Abstract:
A device for connecting a longitudinal bar to a pedicle screw for fixation of the spine includes a body having an axis, an upper end, a lower end, a hole coaxial with the axis, and a through hole positioned perpendicular to the axis. The device also includes a collet chuck slidably disposed within the hole. The collet chuck includes a through hole substantially aligned with the through hole of the body for receiving the longitudinal bar. The collet chuck also includes a chamber defined by elastic tongues for receiving the head of the pedicle screw.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a division of U.S. patent application Ser. No. 10/122,405, filed Apr. 16, 2002, now U.S. Pat. No. ______, which is a continuation of U.S. patent application Ser. No. 09/341,963, now U.S. Pat. No. 6,371,957, which is a national stage of PCT International Application No. PCT/CH97/00019, filed Jan. 22, 1997, all of which are hereby incorporated by reference in their entireties. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention concerns a device for connecting a longitudinal bar to a pedicle screw.  
       BACKGROUND OF THE INVENTION  
       [0003]     From the related art, a large number of pedicle screws for fixation of the spinal column are already known; these known pedicle screws have the advantage that the individual pedicle screw can be attached to or removed from the longitudinal bar at any time without having to dismantle the entire fixation system. Such a pedicle screw is known from European Patent No. 330,881 B, for example.  
         [0004]     The disadvantage of this and similar pedicle screws is the relatively complicated locking mechanisms for securing the longitudinal bar inserted into the open pedicle screw head. Furthermore, in most cases the head of the screw can be aligned with the position of the longitudinal bar only to a limited extent, necessitating complicated bending of the longitudinal bar to correct the angle.  
       SUMMARY OF THE INVENTION  
       [0005]     The invention will provide a remedy in this regard and is based on the problem of creating a device for connecting a longitudinal bar to a pedicle screw, the device being easy to handle and permitting bending of the pedicle screw within a certain range.  
         [0006]     The invention relates to a spinal fixation system including a longitudinal member positionable along the spinal column, a fastener for engaging a vertebra, and a connector for connecting the fastener and the longitudinal member. One part of the connector is a body having a through hole for receiving the longitudinal member and an opening in the bottom surface leading to the interior of the body. Another part of the connector is a collet chuck configured and dimensioned to be slidably received in the interior of the body. The collet chuck has a through hole alignable with the body&#39;s through hole for insertion of the longitudinal member in the connector. The collet chuck also has a plurality of resilient tongues and a chamber defined by inner surfaces of the tongues. The chamber is configured and dimensioned to receive the fastener head. The tongues flex outward for receiving the fastener head in the chamber and flex back inward for retaining the fastener head in the chamber. The connector also includes a locking element for securing the longitudinal member in the body and collet chuck through holes. Engagement of the locking element causes inward movement of the tongue and thereby secures the fastener at a surgeon selected angle.  
         [0007]     In one embodiment, the desired number of devices according to the invention can be aligned on a longitudinal bar and can be simply snapped onto the pedicle screw with a spherical head already implanted in the vertebrae, so that a primary connection between the longitudinal bar and the pedicle screw is established. Other embodiments of the device according to the invention permit subsequent insertion of the longitudinal bar from the side or from above. By screwing the set screw into the fixation device, the longitudinal bar is locked axially and rotationally in the device at the same time, and the device is secured in a stable angular position. The set screw presses on the longitudinal bar inserted into the device, and the longitudinal bar presses on the bushing of the fixation device, and the bushing braces the collet chuck on the preferably spherical head of the pedicle screw by way of corresponding, preferably conical inside surfaces of the bushing and outside surfaces of the collet chuck.  
         [0008]     Other embodiments permit sequential and independent locking of the longitudinal bar and rotation of the device with respect to the pedicle screw.  
         [0009]     Thus, in comparison with known devices, the device according to the invention offers the advantage that the pedicle screws cannot only be secured exactly perpendicular to the longitudinal bar, but also permit an angle bend of up to ±25°. This is especially important when the longitudinal bar has not been bent accurately, which leads to major problems in assembly with traditional systems.  
