Patent Application
20160310187
BACKGROUND
The invention relates to a self-cutting and self-drilling cannulated bone screw with a channel chamber. Bone screws of this kind are used, for example, in osteosynthesis of complicated bone fractures. Self-cutting has the meaning here that there is no need for preliminary cutting of a thread in the bone structure that is to be treated. Self-drilling is to be understood as meaning that the bone screw, during insertion into the bone structure, is able to drill itself in, and there is therefore no need for preliminary drilling.
The object of the present invention is to make available a bone screw which simplifies the treatment of bone fractures and in particular reduces the number of work steps needed for insertion of the bone screw.
In a bone screw of the aforementioned type, this object is achieved by the fact that it comprises a centering tip, which forms a front end of the bone screw. This permits simple positioning and precise insertion of the bone screw according to the invention into the bone structure that is to be treated.
It has proven particularly advantageous in this case if at least one cutting device is arranged in the area of the centering tip. Thus, the cutting procedure begins directly after the bone screw has been applied with precise positioning, which reduces the risk of the bone screw slipping from the desired position. Moreover, only a short uncut depth of penetration of the centering tip into the bone is needed, which reduces the force that has to be applied by the operator and likewise reduces the risk of stress-induced damage to the bone. Overall, the time needed to insert the bone screw is reduced. The overall duration of the operation is shortened in this way, which has an advantageous effect on the wound-healing process. The channel chamber can extend in a rectilinear or spiral shape in this case.
A development of the bone screw according to the invention is characterized in that the cutting device is assigned a preferably substantially axial access opening to the channel chamber. In this way, bone material, which is detached from the bone structure to be treated during the self-drilling and self-cutting insertion of the bone screw, is introduced directly into the channel chamber. If the access opening is at least substantially axial, the bone material is additionally transported away along the shortest path and without any appreciable change of direction, which reduces the risk of a blockage. Moreover, this promotes the fusion of the bone screw according to the invention to the bone structure that is to be treated. By virtue of the self-cutting and self-drilling function of the bone screw, in combination with the removed bone material being carried away into the channel chamber, the occurrence of stress-induced damage on the bone structure to be treated is reduced.
It has proven particularly advantageous if the bone screw according to the invention has at least two cutting devices distributed preferably uniformly about the circumference, and each cutting device is assigned a substantially axial access opening to the channel chamber. A plurality of cutting devices permits more effective and therefore more rapid cutting and drilling of the bone screw into the bone structure that is to be treated. The removed bone material arising on each cutting device can be conveyed to the channel chamber via the axial access openings, and this, as has been stated above, has an advantageous effect on the wound-healing process.
It is also advantageous if the channel chamber opens into a rear end face of the bone screw. In this way, the bone material carried into the channel chamber can as it were migrate into the bone screw, and excess bone material can emerge from the bone screw in the area of the rear end face. In this way, the bone material that has been cut off is collected in the channel chamber and is able to support fusion of the bone screw. This design of the bone screw also promotes the fusion of the bone screw into the bone structure that is to be treated.
It is particularly advantageous if the bone screw according to the invention is a Herbert screw. A Herbert screw is a special bone screw which is used, for example, in the osteosynthesis of fractures of the scaphoid bone. Such a bone screw is a double-threaded screw, that is to say it has an outer thread both in a front area and in a rear area. Herbert screws are generally cannulated, that is to say they are hollow. However, known Herbert screws are neither self-cutting nor self-drilling, and instead they are inserted by the use of a guide wire, also called a Kirschner wire, into a pre-drilled hole in the bone structure to be treated, in which hole a thread has been cut. The two threads in the front area and rear area of the Herbert bone screw have different pitches. The thread pitch on the front thread is greater in this case than on the rear thread, such that a rear bone fragment is drawn mechanically onto a front bone fragment during the screwing-in procedure. In this way, a pressure that favors the healing of the fracture is applied to a fracture gap lying between the front bone fragment and the rear bone fragment. This is also referred to as interfragmentary compression.
