Abstract:
An apparatus for bracing a plurality of vertebrae of the human spine has at least two pedicle screws, each having an annular head with an opening therewithin and including a slot therewithin. Each slot extends into the corresponding opening and includes internal threaded portions. A securing screw to be screwed in each slot is provided. A relatively stiff threaded rod is also provided and is to be inserted into the opening in the head of each of the pedicle screws and to be secured by the securing screws. Adjusting nuts are screwed on the rod and at least one cooperates with each head.

Description:
[0001]    The present invention relates to an apparatus for bracing a plurality of vertebrae of the human spine.  
           [0002]    Known supporting means operate with so-called lamina hooks which are disposed on a threaded rod. A compressing means is disclosed in British patent 2 131 300. A distracting means is disclosed in U.S. Pat. No. 4,383,438. The threaded rod bridges a plurality of vertebras and is not suited to act on vertebras which are disposed between the lamina hooks. The thread of the rod is used to fix the lamina hooks. Before using the supporting means a distraction or, respectively, compression has to be provided by means of an additional device.  
           [0003]    German 90 06 646 U1 discloses an apparatus in which a lamina hook is replaced by a clamp-shaped holding member having a pair of legs of which one can be bent with respect to the other. Thereby the giapophysis of the vertebras may be used as anchoring points for the compressing and distracting apparatus.  
           [0004]    German 88 02 112 U1 teaches a supporting device for the human spine, according to which the so-called pedicel screws are screwed in the pedicel body of the vertebras. The pedicle screws cooperate with tensioning means which bridge across one or more vertebrae to introduce forces between the vertebrae. The known device affords a primary stabilization of the vertebrae with respect to all degrees of freedom. However, when a number of vertebrae of a non-traumatic spine for example, are to be repositioned, separate means necessary to perform the reposition before the known supporting device may be effectively used.  
           [0005]    WO 91/01691 discloses an apparatus for bracing vertebras of the human spine, comprising pedicle screws having slotted heads to receive a rod. The legs of the slotted screw heads include an outer thread on which a nut is screwed which contacts the rod to fix a predetermined position.  
           [0006]    EP 0 443 892 discloses a similar device comprising a pedicle screw, the slotted head thereof including internal threaded portions for receiving a fixing screw which is brought into engagement with a serrated or similarly roughened rod to fix the relative position of the rod and the individual pedicel screw. A ring disposed around the head of a pedicle screw is provided so that the legs of the screw head do not spread apart while fixing the rod, as otherwise the engagement between the fixing screw and the screw head may be lost. A similar apparatus is disclosed in WO 90/09156.  
           [0007]    Again, the devices last mentioned require separate means for repositioning, thus being suited to maintain a repositioned condition, but not suited to perform repositioning.  
           [0008]    It is an object of the present invention to provide an apparatus which is suited to reposition the vertebrae of the human spine as well as to support the vertebrae in the repositioned position thereafter.  
           [0009]    The objects are solved by the apparatus of the invention.  
         SUMMARY OF THE INVENTION  
         [0010]    According to the invention, the apparatus uses a threaded rod (i.e., a distracting rod) in combination with lamina hooks. The thread of the rod, however, is not only used to fix the pedicle screws, but further is used to reposition the vertebrae in that an adjusting nut sitting on the threaded rod is turned with respect to the head of the pedicle screw and thus the vertebra has obtained the desired position. By means of the apparatus according to the invention a spine portion is not only distracted or compressed, but individual vertebrae can be effectively positioned with respect to each other. To this end the threaded rod is designed to be relatively stiff and has a diameter between 7 to 8 mm, for example. On the other hand the rod must be bent to be implanted close to the spine along a bent spine portion. This is facilitated by the design of the pedicle screw heads having slots for receiving the threaded rod. To hold the rod in the slot, a securing screw is provided. Whereas the screw in the pedicle screw head according to EP 0 443 892, for example, axially fixes the rod, the securing screw of the present invention is merely used to prevent a deflection of the rod out of the receiving slot.  
           [0011]    After resetting, the adjusting nut must be fixed on the threaded rod. This can be obtained by means of a suitable counter-nut. Still further, it is possible, to provide the adjusting nut and the front faces of the pedicle screw head with a rotary safety means in form of a toothing or another irregularity cooperating in a clamping fashion. In both cases the nuts are merely fixed by a frictional force. According to a further embodiment of the invention, however, the head of the pedicle screw has a width smaller than the diameter of the securing screw, whereas at least one front face of the adjusting nut has a recess cooperating with the securing screw. Preferably, the adjusting nut includes a plurality of peripherally spaced indentations, wherein the final rotary position of the nut is such that the securing screw cooperates with the indentation. This affords a positive locking of the adjusting nut resulting in a precise rotary locking which cannot be loosened.  
