Abstract:
The invention relates to an intervertebral implant comprising a spacer constituted by first and second parts ( 12, 14 ), said parts being provided with mutual assembly means comprising first clip-fastener means ( 54, 56 ) secured to one of said parts, second clip-fastener means ( 49, 50 ) secured to the other part and suitable for cooperating with the first clip-fastener means to achieve releasable clip-fastening between the two parts, and guide means for guiding the two parts ( 12, 14 ) during clip-fastening, said guide means being distinct from the clip-fastening means and comprising:
       a substantially non-deformable first guide assembly ( 42, 44 ) secured to one of said parts; and   a substantially non-deformable second guide assembly ( 46, 48 ) secured to the other part to co-operate with the first guide assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/579,891, filed Nov. 9, 2006, and entitled “INTERVERTEBRAL IMPLANT,” now pending, which is a 371 application of PCT/FR05/01140, filed on May 9, 2005, which claims priority to FR 0405064, filed May 11, 2004, which are all herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an intervertebral implant for an ordinary portion of the spinal column, and more particularly the invention relates to the spacer of the implant. 
     BACKGROUND 
     Intervertebral spacers are devices that are well known for placing between two adjacent vertebrae in order to secure the two vertebrae to each other so as to maintain a fixed gap between them. French patent application FR 01/03362 in the name of the Applicant describes such spacers. It suffices to recall that the spacer is provided at each of its ends with a notch in which the spinous process of a vertebra is engaged. A system of ties or braids serves to secure each end of the spacer with the spinous process. 
     Nevertheless, putting such a spacer into place raises certain problems associated with the practice of surgery. There is a ligament known as the supraspinous ligament that interconnects the tips of all the spinous processes. In order to put the spacer into place, it is necessary to move that ligament. In practice, it is detached from the two spinous processes concerned, and it is moved away by means of a suitable surgical instrument. To detach the ligament from the spinous processes, a scalpel is used. Once the spacer has been put into place, the ligament is sewn back onto the spinous processes after making a small opening therein to receive the suture. 
     The major drawback of that surgical technique is that by acting on the ligament in order to detach it and then move it out of the way, it is weakened mechanically. In addition, all of those actions take time, which lengthens the duration of the surgery. 
     To remedy that drawback, proposals have already been made for intervertebral spacers that are made up of from two distinct portions. Each portion of the spacer is put into place on either side of the supraspinous ligament, and then by using appropriate surgical instruments, the two portions of the spacer are joined together. Such two-portion spacers are described in particular in U.S. Pat. No. 6,156,038. Nevertheless, the two-portion spacers described in that document are relatively difficult to use. In particular, assembling the two portions of the spacer together in situ is relatively difficult and it is not certain that the two parts will together form the spacer in suitable manner. 
     SUMMARY 
     An object of the present invention is to provide an intervertebral spacer constituted by two distinct parts that are easier for the surgeon to assemble during surgery. 
     To achieve this object, according to the invention, in an intervertebral implant comprising a spacer constituted by first and second parts provided with mutual assembly means, the implant is characterized in that said mutual assembly means comprise:
         first clip-fastener means secured to one of said parts;   second clip-fastener means secured to the other part, suitable for co-operating with the first clip-fastener means to achieve releasable clip-fastening between the two parts in a clip-fastening direction, said first and second clip-fastening means forming integral portions of the two parts; and   guide means for guiding the two parts during clip-fastening, said guide means being distinct from the clip fastener means and comprising:
           a substantially non-deformable first guide assembly secured to one of said parts; and   a substantially non-deformable second guide assembly secured to the other part to co-operate with the first guide assembly so as to provide mutual guidance of the two parts along said clip-fastening direction and provide relative positioning of the two parts in a plane orthogonal to the clip-fastening direction.   
               

     It will be understood that because each part constituting the intervertebral spacer includes firstly guide means and secondly clip-fastener means, the guide means guarantee accurate relative positioning of the clip-fastener means in a manner that is easy for the surgeon. This ensures that the two parts constituting the spacer are properly assembled together, and furthermore, that this operation can be implemented more quickly than with the spacers of the prior art. 
     In addition, since the clip-fastener means form integral portions of the two parts, the implant is made easier for the surgeon to put into place. 
