DE20022673U1 - Screw connection for osteosynthesis - Google Patents

Description

Meissner,

Law firm GbR

PO Box 860624
81633 Munich

MED - Medical Engineering October 31, 2001

Development Ltd. M/KIP-037-DE

3/lA Parliament Lane MB/KR/RB/ob/ft Gibraltar

Screw connection for osteosynthesis

Description

The invention relates to a screw connection for osteosynthesis according to claim 1 and a screw according to
Protection claim 9.
5

In osteosynthesis, especially for healing a bone fracture, the fracture is fixed by a plate made of stainless steel or titanium. The plate is attached to the bone using
Screws are used to fix implants in the body.

by means of screws to the bone. On some bones, such as
for example the tibia or skull bone is a
However, sufficient stable fixation is difficult because either the bone is very thin or the screw connection is too thin.
has an unfavourable shape. Here it is particularly important

the skill of the surgeon in fixing the implant. A stable and variable screw connection would be desirable,
where the angle between screw and implant is variable when screwing into the bone and can be fixed when screwed in.

Accordingly, the invention is based on the object of
To propose a screw connection for osteosynthesis, in which the angle between screw and implant is variable when screwing the screw into the bone, and once the

screw was screwed into the bone.

This task is solved by a screw connection with the features of claim 1 and by a screw with the features

Meissner, Bolte & Partner

M/KIP-037-DE

paint according to claim 9. Advantageous embodiments of the screw connection emerge from the dependent claims.

The core of the invention is the mounting of the screw in the implant or the screwed plate in a ball joint that can be locked by the screw. The ball joint is formed by a ring whose outer surface has a spherical or spherical segment shape and which lies in a bearing ring with an inner surface that is complementary to the outer surface of the ring. The bearing ring itself is fixed in a hole in the implant or plate, for example by a clamp connection, an adhesive connection or a welded connection or similar connection. The ring that can be moved in the bearing ring is open or severed at one point, similar to an expansion ring. The screw that can be guided through the ring has a substantially conical section whose transverse extension is larger than the diameter of the ring, so that the ring can be expanded by the substantially conical section of the screw and pressed against the inner surface of the bearing ring. The ball joint formed by the ring and the bearing ring can be locked in this way. Before the joint is locked, the angular position between the screw and the implant or plate is variable.

Preferably, the conical section of the screw is located on the screw head. The ring is only spread open when the screw is almost completely screwed into the bone. In a particularly preferred embodiment, the screw head itself forms the conical section, so that the screw can be screwed into the bone until the head is almost flush with the implant or plate.

For a particularly stable and secure screw connection, the conical section preferably has a thread that engages with an internal thread of the rotatably mounted ring. This not only screws the screw to the bone, but also to the ring mounted in the implant or plate. If the screw connection of the screw to the

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If the bone becomes loose or dislodged, the screw is secured by this additional screw connection.

In order to make it easier for the surgeon to screw in the screw, in particular to precisely define the angle at which the screw is screwed into the bone, the surgeon can, in a particularly preferred embodiment of the screw connection, use a guide wire which is inserted into a preferably central longitudinal bore in the screw. The guide wire specifies the direction in which the screw is screwed into the bone. To do this, the surgeon first inserts the guide wire into the bone using a drilling jig. The surgeon can then check the position of the guide wire in the bone using an image converter, for example an X-ray machine, and correct it if necessary. The screw is then screwed into the bone in the direction specified by the guide wire so that the guide wire is guided through the central longitudinal bore of the screw. The screw is preferably self-drilling and/or self-tapping and/or back-cutting. To insert such a screw into the bone, advantageously no drill or thread cutter is required.

The screw is preferably designed as a tibial head screw with a cancellous thread, as a support screw with a cortical thread or as a condylar screw with a conical thread on the head. In addition, the condylar screw can be screwed with a nut to form a compression screw. The compression screw is used to compress a fracture. For this purpose, the condylar screw preferably has circumferential notches in predetermined sections in the longitudinal direction, which are used to cut or shorten the screw to predetermined dimensions.

Further advantages and possible applications of the invention will become apparent from the following description of embodiments in conjunction with the figures.

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Fig. IA: The cross-section through a tibial head plate with the screw connection according to the invention;

Fig. IB: A top view of the tibial plate from Figure IA;

Fig. IC: A section along the line AA in Figure IB through the tibial head plate with three screw connections according to the invention;
IO

Fig. 2: A cannulated tibial head screw with a self-tapping, self-drilling and back-cutting cancellous thread;

Fig. 3: A support screw with a self-tapping,

self-drilling and back-cutting cortical threads;

Fig. 4: A nut for screwing with the condylar screw shown in Figure 5B to provide compression

screw to form;

Fig. 5A: A condylar screw with a conical thread on the screw head and notches for cutting the screw to length;

Fig. 5B: A condylar screw with a metric thread for screwing with the nut shown in Figure 4, also with notches for cutting the screw to length;

Fig. 6: A drill bushing with a conical thread for a tibial plate for drilling with an adjustable angle;
35

Fig. 7A: An expansion ring with an internal thread and a spherical or spherical segment-shaped outer surface;

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Fig. 7B: A bearing ring with a spherical or spherical segment-shaped inner surface for receiving the expansion ring shown in Figure 7A.

