Abstract:
Embodiments disclosed herein provide a method of implanting an intervertebral disk prosthesis that can be assembled and disassembled in a minimally invasive fashion. The prosthesis comprises a first fixing element having an anchoring first face and a cooperation second face; a second fixing element having an anchoring first face and a cooperation second face; a first prosthesis element having an active first face and a cooperation second face, the cooperation faces of the first fixing element and the first prosthesis element serving to fasten the two elements together; a second prosthesis element having an active first face and a cooperation second face, the cooperation faces of the second fixing element and the second prosthesis element serving to fasten the two elements together; and each of the active faces of the prosthesis elements defining at least a portion of a spherical cap.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/575,319, filed Oct. 7, 2009, now allowed, entitled “METHOD OF IMPLANTING INTERVERTEBRAL DISK PROSTHESIS,” which is a divisional application of, and claims a benefit of priority under 35 U.S.C. 120 of the filing date of U.S. patent application Ser. No. 10/735,603, filed Dec. 12, 2003, entitled “INTERVERTEBRAL DISK PROSTHESIS,” which claims priority to French Patent Application No. 03 09596, filed Aug. 4, 2003. The content of each application referenced herein is hereby incorporated as if fully set forth herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to an intervertebral disk prosthesis and, more particularly, to a method of implanting said prosthesis. 
       BACKGROUND OF THE INVENTION 
       [0003]    One of the pathological conditions of the vertebral column consists in degeneration of the disks that are interposed between the vertebrae of the vertebral column. This degeneration leads to a reduction in the thickness of the disk and can lead to very severe sensations of pain. When degeneration reaches an advanced stage, it is necessary to remove the natural intervertebral disk and to replace it. In the most frequent cases, a system of intervertebral spacers or cages is put into place to maintain given spacing between the vertebrae and to prevent the two vertebrae from moving relative to each other. That technique naturally presents the drawback, particularly if applied to several vertebrae, of considerably limiting the patient&#39;s ability to move. 
         [0004]    Another possible technique consists in replacing the natural intervertebral disk with an intervertebral disk prosthesis that is mounted between the vertebrae and which, ideally, conserves for the patient all of the relative mobility between the vertebrae, or at least a large fraction thereof. 
         [0005]    Another problem which arises with intervertebral disk prostheses is the surgical technique for putting such a prosthesis into place. Two techniques can be envisaged: an anterior technique, in which the prosthesis is put into place from the front face of the vertebral column; or a posterior technique in which the prosthesis is put into place via the outer face of the vertebral column, i.e. the face which is directly accessible. It will also be understood that when using the posterior technique, one of the major difficulties lies in the fact that the spinal cord is disposed between the outer posterior face of the vertebral column and the intervertebral plates between which the intervertebral disk prosthesis is to be placed. 
         [0006]    Patent application EP 00/42271 describes an intervertebral disk prosthesis suitable for being put into place by the posterior technique. However, the prosthesis described in that document gives only very limited mobility (flexion-extension) between the vertebrae between which the prosthesis is installed. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0007]    A first object of the present invention is to provide an intervertebral disk prosthesis suitable for being put into place by the posterior technique and which nevertheless provides a large amount of relative mobility for the vertebrae between which the prosthesis is located. 
         [0008]    To achieve this object, in a first aspect of the invention, the intervertebral disk prosthesis suitable for being put into place between two vertebrae by the posterior technique or by the anterior technique comprises:
       a first fixing element having both an anchoring first face for anchoring in one of the vertebrae and a cooperation second face;   a second fixing element having both an anchoring first face for anchoring in the other vertebrae and a cooperation second face;   a first prosthesis element having both an active first face and a cooperation second face, said cooperation faces of the first fixing element and of the first prosthesis element serving to fasten the two elements together in a plane substantially orthogonal to the axis of the vertebrae;   a second prosthesis element having both an active first face and a cooperation second face, said cooperation faces of the second fixing element and of the second prosthesis element serving to fasten the two elements together in a plane substantially orthogonal to the axis of the vertebrae; and   each of said active faces of the prosthesis elements defining at least a portion of a spherical cap that is respectively concave or convex, said spherical cap portions cooperating with one another.       
