Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a continuation of U.S. patent application Ser. No. 10/881,166, filed Jun. 30, 2004, now U.S. Pat. No. 7,121,755, which is a continuation of International Patent Application No. PCT/CH2001/000744, filed Dec. 31, 2001, the entire contents of both are expressly incorporated herein by reference thereto. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a device for the ball-and-socket type joint connection of two parts.  
       BACKGROUND OF THE INVENTION  
       [0003]     A stabilization device that interconnects the bone-fixation means, such as pedicle screws, with a longitudinal member, such as a longitudinal spinal rod, extending along at least a portion of a patient&#39;s spinal column, is used, for example, for the internal stabilization of the spinal column. In order to securely stabilize the spinal column, it should be possible to connect the bone-fixation means, on the one hand, firmly with the vertebrae and, on the other, with the longitudinal member. Preferably, the head of the bone fixation means and the longitudinal member are connected by a connecting mechanism, which permits the longitudinal member to be fixed with respect to the bone-fixation means at a variety of different angles. Moreover, the connecting mechanism may be detachable, so that the mechanism may be later removed without large openings being formed in the tissue of the spinal column.  
         [0004]     Such a connection mechanism between a bone-fixation means and a longitudinal member for the internal stabilization of a vertebrae is known, for example, in U.S. Pat. No. 5,466,237 to Byrd which discloses a bone-fixation screw having a screw head, which is constructed with a spherical shaped lower surface and a convexly shaped upper surface. The spherical shaped lower surface is mounted in a borehole formed in the connecting mechanism, this borehole comprising a concave section, which tapers towards the screw shaft, as a result of which, and together with the screw head, a ball-and-socket type joint connection is established between the bone-fixation screw and the connecting mechanism. This connection is locked by tightening a nut, which can be screwed over an external thread formed on the upper portion of the connecting mechanism. Tightening the nut, forces the nut against the longitudinal member, which is placed in a transverse channel formed in the connecting mechanism for this purpose. The longitudinal member thereafter presses on the convexly-shaped upper surface of the bone-fixation screw, so that, as the nut is tightened, the longitudinal member and the bone-fixation screw are locked in the connecting mechanism.  
         [0005]     A bone-fixation screw having a screw head with a spherically shaped lower surface is also disclosed in International Publication No. WO 01/03593 to Frigg (corresponding to U.S. Pat. No. 6,663,635), which discloses that the center of the spherical lower surface and the spherical upper surface can be spaced apart or coincide with respect to the longitudinal axis of the bone-fixation screw.  
         [0006]     Another device for connecting a bone-fixation screw with a longitudinal member, which permits limited, separate locking of the longitudinal member and the bone-fixation screw, is disclosed in German Publication No. DE 43 07 576 to Biedermann (which corresponds to U.S. Pat. No. 5,443,467).  
         [0007]     One disadvantage of the connecting mechanism in these known devices is that the connecting mechanism must have a generally large, overall height.  
         [0008]     A device for connecting a bone-fixation screw with a longitudinal member, which permits a lower overall height due to the configuration of the joint connection and its locking mechanism, is disclosed in International Publication No. WO 01/22893 to Lombardo which discloses a bone-fixation screw having a screw head with a partially lower spherical surface and a top surface having a coaxial, conical cavity for receiving a convexly formed front end of the clamping means which accommodates polyaxially movement and which may be pressed by mounting means against the conical wall of the cavity. The mounting means can be screwed coaxially into the connecting mechanism at the upper end of the connecting mechanism and, when the device is locked, press against the longitudinal member, which is inserted in the transverse channel formed in the connecting mechanism, which in turn, presses on the clamping means. One disadvantage with this device is that, because the convex, front end of the clamping means is pressed into the conical cavity at the screw head of the bone screw, there is a wedging effect which creates a levering force, which aligns the bone screw parallel with the central axis of the connecting mechanism.  
         [0009]     Thus, there remains a need for a connecting mechanism that provides a reduced overall height and which overcomes the problems associated with the prior art.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention addresses these problems and others by providing a device, which comprises a spherically shaped connection between two members, the mechanism comprising clamping means, the front end of which contacts the surface of a depression formed in the joint head of the bone-fixation means, as a result of which a smaller overall height of the connection mechanism is possible, and which, in the unlocked state, permits polyaxially angular position of the central axes of the two parts relative with respect to each another.  