     In a preferred embodiment of the invention, each part of the spacer has an assembly face that is to be pressed against the assembly face of the other part when the two parts are assembled together. 
     Also preferably, the guide means are constituted respectively by two guide studs projecting from one of the assembly faces and by two recesses opening out into the assembly face of the other part. It is thus possible to obtain effective guidance of one of the parts relative to the other by giving the guide studs an appropriate shape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention appear better on reading the following description of an embodiment of the invention given by way of non-limiting example. The description refers to the accompanying figures, in which: 
         FIG. 1  is an exploded view of the various elements constituting the intervertebral implant; 
         FIG. 2  is an assembly face view showing one of the two parts constituting the intervertebral spacer; 
         FIG. 3  is a side view of the spacer after the two parts constituting it have been assembled together; and 
         FIG. 4  is a longitudinal section of the self-locking element used for securing the braids of the implant. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the two parts  12  and  14  which are being assembled together serve to produce the intervertebral spacer  10 . In the figure, there can also be seen a removable element  16  used for fastening purposes and for clamping braids that serve to secure two spinous processes to the spacer. The fastener element  16  is described below. The part  12  constitutes a first side piece of the intervertebral spacer. This part  12  has an inside face  12   a  and an outside face  12   b . The inside face  12   a  defines a top bearing surface  20 , a bottom bearing surface  22 , and a middle assembly face  24 . 
     The second part  14  also constitutes a side piece presenting an inside face  26   a  facing towards the inside face  12   a  of the part  12 , and an outside face  26   b . The inside face  26   a  of the side piece  26  defines a top bearing surface  28  and a bottom bearing surface  30 . In the middle region of the inside face of the side piece  26 , the part  14  has a projection  32  that projects from the central portion of the face  26   a . This projection  32  or space-defining part defines two bearing surfaces, a top surface  34  and a bottom surface  36 , these two faces being substantially parallel. The space-defining part  32  may include transverse recesses such as  38  for imparting a degree of resilience to this portion of the spacer. The free end of the space-defining part  32  defines an assembly face  40  for bearing against the assembly face  24  of the part  12  when the two parts constituting the spacer are assembled together. 
     In the assembly faces  40  and  24  of the two parts, there are provided mutual guidance means that act as these two parts move towards each other in order to  35  secure them one to the other. Preferably, the guidance means are constituted by two guide studs  42  and  44  projecting from the assembly face  40  of the part  14  and by two blind recesses  46  and  48  formed in the assembly face  24  of the part  12 . It would not go beyond the invention if only one stud were to be provided together with only one recess. Preferably, and in conventional manner, the ends of the assembly studs  42  and  44  are conical in order to provide initial positioning of the two parts. The parts  12  and  14  are secured to each other by clip-fastener means formed respectively in the side faces  12   c  and  12   d  of the part  12  and in the side faces  32   a  and  32   b  of the projection  32  of the part  14 . By way of example, for the part  12  these clip-fastener means consist of two pairs of cylindrical pegs  49  and  50  and of two side walls projecting beyond the assembly face  44  of the part  14 , given respective references  51  and  52 . Each side wall is provided with two openings  54  and  56  suitable for receiving the pegs  49  and  50  during clip-fastening. Each opening  54 ,  56  includes a deformable nib  58  or  60 . As also shown in  FIG. 1 , the pegs  49  and  50  project into a recess  60  formed in the side faces  12   c ,  12   d  of the part  12 . It should naturally be added that the guide studs  42  and  44  are of a length that is longer than that of the side walls  51  and  52  defining the female clip-fastener elements. Whatever the particular implementation of the clip-fastener means, they should form integral portions respectively of the two parts  12  and  14 . 
     As shown more clearly in  FIG. 3 , when the parts  12  and  14  are assembled together, in the manner explained below, an intervertebral spacer is obtained having the usual structure. In particular, the bearing faces  20 ,  22  of the part  12  and the bearing faces  28 ,  30  of the side piece  26  of the part  14 , and finally the top and bottom faces  34  and  36  of the extension  32  define two recesses  62  and  64  for receiving the spinous processes of the two vertebrae between which the spacer is placed. 
     Naturally, it should be added that the guide studs  42  and  44  are of a length that is greater than that of the side walls  51  and  52  defining the female clip-fastener elements. 
