Abstract:
A method for osteosynthesis of a spinal column using an assembly including a bone anchor, a connector and a ring, the method comprising: inserting an anchoring part of the bone anchor into bone, the bone anchor including the anchoring part and a head, the head positioned to be in contact with the connector and ring; inserting a connecting member into the connector; and applying a force to the connecting member such that the connecting member applies the force against the ring and the bone anchor, wherein the head of the bone anchor contacts the connector, ring and connecting member during the application of the force.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of application Ser. No. 12/658,838, filed Feb. 16, 2010, which is a continuation of application Ser. No. 10/096,991, filed Mar. 13, 2002, the disclosures of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to osteosynthesis systems particularly for surgery on the spinal column. 
     SUMMARY OF THE INVENTION 
     Document WO 98/12 976 discloses a spinal osteosynthesis system comprising an anchoring member of the polyaxial screw type which is immobilized in position by the link rod bearing against a crown, the rounded lower surface of which bears in a complementary manner on the spherical head of the bone screw lodged in the bottom of a housing made in a connector. Such a system involves a very high bearing force between the rod and the crown in order that the pressure per unit area between the crown and the screw head is high enough to prevent any movement of one with respect to the other, which movement would have the effect of creating instability that is detrimental to the desired osteosynthesis. 
     SUMMARY OF THE INVENTION 
     One object of the invention is to provide a position-locking device which is more reliable for the same clamping force. 
     To do that, an aspect of the invention provides a spinal osteosynthesis assembly comprising a connector, bone anchoring means capable of being received in the connector, a connecting member capable of being received in the connector, and a ring capable of coming into contact with the head, the connecting member being able to come to bear simultaneously against the ring and the head when the ring and the anchoring means are fitted in the connector. 
     Thus, when locking the osteosynthesis system, the bearing of the connecting member on the ring forces the latter to come to bear against the anchoring means to immobilize the anchoring means in position within the connector, and the simultaneous bearing of the connecting member on the anchoring means enhances the previous immobilization, making it more secure while at the same time maintaining the same clamping force for locking. 
     Advantageously, the ring has at least one conical face. 
     Advantageously, the ring has a face able to come into contact with the anchoring means. 
     Advantageously, the ring has a face able to come into contact with a wall of the connector. 
     Advantageously, the faces are coaxial. 
     Advantageously, the ring has a flat upper edge perpendicular to an axis of the ring and able to come into contact with the connecting member. 
     Advantageously, the ring has a flat lower edge perpendicular to an axis of the ring. 
     Advantageously, the ring is able to extend between the wall and the anchoring means when the connecting member bears as mentioned. 
     Advantageously, the ring is deformed when the connecting member bears as mentioned, with reference to the shape that the ring had before fitting. 
     Advantageously, the ring has a wall thickness which varies according to a height. 
     Thus, the ring has a cross section in the shape of a wedge which, when the system is locked, simply wedges between the wall of the connector and the anchoring means and this, in a simple way, will further enhance the positional immobilization. 
     Advantageously, the ring comprises a slot. 
     Advantageously, the slot is arranged in such a way that the ring forms a non-closed annulus. 
     Advantageously, the ring comprises a number of slots distributed uniformly about a circumference of the ring. 
     Advantageously, the anchoring means comprise a head having a roughly spherical face. 
     Advantageously, the head has a first spherical face and a second spherical face which have the same center and significantly different diameters. 
     Advantageously, the anchoring means form a polyaxial screw. 
     Advantageously, the assembly comprises a locking member able to come to bear against the connecting member. 
     Also provided according to the invention is an osteosynthesis system comprising an assembly exhibiting at least one of the above mentioned features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will become apparent during the following description of a preferred embodiment. In the appended drawings: 
         FIG. 1  is a perspective view of the preferred embodiment of the invention; 
         FIG. 2  is a view: in section on II-II of the embodiment of  FIG. 1 ; 
         FIG. 3  is a perspective view of the ring of the preferred embodiment; 
         FIG. 4  is a perspective view of the embodiment of  FIG. 1  prior to the fitting of the connecting member; 
         FIG. 5  is a view in section on V-V of the embodiment of  FIG. 4 ; 
         FIG. 6  is a perspectives view of an embodiment of the ring as a non-closed annulus; and 
         FIG. 7  is a perspective view of an embodiment of the ring with circumferential slots. 
     
    
    
     DETAILED DESCRIPTION 
     A preferred embodiment will be described with reference to the various  FIGS. 1 to 5 . The assembly for osteosynthesis of the spinal column  1  here comprises a connector  2 , a connecting member  6  and anchoring means  4 . Here, the connecting member  6  is an osteosynthesis rod and the anchoring means  4  are formed by a pedicle screw. The assembly  1  also comprises a ring  8  and a locking member  10  capable of locking the assembly  1  in position. 
     The connector  2  comprises a U-shaped opening  21  forming the upper part of the connector  2 . This U-shaped opening  21  is delimited by two branches  25  and  26  which extend roughly parallel with respect to each other. The internal faces of the branches  25  and  26  which extend facing each other comprise a screw thread  24 . Furthermore, the connector  2  in its lower part comprises an internal housing  22  having a wall  23 . The upper part of the internal housing  22  opens into the bottom of the U-shaped opening  21  and the lower part of the internal housing  22  opens onto a lower face  27  of the connector  2 . On the same side as the lower face  27 , the wall  23  has a conical section designed so that the opening at the lower face  27  is smaller than the opening at the bottom of the U-shaped opening  21 . 