When a Herbert screw is used for osteosynthesis, for example of a damaged scaphoid bone, the broken scaphoid bone is first of all positioned and, if necessary, fixed, and then the Herbert screw is inserted. In conventional Herbert screws, this insertion requires a first step of drilling a hole. In a second step, this hole is provided with a thread. Only in a third step can the Herbert screw be inserted. When using the bone screw according to the invention, the first two steps are dispensed with, and the bone screw according to the invention can be inserted directly and therefore very quickly into the bone structure that is to be treated.
It has proven particularly advantageous if the bone screw, at its rear end, has a screw head with an abutment face preferably in the form of a radially outwardly extending collar. In this way, the interfragmentary compression can be increased. Within the context of the present invention, however, it is also in principle conceivable to use bone screws that do not have a screw head.
It has also proven particularly advantageous if at least one substantially radial opening extends from the channel chamber to a thread turn of an outer thread present in a front area and/or in a rear area of the bone screw, preferably to a thread root. Once the bone screw has been inserted into the bone structure that is to be treated, the inner channel chamber is filled with the bone material that arises during the self-drilling and self-cutting. This bone material can fuse with the surrounding bone structure via the radial opening. In this way, the time taken for the treated fracture to heal is reduced, and the stability of the synthesis is improved.
Within the meaning of the invention, it is likewise conceivable that the bone screw has at least one recess, for example an approximately semicircular recess, in a protruding edge of a flank of an outer thread present in the front area of the bone screw, which recess forms, at least in part, a further cutting device. A further cutting device of this kind further improves the self-cutting of the bone screw that is to be inserted into the bone structure that is to be treated. In this way, moreover, there is less irritation of the bone structure that is to be treated, and there is a cleaner cutting process.
Within the meaning of the invention, it is likewise conceivable that the bone screw has at least one substantially axial through-opening in a flank of an outer thread present in a front area and/or in a rear area of the bone screw. In this way, the bone structure to be treated can grow through the thread flanks of the bone screw according to the invention, which promotes fusion of the bone screw to the bone structure. The time needed for the wound-healing process is reduced in this way, and the stability of the synthesis is further improved. Removed bone material is also able to collect in the though-openings, which leads to a reduction of stresses in the bone structure that is to be treated.
Within the meaning of the invention, a bone screw is likewise conceivable which has a through-opening in each of at least two successive flanks of at least one outer thread, wherein the through-openings are preferably in alignment with each other. This permits a stable growth of the bone screw into the bone structure that is to be treated.
According to the invention, it is also conceivable that the bone screw has an outer thread which has at least one thread channel extending inside a flank of the outer thread and preferably extending at least in part in the circumferential direction, one end of said thread channel opening into an outer face of the outer thread. It is particularly preferable here if one end of the thread channel is arranged in an additional cutting edge on the outer thread of the bone screw or if one of the cutting devices extends as far as the channel chamber. It is moreover advantageous if the thread channel substantially follows a pitch of the outer thread.
When such a bone screw with at least one thread channel is inserted into a bone structure, bone material removed from the bone structure by the additional cutting edge is carried away from the cutting site through the thread channel.
It is also advantageous if the thread channel opens with its other end into the channel chamber or into a next additional cutting edge on the outer thread. The next cutting edge is to be understood as that cutting edge which, viewed from the front end to the rear end of the bone screw, follows the previous additional cutting edge along the profile of the outer thread.
In this way, removed bone material is carried away to the channel chamber or carried from one additional cutting edge to the next additional cutting edge.
Both of the above-described types of removal of bone material from the cutting site, i.e. through the thread channels to the channel chamber and/or to the next additional cutting edge, allow the bone screw to be inserted into a bone structure without stresses being caused by bone material that is not removed during the insertion, which stresses could damage the bone structure. This is particularly advantageous if the bone screw is to be inserted into the bone structure without a separate preliminary drilling step.
