Bone fixing device

[0001] This application is a continuation of application Ser. No. 10/279,196, filed Oct. 23, 2002 now U.S. Pat. No. 7,771,458, which claims priority to and the benefit of German Patent Application No. 101 52 094.8 filed on Oct. 23, 2001, the disclosures of which are fully incorporated herein by reference.

[0002] The invention relates to a bone fixing device and in a particular application to a device for stabilising cervical vertebrae.

[0003] A device especially for stabilising cervical vertebrae is known, comprising a plate with at least one bore, having an M-thread, and a bone screw for screwing into the plate. The bone screw has a thread section, having a bone thread, for screwing into the bone and an adjoining thread section with an outer M-thread. In operation the bone screw is guided through the bore and screwed into the bone. Then the second thread section is screwed into the plate. Because the thread pitches are different there is a danger that the bone screw will thereby be loosened from its seat.

[0004] From WO 96/05778 a cervical vertebrae stabilising system is known which has a plate with at least one recess, a bone screw with a bone thread section and an adjoining M-thread section and a radial projection provided between the bone thread section and the M-thread section, and also a nut cooperating with the M-thread section. With this known device first the bone screw is screwed into the bone, then the plate with the recess is guided over the M-thread section until it rests against the radial projection and then the nut is inserted into the recess and screwed on to the M-thread section to fix it. The recess can be constructed as an elongated hole.

[0005] From WO 00/18312 a stabilising device for the spinal column is known, which has a plate with at least one recess, a bone screw with a bone thread section and an M-thread section and a projection provided between these sections and with a plain washer located on top of the edge of the recess, and also a nut which is screwed on over the M-thread section of the bone screw until it is adjacent to the shim. The plain washer has a lateral recess, so the bone screw can take up various angles.

[0006] The known systems are suitable for particular applications in each case. With the first mentioned device, for instance, the plate must always be put in first and then the screw screwed in. With the device known from WO 96/05778, on the other hand, the screw has to be screwed in first and then the plate placed on top. Additionally, with this device it is not possible to change the angle of the screw. The device known from WO 00/18312 admittedly allows different angles of the bone screw, but adjustment of the plate in the longitudinal direction is possible only to a limited extent. Additionally, this device has a relatively high construction.

[0007] The object of the invention is to provide a bone fixing device and in particular a device for stabilising cervical vertebrae, which is improved with respect to adjustability and breadth of application compared with the known devices.

[0008] This object is achieved by a bone fixing device according to patent claim 1. Further developments of the invention are cited in the dependent claims.

[0009] The invention has the particular advantage of a modular system, which considerably enlarges the breadth of application. The apparatus according to the invention is not only usable for cervical vertebrae stabilisation, but also as a bone fixing device for fixing broken bones, e.g. tubular bones. The invention further enables the surgeon in the operating room to make a decision, adapted to the circumstances of the individual case, as to whether the screws should be inserted first and then the plate placed over them and fixed or whether the plate should be put in first and then the bone screws screwed in through the recesses of the plate. The invention further allows monoaxial and polyaxial screws to be used together with one plate or even both types of screws next to one another. In this way adjustment of the angle of the screws to the plate and positioning of the screws for adjusting their longitudinal distance is possible independently for each screw.

[0023] As can be seen from FIGS. 1 to 4, the bone fixing device 1 has a substantially rectangular plate 2 with rounded corners. For further description the midline of the plate running in the longitudinal direction of the rectangle is designated as D and the midline running perpendicularly to it in the crosswise direction as C. The plate has a first end 3 and a second end 4 opposite this with recesses 5, provided in each case near the ends, for receiving bone screws. Each recess 5 has a first area 5a with a first diameter d₁ in a direction perpendicular to midline D and a second area 5b with a second diameter d₂ in a direction perpendicular to midline D, wherein the second diameter d₂ is larger than the first diameter d₁. The total diameter of the recess 5 in the longitudinal direction, in other words on midline D, is larger than the second diameter d₂. Areas 5a and 5b are formed, for example, by an elongated hole, the small diameter of which corresponds to the diameter of area 5a, and an additional bore with the larger diameter d₂ of area 5b. Areas 5a and 5b are arranged on the plate in such a way that area 5b is facing away from the respective end 3 or 4 of the plate and points towards midline C. On the upper side 2a of the plate 2 facing away from the shank of the bone screw 6 in a state of use each recess S has an indentation 7 for receiving a subsequently described connecting element.