 
         [0014]    It will be understood that in this first aspect of the invention, the prosthesis can be put into place by the posterior technique, in particular because the fixing element of each prosthesis element is constituted by a part that is separate from the prosthesis element proper. This allows the prosthesis to be assembled and disassembled in a minimally invasive fashion. In addition, it can be seen that the active faces in contact with each other of the two prosthesis elements are in the form of spherical caps, thus allowing physiological ball-and-socket type movements to take place between the two vertebrae. 
         [0015]    In a first embodiment, each prosthesis element comprises two distinct parts, each active face of one of said parts defining a spherical cap portion such that the spherical cap portions belonging to the same prosthesis element are disposed on the same spherical surface when the two parts are fixed to the vertebrae by said fixing elements. 
         [0016]    It will be understood that in this embodiment of the first aspect of the invention, each prosthesis element is constituted by two distinct parts, thus making it easier to put the prosthesis into place by the posterior technique. Nevertheless, when the two parts constituting the prosthesis element occupy their definitive position, they define an active surface that is in the form of a spherical cap. 
         [0017]    In a second embodiment of the invention, each prosthesis element is constituted by a single part whose active face is constituted by a substantially plane surface in which a single spherical cap is formed, said spherical caps being respectively concave and convex. 
         [0018]    In a second aspect of the invention, the intervertebral disk prosthesis suitable for being put into place between two vertebrae by the anterior technique or by the posterior technique comprises:
       two prosthesis elements, each prosthesis element comprising two distinct parts, each part presenting both a first face for fixing to a vertebra and an active second face in the form of a portion of a spherical cap;   the spherical cap portions forming the active faces of the two parts belonging to the same prosthesis element being disposed on the same spherical surface when said parts are fixed to the vertebra.       
 
         [0021]    It will be understood that in this aspect of the invention, each of the two prosthesis elements is constituted by two distinct parts which can thus be put into place on either side of the spinal cord. Nevertheless, once these two parts form a prosthesis element occupying its definitive position, they together define a portion of a spherical cap, thus enabling the desired ball-and-socket type movements to be obtained. 
         [0022]    In a preferred embodiment of this second aspect of the invention, the two parts forming a prosthesis element are fixed to the vertebrae and positioned appropriately relative to each other so as to define the portion of a spherical cap with the help of a fixing element which is distinct from the two parts forming the prosthesis element. This disposition serves to reduce the size of the prosthesis element and thus to simplify putting the intervertebral disk prosthesis into place by the posterior technique. In this way, the prosthesis can be implanted in a less invasive manner. 
         [0023]    A second object of the invention is to provide a method of implanting an intervertebral disk prosthesis of the above-defined type by a posterior technique which is particularly adapted to said prosthesis. 
         [0024]    This object is achieved by a method comprising the following steps:
       providing a posterior access to the intervertebral plate into which said prosthesis is to be implanted;   moving apart the two vertebrae defining said space;   removing the natural intervertebral disk; and   implanting said prosthesis between the vertebrae by performing the following steps:
           a) inserting at least one fixing element between the vertebrae around one side of the dura mater;   b) causing said fixing element to turn so as to place it beyond the dura mater in its anchoring location;   c) anchoring said fixing element in the vertebra;   d) when necessary, repeating steps a), b), and c) for the second fixing element;   e) introducing the prosthesis elements around at least one side of the dura mater; and   f) causing each prosthesis element to cooperate with a fixing element.   
               
 
         [0035]    A third object of the invention is to provide a method of implanting an intervertebral disk prosthesis of the above-defined type by an anterior technique which is specifically adapted to said prosthesis. 
