mm.

10 EP3 927 264

The length of the head 8 is preferably 1/2 to 1/10 of the total length of the corticalis screw 1, particularly preferably 1/4 to 2/5.

The diameter of the corticalis screw 1 in the region of the screw thread 2 is preferably 2 to 5 mm, particularly preferably 2.5 to 3.5 mm.

In this embodiment, the corticalis screw 1 has a tip 7 comprising a channel 10 that is open at the front.

The channel 10 overlaps in part with the tooth base 3 of the thread 2.

As a result, distributed passages 9 are formed in the tooth base 3.

The passages 9 allow pressure compensation both with respect to gases and with respect to osmotic pressures.

The tip 7 of the corticalis screw 1 is designed to be self-tapping.

In this embodiment, this is achieved by at least one bevel 6 of the first front thread turn.

The tooth base 3 is rounded, in particular having a radius of 0.5 to 1 mm.

This also facilitates the jamming of the implant and reduces damage to soft tissue.

The tooth depth is preferably 0.5 to 0.8 mm.

Fig. 2 is an axial sectional view of the corticalis screw 1 shown in Fig. 1.

In particular the channel 10 is visible, which extends from the rear end of the corticalis screw to the front end of the corticalis screw 1.

As shown in the plan view of the rear face of the corticalis screw according to Fig. 3, the channel is cross-shaped, such that, as can be seen in Fig. 2, four passages, 9 distributed about 90° in each case, result in each thread turn, since the thread base overlaps with the channel 10.

In the plan view of the rear face of the corticalis screw 1, in particular the cross- shaped design of the channel 10 can be seen.

11 EP3 927 264

The channel 10 preferably has a height h (corresponds to the width) of 1.3 to 2.5 mm, particularly preferably 1.5 to 2.1 mm.

The height h or the width of the channel 10 and/or its largest diameter is preferably at least 20 %, preferably at least 40 %, of the outer diameter of the thread through which the channel extends.

As seen in cross section, the channel 10 consists of two rectangles which are twisted by 90° relative to one another and have an identical cross section, and is arranged centrally in the corticalis screw 1.

Preferably, both the outer edges 11 and the inner edges 12 are rounded.

The radius of the outer edges ra and/or the radius of the inner edges ri may in particular be 0.5 to 1 mm.

The height h of the channel is preferably 2 to 4 times, particularly preferably 2.5 to 3.5 times, the thickness d of the arms of the cross.

This embodiment allows easy insertion of the handling tool (see Fig. 6). At the same time, the handling tool stabilizes the entire corticalis screw 1 during screwing in, and the torgue transmission is distributed over the entire channel 10.

Furthermore, the weight of the implant 1 is significantly reduced by the channel 10.

As a result, less bioresorbable material, in particular less magnesium, has to be broken down, which reduces both the gas formation and the osmotic pressures arising due to the formation of metal salts.

Fig. 4 is a plan view of the tip of the corticalis screw 1.

It can be seen that the channel 10 extends continuously from the rear to the front.

Furthermore, it can be seen that the tooth tip 4 of the first thread turn in this embodiment has two bevels 6 opposite one another, which bring about a self- tapping design.

Fig. 5 shows the contour of the corticalis screw, which contour envelops the thread or its shape before, for example, the machining of the thread.

12 EP3 927 264

It can be seen that the boundary 13 from the screw thread 2 to the head 8 takes place in a transition-free manner.

The head 8 provided with a head thread is conical.

The diameter of the corticalis screw 1 in the region of the thread ds is preferably 2 to5mm.

The maximum diameter of the corticalis screw at the end of the conical, in particular frustoconical, head 8 dk is preferably 20 to 40 %, particularly preferably 25 to 35 %, greater than the outer diameter of the screw thread ds.

The rear corner 14 of the corticalis screw is preferably rounded.

The conical head preferably has an acute angle B of 90 to 150°, particularly preferably of 110 to 130°.

The corticalis screw is preferably designed to taper at the tip 7. The tip angle a is preferably 90 to 150°, particularly preferably 110 to 130°.