         [0011]     Pursuant to the invention, this objective is accomplished with a device for the ball-and-socket type connection of two members. The advantages, achieved by the invention, are a result of the fact that: 
        due the coincidence of the center of the joint and of the center of the spherically shaped contact surface at the front end of the clamping means and/or of the depression at the joint head, locking of the two members with respect to one another at different angles of the central axes of the two members becomes possible without the occurrence of levering forces associated with the prior art; and     because the joint head is fixed in the cavity by the clamping means, the front end of which can be brought into contact with a depression at the joint head, the latter can be configured lower, as a result of which the device has smaller dimensions.        
 
         [0014]     As will be described herein, the clamping means in various, different embodiments can be configured differently at their front end, depending on the desired form of contact with the depression, for example: 
        by configuring the front end of the clamping means as a point, which is concentric with the central axis, a punctiform contact between the front end and the depression can be achieved;     by configuring the front end of the clamping means as a flattened surface, orthogonally to the central axis, linear contact between the front end and the depression can be attained and     by configuring the front end of the clamping means spherically, a contact surface can be established between the front end and the depression.        
 
         [0018]     In further embodiments, the depression formed in the joint head of the bone-fixation means may be spherical or conical, as a result of which, by pairing clamping means with a spherically formed front end, a contact surface or a linear contact can be attained between the front end of the clamping means and the depression.  
         [0019]     In further embodiments, the depression is provided with a circular edge, which is concentric with the central axis and, together with the spherically configured front end of the clamping means, also forms a linear contact.  
         [0020]     Preferably, the joint head of the bone-fixation means may be constructed rigidly, so that no expansion of the joint head is possible when the device is locked.  
         [0021]     In a preferred embodiment of the invention, the device may include: 
        a) a first member whish is sized and configured as a bone-fixation means, for example, as a pedicle screw, a pedicle hook, etc., the lower segment of which is used to fix the bone-fixation means to a patient&#39;s bone; and     b) a second member which is sized and configured as a connecting mechanism and/or part for interconnecting the longitudinal member, for example, a longitudinal spinal rod, with the bone-fixation means. The second member may further include a channel, disposed transversely to the central axis, for accommodating the longitudinal member and a central borehole with internally formed threads, disposed coaxially with the central axes.        
 
         [0024]     Furthermore, the device may include mounting means for fixing the longitudinal member, inserted into the transverse channel, so that the device can be used, for example, as a spinal fixation device.  
         [0025]     The clamping means may directly lock and/or unlock, and may be in the form, for example, of a clamping screw, which may threadedly engage, for example, the internal threads formed in the central borehole of the connecting member. By this, it becomes possible that the locking and/or unlocking of the bone-fixation means by means of the clamping screw in the connecting member can take place independently of the locking and/or unlocking of the longitudinal member by means of the clamping means.  
         [0026]     On the other hand, the clamping means may indirectly lock and/or unlock, and coaxially move within the central borehole formed in the connecting member and, for example, may be locked and/or unlocked by means of a mounting means.  
         [0027]     Alternatively, the transverse channel may open toward the side of the device, i.e., a side-loading pedicle screw. The side-loading pedicle screw may also include a covering cap, which may be pushed over the connecting member parallel to the central axis. The covering cap may include a tab formed parallel to the central axis, the tab enabling the channel opening to be closed when the mounting means is tightened, thereby clamping the longitudinal member inside the channel between the wall of the channel and the tab. In this embodiment, with respect to the central axis, the channel preferably is offset from the channel opening so that it becomes possible that the clamping screw may be screwed into the connecting member adjacent to the channel, so that, in comparison to the previous embodiments, the clamping screw can be screwed into the connecting member below the channel, thereby reducing the overall height of the connecting member even more.  
         [0028]     In yet another, different embodiment of the invention, the channel may be configured at the upper end of the connecting member, i.e., a top-loading pedicle screw. The mounting means may be pressed directly onto the longitudinal member, so that the longitudinal member can be fixed in the channel by means of the clamping means.  
