Abstract:
A device is provided for the articulated connection of two bodies comprising a first body, a clamping member, at least one tension member, and a second body. The first body comprises a cavity extending coaxially along a central axis. The clamping included a longitudinal axis and a coaxial bore with at least one aperture, the clamping member being complementary to the cavity and resiliently deformable in a direction orthogonal to the longitudinal axis. The at least one tension member is insertable coaxially with respect to the longitudinal axis into the bore. An axial displacement of the at least one tension member within the corresponding aperture may cause the clamping member to be expanded to contact the cavity wall and be releasably locked within the cavity. The second body is releasably connectable to the first body by means of the at least one tension member and the clamping member. A driving member is provided for displacing the at least one tension member axially relative to the corresponding aperture, wherein the driving member is connected to both the clamping member and the at least one tension member in positive axial engagement while rotatable about the longitudinal axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of the U.S. National Stage designation of co-pending International Patent Application PCT/CH00/00224, filed Apr. 19, 2000. The entire content of this application is expressly incorporated herein by reference thereto. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a device for the articulated connection of two bodies and in particular to a fixation device for fixating two bodies in a joint-like connection. 
     BACKGROUND OF THE INVENTION 
     In the case of various surgical implants such as articulatedly connected, multipart bone plates and osteosynthetic vertebral column fixation devices where, for example, a longitudinal carrier extending approximately parallel to the vertebral column has to be attached by means of a number of bone screws, the joint-like connections must be releasably lockable. For this purpose, resilient tension members, such as collet chucks, are used. The locking of such joint-like connections is realized by means of an expansion of these resilient tension members within a corresponding cavity with fixed dimensions. This expansion process of resilient tension members is preferably achieved by means of clamping cones or clamping wedges. 
     An osteosynthetic fixation device including a bone screw to be anchored in a bone, a longitudinal carrier, and a connection member by means of which the bone screw is attachable to the longitudinal carrier. One example of such a device is shown in Patent No. WO 94/00066 to Schläpfer. This fixation device comprises a resilient clamping member shaped in the form of spherical segment contained between two parallel circles which has a conical bore, and a bone screw having a male taper corresponding to the conical bore of the clamping member and a screw thread arranged in the end portion located opposite to the bone. In the connecting member, a spherical cavity for receiving the clamping member is provided which is adequately dimensioned so as to permit the spherical segment of the clamping member to be pivotably received therein. A second bore serves for receiving the longitudinal carrier. The tightening of a nut screwed over the screw thread formed in said end portion of the bone screw and supported by the clamping member causes the taper formed in the bone screw to be pulled into the inner cone of the clamping member, thus spreading said clamping member apart and pressing it firmly against the wall of the spherical cavity, whereby the connecting member and the bone screw are kept in place relative to each other. 
     A disadvantage common to all these connections realized by means of clamping cones consists in the difficulties encountered in releasing said connections, which often necessitates heavy hammer blows to be struck on the bone screw or the connecting member or which requires the aid of special instruments. 
     The invention relates to a clamping connection based on a cone mechanism or wedge mechanism which is apt to be locked and released again by means of a screw driver. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a joint-like connection of two bodies comprising a first body with a cavity extending coaxially to a central axis and containing a joint pan, a clamping member with a longitudinal axis and a coaxial bore, the clamping member having a shape complementary to that of the cavity and being resiliently deformable in a direction vertical to the longitudinal axis, at least one tension member insertable coaxially to the longitudinal axis into the bore and widening axially, so that an axial displacement of the at least one tension member within the bore may cause the clamping member to be expanded and releasably locked within the cavity, a second body which is releasably connectable to the first body by means of the at least one tension member and the clamping member, and a driving member by means of which the at least one tension member is axially displaceable relative to the bore. The driving member is connected with both the clamping member and the at least one tension member in such a way as to be axially in positive engagement while rotatable about the longitudinal axis. 
     In a first embodiment, the device according to the invention comprises an axially positive connection rotatable about the longitudinal axis existing between the driving member and the clamping member by means of an annular shoulder formed in the driving member and of a complementary, annular groove formed in the clamping member, whereas the axially positive connection rotatable about the longitudinal axis existing between the driving member and the tension member is realized by means of a threaded connection. 
     In a second embodiment of the device according to the invention, the configurations of the axially positive connections rotatable about the longitudinal axis are inversed. The axially positive connection rotatable about the longitudinal axis existing between the driving member and the clamping member is realized by means of a threaded connection rotatable about the longitudinal axis existing between the driving member and the tension member is realized by means of an annular shoulder formed in the driving member and of a complementary, annular groove formed in the tension member. 