           [0012]    The pedicel screws must take up relatively large forces. There is the danger that a pedicel screw breaks out of the bone, primarily when the available bony substance does not provide a sufficiently rigid seat in the vertebra. According to an embodiment of the invention, a mounting strap is attached to the shaft of the pedicel screw laterally extending therefrom, which strap includes an opening for receiving a spongiose screw. The strap has, for example, a pair of openings, wherein one opening receives the shaft of the pedicel screw, while the other opening disposed at the other end of the strap, for example, receives a spongiose screw which is screwed into the vertebra. In this manner, the pedicel screw is laterally stabilized and can receive sub-stantial forces. According to an alternate embodiment of the invention, a mounting strap may be provided to the shaft of the pedicel screw extending therefrom, which strap has a blade or the like to be mounted in the vertebra. The blade is preferably integral with the strap. The blade is beaten into the vertebra wherein the strap may additionally include a hole for receiving a spongiose screw which is screwed into the vertebra. In some cases, a vertebra is displaced with respect to the adjacent vertebra. When the pedicel screw is completely screwed in, it cannot be connected any more with the threaded rod. To accomplish a connection, the pedicel screw is partly screwed into the vertebra bone. According to an embodiment of the invention, the head of the pedicle screw is then rotatably mounted on the screw shaft so that by rotating the shaft the vertebra can be pulled up to the threaded rod for resetting. Preferably the shaft includes tool engaging faces adjacent the head to rotate the shaft of the screw in the desired manner.  
           [0013]    In case of very specially displaced individual vertebrae, not even the features referred to above are suffient. According to a further embodiment of the invention, the upper end of the pedicle screw shaft is ball-shaped, while the pedicel screw head is defined by a ball-engaging cage including a slot for the rod. The cage can be arbitrarily positioned with respect to the shaft of the screw, but can exert a tensioning force to the screw shaft when being screwed in the vertebra. According to both embodiments just referred to, the threaded rod is inserted through a slot of the pedicel screw head, wherein a securing screw referred to several times prevents the rod from sliding out of the slot. Alternatively a closed passage may be provided in the head of the pedicle screw as it is known per se.  
           [0014]    Instead of or in addition to the pedicle screw the apparatus of the present invention provides a hook cooperating with a lamina of a vertebra. Those lamina hooks are generally known. According to the invention, however, the lamina hook is provided with a slotted receiving portion to insert the threaded rod. The slot has threaded portions again to secure the rod in the receiving slot.  
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawing.  
         [0016]    [0016]FIG. 1 schematically shows an apparatus according to the invention to be used as a distracting system,  
         [0017]    [0017]FIG. 2 schematically shows an apparatus according to the invention used as a compressing system,  
         [0018]    [0018]FIG. 3 shows a pedicel screw for the apparatuses according to FIGS. 1 and 2,  
         [0019]    [0019]FIG. 4 shows the pedicel screw of FIG. 3 cooperating with a threaded rod,  
         [0020]    [0020]FIG. 5 schematically shows a side view of a further embodiment of a pedicel screw for the apparatuses of FIGS. 1 and 2,  
         [0021]    [0021]FIG. 6 shows a side view of the pedicel screw of FIG. 5 rotated about 90°,  
         [0022]    [0022]FIG. 7 shows a plain view of the pedicel screw of FIG. 5,  
         [0023]    [0023]FIG. 8 shows a side view of an adjusting nut of the apparatus of FIGS. 1 and 2,  
         [0024]    [0024]FIG. 9 shows a stabilizing strap for the apparatus of FIGS. 1 and 2,  
         [0025]    [0025]FIG. 10 shows a further embodiment of a stabilizing strap of the apparatus of FIGS. 1 and 2,  
         [0026]    [0026]FIG. 11 shows a section of a lamina hook for the apparatus of FIGS. 1 and 2,  
         [0027]    [0027]FIG. 12 shows a plain view of the hook of FIG. 11,  
         [0028]    [0028]FIG. 13 shows a side view of a further embodiment of a pedicle screw for an apparatus according to the invention,  
         [0029]    [0029]FIG. 14 shows a side view of the pedicle screw of FIG. 13 turned about 90°,  
         [0030]    [0030]FIG. 15 shows a side view partly in section of a further embodiment of a pedicle screw for an apparatus according to the invention and  
         [0031]    [0031]FIG. 16 shows a side view of the pedicle screw of FIG. 15 turned around 90°.  