     The above-described spacer is used as follows. The surgeon puts the spacer-constituting parts  12  and  14  into place, going round the supraspinal ligament. Using appropriate surgical instruments, the two parts are moved towards each other so as to cause the guide studs  42  and  44  to co-operate with the guide recesses  46  and  48 . When the resulting relative positioning is achieved, the clip-fastener members  48 ,  50  and  54 ,  56  face one another in pairs. It then suffices for the surgeon to exert pressure on the outside faces of the two parts in order to cause the parts  12  and  14  to clip together, thus obtaining the complete spacer  10 . It should be added that the clip-fastener elements  48 ,  50  and  54 ,  56  are made in such a manner as to ensure effective fastening, while still making it possible for them to be separated in the event of it being necessary to change the spacer. As explained above, it is easy to put the spacer into place since it comprises only two parts. 
     With reference now to  FIGS. 1 and 4 , there follows a description of a preferred embodiment of the means for securing the spacer  10  to the spinous processes of the vertebrae. This system is constituted by the locking or fastener part  16  and by two braids T 1  and T 2 . The fastener part  16  can be secured to the outside face  26   b  of the part  14  by clip-fastener means  80 ,  82 ,  84 , and  86  that are identical to the clip-fastener means of the parts  12  and  14 . 
     The fastener part  16  presents a clip-fastener face  16   b  on the part  14  and an outside face  16   a . The fastener part  16  presents a plane of symmetry P, P′ orthogonal to the faces  16   a  and  16   b  and parallel to the faces  32  and  34  of the extension  30  of the part  14 . The locking part  16  has a central slot  90  that opens out into both faces of the part  16 , and two symmetrical inclined side slots  92  and  94  that also open out into both faces of the part  16 . 
     The clip-fastener face  16   b  of the part  16  presents two setback surfaces  96  and  98  that extend respectively between the side slots  92  and  94  and the top and bottom ends of the part  16  which constitutes braid clamping surfaces. The slot  92  and the setback surface  98  define a first sharp edge  100 . Similarly, the slot  92  and the outside face  16   a  of the part  16  define a second sharp edge  102  that is parallel to the edge  100 . As shown in the figure, the edge  102  is further away from the midplane P, P′ than is the edge  100 . In addition, it should be specified that the clamping surfaces  96  and  98  are disposed in such a manner that when the part  16  is clipped onto the spacer, the distance between the face  26   b  of the spacer and the surface  96  or  98  is slightly less than twice the thickness of the braids T 1  and T 2 . 
     Each braid T 1  and T 2  has a first end A that is secured to the part  12 . To do this, in the example described, the part  12  is provided with a top slot  104  and a bottom slot  106  in which the ends A of the braid can form a loop. After this loop has been stitched together, the braids T 1  and T 2  are effectively secured to each end of the part  12 . The braid T 2  is engaged between the surface  98  and the face  26   b  of the spacer and then in the central slot  90 . Thereafter, it passes over a portion of the outside face  16   a  of the part  16  and penetrates into the slot  62 , passing over the edge  102 . Thereafter, the braid T 2  is engaged under the presser surface  98 , between the first strand of the same braid and said surface. When the surgeon exerts traction on the end B of the braid T 2 , that serves to clamp the braid T 2  against the spinous process of the upper or lower vertebra. The braid T 1  is naturally engaged in the part  16  in the same manner in order to provide a connection with the spinous process of the other vertebra. 
     It will be understood that the fastener part  16  act for each of the braids as a self-locking system. When the surgeon exerts traction on the free end B of the braid, it can move without excessive friction in the slots  90  and  92  until the desired clamping effect is obtained. In contrast, when no traction is exerted on the end B of the braid, i.e. when the intervertebral implant is in normal use, a self-locking effect is obtained by the presence of the sharp edges  100  and  102  and the clamping effect of the presser surface  98  on the two strands of the braid. 
     In a preferred embodiment, the first clip-fastener means comprise at least two male clip-fastener members  54  and  56  that are substantially undeformable, being disposed on either side of the assembly surface  24 , and second clip-fastener means comprising at least two clip-fastener female members  49  and  50  that are elastically deformable and disposed on either side of the assembly surface  40 . 
     Also preferably, said first guide assembly comprises at least one guide stud  42  and  44  projecting from an assembly face  40  of one of the parts and at least one recess  46  and  48  opening out into the assembly face  24  of the other part.