Fig. 6 is a perspective view of the previously illustrated corticalis screw 1.

It can be clearly seen that the bevel 6 is designed as a cut-out segment of the corticalis screw 1. The bevel 6 extends over the first thread turn of the screw thread 2 and then tapers off.

The bevel 6 is designed in particular as a wedge-like angled notch which tapers off to the rear.

The surface 6, which is formed by the bevel, is preferably formed as a radially extending surface facing substantially toward the central axis 25.

The adjacent axially extending surface 26 formed by the bevel preferably encloses an angle of 50° to 120°, in particular an angle of 90°, with a surface of the bevel.

Thus, the bevel can be formed, for example, by means of a plain milling cutter, in that said cutter removes a rectangular segment, proceeding from the tip, which tapers off after the tooth tip of the first thread turn.

13 EP3 927 264

Fig. 7 is a perspective view of a schematically illustrated handling tool 15 for the previously illustrated corticalis screw.

The handling tool 15 is designed as a screwdriver and comprises a handle 20 having a shaft 16.

The shaft 16 is cross-shaped. The shape of the shaft 16 corresponds (except for tolerances) to the shape of the channel of the corticalis screw.

At the tip 17, the shaft 16 is designed as a drill and is used for pre-drilling in the region of the channel of the corticalis screw.

In this embodiment, a thicker shank 18, which forms a stop 19 for the fitted corticalis screw, adjoins the shaft 16.

Thus, the corticalis screw can be placed on the shank 16 in a simple manner and can be screwed in by means of the handling tool 15.

After fully screwing in, the handling tool 15 can be pulled out easily.

It is understood that in another embodiment (not shown), the handling tool can also comprise, for example, an exchangeable bit which is used to receive the corticalis screw.

Fig. 8 is a schematic view of the nozzle 21 of an extrusion machine, as can be used for producing a semi-finished product for a corticalis screw according to the invention.

The nozzle 21 comprises an insert 22 which is connected to the wall of the nozzle 21 by means of at least one connecting piece 23.

The shape of the insert 21 corresponds to the channel of the corticalis screw. A rod (not shown) made of a magnesium alloy is extruded through the nozzle 21. By corresponding pressure and/or temperature control adapted to the melting temperature of the alloy, the material liquefies in the region of the insert, such that it flows around the at least one connecting piece 23.

14 EP3 927 264

The semi-finished product produced in this way (not shown) can then be used to produce the corticalis screw, for example in that the contour shown in Fig. 5 is first produced by machining, and then the thread comprising the bevels is produced.

Fig. 9 is a side view and a plan view of the tip of a further embodiment of a handling tool 24 which is designed as an insert for a medical instrument, in particular a motor-driven instrument (not shown).

This embodiment also comprises a cross-shaped shaft 16 having a tip 17 which is used to drive the implant 1.

In contrast to the embodiment shown in Fig. 7, the stop 19 is provided in that the cross-shaped shaft 16 merges in the region of the stop 19 to another cross section, in particular to a circular cross section.

In this embodiment, the transition does not extend perpendicularly, but rather obliguely, with respect to the central axis. Due to the surfaces formed in this way obliguely with respect to the central axis 27, the corticalis screw is jammed in the region of the stop 19 and is thus secured against unintentional release after the placement.

The handling tool can be inserted into a medical instrument with the shank 18.

A bioresorbable corticalis screw could be provided by the invention, which corticalis screw can be screwed in more easily and more reliably, and for which in addition the weight of the screw can be minimized, which reduces gas pressures and osmotic pressures which arise in particular in the case of implants made of magnesium and magnesium alloys.

15 EP3 927 264

List of reference signs 1 Corticalis screw 2 Screw thread 3 Tooth base 4 Tooth tip 5 Head thread 6 Bevel 7 Tip 8 Head 9 Passage 10 Channel 11 Outer edge 12 Inner edge 13 Boundary from thread to head thread 14 Corner 15 Handling tool 16 Shaft 17 — Tip 18 Shank 19 Stop 20 Handle

16 EP3 927 264 21 Nozzle 22 Insert 23 Connecting piece 24 Handling tool for insertion

Central axis 26 Surface 27 Central axis of the handling tool

Claims

1 EP3 927 264

CORTICALIS SCREW CONSISTING OF BIORESORBABLE MATERIAL

Description

Field of the invention

Background of the invention

Corticalis screws are known from practice in a wide variety of embodiments.

