ZA200207735B - Bone plate for osteosynthesis. - Google Patents

Description

, 1814/PCT 12.03.2001

English translation of the International Patent Application

No. PCT/CH00/00346 “Bone plate for osteosynthesis” in the name of Synthes AG Chur

Bone plate for osteosynthesis

The invention relates to a bone plate for osteosynthesis as claimed in the precharacterising part of claim 1 and to a fixation device as claimed in the precharacterising part of claim 18.

A bone plate permitting to achieve an angularly and axially stable screw anchorage by means of a conical external thread formed in the screw head and a corresponding conical internal thread formed in the plate hole is known from

W097/09000. This known bone plate, however, suffers from the disadvantage that the plate must have a certain minimum thickness for the screw head to be satisfactorily fixed in the plate hole. With plate thicknesses of less than 2 mm, the angular and axial stability of the screw anchorage tends to become critical.

The invention is intended to provide a remedy for this. It is accordingly an object of the invention to create a bone plate which ensures a secure, angularly and axially stable screw anchorage, even if a relatively small plate thickness is used.

The invention resolves this problem by providing a bone plate which shows the features of claim 1.

The thickening in the areas around the holes of the bone plate - as compared to the area situated between said holes - 1s realised by means of a bulge projecting over the bottom surface of the plate and preferably shaped in the form of a hollow cone. This form may be obtained during the fabrication of the plate for example by submitting the area around the plate hole to a deep-drawing process resulting in a conical shape.

The thickness of the bone plate in the areas of the holes provided with a bulge should be between 1.1 and 4.0 times thicker, preferably between 1.5 and 2.5 times thicker than its thickness measured in the area between said holes. The bulge should project over the bottom surface by an amount of between 0.1 and 3.0 mm, preferably between 0.5 and 1.0 mm.

The thickness of the bone plate as measured in the area between the holes provided with a bulge may be between 1 and 2 mm, preferably between 0.8 and 1.2 mm.

In a preferred embodiment, in which the bulge is shaped in the form of a hollow cone, the outward angle of the cone is between 5 and 120 degrees, preferably between 40 and 100 degrees.

In a preferred embodiment, the holes provided with a bulge have an internal screw thread. The internal thread may either be circularly cylindrical or conical; in the latter case also the holes provided with a bulge preferably taper to the bottom surface.

The conically tapered internal screw thread may have a cone angle of between 5 and 50 degrees, preferably between 10 and 30 degrees.

The internal screw thread may be either.a single thread or a double thread. The thread pitch for a single internal thread should be between 0.4 and 1.5 mm, preferably between 0.60 and 1.25 mm. For a double internal thread, the thread pitch should be between 0.2 and 1.5 mm, preferably between 0.3 and 0.8 mm.

The central axes of the holes provided with a bulge are substantially arranged vertically to the top surface and preferably extend parallel to one another.

Advantageously, the bone plate according to the invention is used in combination with bone screws having a conical screw head which are preferably provided with an external thread. The cone angle of the conical screw head should advantageously correspond to the cone angle of the internal thread formed in the plate hole, provided said internal thread is conically shaped. This shaping permits to obtain a bone plate with a thickening in the areas around the holes. In this thickening (or, more precisely speaking, in this plate hole deliberately extended in the axial direction) it is possible to cut more thread turns than would be realisable in a plate with a uniform thickness.

This permits to achieve an improved screw anchorage while maintaining at the same time the mechanical characteristics of the bone plate, i.e. its flexibility and adaptability to the bone.

The bone plate according to the invention may in particular be used in all those cases where thin bone plates are of advantage, particularly in the areas of the vertebral column, of the pelvis, and of long bones.

In the following, the invention and further developments of the invention will be illustrated in greater detail with reference to the partially diagrammatic representation of one embodiment.

In the drawing:

Fig. 1 shows a longitudinal section of a bone plate according to the invention with a bone screw inserted therein.

The single-piece bone plate 1 for osteosynthesis shown in

Fig. 1 has a top surface 2, a bottom surface 3 facing the bone, and a plurality of holes 5 with central axes 6 for receiving bone screws 10, arranged along the longitudinal axis 4 of the plate and connecting the top surface 2 with the bottom surface 3, said figure 1 showing only two such holes 5; a number of further holes 5 may be arranged to the right and to the left thereof, depending on the length of the bone plate 1.

The central axes 6 of the holes 5 are arranged vertically to the top surface 2 and thus extend parallel to each other.

The thickness of the plate as measured in the area between the holes is 1 mm. The two holes 5 shown in the figure have a bulge 8 shaped in the form of a hollow cone, extending concentrically to the central axis 6 and projecting over the bottom surface 3.

The holes 5 are provided with a single internal thread 7 which tapers conically to the bottom surface 3 (however, also a circularly cylindrical and/or a double internal thread may be used). The cone angle 13 of the internal thread 7 is 20 degrees. The outside cone angle 14 of the bulge 8 is 90 degrees. The thread pitch of the internal screw thread 7 is 0.8 mm (in the case of a double internal thread the thread pitch would accordingly be 0.4 mm).