         [0036]    This object is achieved by a method comprising the following steps:
       providing an anterior access to the intervertebral plate into which said prosthesis is to be implanted;   moving apart the two vertebrae defining said space;   removing the natural intervertebral disk; and   implanting said prosthesis between the vertebrae by performing the following steps:
           a) inserting at least one fixing element between the vertebrae;   b) anchoring said fixing element in the vertebra;   c) when necessary, repeating steps a) and b) for the second fixing element;   d) inserting the prosthesis elements between the vertebrae; and   e) causing each prosthesis element to cooperate with a fixing element.   
               
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    Other characteristics and advantages of the invention appear better on reading the following description of embodiments of the invention given as non-limiting examples. The description refers to the accompanying drawings, in which: 
           [0047]      FIG. 1  is a simplified vertical section view showing the first aspect of the invention; 
           [0048]      FIG. 2A  is a simplified vertical section view showing the second aspect of the invention; 
           [0049]      FIG. 2B  is a section view of  FIG. 2A  on line B-B; 
           [0050]      FIG. 3A  is a front view of the fixing element of a first embodiment of the prosthesis; 
           [0051]      FIG. 3B  is a side view of the fixing element of  FIG. 3A ; 
           [0052]      FIG. 4A  is a front view of two parts forming a prosthesis element of the first embodiment; 
           [0053]      FIG. 4B  is a view of a prosthesis element seen looking along arrow B in  FIG. 4A ; 
           [0054]      FIG. 4C  is a plan view of two parts constituting the prosthesis element; 
           [0055]      FIG. 5  is a perspective view showing how the prosthesis elements and the fixing elements are assembled together; 
           [0056]      FIG. 6A  is an elevation view of the fixing element in a second embodiment of the prosthesis; 
           [0057]      FIG. 6B  is a view from below of the fixing element shown in  FIG. 6A ; 
           [0058]      FIG. 7A  is a perspective view showing the prosthesis elements of the second embodiment of the prosthesis; 
           [0059]      FIG. 7B  is a longitudinal section view of one of the prosthesis elements of the second embodiment of the prosthesis; 
           [0060]      FIG. 7C  is a longitudinal section view of the second prosthesis element of the second embodiment of the prosthesis; 
           [0061]      FIG. 8  is a perspective view showing how the prosthesis elements and the fixing elements of the second element of the intervertebral disk prosthesis are assembled together; 
           [0062]      FIGS. 9 and 10  are perspective views showing variant embodiments of the members for anchoring in the vertebrae; 
           [0063]      FIG. 11  shows a variant embodiment for correcting tendencies to scoliosis; 
           [0064]      FIGS. 12A and 12B  show the resections that the surgeon needs to perform in order to put the intervertebral disk prosthesis into place; 
           [0065]      FIGS. 13A to 13G  show different steps in installing a prosthesis of the type shown in  FIG. 5 ; 
           [0066]      FIGS. 14A and 14B  are simplified views showing steps of installing the prosthesis shown in  FIG. 10 ; 
           [0067]      FIGS. 15A to 15C  are simplified views showing steps of installing a prosthesis of the type shown in  FIG. 8 ; 
           [0068]      FIGS. 16A to 16C  show the prosthesis shown in  FIG. 5  being installed by the anterior technique; and 
           [0069]      FIGS. 17A and 17B  show the prosthesis shown in  FIG. 8  being installed by the anterior technique. 
       
    
    
     DETAILED DESCRIPTION 
       [0070]    With reference initially to  FIG. 1 , there follows a description of a first aspect of the intervertebral disk prosthesis. 
