Bone fixation system

Description

[0001] The invention relates to a fixation system for a bone according to the preamble of claim 1.

[0002] Plate osteosynthesis uses bone plates and screws for the surgical treatment of bone injuries, especially complex fractures. Fracture compression is of particular importance: the use of special bone plates allows not only the fixation of bone fragments but also their displacement relative to one another.

[0003] Bone plates that allow fracture compression are well-known and routinely used. For example, suitable bone plates may have oval through-holes into which bone screws can be inserted eccentrically. As the screw is tightened, it gradually centers itself in the through-hole. Since the screw is already connected to the bone, the bone shifts relative to the bone plate. Two bone fragments can thus be shifted relative to each other, compressing the fracture.

[0004] Further fixation systems for bones are known from the prior art that, in addition to fracture compression, enable an angle-stable connection between the bone screw and the bone plate. An angle-stable connection usually refers to a force-fit or material-fit connection between the bone screw and the bone plate and is also called a "blocking".

[0005] German patents DE 10 2010 025 001 A1 and WO 2011 / 160846 A1 describe bone plates with through holes featuring a circumferential radial rib. This rib allows for clamping with the head thread of a bone screw, thus ensuring an angularly stable connection. Additionally, the described through holes have a frustoconical shape that tapers towards the underside of the plate. When using a bone screw with a conical seat, this allows for displacement of the bone plate relative to the bone. Therefore, when used with bone screws with a head thread and conical seat, the described bone plates enable fracture compression and angular stability; however, the bone screw must be inserted parallel to the axis of the hole.

[0006] Prior art also includes bone fixation systems that allow fracture compression and in which the bone screw can be connected to the bone plate at an oblique angle to the hole axis. In this case, it is also referred to as a polyaxial or multidirectional connection between the bone screw and the bone plate.

[0007] EP 2 364 658 A1 discloses, for example, bone plates with through holes that simultaneously allow relative displacement between the bone plate and bone and a polyaxial connection between the bone screw and the bone plate. For this purpose, bone screws with a spherical seat surface and no head thread must be used with the described bone plates. The described bone plates can also be used with screws with a conical seat surface and a head thread. In this case, an angularly stable connection is possible, but not polyaxiality.

[0008] Furthermore, fixation systems for bones that simultaneously enable angularly stable and polyaxial connections between bone screws and bone plates are known from the prior art. For example, DE 43 43 117 A1 describes such a fixation system. Angular stability is achieved by material deformation occurring when the bone screw is inserted, forming a threaded connection between a pre-formed thread on the bone screw or bone plate and the respective other component. However, the described fixation system cannot be used for fracture compression.

[0009] A bone fixation system that allows fracture compression while simultaneously providing an angle-stable, polyaxial connection between the bone screw and bone plate would be advantageous. Several existing fixation systems attempt to achieve this, but these systems have significant drawbacks.

[0010] WO 00 / 66012 A1 attempts to solve this problem by using special bone screws that feature a short, additional locking thread on the screw neck between a screw head with a smooth seating surface and the standard screw thread on the screw shaft. This locking thread engages with a contour in the bone plate, securing the bone screw at an angle. Furthermore, the internal contour is designed to allow for a slight angular displacement of the inserted screw relative to the hole axis. To achieve fracture compression, the screw is inserted eccentrically into a slotted hole. However, a significant disadvantage of the described bone plates and screws is that polyaxiality is very limited, meaning that only a slight angular displacement of the inserted bone screw is possible.

[0011] DE 198 58 889 A1 attempts to solve this problem by using similar bone screws. The described bone screws also have a screw head with a smooth seating surface and an additional locking thread between the screw head and the screw shaft. One of the described embodiments of the bone plates has elongated through-holes intended to allow fracture compression. It should be possible to insert the bone screw at an oblique angle. Furthermore, a malleable projection in the through-hole, in conjunction with the locking thread of the bone screw, should enable an angularly stable connection. However, a significant disadvantage of the described fixation system is that the angular stability can only be achieved to a very limited extent. When screwed in, the bone screw is in contact with the wall of the elongated through-hole over a maximum of 180° of its circumference.Since it cannot screw itself to the malleable projection over its entire circumference, high angular stability cannot be achieved.

[0012] Therefore, there remains a need for a bone fixation system that allows for displacement of bone relative to the bone plate while simultaneously providing an angle-stable polyaxial connection between the bone plate and the bone screw.

[0013] The object of the present invention is to alleviate or eliminate at least some disadvantages of the prior art. In particular, the invention aims to provide a bone fixation system that allows displacement of bone relative to the bone plate and simultaneously provides an angle-stable, polyaxial connection between the bone plate and the bone screw.

