Abstract:
The invention concerns a backbone osteosynthesis system, in particular for anterior fixing comprising: an elongated linking element; a vertebral screw with a threaded head; a connector comprising two branches capable of being engaged onto the screw and clamping between them the linking element; and a threaded clamping member capable of co-operating with the head for clamping the branches. The head has a threaded orifice, the clamping member comprising a threaded rod capable of being urged to be engaged in the orifice.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. Application Ser. No. 09/674,196 filed Feb. 1, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention concerns spinal osteosynthesis systems, in particular for anterior fixation.  
           [0003]    The document FR-2,731,344 (U.S. Pat. No. 5,938,663) discloses a spinal osteosynthesis system comprising a rod, a vertebral screw having a body to be anchored in a vertebra, and a head in the form of a threaded rod. The system comprises a connector with two branches which can be engaged on the screw head. A clamping nut can be fitted on the screw head in order to clamp the two branches between the base of the screw head and the nut. The rod engaged between the branches is thus clamped and immobilized.  
           [0004]    This system has many advantages. As it includes a small number of components and is easy to put in place, it permits rapid fitting during a surgical intervention. However, the nut has a hexagonal outer profile which is necessary to permit its maneuvering and its clamping by means of a socket wrench. Now, such a profile generates numerous sharp edges and projecting corners capable of damaging the body tissues coming into contact with the nut. Similarly, it is difficult to prevent a threaded end part of the screw head from protruding from the nut upon completion of clamping. Now, this thread itself also presents projecting edges which can be damaging to the body.  
         SUMMARY OF THE INVENTION  
         [0005]    An object of the invention is to reduce the number of parts projecting from the system once this has been fitted.  
           [0006]    To achieve this object, the invention provides a spinal osteosynthesis system, in particular for anterior fixation, comprising:  
           [0007]    an elongate connection element;  
           [0008]    a vertebral screw having a threaded head;  
           [0009]    a connector including two branches which can be fitted on the screw and can clamp the connection element between them; and  
           [0010]    a threaded clamping member which can cooperate with the head in order to clamp the branches, in which the head has a threaded orifice, the clamping member comprising a threaded rod which can engage with the orifice.  
           [0011]    Thus, the thread of the vertebral screw extends in an orifice, and the threaded orifice of the screw is closed off by the clamping member once fitting has been completed. Therefore, contact with the patient&#39;s body is no longer possible with the thread of the vertebral screw. Moreover, as the clamping member is a male piece, it is possible to form a maneuvering recess therein of polygonal profile intended to cooperate with a male instrument for maneuvering the clamping member and thereby dispense with the outer edges. This therefore also reduces the number of parts projecting from the clamping member. In addition, the connector is engaged on the head of the vertebral screw without interfering with a thread thereof. Its wedging is thus better, even before clamping by the clamping member. The connector can thus be positioned in advance on the vertebral screw in a reliable manner.  
           [0012]    Advantageously, the clamping member has a recess of polygonal profile along a longitudinal axis of the member.  
           [0013]    Advantageously, the clamping member comprises a head having a spherical and convex lower face, one of the said branches of the connector having a spherical and concave upper face which can be in contact with the convex face upon clamping of the branches.  
           [0014]    It is thus possible to control the relative angular position of the connector and of the vertebral screw which is rigidly fixed to the clamping member.  
           [0015]    Advantageously, the orifice of the vertebral screw has a recess of polygonal profile along a longitudinal axis of the screw.  
           [0016]    This recess too, permitting maneuvering of the vertebral screw, reduces the number of projecting parts.  
           [0017]    Advantageously, the recess extends in the thread of the orifice.  
           [0018]    Thus, despite the presence of the thread and of the recess, it is possible for the head of the vertebral screw, and thus the system, to be given reduced dimensions.  
           [0019]    Advantageously, the profile of the recess of the vertebral screw and the profile of the recess of the clamping member have the same shape and the same dimensions.  
           [0020]    It is thus possible to maneuver the vertebral screw and the clamping member using one and the same male instrument, thereby reducing the equipment needed for the surgical intervention and reducing the risk of error in the choice of instruments.  
           [0021]    Advantageously, the head of the vertebral screw has a lateral face with a smooth outer end.  
           [0022]    Advantageously, the system comprises a second vertebral screw, one of said branches having an extension which can be engaged on the second screw.  
           [0023]    Thus, fixation of the connector to the vertebra by means of the two screws ensures precise, stable and reliable positioning of the connector and thus of the connection element.  
           [0024]    Advantageously, the system comprises a second elongate connection element, the connector being able to be fixed simultaneously to the two connection elements.  
           [0025]    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 if need be 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.  
