Abstract:
The invention is directed to a device for connecting a longitudinal bar to a pedicle screw for fixation of the spine. The device 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 coller chuck slidably disposed within the hole. The coller chuck includes a through hole substantially aligned with the through hole of the body for receiving the longitudinal bar, and a chamber defined by elastic tongues for receiving the head of the pedicle screw.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 09/341,963, now U.S. Pat. No. 6,371,957, filed Jul. 21, 1999, which is a continuation of PCT International Application No. PCT/CH97/00019, filed Jan. 22, 1997. 
    
    
     FIELD OF THE INVENTION 
     This invention concerns a device for connecting a longitudinal bar to a pedicle screw. 
     BACKGROUND OF THE INVENTION 
     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. 
     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 
     This invention will provide a remedy in this regard. This invention is based on the problem of creating a device for connecting a longitudinal bar to a pedicle screw, said device being easy to handle and permitting bending of the pedicle screw within a certain range. 
     The present 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, a plurality of resilient tongues, and a chamber defined by inner surfaces of the tongues and 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 results in inward movement of the tongue and thereby secures the fastener at a surgeon selected angle. 
     In one embodiment, the desired number of devices according to this 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 this 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. 
     Other embodiments in turn permit sequential and independent locking of the longitudinal bar and rotation of the device with respect to the pedicle screw. 
     Thus, in comparison with known devices, the device according to this invention offers the advantage that the pedicle screws can not only be secured exactly perpendicular to the longitudinal bar but also permit an angle bend of up to ±25°. This is especially important if the longitudinal bar has not been bent accurately, which leads to major problems in assembly with traditional systems. 
     A preferred refinement of the device according to this invention consists of the fact that it 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 
       The figures show: 
         FIG. 1 : an exploded perspective view of the device according to this invention with a longitudinal bar, a pedicle screw with a spherical head and a set screw; 
         FIG. 2 : a slotted longitudinal section through the device according to this invention as shown in the plane of the drawing in  FIG. 1 ; 
         FIG. 3 : a perspective view of the device according to  FIG. 1  in the mounted state after locking the longitudinal bar and the pedicle screw by means of the set screw; 
         FIG. 4 : a perspective view of one variant of the device shown in  FIG. 1  with an adjusting nut and a divided bushing; 
         FIG. 5 : a perspective view of one variant 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; 
         FIG. 6 : a perspective view of one variant 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; 
         FIG. 7 : a longitudinal section through one variant of the device illustrated in  FIG. 6  with a set screw integrated into a locking screw; 
         FIG. 8 : a perspective view of one variant 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; 
         FIG. 9 : a perspective view of the device shown in  FIG. 5  without a securing pin; 
         FIG. 10 : a perspective view of one variant of the device shown in  FIG. 5  with a set screw and an inside thread in the collet chuck; 
         FIG. 11 : a perspective view of one variant 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; 
         FIG. 12 : a perspective view of one variant of the device shown in  FIG. 11  with a collet chuck that is open at the top; 
         FIG. 13 : a perspective view of one variant of the device shown in  FIG. 11  with a through hole which is open at the side in the bushing; and 
         FIG. 14 : a perspective view of one variant of the device shown in  FIG. 12  with a through hole which is open at the top in the bushing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The device according to this invention illustrated in  FIGS. 1 and 2  consists essentially of 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 the body  3 . 
     The body  3  has a through hole  6  running across the axis  4 —intersecting the cylindrical surface of the hollow cylinder at two points symmetrically with the axis  4 —and the collet chuck  7  has a through hole  17  running across the axis  4 . Insertion of a longitudinal bar  1  running across the axis  4  is made possibly by the aligned arrangement of the through holes  6  and  17  as illustrated in  FIG. 2 . 
     In its upper part, the collet chuck  7  is secured within the (hollow cylindrical) body  3  by a press fit and can be displaced axially with respect to the body  3  when the relatively high force of the press fit is overcome. 
     The (hollow cylindrical) body  3  and the 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. The collet chuck  7  is designed with tongues  8  spring mounted against the cylinder axis  4  and pointing 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. 
     A hole  10  with an inside thread  11  is provided in the upper part of the 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 the body  3 , as indicated in  FIG. 3 . The collet chuck  7  is designed at its lower end such that the screw shaft  13  of the pedicle screw  2  connected to the spherical head  9  can be locked at an angle α of −25° to +25° with respect to the axis  4 . 
     At its lower end  24 , the 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 the tongues  8  of the collet chuck  7 . As soon as the set screw  12  abuts against the longitudinal bar  1  inserted into the device, the collet chuck  7  begins to push upward against the body  3 . This process is illustrated in  FIG. 2 , where the left half of the figure 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 the collet chuck  7  is pushed upward, with the tongues  8  of the collet chuck  7 , which are designed with a spring action due to the slot  22  being pushed toward cylinder axis  4 , so that the hollow spherical cavity  19  is reduced in size, and the head  9  of the pedicle screw  2  inserted into it is gripped securely. To optimize the locking of the 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 the known screw designs and is expediently provided with a hexagonal socket head  16 . 
     The 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 the head  9  in the hollow spherical cavity  19 . 
     The hollow spherical cavity  19  is preferably designed with a shape complementary to that of the head  9  of the pedicle screw  2  to be accommodated in it. 
     The variant shown in  FIG. 4  of the device according to this invention illustrates the use of a body  3 , which is divided into a bottom part  52  and a top part  53  across the axis  4  in the middle of the through hole  6 , in combination with an adjusting nut  26 . The bottom part  52  of the body  3  must be so tall that the longitudinal bar  1  is always in contact with the bottom part  52 . 