         [0071]    In this figure, there is shown in simplified manner a first vertebra V 1  and a second vertebra V 2  between which the intervertebral disk prosthesis  10  is to be put into place. The prosthesis  10  is constituted by a first prosthesis element  12  and a second prosthesis element  14 , and by a first fixing element  16  and a second fixing element  18 . The prosthesis element  12  has a cooperation face  12   a  and an active face  12   b  also referred to as a rubbing face or a contact face. This face  12   b  is in the form of a convex spherical cap. The prosthesis element  14  also has an active face or contact face  14   b  which is in the shape of a concave spherical cap and which is naturally designed to cooperate with the active surface  12   b  of the prosthesis element  12 . As explained in greater detail below, the radii of curvature of the spherical caps  12   b  and  14   b  are not identical. The prosthesis element  14  also has a cooperation face  14   a.    
         [0072]    The fixing element  16  presents a cooperation face  16   a  and an anchoring face  16   b.  The anchoring face  16   b  is provided with any suitable anchoring member  22  for fixing the fixing element  12  to the plate of the vertebra V 1 . The cooperation face  16   a  of the fixing element  16  is provided with fasteners that cooperate with complementary fasteners of the face  12   a  of the prosthesis element  12  to fasten the prosthesis element to the fixing element, at least in a horizontal plane. 
         [0073]    Similarly, the fixing element  18  has a cooperation face  18   a  and an anchoring face  18   b  provided with an anchoring member  24 . 
         [0074]    It will be understood that in this first aspect of the invention, because the prosthesis elements proper and the fixing elements are distinct parts, it is easier to put the intervertebral disk prosthesis into place between the vertebrae while nevertheless ensuring that it is properly secured to the vertebrae. It will also be understood that since each prosthesis element has an active face in the form of a spherical cap, the ball-and-socket type mobility between the two vertebrae is indeed recreated. 
         [0075]    Reference is now made to  FIGS. 2A and 2B  for describing the intervertebral disk prosthesis in its second aspect. 
         [0076]    In these figures, there can be seen the vertebrae V 1  and V 2  between which the prosthesis is to be put into place. The prosthesis is constituted by a first prosthesis element  12 ′ and by a second prosthesis element  14 ′. Each prosthesis element  12 ′ and  14 ′ is constituted by two distinct parts referenced  26  and  28  for the prosthesis element  12 ′ and  30  and  32  for the prosthesis element  14 ′. Each part forming the prosthesis elements has both a fixing face referenced  a , and an active face referenced b. The fixing faces  a  of the parts  26  to  32  are provided with fasteners for engaging the vertebrae V 1  and V 2 , these fasteners possibly being constituted by separate parts, as explained below and as shown in  FIG. 1 . 
         [0077]    The active faces  a  of the parts constituting the prosthesis elements are defined in such a manner that they form portions of spherical caps that are respectively concave and convex. When the parts  26  and  28  forming the prosthesis element  12 ′ are put into place on the vertebra V 1 , their active faces  a  are disposed on a concave spherical cap C. Similarly, the active faces  a  of the parts  30  and  32  forming the prosthesis element  14 ′ are disposed on a spherical cap C′. As mentioned above, these spherical caps C and C′ may have different radii of curvature. 
         [0078]    It will be understood that because the two parts constituting the same prosthesis element together constitute a friction or contact surface that is in the form of a spherical cap, the same ball-and-socket mobility is obtained as in  FIG. 1 . In addition, because each prosthesis element is constituted by two distinct parts, it will be understood that it is easier for the surgeon to put the prosthesis element into place between the vertebrae. 
         [0079]    With reference to  FIGS. 3 ,  4 , and  5 , a first embodiment of the intervertebral disk prosthesis is described. 
         [0080]    In  FIGS. 3A and 3B , there can be seen a fixing element referenced  40 . The fixing element  40  is constituted by a plate  42  having an anchoring face  42   b  provided with two transverse ribs  44  and  46  which constitute parts for anchoring in a vertebra. The cooperation face  42   a  of the plate  42  is fitted with two locking members for locking to the prosthesis element. Each of the locking members  48  and  50  is constituted by a strip  54  extending parallel to the ribs  44 . The right section of each strip  54  is generally T-shaped, the strip comprising two flanges  56  and  58  in its portion that is furthest from the plate  42 . In addition, in order to enable the strips to deform elastically to a certain extent, each of them has a longitudinal slot  60 . 