[0014] This problem is solved by a fixation system having the features of claim 1.

[0015] According to the invention, the through-hole has a guide section that tapers from the screw entry opening towards the screw exit opening, so that the essentially spherical seating surface of the screw head slides along a guide surface of the guide section when the bone screw is screwed into the bone, displacing the bone plate, and is guided into the blocking section.

[0016] The invention thus simultaneously enables the use of the bone screw at different oblique angles to the hole axis (polyaxiality), an angle-stable connection between the bone plate and the bone screw at these oblique angles, and a displacement of the bone plate relative to the bone when the bone screw is screwed in.

[0017] According to the invention, the spherical seat surface and the head thread of the bone screw form a single unit. This means the bone screw has no additional seat surface above the head thread. In other words, the head thread of the bone screw is part of the spherical seat surface of the screw head. This has the advantage of providing high polyaxiality, allowing the bone screw to be used within a wide angular range. The bone screw can therefore be fixed at various oblique angles to the hole axis with angular stability in the locking section of the through-hole, which is preferably located on the underside of the plate.

[0018] The guide surface of the through-hole according to the invention allows the bone plate to be displaced relative to the bone when the bone screw is inserted. This displacement occurs in a direction transverse to the axis of the hole, i.e., in a direction within the plane of the plate. In this way, for example, the distance between two bone fragments can be reduced and fracture compression achieved. It is particularly advantageous if the guide surface is essentially smooth-walled.

[0019] In a preferred embodiment, the locking section has a circular cross-section. In a particularly preferred embodiment, the locking section is essentially cylindrical. This allows the screw head, when locked, to bear against the walls of the through-hole over its entire circumference when viewed in cross-section. In other words, the screw head can be fixed from all sides when viewed in the plane of the plate. This enables a particularly stable locking of the bone screw.

[0020] In a further preferred embodiment, the locking section is essentially conical. The cone angle can be between 1° and 25°, preferably between 4° and 20°, even more preferably between 8° and 20°, and most preferably between 12° and 16°. This improves the biting behavior of the screw head.

[0021] Preferably, the malleable projection extends over the entire circumference of the locking section in cross-section. This has the advantage that the screw head can be screwed in over the entire circumference of the locking section in cross-section, resulting in a particularly stable locking connection.

[0022] It is particularly preferred if the formable projection is part of a formable thread. The thread preferably has at least one full turn, and even more preferably at least two full turns. This allows the screw head to be screwed into the locking section with particular stability.

[0023] In a preferred embodiment of the present invention, the guide section has an entry surface that is parallel to the hole axis, i.e., perpendicular to the plane of the plate.

[0024] It is also preferred that the guide section has an inclined guide surface leading to the locking section, which preferably connects directly to the entry surface. This allows the seat surface of the screw head to slide easily along the guide surface when the bone screw is inserted. The guide surface is preferably smooth-walled. This allows for particularly easy sliding of the seat surface of the screw head. Alternatively, the guide surface can also be curved. In a preferred embodiment, the angle of the guide surface to the plate plane in longitudinal section (parallel to the hole axis) is between 10° and 80°, preferably between 20° and 70°, even more preferably between 30° and 60°, and even more preferably between 40° and 50°.

[0025] It is particularly preferred if the guide section has an entry surface parallel to the hole axis and an inclined guide surface leading to the blocking section.

[0026] In a further particularly preferred embodiment, the guide surface extends to the screw exit opening on the upper surface of the plate. In this embodiment, the guide section has no recessed entry surface.

[0027] In a particularly preferred embodiment of the present invention, the screw head is completely enclosed within the locking section when locked. "Completely enclosed" in this context means that, viewed in longitudinal section, no part of the screw head protrudes beyond the locking section. The complete enclosure of the screw head within the locking section has the advantage that the screw head can be fixed with exceptional stability.

[0028] In a particularly preferred embodiment, an elongated hole is provided as the screw entry opening. Preferably, the width of the elongated hole corresponds essentially to the diameter of the screw exit opening. In this context, the width refers to the distance between the parallel longitudinal sides of the elongated hole. Preferably, in this embodiment, the extent of the through-hole in the direction of the width of the elongated hole is essentially constant in the entire area between the screw entry opening and the screw exit opening. This has the advantage that the displacement of the bone plate relative to the bone when the bone screw is inserted is only possible along the longitudinal axis of the elongated hole. Thus, the axis along which the displacement is to take place can be predetermined by the placement of the through-hole in the bone plate.