[0024] The plate 2 further has, bordering on areas 5b of the recesses 5, thread bores 8, located opposite one another, with an indentation 9 for screwing in screws 10 with a head 11, which are constructed, for example, as slit screws. The thread bore 8 is provided at such a distance from area 5b of the recess 5, and the indentation 9 and the head 11 of the screw 10 are dimensioned in such a way, that in the screwed in state the head 11 projects just a little into the area of the indentation 7 in area 5b of the recess 5 and thus limits the cross-section of the indentation 7.

[0025] As can be seen in particular from FIGS. 1, 3 and 4, for connecting the bone screw to the plate 2 the bone fixing device has a connecting element in the form of a supporting element or shaped part, constructed as sleeve-shaped, called hereinafter a plain washer 20. The plain washer 20 has a hollow cylindrical section 21, the length of which is slightly greater than the thickness of the plate in the area of the recess 5. On the side arranged in the state inserted into the plate 2 on the upper side 2a of the plate the plain washer 20 is constructed with a section 22, shaped as a hollow spherical segment, the outer diameter of which is smaller than the diameter of the indentation 7 crosswise to midline D, but greater than the diameter d₂ of the second area 5b, so in the inserted state the plain washer 20 with the area 22 lies on top at the edge of the indentation 7. Section 22, shaped as a hollow spherical segment, is constructed on the inside with a spherical radius corresponding to the spherical radius of a head 6a of the bone screw 6 shaped as a spherical segment. At the end facing away from the section 22, shaped as a hollow spherical segment, the plain washer 20 has a ring-shaped projection 23, the outer diameter of which is larger than the diameter d₁ of the first area 5a of the recess 5 and smaller than the diameter d₂ of the second area 5b of the recess 5. The plain washer 20 is thus so dimensioned that it can be inserted through area 5b with the larger diameter d₂ of the recess 5 into the recess 5 and can be displaced in the longitudinal direction of the plate in the indentation 7 until it is in area 5a, from which it cannot fall out. The indentation 7 forms a guide for the plain washer.

[0026] The bone fixing device 1 of the first embodiment further has the bone screw 6, which in this embodiment is constructed in one piece, with a shank 15 with a bone thread for screwing into the bone and with the head 6a, which is shaped as a spherical segment and firmly connected to the shank and on its upper side has a means 16, e.g. one of more slits, for bringing into engagement with a screwing-in tool.

[0027] In operation first the plain washer 20 is guided in through area 5b of the recess 5, so the section 22, shaped as a hollow spherical segment, is located on the upper side 2a of the plate. Then the plain washer is pushed in the direction of area 5a, wherein the underside of section 22, shaped as a hollow spherical segment, is lying on top in the indentation 7. In area 5a with the smaller diameter d₁ the plain washer 20 is held against falling out owing to the larger diameter of section 22, shaped as a hollow spherical segment, and the projection 23. Then the securing screw 9 is screwed into the bore 8. The edge of the head 11 of the securing screw 9 therein projects, as can be seen in particular from FIGS. 1, 2 and 4, slightly into the area of the indentation 7 of the recess 5 and thus limits the diameter of the indentation 7 in area 5b, securing the plain washer 20 from falling out after it has been inserted. However, the plain washer 20 is still therein displaceable in the longitudinal direction in the recess 5 and is pushed to the exact position desired. Then the bone screws 6 with the thread shank 15 with the bone thread are guided through the plain washer and screwed into the bone.

[0028] During an operation the surgeon uses the plate with already inserted plain washers 20, secured against falling out by the screws 9, which thus in each case form an integrated shaped part, and holds them against the bone parts to be fixed and then screws in the bone screws 6. Since the plain washer can be displaced, adjustment of the screwing position is possible before screwing down.

[0029] The embodiment shown in FIGS. 5 and 6 is, as far as the plate 2 is concerned, identical to the embodiment shown in FIGS. 1 to 4. However, in this embodiment the bone screw 60 is different. Bone screw 60 has a first thread shank section 61 with a bone thread and an adjoining second thread shank section 62 with an M-thread. The diameter of the second thread section 62 is smaller than the inner diameter of the plain washer 20, so the second thread section 62 can be guided through the plain washer 20 constructed like a sleeve. At its end opposite the tip of the bone screw the bone screw has a hexagonal recess, not shown, for bringing into engagement with a screwing-in tool for screwing the bone screw into the bone.