     The locking member  10  comprises operating means  11  which here are in the form of a through-orifice  11  with a hexagonal socket. This hexagonal socket is designed to accommodate a hexagonal bit fitted to a screwdriver for operating it. Furthermore, the locking member  10  comprises, on its external side wall, a screw thread  12  that complements the screw thread  24  of the connector  2  between the branches  25  and  26  of which it is able to be received. 
     The anchoring means  4  are here in the form of a pedicle screw comprising an anchoring part  41  exhibiting a bone thread, surmounted by a head  42  which here is roughly spherical. The head  42  has a first spherical surface  43  and, forming the top, a second spherical surface  44 , the diameter of which is smaller than the diameter of the spherical surface  43  but has the same center thereas. 
     Similar osteosynthesis systems can be found in document EP-0 613 664. 
     The ring  8  is of annular shape and has a first face  82  delimiting the internal wall of the ring, a second face  81  delimiting the external wall of the ring and upper  83  and lower  84  edges perpendicular to the geometric axis of revolution A of the ring  8 . The faces  81  and  82  are coaxial and preferably of conical shape. Their respective generators are not mutually parallel. Thus, the faces are arranged one with respect to the other in such a way that the thickness of the ring  2  at the upper edge  83  is greater than the thickness of the ring  8  at the lower edge  84 . The cross section of the ring thus has a wedge shape, giving the ring  8  a tapered shape. However, one of the generators of the faces  81  and  82  may be roughly parallel to the axis of revolution A. 
     Prior to use by a surgeon, the connector  2 , the anchoring means  4  and the ring  8  are fitted together. More particularly, the head  42  of the anchoring means is inserted into the internal housing  22  of the connector  2 . The ring  8  is then itself inserted into the internal housing  22  of the connector  2 . Thus, the head  42  of the anchoring means  4  finds itself held captive in the internal housing  22  against exiting upward by the presence, inside the internal housing  22 , of the ring  8 , which is itself held captive, as will be seen later on. The head  42  is retained against exiting downward by the presence of the conical section of the wall  23  of the internal housing  22 , which has an opening at the lower face  27  of the connector  2 , the dimensions of which are smaller than the diameter of the surface  43  of the head  42 . In addition, the ring  8  is held captive by retaining means  28  present within the internal housing  22 . Here, the retaining means  28  stem from the difference in size between the internal housing  22  and the U-shaped opening  21 , this difference forming a rim against which the upper edge  83  of the ring  8  abuts from below. This assembly is illustrated in  FIGS. 4 and 5 . 
     In use during a surgical operation, the surgeon fits an assembly as described above into the pedicle. He then fits the connecting member  6 , inserting it into the U-shaped opening  21  of the connector  2 . He then fits the locking member  10  between the branches  25  and  26 , engaging the screw thread  12  of the locking member  10  with the complementary screw thread  24  of the connector  2 . Using the hexagonal socket  11 , he drives the locking member  10  so that the underside  13  of the locking member  10  comes into contact with the connecting member  6 . 
     By continuing to screw the locking member  10  between the branches  25  and  26 , the surgeon will exert a force via the locking member  10  on the connecting member  6 , and this will push the connecting member  6  until the latter comes to bear against the upper edge  83  of the ring  8 . 
     As locking continues, the ring  8  then slips along the wall  23  of the internal housing  22  until the face  82  of the ring  8  comes into contact with the surface  43  of the head  42  of the anchoring means  4 . The surface  43  is itself in contact with the conical section of the wall  23  of the internal housing  22  of the connector  2 . The system therefore finds itself in a situation as illustrated in  FIG. 2 . 
     During final locking, which will allow the assembly to be immobilized in position, the clamping force imparted by the surgeon via the locking member  10  will allow the ring  8  to be made to slide on the head  42 . For that, the face  82  will slide on the surface  43 , forcing the ring  8  to open up by deformation until the face  81  of the ring  8  comes into contact over all or part of its surface with the wall  23  of the internal housing  22  of the connector  2 . At that moment, the connecting member  6  comes to bear at a point on the spherical surface  44 . Thus, the head  42  is immobilized in position, on the one hand, by the ring  8  and, on the other hand, by the connecting member  6  directly. There is thus what is known as three-point contact, two of the points being diametrically opposed points of contact of the edge  83  of the ring  8  with the connecting member  6  and one additional point where the connecting member  6  contacts the surface  44  of the head  42  of the anchoring means  4 . 
     Of course, numerous modifications could be made to the invention without departing from its scope. 
     For example, referring to  FIG. 6 , the ring  8  could have at least one slot  90 . This slot could be arranged in such a way that the ring forms a non-closed annulus. 
     Alternately, referring to  FIG. 7 , the tapered shape due to the wedge shape of the cross section of the ring, instead of being continuous over its entire circumference, could consist of a number of sectors separated by slots  92 ,  94  and  96  to form an “umbrella” structure. 
     These various modifications allow easier deformation of the ring  8 . This has the effect of making the ring  8  easier to introduce into the internal housing  22  of the connector  2 , on the one hand, and, on the other hand, of making the final locking during use in a surgical operation easier. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.