     In another embodiment of the device according to the invention, both of the axially positive connections rotatable about the longitudinal axis, the one between the driving member and the clamping member and the one betwen the driving member and the tension member, are realized in the form of threaded connections. Preferably, in one embodiment, one of the two threaded connections is provided with left-hand threads and the other of the two threaded connections is provided with right-hand threads. The thread pitches of the two threaded connections may be of the same amount or different amounts. 
     The advantages of the first and second embodiments reside in their simplicity of manipulation whereas the third embodiment, due to the two threaded connections, permits a rapid releasing and tightening and, in addition, is easy to manufacture. 
     The configuration of the cavity formed in the first body and of the clamping member, on which depends the type of joint-like connection to be realized, may be cylindrical or spherical, depending on the application, and is preferably shaped in the form of a spherical segment contained between two parallel circles. In the case of a cylindrical configuration, the clamping member is rotatable only about the central axis of the cavity, whereas in the case of a configuration of the cavity in the shape of a spherical segment between two parallel circles, the clamping member is rotatable about the central axis and about two other axes extending vertically thereto. 
     In yet another embodiment, the second body is integral with the tension member. This embodiment is specially suitable for the use of the device of the invention in a vertebral column fixation system, the second body being preferably realized in the form of a bone screw and the first body having the form of a connecting member between the bone screw and a longitudinal carrier. A configuration of the joint-like connection suitable for this purpose includes a ball-and-socket joint with a cavity shaped in the form of a spherical segment between two parallel circles. 
     In another embodiment, the first body is shaped in the form of a bone plate, whereas the second body forms a connecting member with another bone plate, said elements forming together a bone fixation device including two articulatedly connected bone plates. A joint-like connection suitable for this purpose has a circularly cylindrical cavity and is pivotable relative to only one axis. 
     The device according to the invention may in various embodiments also comprise a plurality of tension members which are displaceable coaxially to the longitudinal axis in both directions relative to the bore. In the case of embodiments including two tension members, the clamping member is preferably provided, contiguous to its end portions, with two resiliently deformable, longitudinal sections, so that one tension member may be inserted from each side into the bore. 
     The device advantageously provides a clamping connection based on a cone mechanism or a wedge mechanism which may be locked and, inversely, be released again by means of a screw driver and without the aid of any additional instruments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred features of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein: 
         FIG. 1  is a cross-sectional view of one embodiment of the device according to the invention; 
         FIG. 2  is a cross-sectional view of another embodiment of the device according to the invention; 
         FIG. 3  is a cross-sectional view of yet another embodiment of the device according to the invention; 
         FIG. 4  is a perspective view of an embodiment of the device according to the invention for connecting two plate-like bodies; 
         FIG. 5  is a perspective view of a detail of one of the bodies forming the embodiment of the device according to the invention shown in  FIG. 4 ; 
         FIG. 6  is a cross-sectional view of a further embodiment of the device according to the invention; 
         FIG. 7  is a top view of the device according to the invention shown in  FIG. 6  as applied to a vertebral column; and 
         FIG. 8  is a cross-sectional view of the embodiment of the device according to the invention shown in  FIG. 3  as a part of a vertebral column fixation system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows one embodiment of the device according to the invention which comprises a first body  1  shaped in the form of a connecting member and a second body  2  shaped in the form of a pedicle screw. First body  1  includes a top surface  3 , a bottom surface  4  extending parallel to the top surface  3 , and a cavity  5  with a central axis  6  extending vertically to the top surface  3 . Second body  2  is integral with a a tension member  12  and includes a clamping member  8 , and a driving member  19  shaped in the form of a straining screw. The cavity  5  extends through the first body  1  coaxially to central axis  6  and comprises an axial longitudinal section E (N=1) which is spherically concave and rotationally symmetrical relative to the central axis  6 . Corresponding to the spherically concave form of the longitudinal section E, clamping member  8  comprises a longitudinal section D (N=1), so that the clamping member  8  is rotatable within cavity  5  about the central axis  6  and about two other axes extending vertically or perpendicular or orthogonal to the central axis  6  and intersecting the center of the spherical form. Clamping member  8  additionally comprises a longitudinal axis  11 , a top end  13 , a bottom end  14 , and, extending coaxially to the longitudinal axis  11 , a bore  15  and an aperture  50  axially contiguous to each other, so that the clamping member  8  is penetrated between the top end  13  and the bottom end  14 . The aperture  50  has a tapered form beginning from the bottom end  14  and extending over a longitudinal section B (N=1) and is resiliently deformable in a direction vertical or perpendicular to the longitudinal axis  11  over a longitudinal section A (N=1) containing said longitudinal section B. The resilient deformability is obtained by means of slots  47 , the aperture  50  preferably comprising four such slots  47  arranged about the circumference with a radial offset of 90 degrees and penetrating parallel to the longitudinal axis  11  from the bottom surface  14 . 