Figure IA shows a cross-section of a tibial head plate 10, which has a screw 12 through a hole 11 for screwing the plate to a bone. The conical screw head 13 of the screw 12 spreads open a spreading ring 14 that is rotatably mounted in the hole 11, whereby the angle between the screw 12 and the tibial head plate 10 is fixed. The screw also has a continuous, dashed central longitudinal hole 16 for receiving a guide wire. The function of this longitudinal hole and the guide wire is explained in more detail below.

Figure IB shows a top view of the tibial head plate 10 from Figure IA. The expansion ring 14 mounted in the bore 11 of the tibial head plate 10 can be clearly seen. The expansion ring 14 is mounted in a bearing ring 17 fixed in the bore 11 and is movable like a ball joint.

Figure IC shows a cross section along the line A-A through one end of the tibial head plate shown in Figure IB. Screws 12 are guided through the hole 14 and the holes 18 and 19 located to the side next to it, all of which can have a different angular position to the tibial head plate 10. This is intended to illustrate that with the screw connection according to the invention, a wide variety of angles between the screw and the tibial head plate can be realized.

Figure 2 shows a tibial head screw 20 with a cancellous bone thread 21. The conical screw head 22 of the tibial head screw 20 has a thread 23; the expansion ring 14 can be expanded by the screw head 22. The screw has a continuous, central longitudinal bore to accommodate a guide wire. The screw head 22 includes a hexagon socket 25 for screwing in the screw.

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Figure 3 shows a support screw 26 with a cortical thread 27. The screw head 28 has a conical cross-section and is provided with a thread. This screw also has a hexagon socket 30 for screwing in and a continuous, central longitudinal bore 31 for receiving a guide wire. This screw differs from the screw shown in Figure 2 essentially in the cortical thread, which is self-tapping and back-cutting. The screw can be designed as a self-drilling screw, which advantageously makes the use of a drill or thread cutter unnecessary.

Figure 4 shows the nut for a condylar screw. If a condylar screw is to be used simultaneously as a compression screw, for example to compress a fracture, the nut 32 can be screwed to the condylar screw passing through a bone.

The condylar screw 33 shown in Figure 5A, like the previously described screws, has a screw head 35 with a conical cross-section and a hexagon socket 37 for screwing in the screw. The screw head 35 is provided with a thread 34. The condylar screw also has a metric thread that is interrupted by circumferential notches 38 at a distance of e.g. 8 mm. The notches 38 act like predetermined breaking points, through which the screw 33 can be shortened to predetermined lengths. Typical total lengths of the screw are approximately 70 mm to 120 mm in 5 mm increments.

Figure 5B also shows a condylar screw 39 with a metric thread 40, which is interrupted by circumferential notches at predetermined intervals of approximately 8 mm. The screw head 42 is approximately conical in cross-section and has a hexagon socket 43 for screwing in the screw. In contrast to the screws described above, the screw head 42 is smooth, i.e. without a thread. Typical lengths for

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These screws are also about 70 mm to about 120 mm in 5 mm increments.

Figure 6 shows a drill bushing 44 for a tibial head plate. The drill bushing 44 is used to drill holes in the bone at a specific angle. The front end of the drill bushing has an approximately conical cross-section and is provided with a thread 45. The thread 45 is used to screw into the internal thread of an expansion ring which is movably mounted in the tibial head plate. The conical cross-section of the front end of the drill bushing 44 spreads the expansion ring and presses it against an inner ring which is firmly anchored in the tibial plate, so that the drill bushing is at a fixed angle to the tibial head plate. A drill can then be inserted through a longitudinal bore 47 in the drill bushing 44 and penetrates the bone at the angle defined by the fixed drill bushing. The drill bushing 44 can be turned into the expansion ring either by a handle 48, for example a grooved area on the surface of the drill bushing, or by means of an internal hexagon 46.

An expansion ring 49 provided for the screw connection according to the invention is shown in Figure 7A. The expansion ring has a spherical or spherical segment-shaped outer surface 50 and an internal thread 51 into which the screw heads provided with an external thread of the screws shown in Figures 2, 3 and 5A or the thread of the drill bush shown in Figure 6 can be screwed. The expansion ring is expanded by the aforementioned threads.

The expansion ring is movably mounted in a bearing ring 52 shown in Figure 7B. The bearing ring 52 is in turn firmly mounted in a bore of an implant or a plate, for example a tibial head plate, by means of a clamping, welding, soldering, pressing or embedding connection. The inner surface 53 of the bearing ring 52 is designed to be complementary to the outer surface 50 of the expansion ring 49 shown in Figure 7A. The expansion ring 49 embedded in the bearing ring 52 is both rotatable and

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also pivotable without being able to fall out of the bearing ring. If a screw with a conical section, such as the screw shown in Figures 2, 3, 5A or 5B, is guided through the expansion ring, the conical section of the screw spreads open the ring 49 and presses or presses it against the bearing ring 52, more precisely the outer surface 50 of the expansion ring 49 is pressed against the inner surface 53 of the bearing ring 52. This fixes the expansion ring 49 in its current position in the bearing ring 52. The screw guided through the expansion ring 49 is also held in this position or angular setting. The expansion ring and screw act together with the bearing ring 52 like a ball joint that can be locked by the conical section. The screw can therefore be screwed into the bone at different angles, and the angle can be adjusted using the ball joint.