         [0081]    In  FIGS. 4A ,  4 B, and  4 C, there can be seen a prosthesis element  62  which is constituted by two separate parts  64  and  66 . The active faces  b  of the parts  64  and  66  constitute portions of a spherical cap. Thus, as explained above, when the parts  64  and  66  are fixed on a vertebra, the spherical cap portions  b  lie on the same spherical surface. The cooperation face a of each part  64  and  66  includes an anchoring groove  68  over a fraction of its length, the right section of the groove being generally T-shaped and being dimensioned to be capable of receiving the anchoring members  48  and  50 . The grooves  68  extend over a fraction only of the length of the parts  64  and  66  corresponding to the length of the anchor parts  48  and  50 . In addition, and preferably, the cooperation faces  a  of the parts  64  and  66  include respective setbacks  70  and  72  such that when these parts are fixed on a vertebra, the plate  42  of the fixing element  40  penetrates fully into said setback. As can be seen in  FIG. 4C , the grooves  68  open out via their ends  68   a  into end faces of the parts  64  and  66  so as to enable the locking members  48  and  50  to be inserted into the fixing element  40 . 
         [0082]    Naturally, the prosthesis as a whole has a second fixing part  40 ′ identical to the part  40  and a second prosthesis element  62 ° which differs from the prosthesis element  62  solely by the fact that its active surface  b  defines a spherical cap that is concave. 
         [0083]      FIG. 4  shows the two prosthesis elements constituted by the parts  64  and  66  and two other analogous parts mounted on the fixing elements  40  and  40 ′. 
         [0084]    It can be seen that the fixing elements  40  and  40 ′ in this embodiment serve not only the fix each prosthesis element to the corresponding vertebra, but also to position the two parts constituting the same prosthesis element in such a manner that their active surface does indeed constitute a spherical cap. 
         [0085]      FIG. 11  shows a variant of the first embodiment of the intervertebral disk prosthesis suitable for correcting a tendency to scoliosis. 
         [0086]    In this variant, when the prosthesis elements  64 ′ and  66 ′, and the fixing elements  40  and  40 ′ are assembled together, the plates  42  of the fixing elements form between them an angle A. In order to obtain this result, the cooperation faces  a  of the parts  64  and  66  forming the prosthesis element  62  are disposed in a plane PP′, P 1 P 1 ′ which is not orthogonal to the common axis XX′ of the spherical caps C and C′ which are constituted by the active faces of the prosthesis elements. 
         [0087]    With reference now to  FIGS. 6 ,  7 , and  8 , there follows a description of a second embodiment of the intervertebral disk prosthesis. In this second embodiment, each prosthesis element is constituted by a single part and each prosthesis element is fixed to the corresponding vertebra by a separate fixing element. 
         [0088]      FIGS. 6A and 6B  show an embodiment of the fixing element  80 . The fixing element  80  is constituted by a preferably rectangular plate  82  that is relatively massive. The anchoring face  82   b  of the plate  82  is provided with members for anchoring in the vertebra constituted, for example, by two ribs  84  and  86  identical to those fitted to the fixing element  40  shown in  FIG. 3 . As explained below, other anchoring elements could be used. 
         [0089]    As shown in  FIG. 6B , the cooperation face  82   a  is provided with a locking groove  88 . This locking groove has an insertion first portion  90  opening out into a long side of the plate  82  and a locking portion  92  which extends parallel to the long direction of the plate  82 . As shown in  FIG. 6A , the groove  88  has a right section that is T-shaped. 
         [0090]    Naturally, the complete prosthesis has a second fixing element  80 ′. 