         [0029]     In a further embodiment of the invention, the joint head of the bone-anchoring means may include two flat spots, which are parallel to the central axis and which are separated by a distance B from one another, wherein the connecting member further includes a groove, provided parallel to the central axis, having a width W. The groove providing an enlarged opening of the cavity at the lower end of the second member perpendicularly to the width W in such a manner, that the joint head, with the flat spots parallel to the side walls of the groove, can be introduced into and removed from the cavity starting from the lower end of the second member. On the other hand, when the flat spots are rotated with respect to the side walls of the groove, the joint head, due to the support in the cavity, is secured axially against the lower end of the second member.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     To facilitate an understanding of and for the purpose of illustrating the present invention, exemplary and preferred features and embodiments are disclosed in the accompanying drawings, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, and wherein similar reference characters denote similar elements throughout the several views, and wherein:  
         [0031]      FIG. 1  shows a longitudinal section through an embodiment of the inventive device,  
         [0032]      FIG. 2   a  shows a section of the clamping means of an embodiment of the inventive device,  
         [0033]      FIG. 2   b  shows a section of the clamping means of a different embodiment of the inventive device,  
         [0034]      FIG. 3  shows a longitudinal section through a further embodiment of the inventive device,  
         [0035]      FIG. 4   a  shows a section through the joint head of an embodiment of the inventive device,  
         [0036]      FIG. 4   b  shows a section through the joint head of a different embodiment of the inventive device,  
         [0037]      FIG. 5  shows a section through a further embodiment of the inventive device,  
         [0038]      FIG. 6  shows a view from above of the embodiment of the inventive device, shown in  FIG. 5 ,  
         [0039]      FIG. 7  shows a view from below of the embodiment of the inventive device, shown in  FIGS. 5 and 6 ,  
         [0040]      FIG. 8  shows a section through a further embodiment of the inventive device,  
         [0041]      FIG. 9  shows a section once again through a further embodiment of the inventive device,  
         [0042]      FIG. 10  shows an exploded representation of the embodiment of the inventive device shown in  FIGS. 5, 6  and  7  and  
         [0043]      FIG. 11  shows an exploded representation of a part of an embodiment of the inventive device together with the fastening device. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0044]     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to an exemplary, non-limiting embodiment illustrated in the figures and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is hereby intended, such alterations and further modifications, and such further applications of the principles of the invention as illustrated herein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0045]     As shown in  FIG. 1 , the device includes a first member  1  and a second member  2 , wherein the second member  2  includes a cavity  4  and clamping means  7  while the first member  1  has a central axis  5 , an upper end  11 , and a lower end  12 . The upper end  11  of the first member  1  may include a first joint segment  10 , which may be constructed as a spherically shaped joint head  3 , the center of which, preferably lies on the central axis  5  and forms a center of joint Z. As shown, the joint head  3  may be flattened at the upper end  11  of the first member  1 . Furthermore, the joint head  3  may include a depression  8 , which may be partly spherical with a spherical shaped surface  9  and which terminates conically into the upper end  11  of the first part  1 . The spherical shaped surface  9  of the depression  8 , having a center C, which preferably is constructed so that center C lies on the central axis  5  and coincides with the center Z.  
         [0046]     The second member  2  may also have a central axis  6 , an upper end  21 , a lower end  22 , an upper segment  23  and a cavity  4 , which is disposed at the lower end  22  and forms the second joint segment  20 . The cavity  4  may be disposed coaxially with the central axis  6  and is tapered at the lower end  22  of the second member  2  by a constriction  14  formed on the lower end  22 . Preferably, the constriction  14  has a spherical shaped support  37  forming a center which coincides with the joint center Z. The spherically shaped support  37  being directed towards the interior of the cavity  4 . Preferably, the spherically shaped support  37  is complementary with the surface of the joint head  3 , so that the two joint segments  10 ;  20  can be rotated with respect to one another about three mutually perpendicular axes.  