[0030] In this embodiment the head of the screw 60 is formed by a separate nut 63, which is shaped in the form of a spherical segment with a radius corresponding to that of section 22, shaped as a hollow spherical segment, of the plain washer 20. The nut 63 has on its upper side facing away from the part shaped as a spherical segment a means 64, such as e.g. slits, for bringing into engagement with a screwing-in tool.

[0031] In operation again first the plain washer or the plain washers 20 is/are guided into the recesses 5 of the plate 2 and secured against falling out via the screw 10. During the operation first the plate 2 is held against the bone parts to be fixed and the screwing in position for the bone screws marked. Then the bone screws 60 are screwed in and the plate 2 with the recesses 5 placed over the second thread section 62 projecting from the bone. Then the nut 63 is screwed on to the second thread section until it comes to rest in section 22, shaped as a hollow spherical segment, of the plain washer 20, wherein, owing to the spherical sections of the plain washer 20 and the nut 63, angles of the bone screw are possible in a predetermined range of angles.

[0032] The embodiment shown in FIGS. 7 and 8 differs from the embodiments shown in FIGS. 5 and 6 in that on the outer end of section 22, shaped as a hollow spherical segment, the plain washer 20 has an edge 24, projecting inwards by a predetermined measurement, encircling the inserted nut 63, starting from its upper side, by a predetermined measurement, so the nut 63 is secured against falling out.

[0033] In operation with this embodiment the plain washer 20 is prefabricated with the nut 63 already inserted and, as with the previously described embodiments, is first inserted into the plate 2 and secured against falling out with the securing screw 10. Further operation is as with the embodiment shown in FIGS. 5 and 6. This embodiment has the advantage that the nut 63 is held and thus cannot be dropped by the surgeon during the operation.

[0034] In the embodiment shown in FIGS. 9 and 10 the connecting element between the plate and the bone screw is constructed as a nut 30, instead of as a plain washer, for screwing on to the second thread shank section 62 of the bone screw 60. The nut 30 has a first area 31, corresponding in its dimensions to the hollow-cylindrical central part 21 of the plain washer of the previous embodiments, but has an inner thread. Bordering on one end of this central section the nut 30 has a head section 32 with an outer diameter, which, as with the plain washer 20, is slightly smaller than the diameter of the indentation 7 but larger than the diameter d₂ of the second area 5b of the recess 5. Bordering on the other end of the central area 31, as with the plain washer, a ring-shaped projection 33 is provided. The nut 30 additionally also has on its upper side means 34, such as e.g. slits, for engaging with a screwing-in tool.

[0035] In this embodiment the bone screw 60 is provided with a shoulder 65, arranged between the bone thread shank section 61 and the thread shank cutout 62 with the M-thread, which shoulder is formed, for example, as a ring-shaped projection and serves as a stop during screwing in, as illustrated in particular in FIG. 10.

[0036] In operation the bone screw or bone screws 60 is/are screwed in at the previously determined positions and then the plate with the recesses 5 is placed over the thread sections 62 and then the nut 30 screwed on.

[0037] In the embodiment shown in FIG. 11 the bone screw of the bone thread shank section is constructed as hollow and provided with two opposite longitudinal slits 66. Further provided is an expanding element, not illustrated in the figure, on the inside of the shank, which can be actuated in such a way that the shank sections formed by the longitudinal slits 66 can be expanded apart. After the bone thread shank section has been screwed in an expanding effect is thus achieved, which guarantees an improved hold.

[0038] In the embodiment illustrated in FIG. 12 the plate 200 is constructed in particular for application in cervical vertebrae stabilisation and has on each end 3, 4 in each case two recesses 5, wherein in each case two adjacent recesses 5 share a securing screw 10. For this purpose the axis of the bore 8 for the securing screw 10 is arranged on the central longitudinal axis D and the dimension of the screw head 11 and the position of the bore are chosen in such a way that in the screwed in state the screw head 11 engages in both indentations 7 of the adjacent recesses 5. The plate 200 is further constructed as waisted.

[0039] The embodiments described can be combined on a plate in any way or the screws, depending on the purpose, can be used for the various embodiments, guaranteeing a modular system with great versatility.

[0040] Instead of the securing screw 10, a different securing element can be provided, for example a spring element attached to the plate, which is bent away for inserting the plain washer 20 or the nut 30 and then snaps back to limit the cross-section of the recess.

[0041] The term plate is to be understood also to include elements with a not completely flat, for example a bent or in some other way curved, surface.

[0042] The device according to the invention can be not only applied to stabilising cervical vertebrae, but is also suitable for the external fixing of broken bones, e.g. tubular bones.