Bioresorbable screws are also known from practice.

These can in particular consist of a bioresorbable metal.

In particular, the use of magnesium as the bioresorbable material has long been known.

Since pure magnesium does not have very high strength and generally corrodes very guickly, magnesium alloys are usually used in practice.

In particular, yttrium- containing magnesium alloys are known, which have a higher strength than pure magnesium, and whereby the corrosion of the implant is reduced, above all due to the yttrium.

The problem is that the magnesium alloys used still have a significantly lower strength than conventionally used titanium or stainless steel alloys.

In particular in the case of smaller implants having a diameter of less than 5 mm, there is therefore the risk of the drive being damaged when the implant is screwed in.

2 EP3 927 264 Another problem that is long known from practice is that of hydrogen formation during breakdown.

Gas bubble formations may impair the healing process.

Medical screws are known from the following documents: - EP 1234 637 A2

- US 5659497 A - FR 2 803 739 A1 - US 6 283 973 B1 - FR 2 879 915 A1 - US 2001/041937 A1

- US 2012/179163 A1 - EP 3 315 085 A1 - US 2005/177243 A1 - EP 3 072 540 A1 Object of the invention

Summary of the invention

3 EP3 927 264 The object of the invention is already achieved by a corticalis screw according to claim 1. Preferred embodiments and developments of the invention can be found in the subject matter of the dependent claims, the description and the drawings.

The invention relates to a corticalis screw made of a bioresorbable material.

The invention is based on the effect that, by providing a continuous channel, preferably the entire length of the implant can be used for torque transmission.

At the same time, the channel in turn reduces the weight of the corticalis screw,

which reduces the formation of gas during breakdown, when the corticalis screw is made of magnesium or a magnesium alloy.

4 EP3 927 264 According to one embodiment, the screw thread of the corticalis screw has passages to the channel.

The channel is thus open laterally at at least one, preferably at a plurality of, locations.

The passages are used for pressure compensation.

For example, a gas exchange can take place, in particular since gases that may form inside the channel escape easily.

For example, the passages can be provided in a very simple manner, by providing a semi-finished product comprising the channel having the thread.

The tooth base of the thread overlaps with the channel, such that passages result in the tooth base.

According to the invention, the screw thread merges in a transition-free manner into a conical head having a head thread.

Transition-free merging is understood to mean that the last thread flight of the screw thread merges into a thread flight of the head thread.

This embodiment allows the head to become jammed.

The corticalis screw is therefore particularly suitable for fastening ligaments or bone fragments.

According to the invention, the screw thread of the corticalis screw has a larger pitch than the head thread.

At the end of the screwing-in process, the corticalis screw is thus jammed not only due to the conical head, but also due to the different thread pitches.

EP3 927 264

The corticalis screw preferably comprises a channel having a non-circular cross section, such that a torque can be exerted on the screw via a handling tool.

5 The channel preferably has a uniform cross section at least in the region of a thread, particularly preferably over its entire length.

The channel is preferably open at the front, that is to say at the tip of the corticalis

10 screw.

According to another embodiment of the invention, however, it is also conceivable to provide a continuous channel which ends at a tip which is designed, for example, as a drill having cutting edges.

However, the continuous channel preferably extends at least as a blind hole as far as the tip, and extends in particular along a thread of the implant.

According to a preferred embodiment of the invention, the channel is cross- shaped.

In particular, the channel, when viewed in cross section, consists of two intersecting rectangles, which are preferably identical to one another and where preferably the center points of the rectangles line on one another.

In a development of the invention, the corticalis screw comprises a coating.

6 EP3 927 264 In particular, the corticalis screw comprises a magnesium fluoride coating.

Such a layer can be provided in a simple manner by immersing the corticalis screw in hydrofluoric acid.

