Patent Document

BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a device for connecting a longitudinal carrier, for example, a longitudinal spinal rod, to a bone fixation means, for example, a pedicle screw.  
         [0002]     Devices are already known in the art for connecting pedicle screws to longitudinal carriers for fixing the vertebral column. For example, U.S. Pat. No. 5,584,834 to Errico discloses a device for connecting a bone fixation element to a longitudinal carrier.  
         [0003]     The connection device generally consists of a cylindrical central body, which is provided at its lower end with a slotted, tapered outer surface and a hollow-spherical cavity for receiving a spherical head of a bone fixation element and an externally threaded upper end. In its central section, the central body includes a channel, opened on the side, running perpendicular to the central axis for receiving the longitudinal carrier. The connection device further includes a locking collar and a rod securing sleeve. The locking collar has an inner tapered surface corresponding to the outer tapered surface formed on the lower end of the central body while the rod securing sleeve has a passage opening towards the locking collar. When in the assembled state, the locking collar and the rod securing sleeve are axially displaceable with respect to the central body by means of a nut, which can be screwed over the external thread formed on the upper end of the central body. In use, the longitudinal carrier is inserted between the locking collar and the rod securing sleeve so that the longitudinal carrier passes through the channel formed in the central body and the passage formed in the rod securing sleeve. Thereafter, rotation of the nut causes the rod securing sleeve to move downwards, which presses the longitudinal carrier inserted in the channel onto the locking collar, which, in turn, causes the inner tapered surface of the locking collar to pass over the external tapered surface of the central body. As a result, the lower end of the central body compresses, which causes the position of the spherical head of the bone fixation element which is received within the hollow-spherical cavity of the central body to be fixed.  
         [0004]     The disadvantage of this prior art device is, on the one hand, the significant construction height of the connection element due in part to the ball and socket type connection between the spherical head of the bone fixation element and the central body and, on the other hand, the space required for the surgical instrument for tightening the nut over the external thread formed on the upper end of the central body.  
       SUMMARY OF THE INVENTION  
       [0005]     The invention is intended to remedy this situation. The invention discloses a device that requires as little space as possible and which can be implanted with a reduced number of surgical instruments and steps. Specifically, it would be preferable, to insert the implant with a surgical instrument which has a diameter no larger than the diameter of the implant so that as little damage as possible is caused to the surrounding tissue parts.  
         [0006]     The invention discloses a device for connecting a longitudinal carrier to a bone fixation means, specifically a pedicle screw, the device includes a connection element having a central axis, an external surface, an upper end, a lower end, a cavity extending coaxially along the central axis from the upper end to the lower end, the cavity having a reduced diameter portion at the lower end thereof, thereby forming at least one shoulder therein. The connection element further including a transverse channel passing through the connection element for receiving the longitudinal carrier. The device also includes a sealing cap having a front end, a rear end, a second cavity opening at the front end for receiving the connection element, and a second channel extending transversely to the central axis opening towards the front end for receiving the longitudinal carrier inserted within the transverse channel. The sealing cap may also incorporate tensioning means for fixedly securing the position of the longitudinal carrier. The device is characterized in that the connection element and the sealing cap contain complementary arresting means for securing the sealing cap to the connection element.  
         [0007]     In a further embodiment of the device according to the invention, the device comprises a connection element with a sealing cap and a tensioning means. The connection element has a central axis, an upper end, a lower end, and a cavity extending coaxially along the central axis from the upper end to the lower end of the connection element. The cavity has a reduced diameter section at the lower end of the connection element which forms a shoulder. The connection element further includes a transverse channel that is open at the upper end of the connection element so that a longitudinal carrier, for example, a longitudinal carrier representing a vertebral fixation system can be received within the channel, substantially orthogonal to the central axis, whereas a bone fixation means, for example, a pedicle screw can be introduced through the cavity parallel to the central axis, until the screw head of the pedicle screw rests on the shoulder formed in the cavity. The sealing cap is provided with a second channel, which is also arranged transverse to the central axis and which is opened towards the front end of the sealing cap so that, the longitudinal carrier may be received by the sealing cap when the sealing cap is installed on the connection element. The second channel divides the sealing cap into two segments, which are elastically deformable with respect to the central axis so that, in use, the sealing cap may be fixed with respect to the connection element by arresting means. The rear end of the sealing cap may further include tensioning means, which, when tightened, fix the position of the longitudinal carrier and the bone fixation means with respect to the connection element.  
