Abstract:
A spinal osteosynthesis system, in particular for anterior spinal fixation, comprising at least an anchoring member, an elongated linking element and a connector capable of being fixed to the anchoring member and to the linking element by selecting an angular position of the linking element relative to the connector. The system comprises a second elongated linking element, the connector being capable of being fixed simultaneously to both linking elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/FR99/02402, filed Oct. 7, 1999, the disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to spinal osteosynthesis systems, in particular for anterior fixation. 
     Spinal osteosynthesis systems for anterior fixation are known in which the connection element is formed by a plate, and others are known in which the connection element is formed by a rod. Because of their bulk, the plate systems are difficult to use, if they can be used at all, via the endoscopic route. Moreover, their limited size (length) means that they can only be used for simple vertebrectomies involving a single vertebra, or perhaps two. It is impossible to treat scoliosis with this type of system. Finally, a plate is difficult to adapt to the morphology of the vertebrae in which it is anchored. Moreover, the rod systems generally comprise fairly voluminous connectors which cannot always be used via the endoscopic route. 
     A spinal osteosynthesis device is also known from U.S. Pat. No. 5,938,663, which device comprises a clamp or connector with two branches which can clamp a connection rod between them, the branches being able to be engaged on a vertebral pedicle screw. The rod is received between the branches with interposition of a slotted ring which has a spherical face and is engaged on the rod in order to control the angular orientation of the connector relative to the rod before clamping. However, this device, while well suited for posterior fixation of the spine on the vertebral pedicles, does not always provide sufficient rigidity with a view to anterior fixation of the spine. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to make available a different spinal osteosynthesis system, adapted for anterior fixation, easy to fit, ensuring good rigidity of the system on the spine, and compatible with being fitted via the endoscopic route. 
     To achieve this object, the invention provides a spinal osteosynthesis system, in particular for anterior fixation, comprising at least one anchoring member, an elongate connection element and a connector which is able to be fixed to the anchoring member and to the connection element by choosing an angular position of the connection element relative to the connector, the system comprising a second elongate connection element, the connector being able to be fixed simultaneously to the two connection elements. 
     Thus, the presence of the two connection elements gives the system very great rigidity, without complicating its assembly, without increasing the volume of its various components (which renders it compatible with fitting via the endoscopic route), and while maintaining the possibility of controlling the angular position of the connector relative to the first connection element. The system according to the invention does not require identical bending on the two connection elements. Moreover, the number of connectors can remain small. 
     Advantageously, the system is designed in such a way that the second connection element can be fixed to the connector only in a single angular position relative to the connector. 
     Thus, the shape of the second connection element dictates the relative angular position of the connectors which are fixed to it. This angular position can therefore be chosen in advance depending on the prior curvature given to this connection element, either at the time of manufacture or, better still, during the surgical intervention. 
     Advantageously, the second connection element has less resistance to bending than the first connection element. 
     Thus, the first connection element has mainly a function ensuring support of the connectors, and the second connection element has mainly a function ensuring angular positioning of the connectors. 
     Advantageously, the connector comprises two branches which can clamp at least one of the two connection elements. 
     Advantageously, the branches have first ends via which they are connected to each other and second free ends. 
     This simplifies production of the connector. Moreover, by appropriately selecting the flexibility of the connector and/or the diameter of the second connection element, this element can be introduced laterally between the free ends of the branches, which makes fitting easier. 
     Advantageously, the connector is able to receive the second connection element by lateral insertion between the free ends. 
     Advantageously, the branches can simultaneously clamp the two connection elements. 
     Advantageously, the anchoring member comprises a vertebral screw, at least a first of the two branches being able to be engaged on the screw. 
     Advantageously, the vertebral screw has a threaded orifice, the system comprising a clamping screw which can constitute a screw-nut connection with this orifice and is able to bear on one of the branches in order to clamp the branches. 
     Advantageously, the system comprises a second vertebral screw, the first branch being able to be engaged simultaneously on the two vertebral screws. 
     Advantageously, the system is designed in such a way that the second connection element, when fixed to the connector, extends in a trajectory of the second vertebral screw for its disengagement from the connector. 