         [0047]     As shown, at the lower end  22  of the second member  2 , the cavity  4  may have an opening  15 , which may be coaxial with the central axis  6  and through which the lower segment  13  of the first member  1  can pass.  
         [0048]     The clamping means  7  may be disposed coaxially with the central axis  6  of the second member  2 . The clamping means  7  may include a front end  16  and a rear end  17  which are preferably disposed so that they may be displaced coaxially with the central axis  6 . The front end  16  of the clamping means  7  may be constructed circularly cylindrically and may be brought into contact with the spherically shaped surface  9  of the depression  8 . By pressing the front end  16  onto the spherically shaped surface  9  of the depression  8 , the joint head  3  can be locked in the cavity  4  formed in the second member  2 . The first and second members  1 ,  2  with the polyaxially angular arrangement of their central axes  5 ,  6  being lockable because of the identity of location of the center C of the spherically shaped surface  9  of the depression  8  with the joint center Z.  
         [0049]     As shown, in  FIGS. 2   a  and  2   b , in each case showing different embodiments of the clamping means  7 , the front end  16  of the clamping means  7 , as shown in  FIG. 2   a , may have a point which is coaxial with the central axis  6 , whereas, as shown in  FIG. 2   b , the front end  16  of the clamping means  7  is shown as being convexly spherical.  
         [0050]     The device, as shown in  FIG. 3 , differs from the embodiment, shown in  FIG. 1 , only in that the depression  8  in the joint head  3  and the front end  16  of the clamping means  7  are constructed differently. As shown, the front end  16  of the clamping means  7  is hemispherical with the center C lying on the central axis  6 , and has a radius R. While the depression  8  is conical with an annular elevation  38 , which is concentric with the central axis  6 . The elevation  38  has a circular, sharp edge  39 , which is directed towards the interior of the depression  8 . The axial distance between the edge  39  and the upper end  11  of the first part  1  and the diameter of the circular edge  39  are such that the edge  39  lies on an imaginary spherical surface with the center C lying on the central axis  6  and with the radius R.  
         [0051]     As shown in  FIG. 4   a , the joint head  3  differs from the embodiments described above only in that the depression  8  at the upper end  11  of the first member  1  has a conical, coaxial section  40  and an axially adjoining circular cylindrical section  41  with the diameter D at a depth T, measured from the upper end  11 . The diameter D is selected so that the depression  8  is constricted at the depth T by the circular cylindrical section  41 , so that a circular edge  39 , concentric with the central axis  6 , is formed by the transition between the conical section  40  and the circular cylindrical section  41 . Furthermore, the diameter D and the depth T are dimensioned so that the circular edge  39  coincides on an imaginary spherical surface with the center C, lying on the central axis  6 , and with the radius R, as was the case with the embodiment depicted in  FIG. 3 .  
         [0052]     As shown in  FIG. 4   b , the joint head  3  may have a conical depression  8  forming a cone  42 . The diameter of the cone  42  at the upper end  11  of the first member  1  and the conical angle of the cone  42  are dimensioned so that the cone  42  touches an imaginary spherical surface with the center C, lying on the central axis  6 , and with a radius R, as was the case with the embodiment depicted in  FIG. 3 .  
         [0053]     A linear contact between the clamping means  7  and the depression  8  can be achieved by a configuration of the depression  8  and of the front end  16  of the clamping means  7  of one of the  FIGS. 3, 4   a  or  4   b.    
         [0054]     As shown, in  FIGS. 5-7  and  10 , an alternate embodiment of the present device is shown wherein the device comprises, a first member  1  having bone fixation means  24 , which as shown is a pedicle screw, but which may also be a pedicle hook, etc., and a second member  2  having a connecting part  25  for connecting a longitudinal spinal member  26  to the bone fixation means  24 . As partially shown, the bone fixation means  24  may include a lower threaded shaft segment  13  and a joint screw head  3 . The lower surface side of the screw head, i.e., on the side facing the screw shaft, the screw head is preferably constructed with a partially spherically surface having a radius R 2 , the center of the spherical lower surface, preferably lying on the central axis  6 , forming the joint center Z.  