         [0008]     In the preferred embodiment of the device according to the invention, the arresting means are arranged on the periphery of the connection element and also on the periphery of the cavity in the sealing cap. The arresting means preferably includes a plurality of bulges formed on the connection element and a plurality of complementary depressions formed in the cavity of the sealing cap.  
         [0009]     In another embodiment of the device according to the invention, the shoulder that narrows the cavity at the lower end of the sealing cap comprises a planar bearing surface for receiving and supporting, for example, the screw head of a pedicle screw. Alternatively, the bearing surface can also be designed in spherical form or having several concentric steps.  
         [0010]     The present invention provides a device with a very low structural height. Moreover, the present invention provides a device which can maintain the longitudinal carrier within the transverse channel formed in the connection element by means of a single locking mechanism. The present invention also provides a device which can facilitate installation by way of an instrument which has a diameter less than the diameter of the implant, thus minimizing the size of the incision needed for accessing the operational site, which, in turn, reduces the amount of patient trauma and making the device ideal for minimum invasive or navigated surgery. These implants also offer a possibility of treating patients in cases of thorascopic access.  
         [0011]     In a further embodiment the device according to the invention may include securing means which narrows the cavity formed in the connection element between the rear end of the head of the bone fixation means and the upper end of the connection element so that the bone fixation means can not pass through the upper end of the connection element. This enables the implants to be pre-assembled thus reducing the amount of time needed in the operating room and also reducing the risk for example, of mixing up or incorrectly inserting the bone fixation means into the connection elements.  
         [0012]     The invention and further developments of the invention are described in more detail below on the basis of partially schematic illustrations of several embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  shows a longitudinal section through the preferred embodiment of the device according to the invention;  
         [0014]      FIG. 2   a  shows a view of the connection element of the embodiment of the device according to the invention illustrated in  FIG. 1 ;  
         [0015]      FIG. 2   b  shows a view of the embodiment of the device according to the invention illustrated in  FIG. 1 ;  
         [0016]      FIG. 3  shows a longitudinal section through another embodiment of the device according to the invention;  
         [0017]      FIG. 4  shows a view of the embodiment of the device according to the invention illustrated in  FIG. 3 ;  
         [0018]      FIG. 5  shows a longitudinal section through a further embodiment of the device according to the invention; and  
         [0019]      FIG. 6  shows a longitudinal section through a further embodiment of the device according to the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]      FIG. 1  illustrates a bone fixation means  1  designed as a pedicle screw together with a connection element  5 , a longitudinal carrier  11 , a sealing cap  12  axially displaceable over the upper end  6  of the connection element  5  and a tensioning means  13 , i.e., a set screw, incorporated into the sealing cap  12 . The bone fixation means  1  includes a front segment  3  and a rear segment  4 , as shown, the front segment  3  has a screw shaft  24  with external thread  26  so that the bone fixation means  1  may threadedly engage a patient&#39;s pedicle, while the rear segment  4  has a circular-cylindrical screw head  30  having means  29 , illustrated as a hexagon socket, for receiving a screwdriver, which are arranged at an end on the screw head  30 . Alternatively, the means  29  for receiving a screwdriver may be in the form, for example, Torx or Phillips.  
         [0021]     As shown, the connection element  5  generally is in the form of a hollow body having a central axis  2 , an upper end  6 , a lower end  7 , and a cavity  8 . The diameter of the cavity  8  formed in the connection element  5  is configured so as to have a reduced diameter portion at the lower end  7  of the connection element  5 , thus forming a shoulder  9  with a bearing surface  25 , preferably a planar bearing surface, on which the screw head  30  of the bone fixation means  1  can be placed. The lower end  7  of the connection element  5  is further configured so that the screw shaft  24  of the bone fixation means  1  can be passed through the reduced diameter portion of the connection element  5 . The connection element  5  further includes a first channel  10 , generally extending transverse to the central axis  2 , wherein the first channel  10  is open towards the upper end  6  of the connection element  5  so that the longitudinal carrier  11  may be inserted into the first channel  10  from the top. The depth of the channel  10  being sized and configured to receive the longitudinal carrier  11 . More specifically, the depth of the channel  10 , measured from the upper end  6  of the connection element  5  parallel to the central axis  2 , is designed in such a way that a longitudinal carrier  11  is inserted into the channel  10  above the screw head  30  of the bone fixation means  1 .  