         [0010]     A preferred refinement of the device according to the invention also includes a pedicle screw with a preferably spherical head. The head of the pedicle screw is preferably provided with structuring in the form of transverse grooves or transverse ribs to achieve better fixation (bracing against the collet chuck). To be able to screw these pedicle screws into the bone, they are preferably provided with a hexagon socket in the spherical head. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The detailed description will be better understood in conjunction with the accompanying drawings, in which like reference characters represent like elements, as follows:  
         [0012]      FIG. 1  is an exploded perspective view of the device with a longitudinal bar, a pedicle screw with a spherical head, and a set screw;  
         [0013]      FIG. 2  shows a slotted longitudinal section through the device as shown in the plane of  FIG. 1 ;  
         [0014]      FIG. 3  is a perspective view of the device of  FIG. 1  in the mounted state after locking the longitudinal bar and the pedicle screw by means of the set screw;  
         [0015]      FIG. 4  is an exploded perspective view of another embodiment of the device shown in  FIG. 1  with an adjusting nut and a divided bushing;  
         [0016]      FIG. 5  is an exploded perspective view of another embodiment of the device shown in  FIG. 4  with a channel on the collet chuck that is open at the top and with a securing pin;  
         [0017]      FIG. 6  is an exploded perspective view of another embodiment of the device shown in  FIG. 1  with an adjusting nut for securing the spherical head of the pedicle screw and a set screw for locking the longitudinal bar;  
         [0018]      FIG. 7  shows a longitudinal section through another embodiment of the device illustrated in  FIG. 6  with a set screw integrated into a locking screw;  
         [0019]      FIG. 8  is an exploded perspective view of another embodiment of the device shown in  FIG. 5  with a collet chuck that is open at the side to accommodate the longitudinal bar and an adjusting nut as a chucking means for locking the longitudinal bar while at the same time securing the spherical head of the pedicle screw;  
         [0020]      FIG. 9  is an exploded perspective view of the device shown in  FIG. 5  without a securing pin;  
         [0021]      FIG. 10  is an exploded perspective view of another embodiment of the device shown in  FIG. 5  with a set screw and an inside thread in the collet chuck;  
         [0022]      FIG. 11  is an exploded perspective view of another embodiment of the device shown in  FIG. 8  with an adjusting nut for securing the spherical head of the pedicle screw and with a set screw for locking the longitudinal bar;  
         [0023]      FIG. 12  is an exploded perspective view of another embodiment of the device shown in  FIG. 11  with a collet chuck that is open at the top;  
         [0024]      FIG. 13  is an exploded perspective view of another embodiment of the device shown in  FIG. 11  with a through hole in the bushing which is open at the side; and  
         [0025]      FIG. 14  is an exploded perspective view of another embodiment of the device shown in  FIG. 12  with a through hole in the bushing which is open at the top.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     The device according to the invention illustrated in  FIGS. 1 and 2  generally includes a body  3  in the form of a hollow cylindrical bushing with an axis  4  (axis of the hollow cylinder) and a hollow cylindrical collet chuck  7  arranged coaxially so it can slide in the interior of body  3 .  
         [0027]     Body  3  has a through hole  6  running across axis  4  that intersects the cylindrical surface of the hollow cylinder at two points symmetrically with axis  4 . Collet chuck  7  also has a through hole  17  running across axis  4 . Insertion of a longitudinal bar  1  running across axis  4  is made possible by the aligned arrangement of through holes  6  and  17  as illustrated in  FIG. 2 .  
         [0028]     In its upper part, collet chuck  7  is secured within (hollow cylindrical) body  3  by a press fit and can be displaced axially with respect to body  3  when the relatively high force of the press fit is overcome.  
         [0029]     Hollow cylindrical body  3  and collet chuck  7  are preferably in a rotationally locked arrangement relative to one another, e.g., by means of suitable groove/channel guides running axially. Collet chuck  7  is designed with tongues  8  that are spring mounted against cylinder axis  4  and point downward. The spherical head  9  of a pedicle screw  2  can be snapped from below with a spring action into the chamber formed by these tongues.  
         [0030]     A hole  10  with an inside thread  11  is provided in the upper part of collet chuck  7  to accommodate a set screw  12  with a hexagonal socket head  20  which can exert a force on a longitudinal bar  1  inserted into the device, so the longitudinal bar  1  is locked axially and rotationally with respect to body  3 , as indicated in  FIG. 3 . Collet chuck  7  is designed at its lower end such that screw shaft  13  of pedicle screw  2  connected to spherical head  9  can be locked at an angle α of −25° to +25° with respect to axis  4 .  