         [0055]     The upper surface side of the joint head  3  preferably has a depression  8 , which has a partially spherical surface  9  with a center C and a radius R 1 . The partially spherical surface preferably terminating conically into the outer surface at the upper end  11  of the first member  1 . Preferably, the center C coincides with the joint center Z, so that the screw head can be locked in the connecting part  25  in such a manner that the central axis  5  of the first member  1  and the central axis  6  of the second member  2  can polyaxially rotate with respect to each another.  
         [0056]     As shown, the cavity  4  in the connecting part  25 , serving as a second joint segment  20 , preferably includes a constriction  14 , which as shown is a spherical support  37  having a joint center Z so that the spherically configured screw head is mounted on the support  37  so that it can be rotated polyaxially about the joint center Z.  
         [0057]     The device further includes a clamping means  7 , which as shown in  FIG. 5 , may be clamping screw having a rear end  17  with an external thread  47  sized and configured to mate with complementary internal threads  31  formed on the central borehole  30  of the connecting part  25 . The rear end  17  of the clamping means  7  also may include means  44  for accommodating a screwdriver, a hex-driver, etc. As shown, the front end  16  of the clamping means  7  is formed with a spherical tip for contacting the spherical surface  9  in the depression  8  at the screw head. Although other shaped tips are envisioned.  
         [0058]     As best shown in  FIGS. 7 and 10 , the joint head  3  may be equipped with two flat spots  35 , which are preferably parallel to one another and to the central axis  5 . The two flat spots  35  being separated by a distance B from one another. Similarly, the cavity  4  may include a groove  36  of width W, width W being greater than or equal to distance B, which is parallel to the central axis  6 . The depth of the groove  36  is such that the opening  15  of the cavity  4  at the lower end  22  of the second member  2  is enlarged perpendicularly to the width B, so that the joint head  3  with the flat spots  35 , parallel to the side walls of the groove  36 , can be passed into or out of the cavity  4  from the lower end  22  of the second member  2  and then, by rotating the first member  1  about the central axis  5 , the flat spots  35  at the joint head  3  are twisted with respect to the side walls of the groove  36 , so that the joint head  3  can be fixed axially against the lower end  22  of the second member  2  by the constriction  14  formed in the cavity  4 .  
         [0059]     As shown, the device may further include a channel  27  for accommodating the longitudinal member  26 , the channel being mounted in the connecting part  25  with the channel axis  28  extending transversely to the central axis  6 . As shown, the channel  27  may be opened laterally at the connecting part  25  forming a channel opening  32  therein. The channel  27  is provided at the connecting part  25  so that the channel axis  28  is displaced by a distance A away from the central axis  6  towards the channel opening  32 . A covering cap  33  is also provided, the cap  33  being placed coaxially on the central axis  6  over the connecting part  25  in order to fix the longitudinal member  26  in the channel  27 . The covering cap  33  may include a tab  34 , which is parallel to the central axis  6  and by means of which the channel opening  32  can be closed off by the covering cap  33  so that the longitudinal member  26  inserted into the channel  27  may be fixed in the channel  27 . The covering cap  33  may be pressed coaxially along the central axis  6  by mounting means  29 , which are shown herein as a nut which may threadedly engage the external threads  43  formed on the upper end  21  of the connecting part  25  so that the longitudinal member  26 , inserted in the channel  27 , can be fixed within the channel  27 . Alternatively, the connecting member  25  may include internal threads for engaging an externally threaded nut.  
         [0060]     Moreover, as shown, a device to prevent twisting can be mounted between the connecting part  25  and the covering cap  33 . This device may be in the form of a flat spot  48  and a complementary constriction  50 , the flat spot  48  being formed on a portion of the connecting part  25  extending parallel to the central axis  6  while the constriction  50  is formed on the central opening  49  of the covering cap  33 , also extending coaxial with the central axis  6 . So that when the covering cap  33  is pushed over the connecting part  25 , the constriction  50  mates with the flat spot  48 , so that twisting of the covering cap  33  about the central axis  6  with respect to the connecting part  25  is prevented.  