     The tension member  12  (M=1) of this embodiment is integral with second body  2 , the bottom end  17  being contiguous to the second body  2 . Tension member  12  is inserted with its top end  16  from the bottom end  14  into the aperture  50  formed in the clamping member  8 . The tension member  12  has an axially tapered form extending towards the top end  16  over a longitudinal section C (N=1) which is complementary conical to the longitudinal section B of the aperture  50 , so that the tension member  12  and the clamping member  8  form a conical clamping connection  18 . A coaxial displacement of the tension member  12  within the aperture  50  causes the resilient longitudinal section A to be radially spread apart or to regain its initial position, as the tension member  12  is displaced in the opposite direction. This conical clamping connection allows the second body  2 , which is integral with the tension member  12 , to be releasably connected with the first body  1 . 
     The axial displacement of the tension member  12  is made possible by turning the driving member  19 , realized in the form of a straining screw, about the longitudinal axis  11 . A rotatable and axially positive connection  29  between the driving member  19  and the clamping member  8  on the longitudinal section G is realized in the form of a coaxial, annular shoulder  20  formed on the clamping member  8  and of a corresponding annular groove  21  formed in the bore  15 . The connection between the driving member  19  and the tension member  12 , which is also axially positive and rotatable about the longitudinal axis  11 , is realized in the form of a threaded engagement between an external screw thread  22  formed in the driving member  19  and a corresponding internal screw thread  24  formed in a bore  23  which penetrates into the tension member  12  from the top end  16 . This threaded engagement allows the tension member  12  to be axially displaced within the clamping member  8 , as the driving member  19  is rotated, while the axial forces occurring between the driving member  19  and the clamping member  8  are absorbed by the shoulder  20  of the driving member  19  located within the groove  21 . 
       FIG. 2  shows an embodiment of the device according to the invention which differs from the embodiment shown in  FIG. 1  only in so far as the axial displacement of the tension member  12  within the clamping member  8  is realized by means of a threaded connection comprising an external screw thread  25  formed in a longitudinal section G of the driving member  19  and a complementary, internal screw thread  26  formed in the bore  15 . The connection between the driving member  19  and the tension member  12 , which is axially positive and rotatable about the longitudinal axis  11 , is realized by means of anchoring means  29  arranged in the longitudinal section F of the driving member  19  which absorb the axial forces occurring between the driving member  19  and the tension member  12 . These anchoring means are realized in the form of a coaxial, annular shoulder  27  formed in the driving member  19  which is located within an annular groove  28 , said groove  28  being arranged in a bore  23  which penetrates into the tension member  12  from its top end  16 . 
       FIG. 3  shows an embodiment of the device according to the invention which represents a combination of the embodiments shown in  FIGS. 1 and 2 . On the one hand, the driving member  19  is connected to the clamping member  8  by means of a first threaded connection comprising an external screw thread  22  formed in the longitudinal section F of the driving member  19  and a corresponding, internal screw thread  24  arranged in a bore  23  of the tension member  12  which penetrates concentrically to the longitudinal axis  11  into said tension member  12  from the top end  16 . Also provided is a second threaded connection comprising an external screw thread  30  formed in the longitudinal section G of the driving member  19  and a complementary, internal screw thread  31  formed in the bore  15  of the clamping member  8 . The driving member  19  is connected to the clamping member  8  in such a way as to be axially in positive engagement while rotatable about the longitudinal axis  11 . 
       FIG. 4  shows another embodiment of the device according to the invention comprising a first plate-like body  1  with a top surface  3 , a bottom surface  4  extending parallel to the top surface  3 , and a cavity  5  with a central axis  6  extending vertically to the top surface  3 , a second plate-like body  2 , a tension member  12 , a clamping member  8 , and a driving member  19  shaped in the form of a straining screw. The clamping member  8  defines an axis of rotation of a joint-like connection. The cavity  5  extends coaxially to the central axis  6  through the first body  1  and comprises a longitudinal section E (N=1) which is circularly cylindrical and rotationally symmetrical relative to the central axis  6 . Corresponding to the circularly cylindrical form of the longitudinal section E, the clamping member  8  comprises a longitudinal section D (N=1), so that the clamping member  8  is rotatable about the central axis  6  within the cavity  5 . The clamping member  8  comprises in addition a longitudinal axis  11 , a top end  13 , a bottom end  14 , and, extending coaxially to the longitudinal axis  11 , a bore  15  and an aperture  50  axially contiguous to each other, so that the clamping member  8  is penetrated from the top end  13  to the bottom end  14 . This aperture  50  has a tapered form beginning from the top end  13  and extending over a longitudinal section B (N=1) and is resiliently deformable in a direction vertical to the longitudinal axis  11  over a longitudinal section A (N=1) containing said longitudinal section B. The resilient deformability is obtained by the fact that in the longitudinal section A, the opening  50  penetrates the clamping member  8  also in a direction vertical to the longitudinal axis  11 . 