     Thus, the second screw is prevented from starting to come out at an inopportune moment. 
     Advantageously, the system comprises a ring which can be engaged on the first connection element and received between the branches in order to choose the angular position of the first connection element before the branches are clamped. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will become more apparent from the following description of a preferred embodiment given as a nonlimiting example. In the attached drawings: 
     FIG. 1 is a perspective view of the system according to the invention; 
     FIG. 2 is a partial and exploded perspective view of the system in FIG. 1; 
     FIGS. 3 and 4 are two perspective views, from above and below, respectively, showing one of the connectors of the system in FIG. 1; 
     FIG. 5 is a view, half in elevation and half in axial section, of a ring of the system in FIG. 1; 
     FIG. 6 is a view partly from above and partly in section of the connector in FIG. 3 receiving the first rod; 
     FIG. 7 is a partial perspective view showing the head of the main screw; and 
     FIG. 8 shows the system from FIG. 1 fixed on vertebrae. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, the system according to the invention comprises, in the preferred embodiment, a first elongate connection rod  2 , or main rod, of circular cross section, a second elongate connection rod  3  or secondary rod of circular cross section and several connector sub-assemblies  4  which can be fixed simultaneously to the latter. Each of these sub-assemblies, of which only two can be seen in FIG.  1  and of which only one can be seen in FIG. 2, comprises a connector  6 , a first vertebral screw or main screw  8 , a clamping screw  10 , a second vertebral screw or secondary screw  12 , and a ring  13 . 
     In the present example, the connector  6  is made in one piece. The different parts of the system are made of biocompatible metal. 
     Referring to FIGS. 3 and 4, the preferred connector  6  includes two branches  16  extending opposite to and at a distance from each other, giving the connector a general U-shaped profile. The connector  6  includes a plane of symmetry S visible in FIGS. 3 and 6, perpendicular to the width of the branches  16  and parallel to their length. Thus, each branch has a first end and a second end. The branches are connected to each other via their first ends. The second ends are free ends Referring to FIG. 6, at the point of origin of the branches  16 , that is to say of their first end, the connector has two cylindrical and coaxial inner faces  18 ,  20  with axis  22  perpendicular to the plane S and with different radii. The face  20  of greater radius is in two distinct parts and extends on either side of the face  18  of lesser radius, which is traversed by the plane S. At their junctions, the two faces  18 ,  20  form two circular edges  24  with axis  22 . 
     Referring to FIGS. 5 and 6, the preferred ring  13  has a cylindrical inner face  26  and a spherical outer face  28  which are coaxial. The cylindrical inner face  26  has a radius about equal to that of the main rod  2  in such a way that the ring  13 , slotted on one side along its axis, can be received as a sliding fit on the main rod  2 . Moreover, the ring  13  can be lodged between the branches  16  opposite the cylindrical faces  18 ,  20 . The spherical outer face  28  of the ring has a radius which is adapted such that in this position the edges  24  of the connector  6  are in linear contact with the spherical outer face  28  of the ring  13  and serve as bearings for it. In this position, before clamping of the branches  16 , the angular position of the main rod  2  engaged in the ring  13  can be controlled in two mutually perpendicular planes over an amplitude of, for example, 15° on either side of a mean position of the rod in which the rod is perpendicular to the plane S. 
     Referring to FIGS. 3 and 4, the branches  16  have two respective smooth cylindrical openings which, in this case, are through-orifices  30  extending coaxially opposite each other. The preferred main screw  8  is a bicortical vertebral screw and has a threaded body for this purposes, in a manner known per se. Referring to FIG. 7, it has a head  32  having a smooth cylindrical outer face  34 . At the junction between the head and the body, the screw includes an annular flange  36  having a plane lower face perpendicular to a longitudinal axis of the screw, and a frustoconical upper face  38  with the narrowest cross section of the frustum situated towards the head  32  of the screw. The head  32  has a threaded orifice  39  coaxial to the body of the screw and, formed in the threaded face of the orifice  39 , a noncircular shape such as a hexagon socket. The clamping screw  10  includes a threaded body  42  which is able to form a screw-nut connection with this orifice  39 , and a screw head  44  in which a hexagon socket is formed. The head  44  has a spherical and convex lower outer face  46  whose narrowest cross section is situated towards the point of the screw. 