         [0031]     At its lower end  24 , body  3  has a conical inside surface  14  which becomes wider toward the lower end and can come into sliding contact with a suitably designed conical outside surface  18  of the free ends of tongues  8  of collet chuck  7 . As soon as set screw  12  abuts against longitudinal bar  1  inserted into the device, collet chuck  7  begins to push upward against body  3 . This process is illustrated in  FIG. 2 , where the left half of the FIG. shows the condition before pushing collet chuck  7  upward, and the right half shows the conical surfaces  14  and  18  slipping past one another as collet chuck  7  is pushed upward with tongues  8 . Tongues  8  are designed with a spring action due to slot  22  being pushed toward cylinder axis  4  such that hollow spherical cavity  19  is reduced in size and head  9  of pedicle screw  2  inserted into it is gripped securely. To optimize the locking of head  9 , it is provided with a structuring  15 , preferably in the form of transverse grooves or transverse ribs. Otherwise, pedicle screw  2  corresponds to known screw designs and is expediently provided with a hexagonal socket head  16 .  
         [0032]     Hollow spherical cavity  19  may in turn be provided with a structuring  21 , preferably in the form of transverse grooves or transverse ribs. A combination of structuring  21  and structuring  15  is possible to further improve the fixation effect of head  9  in hollow spherical cavity  19 .  
         [0033]     Hollow spherical cavity  19  is preferably designed with a shape complementary to that of head  9  of pedicle screw  2  so the head can be accommodated in the cavity.  
         [0034]     The embodiment of the device shown in  FIG. 4  illustrates the use of a body  3 , which is divided into a bottom part  52  and a top part  53  across axis  4  in the middle of through hole  6 , in combination with an adjusting nut  26 . The bottom part  52  of body  3  should be tall enough that longitudinal bar  1  is always in contact with bottom part  52 .  
         [0035]     Collet chuck  71  differs from collet chuck  7  shown in  FIG. 1  only in that the inside thread  11  on the upper end has been replaced by an outside thread  27  for use by an adjusting nut  26 . When tightened, adjusting nut  26  presses on top part  53  of body  3 , which subsequently presses directly on longitudinal bar  1 . Longitudinal bar  1  is subsequently pressed against bottom part  52  of body  3 , and then locks spherical head  9 , as shown in  FIG. 2 .  
         [0036]     The embodiment of the device shown in  FIG. 5  differs from the embodiment illustrated in  FIG. 9  only in that a peg  55  prevents collet chuck  72 , which has been weakened by channel  54 , from collapsing when adjusting nut  26  is tightened. To prevent this peg  55  from falling out, it is advantageously provided with an outside thread and screwed in.  
         [0037]     The embodiment of the device shown in  FIG. 6  differs from the embodiment illustrated in  FIG. 4  only in that:  
         [0038]     a) collet chuck  73  has an inside thread  11  in addition to outside thread  27 , and  
         [0039]     b) body  3  (which is one piece) and through hole  6  are positioned with respect to through hole  17  so that only spherical head  9  is locked when adjusting nut  26  is tightened. This permits distraction or compression with a stable angular position. Adjusting nut  26  presses on body  3 , and the resulting bracing of body  3  with collet chuck  73  ensures fixation of spherical head  9  of pedicle screw  2  without locking longitudinal bar  1 . Longitudinal bar  1  is pressed separately with the help of set screw  12  against the lower edge of through hole  6  of body  3 . Therefore, body  3  is further wedged with collet chuck  73 , which leads to a greater clamping effect on spherical head  9 . Through hole  6  should be positioned in body  3  so that longitudinal bar  1  also rests on the lower edge of through hole  6  after tightening adjusting nut  26 .  