The thread channel which extends at least in part inside a flank of the outer thread and preferably at least in part in the circumferential direction, and of which one end opens into an outer face of the outer thread, also constitutes an independent invention, which is also worthy of protection without the centering tip. This applies also to the indicated developments and details of said thread channel.
It is also advantageous if the bone screw comprises a receiving part for connecting the bone screw to a rod system. It is particularly advantageous here if the receiving part is connected to the bone screw in a polyaxial, uniplanar or monoaxial manner. In this way, the use of the bone screw in stiffening or fixing procedures is simplified.
According to the invention, it is also conceivable that the bone screw has a screw head, which has a locking device, preferably a head-side outer thread, for locking the bone screw at a stable angle onto a bone plate. It is particularly preferable here if the locking device is a self-cutting head-side outer thread for locking the bone screw at a stable angle onto a bone plate. This configuration has the advantage that the angle can be fixed quickly and in a manner individually adapted to the local circumstances at the operating site.
An alternative embodiment within the meaning of the invention is characterized in that the bone screw has a screw head which in part has a dome-like configuration and via which the bone screw can be connected at a variable angle to a bone plate. This permits mobility between bone screw and bone plate.
It will also be noted that the bone screw according to the invention, independently of its specific design, is preferably produced with the aid of a 3D printing method. With such a 3D printing method, highly complex three-dimensional structures can be produced, in particular for example the above-mentioned internal channels and channel chambers. A powder or another “printable or injectable” material, for example from a titanium alloy, is printed in layers by the 3D printer and fused by the use of a laser, for example. Further possible materials are ceramic, plastic, other metals, for example magnesium, etc.
Further features, details and advantages of the invention will become clear from the attached claims, from the drawing, and from the following description of several preferred embodiments of the bone screw according to the invention. An example of the present invention is explained in more detail below with reference to the attached drawings.
In the drawings:
A bone screw according to the invention is designated overall by reference sign 10 in
The front end 18 is formed by a centering tip 20. The centering tip 20 is integrally formed on a front area 24 of the bone screw 10. A first outer thread 28 is arranged on the bone screw 10 in the front area 24. A first cutting device 32 and a second cutting device 34 are arranged in the area of the centering tip 20. The first cutting device 32 is assigned a first access opening 38 to the channel chamber 12. The second cutting device 34 is assigned a second access opening 40 to the channel chamber 12. The first cutting device 32 and the second cutting device 34 are distributed uniformly about the circumference, i.e. they are arranged diametrically with respect to the centering tip 20. The first access opening 38 and the second access opening 40 extend axially, that is to say they extend substantially parallel overall to the longitudinal axis 14. The first access opening 38 and the second access opening 40 each extend from their assigned cutting devices 32, 34 to the channel chamber 12.
Radial openings 44 extend from the channel chamber 12 to a thread turn 46 of the first outer thread 28 arranged in the front area 24. In this illustrated embodiment, the radial openings 44 shown open from the channel chamber 12 into the thread root 48 of the thread turn 46. However, it is also conceivable that, proceeding from the channel chamber 12, they open into a front or rear face of a flank 52 of the first outer thread 28. The flank 52 of the first outer thread 28 has a protruding edge 56. The latter also plays a role as explained below.
Seen from the front end 18 of the bone screw 10 along the longitudinal axis 14 to the rear end 16, the bone screw 10 has a rear area 60 in front of the rear end 16. A second outer thread 64 is arranged in this rear area 60. The pitch of the outer thread 64 is greater than that of the first thread 28, such that a “Herbert screw” is formed. A screw head 68 is integrally connected to the rear area 60. The screw head 68 has a radially outwardly extending collar 72 which, in the operational position, forms an abutment face 74 toward the bone. A hexagon socket 78 is present on the screw head 72 and constitutes a tool attachment site. Within the meaning of the present invention, however, other types of tool attachment sites are also possible, for example a slot, cross slot, Torx, or similar.