     In the preferred embodiment, one of the branches  16  of the connector  6 , which for the sake of clarity we will here call the lower branch, has an extension  50  extending in the direction away from the cylindrical faces  18 ,  20  of the connector. This is the branch intended to be adjacent to the vertebra. This extension has the second, free, end of the branch. The two branches  16  are able to be engaged simultaneously on the head  32  of the main screw  8  introduced in the orifices  30  starting from the lower branch against which the upper face  38  of the flange  36  comes into abutment. The clamping screw  10  is then introduced into the head  32  of the main screw  8  starting from the upper branch  16 . The tightening of the clamping screw  10  in the head  32  of the main screw  8  causes the branches  16  to move towards each other and causes, inter alia, frictional blocking of the first rod  2  in the chosen position relative to the connector  6 . 
     The orifice  30  of the lower branch  16  has a lower edge, remote from the upper branch and intended to be towards the vertebra, having a concave spherical recess  40  intended to come into contact with the upper face  38  of the flange  36  in order to effect, by friction, rotational blocking of the connector  6  relative to the axis of the main screw  8 . The orifice  30  of the upper branch  16  has an upper edge, remote from the lower branch and intended to be remote from the vertebra, having a concave spherical recess  40  intended to come into contact with the convex and spherical lower face  46  of the head  44  of the clamping screw  10  and making it possible to fix the latter and the main screw  8  by controlling the angular orientation of the main screw  8  relative to the connector. 
     In the preferred embodiment, the extension  50  has an opening in the form of a through-orifice  52 . The lower branch  16  is curved in the area of the extension  50  in a direction away from the upper branch  16  in such a way that the axes of its orifices  30  and  52  are not quite parallel. The secondary screw  12  is a vertebral screw, here a monocortical screw, having a threaded body and a head  56  with a spherical and convex lower face  58  whose narrowest cross section is situated towards the body. Its head has a hexagon socket. The orifice  52  of the extension has an upper edge  60 , oriented towards the other branch  16  and intended to be remote from the vertebra, having a spherical and concave or preferably frustoconical form  60 , intended to come into contact with the spherical and convex lower face  58  of the head  56  of the secondary screw  12 , making it possible to control the angular orientation of this screw relative to the connector  6 . 
     Certain characteristics of the connector  6  which have not been expanded on in detail here will be found in U.S. Pat. No. 5,938,663. 
     The lower branch  16  can be bent in order to accentuate or reduce its curvature for better adaptation to the shape of the anterior part of the vertebra for which it is intended. Once bent, this branch  16  is no longer stressed in flexion since it is fixed to the vertebra by two screws  8 ,  12  along its length. The two screws, namely the main screw  8  and the secondary screw  12 , are self-tapping and include bone threads. 
     In an alternative embodiment, the main screw  8  does not have a hexagon socket in this threaded orifice  39 , and instead the flange  36  has a hexagonal shape or has two parallel and diametrically opposite flats which can cooperate with a tightening wrench for rotating this screw  8  relative to the connector  6 . 
     The two connection rods  2 ,  3  each have a profiled rectilinear shape, the profile here being circular. The secondary rod  3  has a cross section, transverse to its longitudinal axis, having a diameter smaller than that of the main rod  2 . The main rod  2  will, for example, have a diameter of 6 mm. The diameter of the secondary rod  3  will, for example, be between 30% and 80% of the diameter of the main rod  2 . This small diameter allows the surgeon to choose the curvature of the secondary rod  3  corresponding to that of the level of the spine which is being operated on. By contrast, since the rings  13  allow relative angular positioning of the two connectors  6 , the main rod  2  does not have to be bent. It can thus have a substantial diameter in order to be very robust. 
     The branches  16  of the connector have respective cylindrical recesses, grooves or jaws  74  formed in the faces of the branches opposite each other. The recesses  74  extend opposite each other and have axes parallel to each other and perpendicular to the plane of symmetry S. 
