Abstract:
A vertebral fixing system comprising a connecting part with two longitudinal elements coupled to each other at a first end and having mutually facing recesses for receiving a rod. A portion of a flexible ligature extends through orifices of the two longitudinal elements to define a loop opposite two free ends of the flexible ligature. The two longitudinal elements are engaged at a second end of the connecting part via a locking means. When the two longitudinal elements of the connecting part are locked at the second end of the connecting part, two strands of the flexible ligature are pinched between the rod and a wall of the mutually facing recesses of the two longitudinal elements of the connecting part, preventing the flexible ligature from moving in translation relative to the connecting part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims foreign priority benefits under 35 U.S.C. §119 to International Application No. PCT/FR2006/050898, filed Sep. 18, 2006, which claims priority to French Application Nos. FR 0650609, filed Feb. 22, 2006, and FR 0509570, filed Sep. 29, 2005. All applications listed herein are incorporated by reference in their entireties. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to vertebral fixing system suitable for being mounted on a vertebra. 
     An intended field of application is particularly, but not exclusively, the treatment of scoliosis, or more generally correcting abnormal curvatures of the spine. 
     BACKGROUND OF THE RELATED ART 
     The spine is constituted by superposed vertebrae that are normally in alignment along a vertical axis, going from the lumbar vertebrae to the cervical vertebrae, each vertebra presenting a posterior wall from which there projects a spinous process and two sides having walls from which there project the ribs and/or transverse processes. When the spine of an individual presents abnormal curvature, the vertebrae are inclined relative to one another and relative to said vertebral axis. The sides of the vertebrae situated on one side are thus moved closer together forming a concave side, whereas the sides of the vertebrae on the other side are spaced apart from one another and form a convex side. 
     In order to straighten the spinal column, the sides of the vertebrae on the concave side are spaced apart from one another and moved relative to one another to distances that are substantially equivalent to those between the sides of the vertebrae on the other side. In order to keep the vertebrae in that relative positioning, known devices have screws that are inserted in the vertebrae or hooks that are inserted along the inside wall of the vertebral canal, and rods that are for interconnecting the screws or the hooks. 
     The hooks are generally inserted in pairs into each vertebra and on either side close to the pedicles, with their heads projecting from the posterior wall of the vertebra, one on either side of the spinous process. By way of example, the heads form a socket suitable for receiving a rod that is held in place by means of a nut screwed onto the head so as to press against the rod. The rows constituted by the heads of the hooks situated on either side of the spinous processes are interconnected and held in a fixed position by two rods that are parallel to each other and to the axis of the spine. 
     SUMMARY OF THE INVENTION 
     Nevertheless, it is difficult to use such hooks since the operator must under no circumstances interfere with the spinal cord that extends along the center of the vertebral canal, since otherwise there is a danger of paralyzing the patient. 
     The use of screws makes it possible to diminish the risks of the operation. The screws likewise have socket-forming heads and they are inserted in pairs into the posterior walls of the vertebrae in the pedicles on either side of the spinous process. Thus, the screws constitute points for fixing the vertebrae so as to hold them relative to one another. Nevertheless, they are necessarily introduced into the pedicles of the vertebrae, and under certain circumstances such pedicles can be small in size or damaged. 
     SUMMARY OF THE INVENTION 
     The problem that arises and that the present invention seeks to solve is how to establish fixing points when it is not possible to introduce screws into the vertebrae in the curved portion of the spine and when the use of hooks is too dangerous. PCT patent application WO 2004/010881 in the name of the Applicant describes a vertebral fixing system that enables the problem to be solved. 
     That vertebral fixing system adapted to be mounted on a vertebra of the spine to connect it to a rod comprises:
         a connecting part placed facing said rib and/or said transverse process and suitable for being connected to said rod;   an elongate flexible ligature suitable for connecting together said connecting part and at least one rib and/or one transverse process; and   adjustable locking means fastened to said connecting part, said ligature having a first end secured to said connecting part and a free second end suitable for sliding in said connecting part to form a loop, said locking means being suitable for holding in a fixed position both said connecting part relative to said rod, and a length of said ligature between said ends that is suitable for being prevented from moving in translation relative to said connecting part by said adjustable locking means, whereby the loop presents a length that is determined so as to prevent relative displacement of said rod and said vertebra in opposite directions.       