It is provided in particular to provide the corticalis screw with a combination of magnesium fluoride coating and polymer coating.

The magnesium fluoride coating is used inter alia as an adhesion promoter layer.

Such a thin coating minimizes the risk of the layer cracking during insertion.

According to a further embodiment, the corticalis screw has a self-tapping tip.

The corticalis screw can consist of a magnesium alloy having a tensile strength Rm (according to DIN EN ISO 6892-1, version 2017-02) of above 250 MPa, in particular above 350 MPa, and/or below 500 MPa, in particular below 450 MPa.

7 EP3 927 264 Preferably, the inner and/or outer edges of the cross are rounded. The risk of cracking at the edges can thus be reduced. At the same time, the insertion of the handling tool is facilitated by the rounded portions. The cross in cross section preferably has a height and/or a width of 20-60 %, preferably 30-45 % and/or rounded edges having an edge radius of 5-40 %, preferably 10-30 % of the outer diameter of the thread of the implant. By means of this dimensioning, optimal stabilization by the drive, with simultaneously little material volume, could be achieved. The cross section of the cross preferably has a height and/or width of 1.3 to

2.5mm, particularly preferably of 1.5 to 2.1 mm. The rounded edges preferably have an edge radius of 0.1 to 0.8 mm, particularly preferably of 0.2 to 0.6 mm. The invention further relates to a set comprising the above-described corticalis screw and a handling tool. The handling tool is in particular designed as a screwdriver having a handle, or as a motor-driven medical instrument. The handling tool comprises a shaft which is adapted to a channel of the corticalis screw, which channel is formed as a positive-locking element. The shaft is in particular the same shape as the channel. With regard to the tolerances, the shaft and channel are preferably matched to one another in such a way that the corticalis screw can be pushed onto the handling tool in a clamping manner such that it is secured against accidental falling during insertion. Such a clamping can be achieved in particular in a simple manner, since large surfaces are provided via the continuous channel, in contrast to a conventional screw, by means of which surfaces a frictional connection can be established. The shaft of the handling tool preferably extends up to the front end of the corticalis screw.

8 EP3 927 264 According to a development of the invention, the tip of the shaft is formed as a drill. This embodiment therefore relates to screws having a channel that is open at the front, the shaft protruding from the corticalis screw at the front by a portion sharpened for drilling for example. The handling tool can thus be used simultaneously for pre-drilling or expanding an already set pre-bore. The shaft of the handling tool can have a coupling. A coupling makes it possible for the handling tool to be used in particular in manually or motor-driven instruments. The coupling is preferably designed as a quick coupling, that is to say a coupling which can be actuated without tools. As couplings, standard couplings used in the medical, in particular dental, field are preferably possible. The handling tool can be designed, for example, as a bit that can be inserted into an instrument. Brief description of the drawings The subject matter of the invention will be explained in more detail below on the basis of an embodiment with reference to the drawings of Fig. 1 to 9.

Fig. 1 is a side view of a corticalis screw according to the invention.

Fig. 2 is an axial sectional view.

Fig. 3 is a plan view of the corticalis screw from the rear.

Fig. 4 shows the corticalis screw from the front. The design of the corticalis screw will be explained further with reference to Fig. 5, which shows the geometry of the corticalis screw enveloping the thread.

Fig. 6 is a perspective view of the corticalis screw.

9 EP3 927 264

Fig. 9 shows an alternative embodiment of a handling tool which is designed as an insert for a handpiece. Detailed description of the drawings

Fig. 1 is a side view of an embodiment of a corticalis screw 1 according to the invention. The corticalis screw 1 comprises a screw thread 2 which, in this embodiment, extends from the front to a head 8 having a head thread 5. The tooth tips 4 of the screw thread 2 are flattened, in particular flat, in order to improve the clamping of the inserted corticalis screw 1 and to reduce damage to soft tissue. The flattened portion formed by the tooth tips 4 can in particular have a length of 0.3 to 2 mm. The screw thread 2 merges in a transition-free manner, that is to say without a step, into an otherwise conical, in particular frustoconical, head 8. Both the screw thread 2 and the head thread 5 formed in this way are designed in a single-duct manner in this embodiment. The screw thread 2 has a larger pitch than the head thread 5. In particular, the pitch of the screw thread 2 is 5 to 20 %, particularly preferably 8 to 15 %, larger than the pitch of the head thread 5. The corticalis screw 1 is thus jammed at the end of the screwing-in operation. The pitch of the screw thread 2 is preferably 2 to 5 mm. The corticalis screw 1 preferably has a length of 6 to 20 mm, particularly preferably of 8 to 14 mm.