     On the upper branch  16 , the recess  74  extends at a free end of the branch such that the orifice  30  is interposed between the faces  18 ,  20 , on the one hand, and the recess  74  on the other. On the lower branch  16 , the recess  74  extends between the two orifices  30  and  52 , at the origin of the extension  50 . It is contiguous with the orifice  52  so that it engages on its edge  60 , i.e. recess  74  intercepts the upper opening of orifice  52  as shown in FIG.  3 . 
     The secondary rod  3  is intended to be received in the recess  74  of the lower branch  16  in a unique angular position relative to the connector, perpendicular to the plane of symmetry S. The connector and the rod are dimensioned in such a way that the secondary rod can be introduced laterally between the free ends of the branches (that is to say without engaging the rod via one end in the connector). Before clamping, the space between the branches is wider than the diameter of the rod which can thus be freely inserted. When the two branches  16  are then clamped in the direction of each other, the recess  74  of the upper branch comes into contact with the secondary rod  3  which is thus in surface contact with each of the two recesses, which effect frictional blocking of the secondary rod  3  relative to the connector  6 , which are thereby rigidly fixed to each other. 
     The secondary rod  3  is placed in the recess  74  of the lower branch after the secondary screw  12  has been introduced into the orifice  52 . The position of the recess  74  of the lower branch is such that the secondary rod  3  then extends in the trajectory of the head of the secondary screw  12  for its disengagement from the connector and its exit from the orifice  52 . Consequently, once the secondary rod  3  has been fixed to the connector, the secondary screw  12  can no longer be separated from the connector. 
     The upper branch  16  of the connector has at its free end a notch  76  which engages recess  74  with which it is contiguous, and facilitates maneuvering of the clamping screw  12  by means of a tool despite the space occupied by the upper branch. 
     Such a device is fitted in the following manner, with reference to FIG.  8 . After exposing the affected vertebra  70  and the two adjacent vertebrae  72 , a vertebrectomy is performed while preserving, if possible, the respective plates of these vertebrae. For each subassembly  4 , a pilot hole is made on the lateral side of the associated vertebra  72  at an equal distance from the upper and lower plates, and at the limit of the most posterior quarter of the vertebral body. The main screw  8  is then inserted into this pilot hole as far as the limit flange  36 . The connector  6  is then positioned on the main screw  8 , blocked in translation by the conical face  38  of the main screw  8  matching the recess  40  of the connector  6 . The fit of the lower branch  16  of the connector  6  on the vertebra is then checked and can be adjusted by withdrawing the connector in order to bend, to a greater or lesser extent, the lower branch  16 , which is its most anterior part. 
     The secondary screw  12  is then screwed relative to the main screw  8  into the second orifice  52  of the lower branch  16  until the spherical seat  60  of the extension, provided for this purpose, comes into contact with the spherical part  58  of the secondary screw  12 . It is desirable to position the connector  6  as parallel as possible to the plates. 
     After the two adjacent vertebrae  72  have been thus equipped, the main rod  2  is positioned by engaging it via one end in the rings  13  of the connectors  6  and the angular position of each sub-assembly.  4  relative to this rod  2  is controlled. The secondary rod  3  is then introduced laterally, and generally in the medial-lateral direction, into the recesses  74  of the connectors  6  after it has first been bent manually to obtain the curvature required for the corresponding level of the spine. In the event of an error, this rod  3  can be removed laterally in order to correct its curvature and then put back in place. FIG. 1 shows the system before the clamping of the branches. Final clamping is effected by virtue of the clamping screw  10  which is inserted into the main screw  8  and thereby compresses the connector  6  in order to clamp its two branches  16  towards each other. During this clamping, the clamping force is directed first on the main rod  2  via the ring  13 , until the recess  74  of the upper branch comes into contact, with the secondary rod  3 . Thereafter, the clamping force is distributed on the two rods  2 ,  3 . Thus, the reaction at the level of the pairing of main screw  8  and clamping screw  10  is substantially coaxial to these. 
     The characteristics relating to the association of the first screw  8  with the clamping screw  10  will be able to be implemented independently of the presence of the extension  50  and of the secondary screw  12 . 
     Although less advantageous, the extended branch can be the one which is intended to be farthest from the vertebra. 
     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.