[0029] In a further preferred embodiment, the through-hole has a cylindrically shaped side wall extending between the screw entry opening and the screw exit opening. Preferably, in this embodiment, the screw entry opening is an elongated hole and the screw exit opening is a round hole, the width of the elongated hole corresponding to the diameter of the round hole. Preferably, in this embodiment, the screw entry opening and the screw exit opening are positioned one above the other such that the circular segment closing off the screw entry opening on one side is, in longitudinal section, arranged substantially parallel to the circle describing the screw exit opening. Preferably, the cross-section of the cylindrical surface is a circular arc with a central angle of 180°.This embodiment has the advantage that the displacement of the bone plate relative to the bone when the bone screw is inserted is only possible in the direction of the longitudinal axis of the elongated hole. Thus, the direction in which the displacement should occur can be predetermined by the placement of the through-hole in the bone plate. A further advantage is that a cylindrically shaped side wall extending between the screw entry and exit openings allows for simple manufacturing.

[0030] Preferably, the blocking section extends along the hole axis over 1 / 5 to 4 / 5, more preferably between 2 / 5 and 4 / 5, and even more preferably between 3 / 5 and 4 / 5 of the distance between the screw entry opening and the screw exit opening (i.e., the longitudinal extent of the through-hole). It is particularly preferred if the blocking section extends along the hole axis over a distance of at least 0.5 millimeters, more preferably at least 1 millimeter, and most preferably at least 1.5 millimeters.

[0031] Preferably, the guide section extends along the hole axis over 1 / 5 to 4 / 5, more preferably between 2 / 5 and 4 / 5, and even more preferably between 3 / 5 and 4 / 5 of the distance between the screw entry opening and the screw exit opening. It is particularly preferred if the guide section extends along the hole axis over a distance of at least 0.25 millimeters, more preferably at least 0.5 millimeters, and most preferably at least 1.0 millimeter.

[0032] The bone screws of the fixation system according to the invention can be, for example, cancellous bone screws or cortical bone screws. Cancellous bone screws can be used in a fixation system according to the invention within an angle range of up to 70°. Cortical bone screws can be used within an angle range of up to 45°.

[0033] The invention will now be explained in more detail with reference to preferred, non-limiting embodiments and the drawings. The drawings show: Figure 1 shows a fixation system according to the invention with a bone screw and a bone plate before they are connected to each other; Figure 2 shows the bone plate made of Fig. 1 Top view; Fig. 2B the through-hole of the bone plate in a schematic perspective view; Figures 3A to 3E the fixation system according to Fig. 1 in different positions when screwing in the bone screw perpendicular to the plane of the bone plate; and Figures 4A, 4B, each showing the fixation system according to Fig. 1 bis Fig. 3 in two positions when screwing in the bone screw at an angle to the plate plane of the bone plate.

[0034] For the purposes of this disclosure, all references to location and direction, such as "top" and "bottom," refer to the intended state of use when the bone plate rests on the bone. The "plate plane" is understood to be the main plane of the bone plate in the area of ​​the through-hole. The following explanations refer to a design in which the "hole axis" extends perpendicular to the plate plane. However, the hole axis can also run obliquely to the plate plane, in which case the directions must be transferred accordingly.

[0035] Fig. 1 Figure 1 shows a fixation system 1 for a bone (not shown). The fixation system 1 comprises a bone screw 2 with a screw head 3 having a substantially spherical seat 4. A head thread 5 is also formed on the seat 4.

[0036] The fixation system 1 also includes a bone plate 6 for angularly stable, polyaxial locking of the bone screw 2. The bone plate 6 has a top surface 7 with a screw entry opening 8 for inserting the bone screw 2 and a bottom surface 9 designed for bone contact with a screw exit opening 10. A through-hole 11 extends between the screw entry opening 8 and the screw exit opening 10.

[0037] The through-hole 11 has a locking section 12, which serves to stably fix the bone screw 2 at various angles to the hole axis 13. For this purpose, the locking section 12 has at least one malleable projection 14. In the Fig. 1 In the illustrated embodiment, the locking section 12 is essentially cylindrical and has a formable thread. The formable projection 14 is therefore part of a formable thread in this embodiment.

[0038] The through-hole 11 also has a guide section 15 that tapers from the screw entry opening 8 towards the screw exit opening 10. In the Fig. 1 In the illustrated embodiment, the guide section 15 has an entry surface 16 parallel to the hole axis and an inclined guide surface 17 leading to the blocking section 12.

[0039] Fig. 2A schematically shows a top view and Fig. 2B Figure 1 shows a schematic perspective view of a preferred embodiment of the through-hole 11. In this embodiment, the screw entry opening 8 is an elongated hole and the screw exit opening 10 is a circular hole. The width b of the elongated hole corresponds to the diameter of the screw exit opening 10. The extent of the through-hole 11 in the direction of the width b of the elongated hole is constant in the entire area between the screw entry opening 8 and the screw exit opening 10. In the Fig. 2A, 2B In the illustrated embodiment, the through-hole 11 also has a cylindrically shaped side wall 18 extending between the screw entry opening 8 and the screw exit opening 10, which in cross-section describes a circular arc with a central angle of 180°.