     That system is satisfactory, but under certain circumstances it can present the following drawback. When the surgeon exerts traction on the free end of the flexible ligature, the ligature can be jammed by friction against the bottom face of the process. Under such circumstances, it will be understood that although the length of the ligature between the bottom face of the process and the zone where traction is applied to the ligature is indeed under tension, the length that extends between the end of the ligature that is secured to the elongate passageway and the bottom face of the process is not under tension. Thus, overall, the ligature does not perform its function of fastening to the vertebra in appropriate manner. 
     An object of the present invention is to provide a vertebral fixing system that enables the above-mentioned drawbacks to be avoided and that provides controlled locking of the ligature. 
     According to the invention, to achieve this object, the vertebral fixing system suitable for being mounted on a vertebra of the spine in order to connect it to a rod comprises:
         a connecting part presenting first and second sides and suitable for being connected to said rod;   a flexible ligature of elongate shape suitable for connecting together said connecting part and at least one rib and/or transverse process and/or a portion of the posterior arc of a vertebra; and   adjustable locking means mounted on said connecting part;       

     and said system is characterized in that:
         said ligature presents two free ends;   said connecting part defines at least one passageway for passing said ligature in such a manner that two distinct strands of said ligature can be engaged in said passageway(s) so that said two ligature strands define a first ligature portion forming a loop that extends from a first side of said connecting part, and second and third ligature portions extending from the other side of said connecting part between respective ones of said ligature strands and said free ends; and   said locking means are distinct from the connecting part and co-operate therewith by screw-fastening, said locking means being capable of taking a first position relative to the connecting part in which the two ligature strands are free in said strand-passing passageway(s), a second position relative to the connecting part in which the two ligature strands are prevented from moving in translation relative to the connecting part, and intermediate positions in which a coefficient of friction is created between said ligature strands and said connecting part.       

     It will be understood that because the two ligature strands that are on either side of the transverse process are both placed in one or more passageways, when the locking means are brought into their locking position, both ligature strands can be used to exert the tension needed for fixing to the vertebra by means of a rib and/or a portion of the posterior arc of a vertebra and/or a transverse process. 
     In addition, since the locking means co-operate with the connecting part by screw-fastening, the “dimensions” of the passageways can be defined accurately during the various stages of clamping and then locking the ligature. 
     Preferably, the connecting part defines a single passageway and both ligature strands are engaged in the single passageway. 
     Also preferably, the single passageway is defined firstly by the outside surface of the portion of the rod that is engaged in the connecting part and secondly by a wall of the connecting part, and the locking means are suitable for modifying the section of the passageway. 
     When the locking means are in their second position, this ensures effective clamping of the two ligature strands, thereby preventing them from moving. 
     In a first embodiment, the connecting part comprises two longitudinal elements having first ends that are hinged together, each of said longitudinal elements presenting a recess suitable for receiving a portion of a section of said rod, a wall of said recess co-operating with the side surface of said rod to define said passageway for passing said ligature strands, said locking means being mounted at the two second ends of said longitudinal elements. 
     In a second embodiment, the connecting part comprises a part that is generally U-shaped, suitable for receiving said rod, and having the outer ends of the limbs of the U-shape threaded, and the adjustable locking means comprise a tapped ring suitable for co-operating with the thread on the U-shaped part, tightening the ring causing the limbs of the part to be clamped against the rod. 
     Preferably, said passageway(s) is/are constituted by the space between the inside wall of the recess formed in said connecting part and the side wall of said rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention appear better on reading the following description of embodiments of the invention given by way of non-limiting example. The description refers to the accompanying figures, in which: 
         FIG. 1  is a perspective view of a first embodiment of a vertebral fixing system; 
         FIGS. 2A ,  2 B, and  2 C are vertical section views of the fixing system showing the use of said system as shown in  FIG. 1 ; 
         FIG. 3  is a face view showing the  FIG. 1  fixing system put into place on a vertebra; 
         FIG. 4  is a perspective view of a second embodiment of the fixing system, the ligature not being shown; 
         FIG. 5  is an exploded view of the connection device of  FIG. 4 ; 
         FIG. 6  is a plan view of a portion of the  FIG. 1  connection device; 
         FIG. 6A  is a section view on line AA of  FIG. 6 ; 
         FIG. 7  is a face view of the fixing system of the second embodiment; and 
         FIGS. 7A and 7B  are section views on line VII-VII of  FIG. 7  showing two ways in which the flexible ligature can be put into place. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , in the first embodiment, the vertebral fixing system comprises a connecting part  12 , a flexible ligature  14 , and adjustable locking means  16 . The flexible ligature  14  is of elongate shape and is capable of matching the outline of the parts it is to connect together. In this figure, there can also be seen the rod  18  that is to be secured to the vertebra by means of the vertebral fixing system. In the first embodiment, the connecting part  12  is constituted by two longitudinal elements given respective references  20  and  22 , each having a first end  22   a ,  20   a  and a second end  22   b ,  20   b.    