         [0091]      FIGS. 7A ,  7 B, and  7 C show the prosthesis elements of the prosthesis constituting the second embodiment. The prosthesis element  100  is constituted by a massive part whose cooperation face  a  presents a shoulder  102  defining a setback portion  104  with the length of the setback portion  104  corresponding to the width of the plate  82  of the fixing element  80 . A locking member  106  projects from the setback portion  104 . The shoulder  102  corresponds to the thickness of the plate  82 . This locking member which is preferably circularly symmetrical about the axis xx′ is constituted by a head  108  and a body  110 . The diametral section of the locking member  108  is of a shape which corresponds to the shape of the T-groove  88  formed in the plate  82  of the fixing element  80 . The active or contact face  b  of the prosthesis element  100  comprises a substantially plane portion  112  and a portion  114  in the form of a concave spherical cap. 
         [0092]    The second prosthesis element  120  is identical to the prosthesis element  100  with the exception of its active face  b  which comprises a substantially plane portion  122  and a portion in the form of a convex spherical cap  124  suitable for cooperating with the concave spherical cap  114  of the prosthesis element  100 . 
         [0093]    In  FIG. 8 , there can be seen the prosthesis elements  100  and  120  mounted on the two fixing elements  80  and  80 ′. As can be seen more clearly in this figure, in the assembled position, the prosthesis elements  100  and  120  are orthogonal to the fixing elements  80  and  80 ′. 
         [0094]      FIG. 9  shows a variant embodiment of the anchoring element provided on the anchoring faces of the fixing elements  80  or  40 . In this embodiment, the anchoring elements given general reference  130  is constituted by two projecting triangular parts  132  and  134  each having one of its short sides connected to the short side of the other triangle to form an edge  136 , the angle between the triangles  132  and  137  being less than 180 degree. This method of anchoring serves to prevent any displacement in the planes of the vertebral plates. 
         [0095]    In  FIG. 10 , there can be seen another variant embodiment of the anchoring element which is in this particular case consists in four generally cylindrical studs  140  terminating in conical portions. This figure also shows that the locking members  48  and  50  of the fixing element  40  are preferably spaced further apart than the locking members  48 ′ and  50 ′ of the fixing element  40 ′. This makes it possible for the two fixing elements  40  and  40 ′ to be placed in the configuration shown in the figure. The total thickness of the assembly constituted by the two fixing elements is thus reduced, thereby enabling them to be inserted simultaneously between the two vertebrae. 
         [0096]    The description above relates to two embodiments of the intervertebral disk prosthesis of the invention, together with variants thereof. As mentioned above, one of the advantages of these prostheses is that they can be put into place using a posterior technique. 
         [0097]    With reference initially to  FIGS. 12A and 12B , there follows a description of the method of putting the prosthesis shown in  FIGS. 3 ,  4 , and  5  into place by the posterior technique. 
         [0098]    As in the conventional posterior technique for putting intervertebral cages into place, the surgeon begins by providing posterior access to the vertebrae between which the prosthesis is to be placed: the surgeon must also move the two vertebrae apart and remove the natural disk. 
         [0099]    Thereafter, the surgeon usually performs certain resections of portions of the two vertebrae onto which the prosthesis is to be fixed. These resections relate essentially to the epiphysis and to the facets of the vertebrae. 
         [0100]    Functionally, the major resections are those enabling the fixing elements to be anchored to the vertebrae where that is necessary. These resections performed in the vertebral plate are of a shape that is adapted to the anchoring elements with which the fixing elements are fitted. For the rib-shaped fixing elements ( FIGS. 3 and 6 ), these resections consist in slots F 1  and F 2  formed in the posterior portions of the vertebral plates ( FIG. 12A ). For anchoring elements in the form of pegs ( FIG. 10 ), the resections are in the form of holes T 1 , T 2 , . . . pierced in the vertebral plate ( FIG. 12B ). In other circumstances there is no anchoring element proper. 
         [0101]      FIGS. 13A to 13G  show a vertebral disk prosthesis of the shape shown in  FIGS. 3 to 5  being put into place. 
