Abstract:
A device pivotally connects two stabilizing parts to a bone. The device comprises at least one bone fixing element with a central axis, an anchor part designed to be fixed in or onto the bone, and a head part that can be attached to both stabilizing parts. The two stabilizing parts are located axially one below the other. Each stabilizing part has a cavity there through running coaxially to the central axis. A clamping element, which can be elastically deformed transversely to the central axis, is rotatably mounted in each cavity. The clamping element has a central bore running coaxially to the central axis for receiving the head part. The device comprises at least one wedge or cone that can be axially clamped in the central bores, enabling the head part of the bone fixing element to be removably fixed in at least one of the stabilizing parts.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 11/147,136, filed on Jun. 6, 2005 entitled “Device For Stabilizing Bones”, now U.S. Pat. No. 7,621,941, which is a continuation of International Patent Application No. PCT/CH2002/000672, filed Dec. 6, 2002, the entire contents of which are incorporated herein by reference thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a device for pivotally connecting two stabilization parts belonging to a fixing device for bones to a bone-fixing element. 
     An osteosynthetic fixing device for connecting a fixing element, such as a pedicle screw with a longitudinal member, is known. This known fixing device is suitable as a plate/screw system, as an external or internal fixator, and particularly for fixing a spinal column. It has an articulated connection between the fixing element and the longitudinal member, comprising a connecting element with a completely open, spherically configured cavity and an elastically expandable clamping element with a spherical outer wall with a complementary, spherically configured cavity. The fixing element has a conical element abutting the anchoring segment in the bones that can be screwed into the bone. The conical segment can be wedged into an inner cone in the clamping element, whereby the clamping element is radially expanded and secured in the cavity. The mounting device for the longitudinal member in the connecting element is realized by a borehole, with its axis running transversely to the central axis of the fixing element. Such a device, however, permits only the connection of two objects. If three or more have to be connected, the system fails. 
     Therefore, it is an object of the invention to create a connection between a bone-fixing element and two longitudinal members, whereby the angles of the two members can be adjusted individually and attached to the bone-fixing element. This makes it possible to build on a multi-segmental fixation system sequentially, from one object to the other. 
     BRIEF SUMMARY OF THE INVENTION 
     Pursuant to the invention, this objective is accomplished with a device for a pivotable connection between two stabilizing parts of a fixing device for bones and a bone-fixing element. 
     The advantages of the invention allow two stabilizing parts, for example, to be connected pivotably and independently of one another relative to a bone fixation element, such as a pedicle screw or a pedicle hook. An expensive pre-bending of the longitudinal members is thus avoided. 
     In a preferred embodiment, the device also comprises a tensioning element, which engages the head part of the bone fixation element for the axial displacement of at least one wedge or cone. 
     In other preferred embodiments, the device comprises the following distinguishing features: 
     at least one wedge or cone that forms a single unit with the head part of the bone-fixing element, and/or 
     at least one wedge or cone that forms a single unit with the tensioning element. 
     In yet another embodiment, the device comprises an upper and a lower wedge or cone, the lower wedge or cone expanding toward the anchoring element at the bone-fixing element and the upper wedge or cone expanding toward the rear end of the bone-fixing element. 
     In another embodiment with two wedges or cones, the following configurations, for example, are possible: 
     the upper wedge or cone forms a single unit with the clamping device; and/or 
     the lower wedge or cone forms a single unit with the head part of the bone-fixing element. 
     In another embodiment, the bone-fixing elements are configured in such a way that their head part, at the end, comprises a bolt with an external thread that is coaxial with the central axis. The clamping elements preferably comprise a nut, which can be screwed over the external thread onto the head part of the bone-fixing element. 
     In yet another embodiment, the bone-fixing elements are configured in such a way that their head part at the rear end has a borehole with an internal thread that is coaxial to the central axis. Here, the clamping elements preferably include a screw with an internal thread. 
     In another embodiment of the inventive device, the cavities in the stabilizing parts are spherical and the outer walls of the clamping element are spherically complementary thereto. 
     In another embodiment of the inventive device, the outer walls of the clamping elements are configured spherically, whereas the cavities in the stabilizing parts have a central cavity, enlarged in relation to the clamping elements, with two terminal constrictions. The constrictions terminally have circular edges, which are concentric with the central axis and against which the clamping elements rest. A linear contact can be established between the clamping elements and the cavities by means of this configuration of the cavities. 