Due to the bulge 8, having a height of 0.8 mm, the bone plate in the areas of the holes 5 has an increased thickness, which is 1.8 times thicker than the area situated between said holes 5 (which is 1 mm thick).

The bone screw 10 inserted in the right-hand hole 5 has a conical screw head 11 which is provided with an external thread 12. The cone angle 15 of the conical screw head 11 is 20 degrees and thus corresponds to the cone angle of the conical internal thread 7.

The contact surface of the bone plate 1 with the bone is limited to the annular front portions of the bulges 8 facing the bone, which results in a better healing process of the bone segment situated under the bone plate 1.

Claims (27)

Claims

1. A bone plate for osteosynthesis including a top surface, a bottom surface facing the bone, and a plurality of holes with central axes for receiving bone screws, arranged along the longitudinal axis of the plate and connecting the top surface with the bottom surface, at least two of the holes being provided with a bulge arranged concentrically to the central axis and projecting over the bottom surface, characterized in that the bone plate consists of a single piece.

2. A bone plate as claimed in claim 1, characterised in that che hcles provided with =z zulge have =z treiferzkbls circularly cylindrical intermal thread.

3. A bone plate as claimed in claim 1 or 2, characterised in that the holes provided with a bulge taper conically to the bottom surface.

4. A bone plate as claimed in claim 1 or 3, characterised in that the internal thread tapers conically to the bottom surface.

5. A bone plate as claimed in claim 4, characterised in that the conically tapered internal thread has a cone angle of between 5 and 50 degrees.

6. A bone plate as claimed in claim 4, characterised in that the conically tapered internal thread has a cone angle of between 10 and 30 degrees.

7. A bone plate as claimed in any of the claims 1 to 6, characterised in that the internal thread is a single thread.

8. A bone plate as claimed in claim 7, characterised in that the thread pitch of the single internal thread is between 0.4 and 1.5 mm.

9. A bone plate claimed in claim 7, characterised in that the thread pitch of the single internal thread is between 0.60 and

1.25 mm.

10. A bone plate as claimed in any of the claim 1 to 6, characterised in that the internal thread is a double thread.

11. A bone plate as claimed inn claim 10, characterised in that the thread pitch of the double internal thread is between 0.2 and 1.5 mm.

12. A bone plate as claimed in claim 10, characterised in that the thread pitch of the double internal thread is between 0.3 and 0.8 mm.

13. A bone plate as claimed in any of the claims 1 to 12, characterised in that it has a greater thickness in the areas of the holes provided with a bulge than in the area between said holes.

14. A bone plate as claimed in claim 10, characterised in that the thickness of the bone plate as measured in the areas of the holes provided with a bulge is between 1.1 and 4.0 times, thicker than in the area between said holes.

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15. A bone plate as claimed in claim 10, characterised in that the thickness of the bone plate as measured in the areas of the holes provided with a bulge is between 1.5 and 2.0 times thicker than in the area between said holes.

16. A bone plate as claimed in any of the claims 1 to 15, characterised in that the bulge projects over the bottom surface by an amount between 0.1 and 3.0 mm.

17. A bone plate as claimed in any of the claims 1 to 15, characterised in that the bulge projects over the bottom surface by an amount between 0.5 and 1.0 mm.

18. A bone plate as claimed in anv of the claims 1 to 17, characterised in that the bulge, beginning from the Done plate, tapers in the from of a hollow cone.

19. A bone plate as claimed in claim 18, characterised in that the bulge shaped in the form of a hollow cone has an outside cone angle of between 5 and 120 degrees.

20. A bone plate as ciaimed in ciaim 18, characterised in that the bulge shaped in the form of a hollow cone has an outside cone angle of between 40 and 100 degrees.

21. A bone plate as claimed in any of the claims 1 to 20, characterised in that the thickness of the bone plate as measured in the area between the holes provided with a bulge is between 1 and 2 mm.

22. A bone plate as claimed in claim 21, characterised in that the thickness of the bone plate as measured in the area between the holes provided with a bulge is between 0.8 and 1.2 mm.

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23. A bone plate as claimed in any of the claims 1 to 22, characterised in that the central axes of the holes provided the bulge are substantially arranged vertically to the top surface.

24. A fixation device including a bone plate as claimed in any of the claims 1 to 24, characterised in that it comprises at least twc bone screws having a conical screw head provided with an external thread.

25. A fixation device including a bone plate as claimed in any of the claims 1 tc 24, characterised in that it comprises at least two bone screws having a conical screw head provided with an external thread.

26. A fixation device as claimed in claim 25, characterised in that the cone angle of the conical screw head corresponds to the cone angle of the conical internal thread.

27. A bone plate substantially as herein described with reference to Figure 1.