         [0061]     As shown in  FIG. 8 , the device differs from the embodiment, shown in  FIGS. 1 and 3 , only in that the second member  2  may include a channel  27  formed in the connecting part  25  for accommodating a longitudinal member, the channel  27  being open at the upper end  21  of the connection part  25 . The clamping means  7  may be screwed coaxially along the central axis  6  against the internal threads  31  formed in the central borehole  30  of the connecting part  25 , so that the front end  16  of the clamping means  7  can be pressed against the surface  9  of the depression  8  at the upper end  11  of the first member  1 . When the device is installed, the clamping means  7  is thus disposed between the longitudinal member  26  placed in the channel  27 , and the cavity  4  in the second member  2 . The longitudinal member  26  being locked in the channel  27  by mounting means  29 , which is shown as an externally threaded setscrew and which, after the longitudinal member  26  is placed in the channel  27 , can be screwed from the upper end  21  of the connecting part  25  into engagement with the internal threads  52 . The internal thread  52  and the internal thread  31 , both of which are disposed coaxially with the central axis  6  in the central borehole  30 , can also be formed as a single internal thread.  
         [0062]     As shown in  FIG. 9 , the device differs from the embodiment shown in  FIG. 8  only in that the internal thread  52  formed in the central borehole  30  extends only so far from the upper end  21  of the connecting part  25 , so that a longitudinal member  26  placed in the channel  27  can be locked in the channel  27  by means of the mounting means  29 . As shown, the central borehole  30  is configured circularly cylindrically between the longitudinal section of the central borehole  30 , which is provided with the internal thread  52 , and the cavity  4 , so that the clamping means  7  can be moved parallel to the central axis  6  in the central borehole  30 . At its rear end  17 , the clamping means  7  may include a notch  51 , which extends transversely to the central axis  6 . In the installed device, the longitudinal member  26 , placed in the channel  27 , rests in the notch  51 , so that when the mounting means  29  is tightened, it presses against the longitudinal member  26 , which in turn presses on the clamping means  7 . The clamping means  7  thereafter being moved parallel to the central axis  6  against the front end  22  of the connecting part  25 , thereby pressing with its front end  16  onto the surface  9  of the depression  8  at the upper end  11  of the first member  1 . Thus, tightening the mounting means  29 , locks the longitudinal member  26  and the first member  1  simultaneously in the device.  
         [0063]     As shown in  FIG. 11 , the device may include a second member  2  which is configured as a connecting part  25 , clamping means  7  and a fastening device  57 . As shown, the fastening device  57  may include a sleeve-like holder  58  and a threaded bolt  59 , which can be moved coaxially along the central axis  6  of the holder  58 . At its front end  63 , the holder  58  has a hexagon drive  62 , which is parallel to the central axis  6 , and which is sized and configured to mate with a complementary hexagon socket  56  formed on the rear end  21  of the connecting part  25 . At its front end  60 , coaxially with the central axis  6 , the threaded bolt  59  may include external threads  61 , so that the threaded bolt  59  may threadedly engage the complementary internal threads  55  formed in the borehole  54 , which penetrates from the rear end  17  of the clamping means  7  coaxially with the central axis  6  so that the clamping means may be connected with the fastening device  57 .  
         [0064]     The clamping means  7 , which, as shown, is provided with an external thread  47  extending axially from the rear end  17 , may threaded engage the complementary internal threads  31  formed in the central borehole  30  of the connecting part  25 . Furthermore, in the rear end  17 , coaxial with the central axis  6 , the clamping means  7  may include means  44  for accommodating a screwdriver, a hex-driver, etc. As shown, the hexagon socket may include a cross-sectional dimension, which corresponds to the external diameter of the internal thread  55 . Similarly, the hexagon socket  56 , mounted at the rear end  21  of the connecting part  25  coaxially with the central axis  6  in the central borehole  30 , may have a cross-sectional dimension, which corresponds to the internal diameter of the internal thread  31  formed in the central borehole  30 .  
         [0065]     The present invention has been described in connection with the preferred embodiments. These embodiments, however, are merely for example and the invention is not restricted thereto. It will be understood by those skilled in the art that other variations and modifications can easily be made within the scope of the invention as defined by the appended claims, thus it is only intended that the present invention be limited by the following claims.

Technology Category: 4