     The tension member  12  is inserted with its bottom end  17  from the top end  13  into the aperture  50  formed in the clamping member  8 . The tension member  12  has a tapered form extending parallel to the longitudinal axis  11  on a longitudinal section C (N=1) which is complementary to the longitudinal section B of the aperture  50 , so that the tension member  12  and the clamping member  8  form a wedge-shaped clamping connection  49 . A coaxial displacement of the tension member  12  within the aperture  50  causes the resilient longitudinal section A to be radially spread apart or to resiliently regain its initial position, as the tension member  12  is displaced in the opposite direction. From the bottom end  17  to the longitudinal section C, the tension member  12  is shaped in a square form corresponding to the square socket  37  ( FIG. 5 ) formed in the bore  36  of the second body  2  extending coaxially to the longitudinal axis  11 , which allows the second body  2  to be kept in place together with the tension member  12  relative to a rotation about the longitudinal axis  11 . 
     The displacement of the tension member  12  parallel to longitudinal axis  11  is made possible by turning the driving member  19 , realized in the form of a straining screw, about the longitudinal axis  11 . On the one hand, a first threaded connection is provided comprising an external screw thread  22  formed in the longitudinal section F of the driving member  19  and a complementary, internal screw thread  24  formed in the tension member  12 , and the driving member  19  is connected to the clamping member  12  in such a way as to be axially in positive engagement while rotatable about the longitudinal axis  11 . The internal screw thread  24  is arranged in a bore  23  extending concentrically to the longitudinal axis  11  through the tension member  12 . Also provided is a second threaded connection comprising an external screw thread  30  formed in the longitudinal section G of the driving member  19  and a complementary, internal screw thread  31  formed in the bore  15  of the clamping member  8 , and the driving member  19  is connected to the clamping member  8  in such a way as to be axially in positive engagement while rotatable about the longitudinal axis  11 . In order to be secured against rotation about the central axis  6 , clamping member  8  is provided with an external toothing  33  formed in the longitudinal section D which is engageable with a corresponding internal toothing  35  formed in a longitudinal section E of the cavity  5 . 
       FIG. 6  shows an embodiment of the device according to the invention which differs from the embodiment shown in  FIG. 4  only in so far as it comprises a clamping member  8  with a first aperture  50  having a first, conically or wedge-shaped, tapered form beginning from the top end  13  and extending over a longitudinal section B, and a second aperture  50 ′ having a second, conically or wedge-shaped, tapered form beginning from the bottom end  14  and extending over a longitudinal section B′, as well as two tension members  12 ; 12 ′ which are complementary thereto. The driving member  19  is mounted within the clamping member  8  in such a way as to be axially in positive engagement while rotatable about the central axis  6 . By analogy with the embodiment shown in  FIG. 2 , the anchoring means  29  consist of a concentric, annular shoulder  27  formed in the longitudinal section G of the driving member  19  which is mounted in a complementary, annular groove  28  formed in the clamping member  8 . Both tension members  12 , 12 ′ are connected to the driving member  19  by means of threaded connections, one of said threaded connections having a right-hand thread whereas the other threaded connection has a left-hand thread. 
       FIG. 7  shows an application of the embodiment of the device according to the invention shown in  FIG. 6  as a multipart bone plate attached laterally on a vertebral column. The body  1  forms a first part of the bone plate attached to the cranial vertebral body  43  by means of bone screws  41 , whereas the body  2  serves as a connecting member with a part  40  of the bone plate attached to the caudal vertebral body  44 . By means of the clamping member  8  which is mounted in the body  1  in such a way as to be rotatable about the central axis  6  ( FIG. 6 ) extending vertically to the surface of the vertebral body  43 , the body  2  is on one side articulatedly connected to the body  1 . The second part  40  of the bone plate is connected to the other side of the body  2  in such a way as to be displace-able parallel to the longitudinal axis of the vertebral column and lockable by means of two set screws  42 ,  80  that the bone plate allows an angular movement of the vertebral bodies  43 ; 44  relative to each other and a displacement of said vertebral bodies parallel to the longitudinal axis of the vertebral column. The joint can be locked by means of the driving member  19 . 
       FIG. 8  illustrates the application of the embodiment of the device according to the invention shown in  FIG. 3  as a connecting member within a vertebral column fixation system. The body  1  serves as a connecting member between the body  2  shaped in the form of a pedicle screw and a longitudinal carrier  45 . The longitudinal carrier  45  is kept in place within the body  1  for example by means of a screw  46 . One example of such a device is shown in International Patent Publication No. WO 94/00066 to Schläpfer et al. 
     One of ordinary skill in the art can envision numerous variations and modifications to the invention disclosed herein. All of these modifications are contemplated by the true spirit and scope of the following claims.