10 EP3 927 264 The length of the head 8 is preferably 1/2 to 1/10 of the total length of the corticalis screw 1, particularly preferably 1/4 to 2/5. The diameter of the corticalis screw 1 in the region of the screw thread 2 is preferably 2 to 5 mm, particularly preferably 2.5 to 3.5 mm. In this embodiment, the corticalis screw 1 has a tip 7 comprising a channel 10 that is open at the front. The channel 10 overlaps in part with the tooth base 3 of the thread 2. As a result, distributed passages 9 are formed in the tooth base 3. The passages 9 allow pressure compensation both with respect to gases and with respect to osmotic pressures. The tip 7 of the corticalis screw 1 is designed to be self-tapping. In this embodiment, this is achieved by at least one bevel 6 of the first front thread turn. The tooth base 3 is rounded, in particular having a radius of 0.5 to 1 mm. This also facilitates the jamming of the implant and reduces damage to soft tissue. The tooth depth is preferably 0.5 to 0.8 mm.

Fig. 2 is an axial sectional view of the corticalis screw 1 shown in Fig. 1. In particular the channel 10 is visible, which extends from the rear end of the corticalis screw to the front end of the corticalis screw 1. As shown in the plan view of the rear face of the corticalis screw according to Fig. 3, the channel is cross-shaped, such that, as can be seen in Fig. 2, four passages, 9 distributed about 90° in each case, result in each thread turn, since the thread base overlaps with the channel 10. In the plan view of the rear face of the corticalis screw 1, in particular the cross- shaped design of the channel 10 can be seen.

11 EP3 927 264 The channel 10 preferably has a height h (corresponds to the width) of 1.3 to

2.5 mm, particularly preferably 1.5 to 2.1 mm. The height h or the width of the channel 10 and/or its largest diameter is preferably at least 20 %, preferably at least 40 %, of the outer diameter of the thread through which the channel extends. As seen in cross section, the channel 10 consists of two rectangles which are twisted by 90° relative to one another and have an identical cross section, and is arranged centrally in the corticalis screw 1. Preferably, both the outer edges 11 and the inner edges 12 are rounded. The radius of the outer edges ra and/or the radius of the inner edges ri may in particular be 0.5 to 1 mm. The height h of the channel is preferably 2 to 4 times, particularly preferably 2.5 to

3.5 times, the thickness d of the arms of the cross.

This embodiment allows easy insertion of the handling tool (see Fig. 6).

At the same time, the handling tool stabilizes the entire corticalis screw 1 during screwing in, and the torgue transmission is distributed over the entire channel 10.

Fig. 4 is a plan view of the tip of the corticalis screw 1.

12 EP3 927 264 It can be seen that the boundary 13 from the screw thread 2 to the head 8 takes place in a transition-free manner. The head 8 provided with a head thread is conical. The diameter of the corticalis screw 1 in the region of the thread ds is preferably 2 to5mm. The maximum diameter of the corticalis screw at the end of the conical, in particular frustoconical, head 8 dk is preferably 20 to 40 %, particularly preferably 25 to 35 %, greater than the outer diameter of the screw thread ds. The rear corner 14 of the corticalis screw is preferably rounded. The conical head preferably has an acute angle B of 90 to 150°, particularly preferably of 110 to 130°. The corticalis screw is preferably designed to taper at the tip 7. The tip angle a is preferably 90 to 150°, particularly preferably 110 to 130°.