           [0026]    The system according to the invention can be put into place via the endoscopic route and is designed to be fixed in the anterior position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    Other characteristics and advantages of the invention will become more apparent from the following description of two preferred embodiments given as nonlimiting examples. In the attached drawings:  
         [0028]    [0028]FIG. 1 is a perspective view of the system according to a first embodiment of the invention;  
         [0029]    [0029]FIG. 2 is a partial and exploded perspective view of the system in FIG. 1;  
         [0030]    [0030]FIGS. 3 and 4 are two perspective views, from above and below, respectively, showing one of the connectors on the system in FIG. 1;  
         [0031]    [0031]FIG. 5 is a view, half in elevation and half in axial section, of a ring of the system in FIG. 1;  
         [0032]    [0032]FIG. 6 is a view, partly from above and partly in section, of the connector in FIG. 3 receiving the rod;  
         [0033]    [0033]FIG. 7 is a partial perspective view showing the head of the main screw;  
         [0034]    [0034]FIG. 8 shows the system from FIG. 1 fixed on vertebrae;  
         [0035]    [0035]FIG. 9 is a perspective view of the system according to a second embodiment of the invention;  
         [0036]    [0036]FIG. 10 is a partial and exploded perspective view of the system in FIG. 9;  
         [0037]    [0037]FIGS. 11 and 12 are two perspective views, from above and below, respectively, showing one of the connectors of the system in FIG. 9; and  
         [0038]    [0038]FIG. 13 shows the system from FIG. 9 fixed on vertebrae. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    Referring to FIGS.  1  to  8 , the system according to the invention comprises, in the first embodiment, an elongate connection rod  2  of circular cross section and several connector sub-assemblies  4  which can be fixed to the latter. Each of these sub-assemblies, of which two can be seen in FIG. 1 and of which 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 .  
         [0040]    Referring to FIGS. 3 and 4, the 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 perpendicular to the width of the branches  16  and parallel to their length. Referring to FIG. 6 at the point of origin of the branches  16  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 being in two distinct parts and extending 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 .  
         [0041]    The 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 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 rod. 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 rod  2  engaged in the ring  13  can be controlled in two mutually perpendicular planes over an amplitude of, for example,  150  on either side of a mean position of the rod in which the rod is perpendicular to the plane S.  
         [0042]    The branches  16  have two respective smooth cylindrical openings which, in this case, are through-orifices  30  extending coaxially opposite each other. The main screw  8  is a bicortical vertebral screw and has a threaded body for this purpose, in a manner known per se. 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 the 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.  
         [0043]    One of the branches  16 , 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. The two branches  16  are able to be engaged simultaneously on the head  32  of the main screw  8  introduced 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 screw  10  in the head  32  of the main screw  8  causes the branches  16  to close towards each other and causes frictional blocking of the rod  2  in the chosen position relative to the connector  6 .  
         [0044]    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.  
         [0045]    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, oriented towards the other branch  16  and intended to be remote from the vertebra, having a spherical and concave recess  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 .  
         [0046]    Certain characteristics of the connector  6  which have not been expanded on in detail here will be found in the abovementioned related documents FR-2,731,344 and WO 96/27340 (U.S. Pat. No. 5,938,663), the teachings of which are incorporated herein by reference.  
         [0047]    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.  
         [0048]    In an alternative embodiment, the main screw  8  does not have a hexagon socket in its 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 .  
         [0049]    In the present example, the connector  6  is made in one piece. The different parts of the system are made of biocompatible metal.  
         [0050]    Such a device is fitted in the following manner, with reference to FIG. 8. After exposing the affected vertebra  70  and two adjacent vertebra  72 , a vertebrectomy is performed while preserving, if possible, the respective plates of these vertebrae. For each subassembly, 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 said main screw  8 , blocked in translation by the conical face  38  of the said main screw  8  matching the recess  40  of the connector  6 . The fit of the connector  6  on the vertebra is then checked and can be adjusted by withdrawing the said connector in order to bend the lower branch  16  which is its most anterior part.  
         [0051]    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 said secondary screw  12 . It is desirable to position the connector  6  as parallel as possible to the plates.  
         [0052]    After the two adjacent vertebrae  72  have been thus equipped, the rod  2  is positioned in the rings of the connectors  6  and its angular position on each sub-assembly is controlled. 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 the rod.  
         [0053]    In the second embodiment illustrated in FIGS.  9  to  13 , the system is very similar to that of the first embodiment. However, it is distinguished by the presence of a second elongate connection rod  3  or secondary rod of circular cross section, and by the adaptation of the connector  6  for receiving this second rod. The ring  13  is received on the first rod or main rod  2 .  
         [0054]    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.  
         [0055]    The branches  16  of the connector have respective cylindrical recesses 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.  
         [0056]    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 .  
         [0057]    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. When the two branches  16  are 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.  
         [0058]    The secondary rod  3  is placed in the recess  74  of the lower branch after the secondary screw  12  has bee 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, secondary screw  12  can no longer be separated from the connector.  
         [0059]    The upper branch  16  of the connector has at its free end a notch  76  which engages on the recess  74  with which it is contiguous and facilitates maneuvering of the secondary screw  12  by means of an instrument despite the space occupied by the upper branch.  
         [0060]    The system according to the second embodiment is fitted in a similar way to the system of the first embodiment. The placement of the main screw  8  and of the secondary screw  12  remains unchanged.  
         [0061]    After the two adjacent vertebrae  72  have been equipped, the main rod  2  is positioned 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 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 in order to correct its curvature and then put back in place. FIG. 9 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.  
         [0062]    When the system is in place, the connectors  6 , of which there are at least two, are each rigidly and simultaneously fixed to the same main rod and secondary rod.  
         [0063]    In each of these embodiments, 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 second screw  12 .  
         [0064]    Although less advantageous, the extended branch can be the one which is intended to be farthest from the vertebra.  
         [0065]    The characteristics relating to the presence of the two vertebral screws on the connector will be able to be implemented independently of those relating to the presence of the main and secondary rods, and vice versa.  
         [0066]    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.