         [0022]     The sealing cap  12  is sized and configured so that, in use, the sealing cap  12  is axially displaceable, i.e., pushed, over the connection element  5  so that the front end  20  of the sealing cap  12  is directed towards the lower end  7  of the connection element  5  and the connection element  5  is partially received parallel to the central axis  2  in a second cavity  18  formed in the sealing cap  12 . The sealing cap  12  also incorporates a second channel  17  which enables the acceptance of the longitudinal carrier  11  inserted in the connection element  5  in the first channel  10  to be received in the sealing cap  12 . The second channel  17  is open at the front end  20  of the sealing cap  12  so that, in use, when the sealing cap  12  is axially displaced over the connection element  5 , the second channel  17  receives the longitudinal carrier  11  inserted in the connection element  5 .  
         [0023]     The device may also include arresting means  21  for securing the connection element  5  and the sealing cap  12 . More specifically, the outer surface of the connection element  5  may include bulges  15  while the inner surface of the sealing cap  12 , and more specifically, the inner surface of the second cavity  18 , includes complementary depressions  16  for engaging the bulges  15 . Preferably, the connection element  5  and the sealing cap  12  include a plurality of arresting means  21  so that different latch positions are possible. That is, preferably, the arresting means  21  includes a plurality of bulges  15  and a plurality of depressions  16  so that when the first depression  16  has been pushed over the first bulge, i.e., the first latch position, the longitudinal carrier  11  may still be longitudinally moved with respect to the bone fixation means  1  so that the bones and/or bone fragments affixed thereto may be repositioned. However, as the sealing cap  12  is further axially displaced over the connection element  5  such that subsequent bulges  15  are aligned with subsequent depressions  16 , the longitudinal carrier  11  becomes fixed with respect to the bone fixation means  1 .  
         [0024]     Preferably, as shown, the bulges  15  and the depressions  16  are provided with a saw-tooth shaped profile, when viewed in a cross section surface parallel to the central axis  2 , so that the steep flanks of the bulges  15  are oriented towards the lower end  7  of the connection element  5  and the steep flanks of the depressions  16  are oriented towards the rear end  19  of the sealing cap  12  such that, in use, as the sealing cap  12  is axially displaced over the connection element  5  parallel to the central axis  2 , the sealing cap  12 , and more specifically, the two segments  27 ,  28  ( FIG. 2   b ) of the sealing cap  12  formed by the second channel  17  are more easily biased apart, i.e., resiliently spread transverse to the central axis  2 . This enables the sealing cap  12  to pass over the bulges  15  formed on the connection element  5  until the bulges  15  align with the depressions  16  formed in the second cavity  18 , at which point the two segments  27 ,  28  ( FIG. 2   b ) resiliently move back, i.e., elastically move towards the central axis  2 , so that the bulges  15  engage the depressions  16 .  
         [0025]     The sealing cap  12  may further incorporate tensioning means  13 , which as shown is in the form of a set screw that can be screwed into an internally threaded hole  31  formed at the rear end  19  of the sealing cap  12  coaxial to the central axis  2 . Rotation of the tensioning means  13  causes the tensioning means  13  to press against the longitudinal carrier  11 , which in turn causes the longitudinal carrier  11  to press against the head  30  of the bone fixation means  1  resulting in the head  30  being clamped between the shoulder  9  formed at the lower end  7  of the connection element  5  and the longitudinal carrier  11  thereby fixing the position of the bone fixation means  1  together with the longitudinal carrier  11  with respect to the connection element  5 .  
         [0026]      FIG. 2  shows the connection element  5  from the perspective of the upper end  6 . As shown, the cavity  8  and the arresting means  21  are arranged concentrically about the central axis  2  ( FIG. 1 ), wherein the arresting means  21  is configured in the form of bulges  15  that are, when seen parallel to the central axis  2 , arranged on the outer circumference of the connection means  5 . The ring-shaped side wall of the connection element  5  and the bulges  15  are interrupted by the channel  10 , wherein the channel axis  14  runs transverse to the central axis  2  ( FIG. 1 ).  
         [0027]     The longitudinal carrier  11  is inserted in the channel  10 . In addition, the channel  10  forms, on the connection element  5 , two sidewalls  22 ,  23  for a section of its length, wherein the bulges  15  are provided only on these two sidewalls  22 ,  23  and do not surround the entire connection element  5 .  
         [0028]      FIG. 2   b  shows the sealing cap  12  with the tensioning means  13  assembled onto the connection element  5 . As shown, the second channel  17  formed in the sealing cap  12  forms two segments  27 ,  28  in the sealing cap  12 , which resiliently spread radially when the sealing cap  12  is axially displaced. i.e., pushed, over the connection element  5 , which allows the sealing cap  12  to be pushed over the bulges  15  formed on the connection element  5  ( FIG. 1 ). As soon as the sealing cap  12  is displaced far enough over the connection element  5  so that the depressions  16  ( FIG. 1 ) in the sealing cap  12  align with the bulges  15  formed on the connection element  5  ( FIG. 1 ), the two segments  27 ,  28  will elastically snap back towards the central axis  2  ( FIG. 1 ), wherein the bulges  15  formed on the connection element  5  will engage the depressions  16  formed on the sealing cap  12 .  