     In yet another embodiment of the inventive device, the cavities are spherical whereas the outer walls of the clamping element are configured with circular cylindrical segments that are arranged axially one behind the other. In addition, a linear contact can be established between the clamping elements and the cavities also by this configuration of the clamping elements. 
     In a further embodiment, the clamping element, disposed in the lower stabilizing part, can be fixed by the first clamping element in the cavity of the lower stabilizing part, and the clamping element, arranged in the upper stabilizing part, can be fixed by the second clamping device in the cavity of the upper stabilizing part. It is thus possible to achieve the advantage that the two stabilizing parts can be attached, independently of one another, to the head part of the bone-fixing device. Preferably, the head part comprises two cones separated by a threaded spacer, the threaded spacer being positioned axially with respect to the clamping element in such a manner that the clamping element can be blocked by a tensioning device that can be mounted on the threaded spacer. 
     In another embodiment, a tensioning device comprises a threaded part and a cone, which adjoins axially, expands toward the threaded part and is configured complementary to the internal cone in one of the clamping elements. Further, the clamping element projects axially beyond the head part and, at the rear end of the bone fixing device, the head part has a borehole with an internal thread, so that the threaded part can be screwed into this internal thread. The cone of the tensioning device preferably ends at a threaded bolt, which protrudes axially beyond the clamping element and onto which the second tensioning device, which is provided with an internal thread, can be screwed. 
     Conversely, the first tensioning device can be configured in such a way that the tapered end of the cone has a borehole with an internal thread, into which a second tensioning device, having an external thread and a head, can be screwed. 
     Other embodiments are distinguished in that: 
     the outer surfaces of the clamping elements are roughened; 
     the surfaces of the cavities are roughened; 
     the outer surfaces of the clamping element comprise a three-dimensional structuring; 
     the surfaces of the cavities comprise a three-dimensional structuring; and/or 
     at least one clamping element includes a material that is softer than the material of the wall of the corresponding cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention is explained in greater detail by means of the partially diagrammatic representations of several examples. 
       In the drawings: 
         FIG. 1  shows an embodiment of the inventive device with a cone, which is formed in one piece with the bone-fixing element; 
         FIG. 2  shows a different embodiment of the inventive device with two cones; 
         FIG. 3  shows an embodiment of the inventive device, the cavities for accommodating the clamping element including several cylindrical segments; 
         FIG. 4  shows an embodiment of the inventive device, the clamping elements including several axially abutting cylindrical segments; 
         FIG. 5  shows an embodiment of the inventive device, the upper and the lower stabilizing parts comprising bushings for accommodating the longitudinal members; 
         FIG. 6  shows an embodiment of the inventive device, the one-piece cone of the embodiment of  FIG. 1  having been divided into two independent cones, with one of the cones serving as the fixing element when connecting the other cone; and 
         FIG. 7  shows an embodiment of the inventive device, the one-piece cone of the embodiment of  FIG. 1  being interrupted by a screw thread, so that the lower cone connection can be fixed independently of the upper cone connection. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an embodiment of the inventive device with a bone-fixing element  1  configured as a pedicle screw, an upper stabilizing part  2  and a lower stabilizing part  3 , which could, for example, be parts of a spine fixing device. Both of the stabilizing parts  2 , 3  have an articulated connection with the head part  6  of the bone-fixing element  1 . The anchoring part  5  of the bone-fixing element  1 , constructed as a bone screw, can be fixed, for example, in a pedicle. The stabilizing parts  2 , 3  are arranged axially one behind the other. Each comprises a spherical cavity  7 , 8  passing through the respective stabilizing part  2 , 3  coaxially to a central axis  4 . A clamping element  9 , 10 , configured externally complementary to the cavity  7 , 8  and having a central borehole  11 , 12 , is inserted into each of the cavities  7 , 8 . By means of the spherical configuration of the cavities  7 , 8 , as well as that of the clamping elements  9 , 10 , a ball and socket connection between each stabilizing part  2 , 3  and the clamping element and the bone-fixing element  1  is established. The central boreholes  11 , 12  penetrate the clamping elements  9 , 10  coaxially to the central axis  4  and are