Abstract:
Spinal implant comprising a quick closure ( 4 ) for securing a connecting element ( 2 ) in a bone screw ( 1 ) where the quick closure ( 4 ) is rotatively attachable in the clockwise or counterclockwise direction and lockable such as to be able to take up torques applied to the bone screw ( 1 ) while preserving the bone anchorage from manipulative stress.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a 35 U.S.C. §371 National Phase conversion of PCT/CH2010/000169, filed Jul. 1, 2010, which claims benefit of Swiss Application No. 1114/09, filed Jul. 16, 2009, the disclosure of which is incorporated herein by reference. The PCT International Application was published in the English language. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a spinal implant set including a quick closure device according to the preamble of claim  1 . 
     Such closure devices are typically used in the surgical treatment of the spine. As the patients are increasingly aged, they have more often porotic bones, thereby limiting the anchoring ability of screws. It is therefore particularly important that connecting elements can be fastened in screw heads with minimum stress, ideally in such a manner that the screw anchorage in the bone remains unaffected. 
     Various quick closures are known in the art, all of which suffer from one or several drawbacks, however, as shown below. 
     For their comparative assessment, quick closures of the prior art are classified as follows: Internally or externally slidingly attachable quick closures, internally or externally rotatively attachable quick closures, as well as internal and external bayonet-like quick closures. Also, a vertically snapping quick closure is referenced in the prior art. 
     Among the internally slidingly attachable quick closures, the following ones are e.g. known in the art: EP0672388 (Metz-Stavenhagen et al., 1995), slidingly insertable with an end stop in the insertion direction; U.S. Pat. No. 6,110,172 (Jackson, 1998), insertable from two directions with an end stop in both directions after raising the cap; U.S. Pat. No. 6,302,888 (Mellinger, 1999), insertable without end stops. EP0836436 (Wisnewski et al., 1995), not only slidingly but pivotably insertable without end stops. 
     Among the externally slidingly attachable quick closures, the following ones are e.g. known in the art: DE4107480 (Ulrich et al., 1991) and U.S. Pat. No. 6,139,549 (Keller, 1997), insertable at the bottom of the screw head near the bone thread without stops and with high space requirement. 
     Among the internally rotatively attachable quick closures, the following ones are e.g. known in the art: EP1119304 (Yuan, 1998), rotatively insertable in one direction with an end stop; U.S. Pat. No. 6,258,090 (Jackson, 2000), rotatively insertable in one direction without an end stop; U.S. Pat. No. 6,652,526 (Arafiles, 2001), rotatively insertable in two directions without an end stop; U.S. Pat. No. 6,786,903 (Lin, 2002), rotatively insertable in two directions with a positioning aid on the rod. 
     Among the externally rotatively attachable quick closures, the following ones are e.g. known in the art: U.S. Pat. No. 5,346,493 (Stahurski et al., 1993), rotatively insertable in both directions without an end stop; U.S. Pat. No. 6,251,112 (Jackson, 2000), rotatively insertable in one direction without an end stop; EP1190678 (Bono et al., 2001), rotatively insertable in one direction with an end stop. 
     Among the internal and external bayonet-like quick closures, the following ones are e.g. known in the art: DE9403231 (Aesculap, 1994), insertable at the bottom of the screw head from one side, with an end stop; U.S. Pat. No. 7,235,075 (Metz-Stavenhagen, 2003), insertable at the top of the screw head from one side, with an end stop. 
     A snapping quick closure is proposed by US 2005/0027292 (Bernard et al., 2005). 
     In this respect, a main disadvantage of slidingly insertable quick closures is that relatively high moments have to be applied to the typically long instruments used in spinal surgery by the surgeon with the risk of creating uncontrolled situations at the location of the screw. For rotatively insertable quick closures, the required torque along the instrument always remains the same. A rotational insertability from two sides is therefore important as due to the increasingly frequent application of dynamic stabilizing systems, plastic rods are being used more and more frequently. They are, however, larger than metal rods for reasons of stability and therefore require more space. 
     In situations of limited space at the pedicle entrance, a quick closure that is rotatively insertable from only one side may lead to collisions with transverse processes or facet joints, which is less probable in the case of a rotational insertability from two sides. With quick closures without end stops, screws cannot be tightened without being retained by an additional instrument for which the access to the screw is difficult. Consequently, an end stop in the tightening direction preserves the bone bed while fastening the clamping screw whereas an end stop against the tightening direction preserves the bone bed while releasing the clamping screw. An end stop in both directions optimally preserves the bone bed in both directions. 
     A major disadvantage of a metallic snapping mechanism are the required macroscopic elastic deformation achievable only through limited local strength and the rather complicated instruments required to unlock a snapped-in junction while demanding important removal forces with the risk of overloading the elastic elements. Also the tightening screw of Bernard et al. does not have a matching seat in the screw head and consequently cannot transfer the rod&#39;s load directly into the screw head, but must rather transfer them through the threads of the closure. 