         [0040]     The embodiment of the device illustrated in  FIG. 7  differs from the device illustrated in  FIGS. 1-3  only in the design of locking screw  91  and the positioning of through hole  6  with respect to through hole  17 . Collet chuck  7  is provided with an inside thread  11 . A locking screw  91 , which is screwed into inside thread  11 , and a set screw  12 , which is integrated into locking screw  91 , serve to lock spherical head  9  and longitudinal bar  1 . Body  3 , which is designed in one piece by analogy with  FIGS. 1-3 , is provided with a turning  94  at the top, accommodating the shoulder  93  of locking screw  91 . Through hole  6  is positioned in body  3  with respect to through hole  17  in collet chuck  7  in such a way that only spherical head  9  is locked when locking screw  91  is tightened. Longitudinal bar  1  is secured afterwards by means of set screw  12 . As long as this set screw  12  is screwed completely into locking screw  91 , and locking screw  91  has been screwed back to the extent that longitudinal bar  1  touches the lower edge of through hole  6  in body  3 , spherical head  9  can be secured or removed. Furthermore, collet chuck  7  is released again from the tightened state when locking screw  91  is screwed back. To accommodate longitudinal bar  1 , collet chuck  7  may be provided with a through hole  17  according to  FIG. 4 , with a channel  54  that is open at the top according to  FIG. 9 , or with a channel  42  which is open at the side according to  FIG. 8 . In these latter two cases, either a two-piece design of body  3  or a design according to  FIGS. 11 and 12  is advantageous to facilitate insertion of the longitudinal bar. However, with the two-piece design, the two parts of body  3  must be designed so that top part  53  presses directly on bottom part  52  and not on longitudinal bar  1  even after bracing.  
         [0041]     The embodiment of the device shown in  FIG. 8  differs from the embodiment illustrated in  FIG. 4  only in that, in contrast with collet chuck  71 , collet chuck  74  has a channel  42  that is open at the side instead of having a through hole  17  to accommodate longitudinal bar  1 , but slot  22  does not extend into this open channel.  
         [0042]     The embodiment of the device shown in  FIG. 9  differs from the embodiment illustrated in  FIG. 4  only in that, in contrast with collet chuck  71 , collet chuck  72  has a channel  54  that is open at the top instead of having a through hole  17  to accommodate longitudinal bar  1 , and slot  22  does not extend into this open channel. To prevent collet chuck  72  from collapsing when adjusting nut  26  is tightened, the thread should be designed so that negligible radial forces occur in tightening. A sawtooth thread, for example, would meet this requirement.  
         [0043]     The embodiment of the device shown in  FIG. 10  illustrates the use of a collet chuck  75 , which is provided with an inside thread  11  instead of an outside thread  27 , in contrast with collet chuck  72  illustrated in  FIGS. 5 and 9 . A set screw  56  with an outside thread  57  and a flange  58  serves as the clamping means. When tightened, set screw  56  presses against longitudinal bar  1 , which in turn presses on bottom part  52  of body  3 . This bracing of bottom part  52  and collet chuck  75  locks spherical head  9  of pedicle screw  2 , as illustrated in  FIG. 2 . Top part  53  of body  3  prevents widening of collet chuck  75  when set screw  56  is tightened. Top part  53  rests on shoulder  63 .  
         [0044]     The embodiment of the device shown in  FIG. 11  differs from the embodiment illustrated in  FIG. 6  only in that collet chuck  76 , in contrast with collet chuck  73 , has a channel  42  that is open at the side instead of having a through hole  17 , and slots  22  do not extend into the channel.  
         [0045]     According to  FIG. 13 , through hole  6  in body  3  is preferably open at side  80  to permit unhindered insertion of longitudinal bar  1 .  
         [0046]     The embodiment of the device shown in  FIG. 12  differs from the embodiment illustrated in  FIG. 11  only in that, in contrast with collet chuck  76 , collet chuck  77  has a channel  54  that is open at the top to accommodate longitudinal bar  1 . According to  FIG. 14 , through hole  6  in body  3  is open toward top  81  for unhindered insertion of longitudinal bar  1 .  
         [0047]     The embodiment of the device shown in  FIG. 13  differs from the embodiment illustrated in  FIG. 11  only in that a through hole  80  which is open at the side is provided in body  3 .  
         [0048]     The embodiment of the device shown in  FIG. 14  differs from the embodiment illustrated in  FIG. 12  only in that a through hole  81  which is open at the top is provided in body  3 .