     The collet chuck  71  differs from the 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 of an adjusting nut  26 . When tightened, the adjusting nut  26  presses on the top part  53  of body  3 , which subsequently presses directly on longitudinal bar  1 . The longitudinal bar  1  is subsequently pressed against the bottom part  52  of the body  3 , and then it locks the spherical head  9 , as shown in  FIG. 2 . 
     The variant shown in  FIG. 5  of the device according to this invention differs from the variant illustrated in  FIG. 9  only in that one peg  55  prevents the collet chuck  72 , which has been weakened by the channel  54 , from collapsing when the adjusting nut  26  is tightened. To prevent this peg  55  from falling out, it is advantageously provided with an outside thread and screwed in. 
     The variant shown in  FIG. 6  of the device according to this invention differs from the variant illustrated in  FIG. 4  only in that
     a) the collet chuck  73  has an inside thread  11  in addition to outside thread  27 , and   b) the body  3 , which is in one piece, and the through hole  6  are positioned with respect to the through hole  17  so that only the spherical head  9  is locked when the adjusting nut  26  is tightened. This permits distraction or compression with a stable angular position. The adjusting nut  26  presses on the body  3 , and the resulting bracing of the body  3  with the collet chuck  73  ensures fixation of the spherical head  9  of the pedicle screw  2  without locking the longitudinal bar  1 . The longitudinal bar  1  is pressed separately with the help of the set screw  12  against the lower edge of the through hole  6  of the body  3 . Therefore, the body  3  is further wedged with the collet chuck  73 , which leads to a greater clamping effect on the spherical head  9 . The through hole  6  must be positioned in the body  3  so that the longitudinal bar  1  also rests on the lower edge of the through hole  6  after tightening the adjusting nut  26 .   

     The variant illustrated in  FIG. 7  of the device according to this invention differs from the device illustrated in  FIGS. 1 through 3  only in the design of the locking screw  91  and the positioning of the through hole  6  with respect to the through hole  17 . The collet chuck  7  is provided with an inside thread  11 . A locking screw  91  which is screwed into the inside thread  11  and a set screw  12  which is integrated into the locking screw  91  serve to lock the spherical head  9  and the longitudinal bar  1 . The body  3 , which is designed in one piece by analogy with  FIGS. 1 through 3 , is provided with a turning  94  at the top, accommodating the shoulder  93  of the locking screw  91 . The through hole  6  is positioned in body  3  with respect to the through hole  17  in the collet chuck  7  in such a way that only spherical head  9  is locked when locking screw  91  is tightened. The longitudinal bar  1  is secured afterwards by means of the set screw  12 . As long as this set screw  12  is screwed completely into the locking screw  91 , and the locking screw  91  has been screwed back to the extent that the longitudinal bar  1  touches the lower edge of the through hole  6  in the body  3 , the spherical head  9  can be secured or removed. Furthermore, the collet chuck  7  is released again from the tightened state when the locking screw  91  is screwed back. To accommodate the longitudinal bar  1 , the collet chuck  7  may be provided with a through hole  17  according to  FIG. 4 , with a channel  54  which is open at the top according to  FIG. 9 , or with a channel  42  according to  FIG. 8  which is open at the side. In these 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 the body  3  must be designed so that the top part  53  presses directly on the bottom part  52  and not on the longitudinal bar  1  even after bracing. 
     The variant shown in  FIG. 8  of the device according to this invention differs from the variant illustrated in  FIG. 4  only in that, in contrast with the collet chuck  71 , the collet chuck  74  has a channel  42  that is open at the side instead of having a through hole  17  to accommodate the longitudinal bar  1 , but the slot  22  does not extend into this open channel. 
     The variant shown in  FIG. 9  of the device according to this invention differs from the variant illustrated in  FIG. 4  only in that, in contrast with the collet chuck  71 , the collet chuck  72  has a channel  54  that is open at the top instead of a through hole  17  to accommodate the longitudinal bar  1 , and the slot  22  does not extend into this open channel. To prevent the collet chuck  72  from collapsing when the adjusting nut  26  is tightened, the thread must be designed so that negligible radial forces occur in tightening. A sawtooth thread, for example, would meet this requirement. 
     The variant shown in  FIG. 10  of the device according to this invention 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 the 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, the set screw  56  presses against the longitudinal bar  1 , which presses in turn on the bottom part  52  of the body  3 . This bracing of the bottom part  52  and the collet chuck  75  locks the spherical head  9  of the pedicle screw  2 , as illustrated in  FIG. 2 . The top part  53  of the body  3  prevents widening of the collet chuck  75  when the set screw  56  is tightened. The top part  53  rests on the shoulder  63 . 
     The variant shown in  FIG. 11  of the device according to this invention differs from the variant illustrated in  FIG. 6  only in that the collet chuck  76 , in contrast with the collet chuck  73 , has a channel  42  that is open at the side instead of a through hole  17 , and the slots  22  do not extend into the channel. 
     According to  FIG. 13 , the through hole  6  in the body  3  is preferably open at the side ( 80 ) to permit unhindered insertion of longitudinal bar  1 . 
     The variant shown in  FIG. 12  of the device according to this invention differs from the variant illustrated in  FIG. 11  only in that, in contrast with the collet chuck  76 , the collet chuck  77  has a channel  54  that is open at the top to accommodate the longitudinal bar  1 . According to  FIG. 14 , the through hole  6  in the body  3  is open toward the top ( 81 ) for unhindered insertion of the longitudinal bar  1 . 
     The variant shown in  FIG. 13  of the device according to this invention differs from the variant illustrated in  FIG. 11  only in that a through hole  80  which is open at the side is provided in the body  3 . 
     The variant shown in  FIG. 14  of the device according to this invention differs from the variant illustrated in  FIG. 12  only in that a through hole  81  which is open at the top is provided in the body  3 .