     As can be seen better in  FIG. 2A , the longitudinal elements  20  and  22  are hinged to each other at their second ends  20   b ,  22   b  about a pivot pin  24 . 
     In the embodiment described, the locking means are constituted by a screw  26  having a head  26   a  that is engaged in a bore  28  formed in the first end  22   a  of the longitudinal element  22 . The first end  20   a  of the longitudinal element  20  is pierced by a tapped bore  28  for co-operating with the threaded shank  26   b  of the screw  26 . Each longitudinal element  20 ,  22  has an outside face  20   c ,  22   c  and an inside face  20   d ,  22   d . The longitudinal elements  20  and  22  are mounted in such a manner that the inside faces  20   d ,  22   d  of the longitudinal elements face each other. The inside faces  20   d ,  22   d  of the longitudinal elements  20  and  22  have respective mutually-facing recesses  30  and  32 , each of substantially semicylindrical shape. The recesses  30  and  32  define walls  34  and  36  which are ruled surfaces having generator lines parallel to the pivot axis  24 . Finally, slots  38  and  40  cause the bottoms of the recesses  30  and  32  to communicate with the outside faces  20   c  and  22   c  of the longitudinal elements  20  and  22 . As explained in greater detail below, the recesses  30  and  32  are for receiving the rod  18  together with a strand of the ligature  14 , the slots  38  and  40  serving to pass the ligature  14 . 
     With reference to  FIGS. 2A to 2C , there follows an explanation of how the fixing system is used. 
     In  FIG. 2A , there can be seen the longitudinal elements  20  and  22  in the spaced-apart position, a position in which the locking means  16  are naturally not active, the threaded shank  26   b  of the screw  26  not being engaged in the bore  28 . The ligature  14  is engaged in the slots  38  and  40  of the longitudinal elements against one portion of the inside wall  34 ,  36  of the recesses  30  and  32 . The rod  18  is then introduced into the recess  30  of the longitudinal element  20  so that the two strands  42  and  44  of the ligature  14  are disposed between the inside wall of the recesses  30  and  32  and the side face  18   a  of the rod  18 . These two surfaces define a passageway  46  for passing the ligature  14  and having the strands  42  and  44  of the ligature  14  placed therein. 
     As shown better in  FIG. 2B , the strands  42  and  44  of the ligature define a portion of the ligature  14  that forms a loop  48  that extends beyond the outside face  20   c  of the longitudinal element  20 , and also two free portions  50  and  52  that extend beyond the outside face  22   c  of the longitudinal element  22 . When the longitudinal elements  20  and  22  are spaced apart as shown in  FIG. 2B , the ligature  14  can slide freely along the passageway  46 . Once the portion  48  of the ligature  14  forming the loop is placed around the transverse process or a rib or indeed a portion of the posterior arc of a vertebra, the surgeon engages the threaded shank  26   b  of the screw  26  in the tapped bore  28 , causing the longitudinal element  22  to come progressively closer to the longitudinal element  20 . This approach simultaneously reduces the section of the passageway  46  in which the strands  42  and  44  of the ligature are engaged and simultaneously introduces a certain coefficient of friction between the ligature and respectively the rod  18  and the walls of the recesses  30  and  32 . Nevertheless, it is still possible for the surgeon to extract traction on the free ends  50  and  52  of the ligature  14  until sufficient tension is obtained in the ligature around the vertebral process. Once the tension in the ligature is sufficient for providing appropriate fastening, the surgeon finishes off tightening the screw  26  in the tapped bore  28 , thus locking the longitudinal elements  20  and  22  together. Simultaneously, it will readily be understood that the strands  42  and  44  of the ligature are pinched between the rod  18  and the wall of the recesses  30  and  32 . 