     
    
       [0032]    [0032]FIG. 1 shows a bent spine portion  10  wherein the individual vertebras shall be distracted by means of a distracting system  12 . The system comprises a relatively stiff threaded rod  14  having a diameter of 6 to 9 mm, preferably 7 to 8 mm. It cooperates with an individual pedicel screw  16  screwed in the vertebras. Details of the screws are shown in the following figures. The threaded rod  14  is received in slots of the pedicel screw heads  16  and a plurality of adjusting nuts  18  is disposed on the rod  14 , at least one nut each for a pedicel screw  16 . Stabilizing latches  20  cooperate with the pedicel screws, which latches include a hole  22  in a distance from the pedicle screw to receive a spongise screw screwed in the vertebra. By means of the adjusting nut  18  a pedicel screw screwed in the vertebra may be displaced relative to the rod  14  and thus with respect to the vertebra receiving the screw. By means of the adjusting nuts  18  the vertebrae of the portion  10  may be thus adjusted to accomplish a distraction.  
         [0033]    The spine portion  30  shown in FIG. 2 comprises a compressing means including components identical with those shown in the system  12  so that identical components carry identical reference numerals. To reduce the bending of the spine portion  30  a tension force must be exerted on the vertebras to straighten the bent threaded rod  14 . This is accomplished by adjusting the individual pedic screws  16  as described in FIG. 1. In the following the components of the system referred to are described in more detail.  
         [0034]    [0034]FIG. 3 shows a pedicel screw  16   a  having a shaft  32  and an annular head  34 . The head  34  includes a slot  36  in which the rod  14  is inserted. A securing screw  38   a  cooperating with threaded portions in the slot  36  holds the threaded rod  14  in the slot  36 . FIG. 4 shows adjusting nuts  18   a  located on either side of the head  34  to displace the screw  16   a  along the rod  14 .  
         [0035]    In the embodiment of FIGS. 5 and 6 the pedicel screw  16   b  has a relatively narrow head  34   b  so that the securing screw  38   b  laterally projects. This is shown by the dashed line in FIG. 7. when an adjusting nut  40  according to FIG. 8 is used, which nut is provided with indentations  42  on the opposite front faces thereof, the nut  40  can be secured to the rod  14  when an indentation  42  of the screw  38   b  cooperates with the adjusting nut  38   b.    
         [0036]    [0036]FIG. 9 shows a mounting strap. The plate-shaped strap  20  includes a first hole  44  receiving the shaft of a pedidel screw. A second hole  22  receives a spongiose screw as mentioned before.  
         [0037]    [0037]FIG. 10 shows an alternate embodiment  20   a  of a stabilizing latch, again comprising a hole  44   a  for a pedicle screw and a hole  22   a  located substantially in the center for receiving a spongiose screw. FIG. 10 further shows a blade  46  integrally shaped on the end opposite the hole  44   a  which blade is driven home in the vertebra.  
         [0038]    [0038]FIGS. 11 and 12 show a lamina hook  50  comprising a hook portion  52  and a receiving portion  54  including a slot  56 . The slot  56  receives a threaded rod such as the rod  14  shown in FIGS. 1 and 2. Threaded portions as indicated at  58  in FIG. 11 are provided inside the slot  56  to receive a securing screw not shown to hold the rod in the slot  56 . The position of the rod in the slot  56  is determined by the position of the securing screw not shown, wherein a relative position between the hook  50  and the rod is possible to a limited extent.  
         [0039]    [0039]FIGS. 13 and 14 show a pedicel screw  16   c  comprising a shaft  32   c  and an annularly closed head  34   b  through which a rod  14  extends. A fixing screw  60  in the head  34   b  is used to fix the threaded rod  14 . However, adjusting nuts may be used as mentioned before. According to the embodiment of FIGS. 13, 14 the shaft  32   c  is rotatably mounted in the head  34   b.  Accordingly, a circular blind bore  62  holds a ring  64  cooperating with an annular groove  66  in the shaft  32 . Tool faces  68  facilitate a rotation of the shaft  32   c  relative to the head  34   c  when it fixedly sits on the rod  14  for example. It should be understood that the head  34   c  may provide a slot as shown in FIGS.  3  to  7  for example.  
         [0040]    In the embodiment of FIGS. 15 and 16 a pedicel screw  16   d  is provided comprising a shaft  32   d  which upper end is formed as a ball  50 . A cage  72  cooperates with the ball, the cage further having a passage  74  to receive a threaded rod  14 . Furthermore, the cage  72  has threaded portions to receive a securing screw  38   c.  This allows to rotate the shaft  32 , wherein tool faces  68   d  are provided. Furthermore, the shaft  32   d  may be pivoted relative to the cage  72  in a limited angle.