conically tapered toward the rear end  19  of the bone-fixing element  1  The head part  6  of the bone-anchoring element  1 , which comprises a cone  13 , which is complementary to both central boreholes  11 , 12  and tapers toward the rear end  19  of the bone-fixing element  1 , is inserted into the central boreholes  11 , 12 . A bolt  20  with an external thread  21 , which is also coaxial with the central axis  4 , is mounted at the rear end  19  of the bone-fixing element  1 . A nut  22 , resting at the end of the first stabilizing part  2 , can be screwed on over the external thread  21  as a tensioning device  14 , so that, when the nut  22  is tightened, the two stabilizing parts  2 , 3  can be shifted axially on the head part  5  and pressed in the direction of the front end  18  of the bone-fixing element  1 . Furthermore, by means of parallel slots  23  parallel to the central axis  4 , the clamping elements  9 , 10  are constructed to be elastically deformable in the radial direction, that is, transversely to the central axis  4 . It is thus possible that a bridge effect occurs between the cone  13  and the walls of the central conical boreholes  11 , 12  when the two conical central boreholes are pushed over the cone  13  at the head part  5  of the bone-fixing element when the nut  22  is tightened. As a result, the two clamping elements  9 , 10  are expanded transversely to the central axis  4  and the spherical outer walls of the clamping elements  9 , 10  and the spherical outer walls of the clamping element  9 , 10  are pressed against the spherical walls of the cavities  7 , 8 . For a connection with another element belonging to the spinal column fixing device, the upper stabilizing part  2  is provided with a depression  24 , which is open on the outside at the stabilization part  2  and has a longitudinal axis  25 , which is transverse to the central axis  4 , so that, for example, a rod-shaped longitudinal member ( FIG. 5 ) can be introduced into the depression  24  and detachably fixed by means of an arresting screw  26 , which can be screwed perpendicularly to the longitudinal axis  25  into the upper stabilizing part  2 . The lower stabilizing part  3  is provided with a second rod-shaped continuation  28  having a longitudinal axis  27 , which is also transverse to the central axis, the continuation  28  and the depression  24  being configured complementary to one another, so that, instead of a longitudinal member, a rod-shaped continuation  28  can also be introduced into the depression  24  of the upper stabilization part  2 . The depression  24  and the rod-shaped continuation  28  are arranged on the stabilizing parts  2 , 3 , so that the two longitudinal axes  25 , 27  are coaxial in the starting position of the device, that is, when the joints have not been rotated. 
     The embodiment of the inventive device, shown in  FIG. 2 , differs from the embodiment shown in  FIG. 1  in that the cone  13  at head part  6  of the bone-fixing element  1 , only passes through the clamping element  10  in the lower stabilizing part  3  and subsequently passes through the bolt  20 , which is disposed terminally at the head part  6  of the bone-fixing element  1 . Furthermore, the tensioning device  14  is designed as sleeve  29  with a central borehole  30 . The internal thread  31 , provided in the central borehole  30 , can be screwed over the external thread  21  onto bolt  20  and, at the outside, has a second cone  13 ″, which tapers toward the front end  15  of the tensioning device  14 . The central boreholes  11 , 12  in the clamping elements  9 , 10  are conically complementary, so that the two cones  13 ′, 13 ″ taper toward the contacting ends of the clamping elements  9 , 10 . In order to tighten tensioning device  14 , devices  32  for accommodating a screwdriver are provided in the central borehole  30  at the rear end  33  of the tensioning device  14  and are constructed here as an hexagonal socket. 
     A further embodiment of the inventive device is shown in  FIG. 3 . It differs from that shown in  FIG. 2  in that the cavities  7 , 8  in the two stabilizing parts  2 , 3  are equipped with a central cavity  34 , which is larger than the clamping elements  9 , 10 , and with two axial, terminal constrictions  35 , the constrictions  35  directed toward cavity  34 , each having a circular edge, which is concentric with the central axis  4 , so that the spherically constructed clamping elements  9 , 10  lie against the edges  36 , and a linear contact being produced between each cavity  7 , 8  and the clamping elements  9 , 10  inserted therein. 
     A further embodiment of the inventive device is shown in  FIG. 4 , which differs from that shown in  FIG. 2  in that the clamping elements  9 , 10  are externally complementary to the spherical cavities  7 , 8 . Instead, the spherical shape of the cavities  7 , 8  approach the clamping elements  9 , 10  is approximated by circular cylindrical segments  17 , which are disposed one behind the other axially. Linear contact between the clamping elements  9 , 10  and the walls of the cavities  7 , 8  can be produced also with this arrangement. 