     In this locking position, the rod  18  is thus secured to the ligature  14  via the connecting part  12 . 
     It will also be understood that because the surgeon exerts traction only on the free ends  50  and  52  of the ligature  14 , there is no risk of jamming between the ligature  14  and the bottom face of the transverse process or of the rib, thus guaranteeing that effective fastening is provided with the transverse process or the rib or indeed a portion of the posterior arc of a vertebra. 
     This is shown in  FIG. 3 , where reference AT identifies the transverse process. 
     In the above description, both of the strands  42  and  44  of the ligature are disposed in the recesses  30  and  32  on the same side of the rod  18 . This disposition serves to obtain an optimum result. Nevertheless, it would not go beyond the invention if the strands  42  and  44  of the ligature  14  were to be placed on opposite sides of the rod  18 . Under such circumstances, it should be considered that the outside face  18   a  of the rod  18  and the inside walls of the recesses  30  and  32  define two passageways, respectively for passing each of the strands  42  and  44  of the ligature  14 . 
       FIGS. 4 to 7B  show a second embodiment of the fixing system. 
     In these figures, there can be seen the rod  18 , the connecting part now referenced  12 ′, and the flexible ligature  14 . 
     In this embodiment, the connecting part  12 ′ is constituted by a part  50  that is generally U-shaped. The inside wall of this part is constituted by a bottom  52  of substantially semicylindrical shape and by two substantially plane portions  54  and  56  that correspond to the two limbs of the part  50 . The width l of the recess  58  formed in the part  50  is substantially equal to the diameter d of the rod  18 . On its outside face  50   a  which is circularly symmetrical about a longitudinal axis of the part  50 , there is provided a thread  60  occupying its upper portion. The thread  60  is located entirely above the rod  18  when it is put into place in the recess  58 . The thread  60  is designed to co-operate with a clamping ring  62  that constitutes the adjustable locking means. This ring has a slightly frustoconical bore  64  with an inside face  66  that carries tapping  68 . 
     It can thus be understood that when the ring  62  is screwed tight on the threaded portion  60  of the part  50 , it deforms the limbs of the part  50  elastically, thereby pinching and clamping strands of the ligature  14  between the rod  18  and the inside wall(s) of the recess  58 , in a manner explained below. 
     As shown better in  FIGS. 6 and 6A , the part  50  includes in its bottom  70  a passage  72  for passing the ligature  14  in a manner explained below. 
     With reference to  FIGS. 7 ,  7 A, and  7 B, there follows a description of two different ways of putting the flexible ligature  14  into place inside the connecting part  12 ′ in the second embodiment. The side wall of the rod  18  and the inside wall of the recess  58  of the part  50  potentially define two passageways  74  and  76  for passing the middle strands of the flexible ligature  14 . In the configuration shown in  FIG. 7A , only the passageway  74  is used. Thus, both intermediate strands  42  and  44  of the flexible ligature  14  are disposed in the passage  74 . This disposition presents all of the advantages described with reference to the first embodiment. 
     In the configuration shown in  FIG. 7B , the middle strands  42  and  44  of the flexible ligature  14  are disposed respectively one in each of the passageways  76  and  78 , i.e. on either side of the rod  18 . This configuration likewise presents all of the advantages described with reference to the first embodiment of the device since the free ends  50  and  52  of the ligature  14  are accessible for exerting the desired traction in order to obtain suitable clamping on the spinous process prior to locking the clamping ring  62  on the part  52 . 
     This second embodiment presents the advantage of being simpler in design since it serves in particular to avoid making two longitudinal parts constituting a kind of clamp hinged on the pin  24 . 
     It will be understood that in both embodiments, the locking means are constituted by an element that is distinct from the connecting part and that is removable therefrom. In addition, in both cases, the locking means co-operate with the connecting part by screw engagement. It is thus possible to adjust accurately the dimensions of the ligature-passing passageway(s) as defined by the connecting part and the rod. In an initial stage, the coefficient of friction between the coefficient of the ligature and secondly the rod and the connecting part can be adjusted. In the final stage, very effective clamping of the ligature is obtained between the rod and the locking part.