         [0102]    Initially, the bottom fixing element  40 ′ is inserted between the vertebrae V 1  and V 2  via their posterior portions ( FIG. 13A ) from one side or the other of the dura mater. Then the fixing element  40 ′ is pushed to go around the spinal cord (dura mater) ( FIG. 13B ) by pivoting and come into position in such a manner that the anchoring ribs are in register with the slots F 1  and F 2  ( FIGS. 13C and 13D ), after which the anchoring ribs are pushed into the slots F 1  and F 2  ( FIG. 13E ). The same process is used for putting into place the upper fixing element  40  under the upper vertebra V 1 . 
         [0103]    As shown in  FIG. 10 , it is also possible to introduce two fixing elements simultaneously between the vertebrae and then to put them into place separately in the resections. 
         [0104]    Still using the posterior technique, the parts  64  and  64 ′ constituting the right-hand portions of the prosthesis elements are put into place around the right-hand side of the dura mater, going around the spinal cord. 
         [0105]    The fastening grooves  68  are engaged on the ends of the fastening strips  48  of the fixing elements. This engagement is made possible by the ability of the strips  48  to deform. The prosthesis elements are pushed until the plates  42  of the fastening elements  40 ,  40 ′ penetrate into the setbacks  72  of the prosthesis parts  64  ( FIG. 13G ). 
         [0106]    Finally, the same operation is performed on the parts  66  of the prosthesis elements by engaging them via the left side of the dura mater. 
         [0107]      FIG. 14A  shows fixing elements being inserted when they are implemented as shown in  FIG. 10 .  FIG. 14B  shows subsequent placement of the prosthesis elements. 
         [0108]      FIGS. 15A to 15C  show the main steps in putting the intervertebral disk prosthesis shown in  FIG. 8  into place. 
         [0109]      FIG. 15A  shows the bottom fixing element  80 ′ being put into place by being engaged using the posterior technique around one side of the dura mater, after which this part is turned so as to put into position beyond the dura mater. This operation ends with anchoring ribs being inserted into the slots F 1 , F 2 .  FIG. 15A  also shows in “symbolic” manner the upper fixing element  80  put into place. 
         [0110]      FIG. 15B  shows the initial stage of putting the prosthesis elements  100  and  120  into place. In this stage, the prosthesis elements are inserted between the vertebrae on one side of the spinal cord, moving in their long direction. The locking members  106  are presented to the inlets to the first portions  90  of the locking grooves  88  in the fixing elements until they come into abutment. 
         [0111]    Thereafter ( FIG. 15C ), the surgeon pushes the prosthesis elements sideways so that the locking members  106  come into abutment at the ends of the second portions  92  of the locking grooves  88 . The prosthesis elements are locked to the fixing parts by cooperation between the shoulders  102  and the edges of the fixing elements. 
         [0112]    As explained above, an important advantage of the intervertebral disk prosthesis is that it can be put into place by the posterior technique. Nevertheless, this prosthesis can naturally also be put into place by the anterior technique. 
         [0113]      FIGS. 16A to 16C  show the prosthesis shown in  FIG. 5  being put into place by the anterior technique, and  FIGS. 17A to 17B  show the prosthesis shown in  FIG. 8  being put into place by the anterior technique. 
         [0114]    Firstly, it should be observed that the slots F′ 1  and F′ 2  are adapted to anterior placement so they open out into the periphery of the vertebral plate ( FIG. 16A ). Thereafter, the fixing elements  40  and  40 ′ are put into place between the vertebrae and inserted into the slots F′ 1  and F′ 2 . 
         [0115]    Finally, the parts  26 ,  28 ,  30 , and  32  forming the prosthesis elements are put into place on the fixing elements  40  and  40 ′. 
         [0116]      FIG. 17A  shows fixing elements  80  and  80 ′ being put into place by the anterior technique, and  FIG. 17B  shows the prosthesis elements  100  and  120  being put into place on the fixing elements.