[0040] Fig. 3A bis 3E shows the application of the in Figur 1 Bone screw 2 and bone plate 6 shown. Fig. 3A bis 3E This shows successive states during the insertion of the bone screw 2.

[0041] Fig. 3A Figure 2 shows the insertion of the bone screw 2. To achieve a displacement of the bone plate 6 relative to the bone (not shown), the bone screw 2 is inserted off-center with respect to the blocking section 12. Fig. 3B The bone screw 2 is screwed in until the point where the screw head 3 with its seat surface 4 abuts the guide surface 17. Fig. 3C Figure 1 shows how the bone plate 6 shifts as the screw head 3 slides along the guide surface 17. As the bone screw 2 is tightened, it moves successively from the edge of the blocking section 12 towards its center. Since the bone screw 2 has already entered the bone (not shown), this results in a displacement of the bone plate 6 relative to the bone (not shown). Fig. 3D Figure 1 shows a state of the fixation system 1 in which the displacement of the bone plate 6 is complete. The bone screw 2 is centered in the blocking section 12 but not yet locked. Fig 3E Figure 1 shows the blocked state of the fixation system 1. The screw head 3 is fully incorporated into the blocking section 12 and the bone screw 2 is stably blocked.

[0042] Fig. 4A This shows in Figur 1 The fixation system 1 shown, wherein the bone screw 2 was inserted at an oblique angle to the hole axis 13. Fig. 4B shows the angle-stable blocked state after the displacement of the bone plate 6 relative to the bone (not shown) has taken place and the screw head 3 has entered the blocking section 12.

[0043] The fixation system can be used to compress a bone fracture as follows: The bone plate is placed on the bone fragment to be fixed and screwed to the bone with a bone screw. The bone screw can be inserted either parallel to the axis of the hole or at an angle. Once fully screwed in, the bone screw is angularly locked. To achieve fracture compression, the bone plate is screwed to another bone fragment. The bone screw is inserted eccentrically relative to the section being fixed and screwed into the bone either parallel to the axis of the hole or at an angle. As the bone screw is successively centered within the section being fixed, the bone fragment connected to the screw shifts towards the bone fragment already fixed to the bone plate.Once fully screwed in, the bone screw is angularly stable and the fracture compression is complete.

Claims

1. Fixation system (1) for a bone comprising: - a bone screw (2) having a screw head (3) with an essentially spherical seat (4) on which a head thread (5) is built and - a bone plate (6) for fixed-angle polyaxial blocking of the bone screw (2) comprising: a topside of the plate (7) with a screw inlet opening (8) for inserting the bone screw (2), an underside of the plate(9) provided for bone contact with a screw outlet opening (10), a through hole (11) extending between the screw inlet opening (8) and the screw outlet opening (10), a blocking section (12) comprising at least one formable protrusion (14), formable by screwing in the bone screw (2) for stable blocking of the bone screw (2) at different angles to the hole axis (13), characterized in that the through hole (11) comprises a guide section (15) which tapers from the screw inlet opening (8) in the direction of the screw outlet opening (10), so that the essentially spherical seat (4) of the screw head (3) slides along a guide surface (17) of the guide section (15) when the bone screw (2) is screwing into the bone, displacing the bone plate (6), and is guided into the blocking section (12).

2. Fixation system (1) according to claim 1, characterized in that the blocking section (12) is essentially cylindrical or conical.

3. Fixation system (1) according to claim 1 or 2, characterized in that the formable protrusion (14), from a cross-sectional view, extends over the entire circumference of the blocking section (12).

4. Fixation system (1) according to one of claims 1 to 3, characterized in that the formable protrusion (14) is part of a formable thread.

5. Fixation system (1) according to one of claims 1 to 4, characterized in that the guide section (15) comprises an inlet surface (16) parallel to the hole axis (13) and an inclined guide surface (17) leading to the blocking section (12) .

6. Fixation system (1) according to one of claims 1 to 5, characterized in that the screw head (3) is completely received in the blocking section (12) in the blocked state.

7. Fixation system (1) according to one of claims 1 to 6, characterized in that a slot is provided as a screw inlet opening (8).

8. Fixation system (1) according to claim 7, characterized in that the width (b) of the slot essentially corresponds to the diameter of the screw outlet opening (10).

9. Fixation system (1) according to one of claims 1 to 8, characterized in that the through hole comprises a cylindrically shaped side wall (18) extending between the screw inlet opening (8) and the screw outlet opening (10).