The following briefly explains the use of a guide wire when screwing the screw into the bone: This requires a screw with a continuous longitudinal hole, such as the screws shown in Figures 2 and 3. The surgeon uses a drilling jig to insert a guide wire into the bone at the angle at which he later wants to screw in the screw. He can check the position of the guide wire using an image converter, such as an X-ray machine, and correct it if necessary. The guide wire is then guided through the longitudinal hole of the screw and the screw is screwed into the bone. The guide wire defines the position of the screw in the bone. As soon as the screw is completely screwed into the bone, the guide wire can be removed from the bone via the longitudinal hole that goes completely through the screw. Using the guide wire with a self-drilling and self-tapping screw is particularly advantageous. This eliminates the need for a drill or thread cutter.

I fs : :

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List of reference symbols

10 Tibial plate 11 Hole

12 Screw

13 Screw head

14 Spreader ring

15 angles

16 Longitudinal bore 17 Bearing ring 18, 19 Bore

20 Tibial head screw

21 Cancellous bone thread 22 Screw head

23 threads

24 Longitudinal bore

25 Hexagon socket 2 6 Support screw 27 Cortical thread

28 Screw head

29 threads

30 hexagon socket

31 Longitudinal bore 32 Nut

33 Condylar screw

34 threads

35 Screw head

36 metric thread 37 hexagon socket

38 Notch

39 Condylar screw

40 metric thread

41 Notch

42 Screw head 43 Hexagon socket 4 4 Drill bushing 45 Thread

Meissner, Bolte & Partner

4 6 Hexagon socket

47 Longitudinal bore

48 Handle

49 Spreader ring

50 outside area

51 internal thread

52 Bearing ring

53 Interior surface

M/KIP-037-DE

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Claims (9)

1. Screw connection for osteosynthesis, in particular for fixing a tibial head plate ( 10 ), with: - a screw ( 12 ) having a substantially conical section ( 13 ) in the longitudinal direction, - a ring ( 14 ) whose outer surface ( 50 ) has a spherical or spherical segment shape and which is open or severed at one point, - an implant, in particular a tibial head plate ( 10 ), which comprises a bearing in the form of a bore ( 11 ) and a bearing ring ( 17 ) fastened therein for supporting the ring ( 14 ), wherein the inner surface ( 53 ) of the bearing ring ( 17 ) has a shape complementary to the outer surface ( 50 ) of the ring ( 14 ), so that the ring ( 14) arranged in the bearing ring (17 ) can be moved like a ball joint, wherein - the ring ( 14 ) can be spread open by the conical section ( 13 ) of the screw ( 12 ), whereby the outer surface ( 50 ) of the ring ( 14 ) can be pressed against the inner surface ( 53 ) of the bearing ring ( 17 ) and thus the angular position ( 15 ) of the screw to the implant can be fixed. 2. Screw connection according to claim 1, characterized in that the section is located on the screw head ( 13 ; 22 ; 28 ; 35 ; 42 ), in particular the screw head is substantially conical. 3. Screw connection according to claim 1 or 2, characterized in that the section has a thread ( 23 ; 29 ; 34 ) and the ring ( 49 ) has a complementary internal thread ( 51 ). 4. Screw connection according to one of the preceding claims, characterized in that the screw ( 12 ; 20 ; 26 ) has a longitudinal bore ( 16 ; 24 ; 31 ) through which a guide wire can be introduced, which is intended to specify the position in the bone. 5. Screw connection according to one of the preceding claims, characterized in that the screw is self-drilling and/or self-tapping and/or back-cutting. 6. Screw connection according to one of the preceding claims, characterized in that the screw is a tibial head screw ( 20 ) with a particularly self-tapping, self-drilling and back-cutting cancellous thread ( 21 ) or a support screw ( 26 ) with a particularly self-tapping, self-drilling and back-cutting cortical thread ( 27 ) or a condylar screw ( 33 ; 39 ) with a metric thread. 7. Screw connection according to claim 6, characterized in that the condylar screw ( 33 ) with metric thread can be screwed to a nut ( 32 ) for compressing a fracture. 8. Screw connection according to claim 7, characterized in that the condyle screw ( 33 ; 39 ) has in the longitudinal direction in particular radially circumferential notches ( 38 ; 41 ) at predetermined intervals, by means of which the screw can be shortened to predetermined lengths. 9. Screw ( 12 ; 20 ; 26 ; 33 ; 39 ), in particular for a screw connection according to one of claims 1 to 8, which serves to fasten an implant, in particular a tibial head plate, to a bone and has a substantially conical section ( 13 ; 22 ; 28 ; 35 ; 42 ) in the longitudinal direction, which is smooth or provided with a thread.