In the rear area 60, radial openings 44 are likewise arranged which extend from the channel chamber 12 to a thread root 82 of the rear outer thread 64. Axial through-openings 86, i.e. extending parallel to the longitudinal axis 14 and in alignment with one another, extend through the flanks 52 of the first outer thread 28 and also through flanks 90 of the second outer thread 64.
As can be seen in particular from
When the bone screw 10 shown in
Once the bone screw 10 has been inserted fully into the bone structure that is to be treated, the channel chamber 12 is substantially full of removed bone material. This bone material is in part guided outward through the radial openings 44. In this way, it comes into contact with the surrounding bone structure. As the bone screw 10 remains in the bone structure to be treated, this promotes fusion of the bone screw 10 to the surrounding bone structure. By way of the axially extending through-openings 86, the bone structure is also able to grow through the flanks 52, 90 of the outer threads 28, 64. An advantage of the bone screw 10 according to the invention is that, by virtue of the centering tip 20 in combination with the cutting devices 32, 34, there is no need for preliminary drilling of a hole and preliminary cutting of a thread in the bone structure. Moreover, no guide wire or Kirschner wire is needed to insert the bone screw 10 into the bone structure that is to be treated. By means of the centering tip 20, the bone screw 10 can be positioned precisely and inserted into the bone structure. This shortens the operating time, as a result of which the wound-healing process is promoted. Overall, therefore, the use of the bone screw 10 has a positive effect on the course of treatment.
On the additional cutting edges 98 belonging to the outside of the outer thread 28, openings are visible which constitute one end of thread channels 102 and 108 and which are circular in the present example. Within the meaning of the invention, however, other shapes of the openings are also possible, for example triangular, square, star-shaped or similar. The thread channels 102 here extend from said openings as far as the channel chamber 12. The thread channels 102 extend inside the flank 52 of the outer thread 28 and approximately in the circumferential direction, but spiraling inward in the direction of the channel chamber 12.
The thread channels 108 each extend from said openings in an additional cutting edge 98 to a next additional cutting edge 98 as seen in the circumferential direction. Thus, the next cutting device 98 is in each case to be understood as the cutting device 98 following along the profile of the flank 52 of the outer thread 28, as seen from the front end 18 to the rear end 16 of the bone screw 10.
The profile of the thread channels 102 can be seen particularly clearly from the view in
When the bone screw 10 shown in
The thread channels 108, which extend from an additional cutting edge 98 to a next additional cutting edge 98, carry removed bone material from an additional cutting edge 98 to the next cutting edge 98.
Both of the above-described types of removal of bone material, from the cutting site through the thread channels 102 to the channel chamber 12 and through the chip-conveying openings 108 to the next additional cutting edge 98, allow the bone screw 10 to be inserted into a bone structure without stresses occurring during the insertion that could damage the bone structure. This is particularly advantageous if the bone screw 10 is to be inserted into the bone structure without a separate preliminary drilling step.
In the present case, the receiving part 110 is connected to the bone screw 10 in a polyaxial manner. The term “polyaxial” is to be understood as a connection in which the receiving part 110 is pivotable and rotatable with respect to the rest of the bone screw 10. The polyaxial connection between the receiving part 110 and the rest of the bone screw 10 is realized by a screw head 68, which in particular has a dome-like shape on its underside, and by a corresponding and complementary mating surface on the receiving part 110. The dome-like screw head 68 is shown in
In addition to a polyaxial connection, however, a uniplanar connection is also possible within the meaning of the invention. A uniplanar connection is to be understood as a connection in which the receiving part 110 is pivotable with respect to the rest of the bone screw 10 only within one plane. Within the meaning of the invention, a monoaxial connection is also possible, that is to say a connection in which the receiving part is not pivotable with respect to the rest of the bone screw. In the case of a monoaxial connection, the receiving part 110 can be rotatable with respect to the rest of the bone screw 10 or can be rigidly connected to the rest of the bone screw 10, for example formed in one piece with the latter.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102013226704.5 | Dec 2013 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/078669 | 12/19/2014 | WO | 00 |