Fig. 6 is a perspective view of the previously illustrated corticalis screw 1. It can be clearly seen that the bevel 6 is designed as a cut-out segment of the corticalis screw 1. The bevel 6 extends over the first thread turn of the screw thread 2 and then tapers off. The bevel 6 is designed in particular as a wedge-like angled notch which tapers off to the rear. The surface 6, which is formed by the bevel, is preferably formed as a radially extending surface facing substantially toward the central axis 25. The adjacent axially extending surface 26 formed by the bevel preferably encloses an angle of 50° to 120°, in particular an angle of 90°, with a surface of the bevel. Thus, the bevel can be formed, for example, by means of a plain milling cutter, in that said cutter removes a rectangular segment, proceeding from the tip, which tapers off after the tooth tip of the first thread turn.

13 EP3 927 264

Fig. 7 is a perspective view of a schematically illustrated handling tool 15 for the previously illustrated corticalis screw. The handling tool 15 is designed as a screwdriver and comprises a handle 20 having a shaft 16. The shaft 16 is cross-shaped. The shape of the shaft 16 corresponds (except for tolerances) to the shape of the channel of the corticalis screw. At the tip 17, the shaft 16 is designed as a drill and is used for pre-drilling in the region of the channel of the corticalis screw. In this embodiment, a thicker shank 18, which forms a stop 19 for the fitted corticalis screw, adjoins the shaft 16. Thus, the corticalis screw can be placed on the shank 16 in a simple manner and can be screwed in by means of the handling tool 15. After fully screwing in, the handling tool 15 can be pulled out easily. It is understood that in another embodiment (not shown), the handling tool can also comprise, for example, an exchangeable bit which is used to receive the corticalis screw.

Fig. 8 is a schematic view of the nozzle 21 of an extrusion machine, as can be used for producing a semi-finished product for a corticalis screw according to the invention. The nozzle 21 comprises an insert 22 which is connected to the wall of the nozzle 21 by means of at least one connecting piece 23. The shape of the insert 21 corresponds to the channel of the corticalis screw. A rod (not shown) made of a magnesium alloy is extruded through the nozzle 21. By corresponding pressure and/or temperature control adapted to the melting temperature of the alloy, the material liquefies in the region of the insert, such that it flows around the at least one connecting piece 23.

14 EP3 927 264 The semi-finished product produced in this way (not shown) can then be used to produce the corticalis screw, for example in that the contour shown in Fig. 5 is first produced by machining, and then the thread comprising the bevels is produced.

Fig. 9 is a side view and a plan view of the tip of a further embodiment of a handling tool 24 which is designed as an insert for a medical instrument, in particular a motor-driven instrument (not shown). This embodiment also comprises a cross-shaped shaft 16 having a tip 17 which is used to drive the implant 1. In contrast to the embodiment shown in Fig. 7, the stop 19 is provided in that the cross-shaped shaft 16 merges in the region of the stop 19 to another cross section, in particular to a circular cross section. In this embodiment, the transition does not extend perpendicularly, but rather obliguely, with respect to the central axis. Due to the surfaces formed in this way obliguely with respect to the central axis 27, the corticalis screw is jammed in the region of the stop 19 and is thus secured against unintentional release after the placement. The handling tool can be inserted into a medical instrument with the shank 18. A bioresorbable corticalis screw could be provided by the invention, which corticalis screw can be screwed in more easily and more reliably, and for which in addition the weight of the screw can be minimized, which reduces gas pressures and osmotic pressures which arise in particular in the case of implants made of magnesium and magnesium alloys.

15 EP3 927 264 List of reference signs 1 Corticalis screw 2 Screw thread 3 Tooth base 4 Tooth tip 5 Head thread 6 Bevel 7 Tip 8 Head 9 Passage 10 Channel 11 Outer edge 12 Inner edge 13 Boundary from thread to head thread 14 Corner 15 Handling tool 16 Shaft 17 — Tip 18 Shank 19 Stop 20 Handle

16 EP3 927 264 21 Nozzle 22 Insert 23 Connecting piece 24 Handling tool for insertion Central axis 26 Surface 27 Central axis of the handling tool