     Also as a result of the increasing dimensions of plastic rods for dynamic stabilizing systems, the space left between the screw head and the pedicle entrance is mostly insufficient for a quick closure coupling. In such cases, only systems are applicable where the quick closure is arranged at the top of the screw head. 
     SUMMARY OF THE INVENTION 
     Thus, an object of the present invention is to design a spinal implant set including a quick closure for fastening a connecting element in a bone screw in such a manner that it is easier to assemble and better protects the bone bed of the bone screw from manipulative stress. 
     Such an implant set is suggested according to claim  1 . The further claims define preferred embodiments thereof. 
     Accordingly, the quick closure is attachable in two directions (clockwise and counterclockwise direction) and subsequently lockable so as to be able to take up torques acting upon the screw in both directions. 
     Preferably, the invention proposes the quick closure defined in claim  1 , which is rotatively attachable over protrusions on the screw head from the left or from the right. Furthermore, the rotative attachment of the quick closure in the screw head may be assisted by centering properties of the preassembled clamping element. 
     In a preferred use, the quick closure is retracted manually or by means of a clamping screw so that hooks of the quick closure engage in protrusions of the screw head and a filler of the quick closure in a recess of the protrusion of the screw head and lock therewith. In this manner, torques transmitted from the clamping element to the bone screw can be taken up by the quick closure without applying additional stresses to the bone bed of the bone screw. Furthermore, due to its guidance in the screw head, the clamping element is able to directly transmit longitudinal forces from the connecting element to the bone screw. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is explained in more detail hereinafter by means of a preferred exemplary embodiment with reference to the appended drawings which merely illustrate the exemplary embodiment. 
       The drawings schematically show: 
         FIG. 1  3D-view of an implant set assembly. 
         FIG. 2   a  an exploded view of the bone screw, the quick closure, and the clamping element. 
         FIG. 2   b  an assembly drawing of the bone screw, the quick closure, and the clamping element. 
         FIG. 3   a  a sectional view of the locked and non-clamped quick closure. 
         FIG. 3   b  a sectional view of the locked and clamped quick closure. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  illustrates the bone screw  1 , the connecting element  2 , the clamping element  3 , and the quick closure  4  in the assembled state. 
       FIG. 2   a  illustrates the bone screw  1  with the screw head protrusions  1   a , the recess  1   b  between the protrusions  1   a , and the clamping element guide  1   c  on one half of the bone screw head, as well as the seat  1   d  of a connecting element; the clamping element  3  with its surface  3   a  that fits the clamping element guide  1   c  and its threaded portion  3   b ; the quick closure  4  with its hooks  4   a  that fit the screw head protrusions  1   a  and its filler  4   b  that fits the recess  1   b.    
       FIG. 2   b  illustrates the bone screw  1  with the hooks  4   a  abutting the screw head protrusions  1   a  from below  1   a , the filler  4   b  of the quick closure  4  inserted in the recess  1   b , and the clamping element surface  3   a  of the clamping element  3  inserted in the clamping element guide  1   c.    
       FIG. 3   a  illustrates a longitudinal section of the bone screw  1  with the connecting element  2 , the clamping element  3 , and the cross-section of the quick closure  4  in the locked but non-clamped state. 
       FIG. 3   b  illustrates the longitudinal section of the bone screw  1 , of the connecting element  2 , the clamping element  3 , and the cross-section of the quick closure  4  in the locked and clamped state. 
     This assembly provides a quick and secure attachment of a connecting element  2  in a pedicle screw  1 . 
     Notably, the clamping element guides is cover a sufficient wrap angle that the clamping element  3  is safely held even in the longitudinal direction of the connecting element  2 . 
     For use of the closure, the connecting element  2  is placed in the head  1   a  of the bone screw  1 . The quick closure  4  with the clamping element  3  in a retracted position is set on the screw head in sliding the connecting element down the clamping element guides  1   c . Quick closure  4  is set on the head in a position that the locking extensions bearing the hooks  4   a  and the filler  4   b  pass between the screw head protrusions  1   a  or stops arrangements. The quick closure  4  is turned so that the fillers  4   b  slide into recesses  1   b  when the quick closure  4  is retracted. This backward movement is limited by the hooks  4   a  hitting the protrusions  1   a . Then, the clamping element  3  is screwed down using a tool attached to the accessible end of the threaded portion  3   b . Once it hits the connecting element  2  (cf.  FIG. 3   b ), it will exert a force on the connecting element  2  as well as on the quick closure  4  keeping both in their locked position. The quick closure  4  is now locked by positive interlockings: In axial direction, the hooks  4   a  engage with the screw head protrusions  1   a , and a rotation in both directions is inhibited by the filler  4   b  resting in the recess  1   b  between the head protrusions  1   a  providing stop faces on both sides of the filler  4   b.    
     Based on the aforegoing description the one skilled in the art is able to derive modifications without leaving the scope of protection which is defined by the claims.