         [0029]     The embodiment of the device according to the invention illustrated in  FIG. 3  and  FIG. 4  differs from the embodiment illustrated in  FIGS. 1 and 2  only in that the sealing cap  12  is provided with two slots  34  orthogonal to the second channel  17 , which are formed in the wall of the sealing cap  12 , the slots  34  extending from the front end  20  of the sealing cap  12 . The slots  34  divide the sealing cap  12  into four segments  27 ,  28 ,  32 ,  33  thereby increasing the elasticity of the sealing cap  12  so that the sealing cap  12  may be more easily axially displaced over the bulges  15  formed on the connection element  5  as compared to a sealing cap  12  having only two segments  27 ,  28  as described above.  
         [0030]     In use, the pre-assembled implant comprising the bone fixation means  1  and the connection element  5  may be removed from an implant carrying container by a screw driver which engages the means  29 , without any need for a further instrument for holding the implant and without a surgeon having to join the bone fixation means  1  and the connection element  5  together. Thereafter, the pre-assembled implant may be screwed into the prepared pedicle. After the longitudinal carrier  11  is inserted into the first channel  10  arranged in the connection element  5 , the same screwdriver may again be used to remove the pre-assembled sealing cap  12  provided with the tensioning means  13  from the implant carrying container, in which operation there is again no need for a special holding instrument. By means of a special clamp, the sealing cap  12  is locked into the first latch position, i.e., the first depression  16  formed in the sealing cap  12  is pushed over and aligned with the first bulge  15  formed on the connection element  5  so that the longitudinal carrier  11  inserted within the first channel  10  is prevented from escaping from the channel  10  formed in the connection element  5  but the longitudinal carrier  11  is free to longitudinally move with respect to the connection element  5  so that the bone and/or bone fragments attached to the bone fixation means  1  may be repositioned. After repositioning is completed, the sealing cap  12  is placed in the second or third latch position and locked. The tensioning means  13  is then tightened by means of the screwdriver so that the longitudinal carrier  11  inserted in the first channel  10  is pressed onto the screw head  30  of the bone fixation means  1 , which, in turn, clamps the head  30  in-between the shoulder  9  formed on the lower end  7  of the connection element  5  and the longitudinal carrier  11 , thus fixing the position of the bone fixation means  1  together with the longitudinal carrier  11  with respect to the connection element  5 .  
         [0031]      FIG. 5  illustrates an embodiment of the device according to the invention that differs from the embodiments described above only in that the screw head  30  of the bone fixation means  1  is secured against falling out of the cavity  8  by means of a securing means  35 . As shown, the securing means  35  comprises a pin  37  that is pressed, for example, in a hole  38  running transverse to the central axis  2  and which extends into the cavity  8 . The hole  38  is arranged axially between the rear end  41  of the screw head  30  of the bone fixation means  1  and the upper end  6  of the connection element  5 . Alternatively, the connection element  5  may include several holes  38  spread across the circumference of the connection element  5  for receiving several pins  37 .  
         [0032]      FIG. 6  shows an embodiment of the device according to the invention wherein the securing means  35  may be in the form of a snap ring  39 . The snap ring  39  is received within a groove  40  formed on the rear end  41  of the screw head  30  and which protrudes into the cavity  8 . The groove  40  is arranged axially in such a way that the snap ring  39  inserted therein does not extend beyond the rear end  41  of the screw head  30  towards the upper end  6  of the connection element  5 , which means that the longitudinal carrier  11  does not lie on the snap ring  39 . To achieve this, for example, the screw head  30  is designed with a reduced diameter portion at its rear end  41 . That is, the screw head  30  is provided at this rear end  41  with an axial segment  42  which has a diameter smaller than the screw head  30  thus forming a shoulder  43  for receiving the securing means  35  provided here in the form of a snap ring  39 . The reduced diameter portion  42  of the screw head  30  passes through the ring-shaped opening of the snap ring  39  and protrudes beyond the snap ring  39 , so that the longitudinal carrier  11  can rest on the rear end  41  of the screw head  30 . Therein, in use, the securing means  35  prevents the screw head  30  from axial movement towards the upper end  6  of the connection element  5 .

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