       FIG. 5  shows an embodiment of the inventive device, which differs from that of  FIG. 1  in that both stabilizing parts  2 , 3  have recesses  24  for accommodating for example a longitudinal member  16  each, the longitudinal axes  17  being aligned with one another and disposed perpendicularly to the central axis  4  of the bone-fixing element  1 . Furthermore, stabilizing parts  2 , 3  are constructed so that longitudinal axes  17  of recesses  24  extend approximately at the boundary surface between the two stabilizing parts  2 , 3 . 
       FIG. 6  shows an embodiment of the inventive device, which differs from those of  FIGS. 1 to 5 , in that the clamping element  10 , disposed in the lower stabilizing part  3 , can be fixed by first tensioning devices  14  in the cavity  8  of the lower stabilizing part  3  and in that the clamping element  9 , disposed in the upper stabilizing part  2 , can be fixed by the second tensioning devices  14 ″ in the cavity  7  of the upper stabilizing part  2 . The clamping element  10  axially protrudes beyond head part  6  of the bone-fixing element  1 , the head part  6  having a borehole  38  with an internal thread  39  at the rear end  19  of the bone-fixing element  1 . An axially terminal threaded part  41  on the first tensioning device  14  can be screwed into this internal thread  39 , so that, when the first tensioning device  14 ′ is tightened by means of screwdriver inserted into the means for accommodating a tool  49 , the connection between head part  6  of the bone-fixing element  1  and the lower stabilizing part  3  can be detachably blocked. Furthermore, the first tensioning device  14 ′ comprises a cone  42 , which is axially adjacent to the threaded piece  41  at the top, expands toward the threaded piece  41  and can be inserted into the complementary cone  13 ″ in the central borehole  11  in clamping element  9 . The clamping element  9  in cavity  7  in the upper stabilizing part  2  extends axially beyond the tapered end of the cone  42  disposed on the first tensioning device  14 ′. By means of the second tensioning devices  14 ″, which is constructed as a screw and comprises a head  48  contacting the clamping element  9  terminally, as well as an external thread  47 , which can be screwed into the borehole  45  having an internal thread  45  and mounted coaxially in the first tensioning device  14 ′, the clamping element  9  can be blocked detachably together with the first tensioning device  14 ′ in the cavity  7  in the upper stabilizing part  2 . Instead of being configured as a screw, the second tensioning device  14 ″ may also be configured as a nut and can be screwed over a threaded bolt, which is mounted terminally at the first tensioning device  14 ′. 
     The embodiment of  FIG. 7  differs from that of  FIG. 1  in that the head part  6  of the bone-fixing element  1  comprises two cones  13 ′, 13 ″ arranged axially one behind the other. A threaded spacer  40  is disposed between the first cone  13 ′ abutting the anchoring part  5  of the bone-fixing element  1 , and the axially terminally disposed second cone  13 ″. Moreover, the first cone  13 ′ is inserted into the central borehole  12  in the clamping element  10 , which is constructed conically complementary and serves for fixing the lower stabilizing part  3 . The second cone  13 ″ is inserted into the central borehole  11  in the clamping element  9 , which is constructed conically complementary and serves for fixing the upper stabilizing part  2 . The axial position of the threaded spacer  40  is selected in such a way relative to the clamping element  10 , that a first tensioning device  14 ′, constructed as a nut, can be screwed and brought to rest against the end of the clamping element  10  located between the clamping elements  9 , 10 . Accordingly, by tightening the first tensioning device  14 ′, the lower stabilizing part  3  can be blocked detachably independently of the blocking of the upper stabilizing part  3  at the head part  6  of the bone-fixing device  1 . Analogously to the embodiment shown in  FIG. 1 , a bolt  20  with an external thread  21  can be mounted coaxially to the central axis  4  at the rear end  19  of the bone-fixing element  1 . A nut  22 , resting terminally on the upper stabilizing part  2 , can be screwed as second tensioning device  14 ″ over the external thread  21 , so that, when the nut  22  is tightened, the upper stabilizing part  2  can be blocked detachably independently of the blocking of the lower stabilizing part  3  at the head part  6  of the bone-fixing device  1 .