The present disclosure relates to the subject matter disclosed in German patent application 10 2008 005 998.6 of Jan. 25, 2008, which is incorporated herein by reference in its entirety and for all purposes. 
     BACKGROUND OF THE INVENTION 
     The invention relates to an intervertebral implant having a core made of a swellable material and having a vertebral-body locating face on its top and/or bottom side, which is connected to the swellable core. 
     Such an intervertebral implant is described for example in DE 20 2006 005 896 U1. Such an intervertebral implant comprises two end plates made of metal or plastics material, between which is disposed a hydrogel core that is made of a swellable material, which by absorbing water may increase its volume and hence bear a specific structural similarity to a natural intervertebral disk. In order to connect the swellable core to an integral, rigid end plate, in the known intervertebral implant the end plate is provided with thread- or rod-shaped anchoring portions, which extend at a spacing from the end plate and project into the core of swellable material. 
     Since in the known design a rigid end plate is used, the different expansion behaviour of the end plate made of metal or plastics material, on the one hand, and the swellable core, on the other hand, leads to the production of high shearing forces during the swelling of the swellable material. Such an intervertebral implant moreover has a relatively large cross section because this cross section is determined i.a. by the extent of the end plate. 
     The object of the invention is to provide an intervertebral implant of the described type in a way that avoids the occurrence of high shearing forces between the vertebral-body locating face, on the one hand, and the swellable core, on the other hand, and moreover facilitates the insertion of the intervertebral implant through a narrow body opening. 
     SUMMARY OF THE INVENTION 
     In an intervertebral implant of the type described in the introduction this object is achieved according to the invention in that the vertebral-body locating face comprises a plurality of support elements, which are anchored respectively adjacent to one another and individually in the core, and a plurality of mutually separate locating elements, which are disposed adjacent to one another and outside of the core and which are carried by the support elements and are movable relative to one another in the plane of the vertebral-body locating face. 
     With the disclosed construction of an intervertebral implant, therefore, the vertebral-body locating face is broken up into individual, mutually adjacent locating elements that may move relative to one another in the plane of the vertebral-body locating face. These locating elements are supported by means of support elements in the core, so that during swelling of the core and during its expansion in a direction parallel to the plane of the vertebral-body locating face such an expansion is in no way impeded by the locating elements because these locating elements are able to move freely independently of one another in the plane of the vertebral-body locating face and therefore do not lead to any obstruction of the expansion of the core as a result of the swelling operation. 
     In a preferred embodiment of the invention, in each case a support element and a locating element are permanently connected to one another, in particular a support element and a locating element may be constructed integrally with one another. Given such an arrangement, it is clearly evident that during the swelling of the core and the variation of the dimension of the core in the plane of the vertebral-body locating face the individual locating- and support elements are simply moved only laterally, i.e. the mutual spacing of the locating elements is increased but no increased shearing forces are introduced into the core. 
     By virtue of the arrangement of the vertebral-body locating face, the intervertebral implant in the non-swollen state of the core, i.e. during introduction into the body, has a particularly small cross section because the individual locating elements are as close as possible to one another and it is only during swelling of the swellable material in the body that the locating elements move apart from one another and then cover the entire vertebral-body locating face, by means of which the support on the adjacent vertebral body is effected. The cross-sectional area taken up by the locating elements during introduction is therefore smaller than the cross-sectional area of the vertebral-body locating face after swelling occurs. 
     In a first preferred embodiment, the support elements are spheres, which are partially embedded in the core and of which the part projecting from the core forms in each case a locating element. These spheres may be distributed uniformly over the cross-sectional area of the core and hence form a plurality of support points, against which the adjacent vertebral body is supported. 
     In another embodiment, it may be provided that the support element comprises a foot, which engages into the core and has a widened portion, in particular the widened portion may have the shape of a sphere. In this way the support element is securely anchored in the core, the widened portion forming an undercut that ensures that the support element is supported in the core and is therefore capable of transferring a load, the foot moreover also being locked against rotation because it projects partially into the material of the expandable core. 
     It is advantageous if the locating element is of a plate-shaped configuration. 
     In this case, in particular all of the locating elements may lie in one plane. 
     In a first preferred embodiment it is provided that the locating elements in the non-swollen state of the core lie adjacent to one another without an overlap. During insertion into the body the locating elements therefore form a closed locating face, which after introduction is then pulled apart into individual regions as a result of the swelling of the swellable material. 
     In another preferred embodiment it is provided that the locating elements in the non-swollen state of the core lie adjacent to one another so as to mutually overlap in an edge region. In particular, the locating elements may be bevelled in the edge region of mutual overlap in the non-swollen state of the core. The effect achievable thereby is that, even when the core has expanded and the locating elements have moved apart from one another, only a small gap or no gap at all arises between the locating elements, i.e. support over substantially the entire surface area is possible. 
     The individual support elements and/or locating elements may be movable totally independently of adjacent support elements and/or locating elements. In a particularly preferred embodiment it is however provided that mutually adjacent support elements and/or locating elements are connected to one another by means of a limiting element, which during the expansion of the core allows but limits a moving of the support elements and/or locating elements apart from one another. Such a limiting element may for example be of an annular configuration and surround in each case two mutually adjacent support elements and/or locating elements. The limiting element then practically forms a chain link between the adjacent support elements and/or locating elements, which in the non-swollen state of the core loosely surrounds the two parts but during the swelling and during the moving-apart of the parts comes into abutment with these parts and then upon attainment of a specific maximum spacing prevents any further movement apart. 
     In a preferred embodiment, the support element and/or the locating element has an eye-shaped portion, through which the limiting element engages. 
     It is advantageous if all of the mutually adjacent support elements and/or locating elements in a row are connected to one another by limiting elements. In this way, the extent of the vertebral-body locating face is limited to a maximum value in one dimension but not transversely thereto. 
     It is however also possible for support elements and/or locating elements from mutually adjacent rows to be additionally connected to one another by limiting elements. This leads to a limiting of the moving-apart in two directions, which extend at right angles to one another and which both lie in the plane of the vertebral-body locating face. 
     It may be provided that the support elements and the locating elements at their sides facing one another are of an eye-shaped configuration and engage around one another in this eye-shaped region. In this case, locating elements and support elements are therefore connected to one another, not rigidly, but so as to be displaceable relative to one another, wherein the displacement movement is limited by the engagement of the eye-shaped regions with one another. 
     In other embodiments, the support elements and the locating elements at their sides facing one another are of an eye-shaped configuration, and are connected to one another in this eye-shaped region by limiting elements so as to be movable up to a maximum spacing apart from one another. 
     The eye-shaped regions are preferably of a circular configuration, with it however also being possible in a modified embodiment to design the eye-shaped regions in such a way that they are formed by the lateral faces of a three-dimensional body composed of rod-shaped edge elements, with it being possible in particular for this three-dimensional body to be a cuboid and in particular a cube. 
     In a further preferred embodiment, it is provided that there are disposed between the locating elements fixing projections, which are displaceable transversely of the plane of the vertebral-body locating face and which are displaceable from a normal position, in which they do not project beyond the locating elements, into a fixing position, in which they project beyond the locating elements, and that for displacement of the fixing projections drive elements are provided, which can be activated by the movement of the support elements and/or the locating elements apart from one another during the swelling of the core. The displacement of the support elements and/or of the locating elements that occurs because of the increase of the volume of the core during swelling is therefore utilized and this displacement movement is simultaneously used to displace the fixing projections transversely of the vertebral-body locating face. As a result, the fixing projections protrude from the vertebral-body locating face and penetrate into the adjacent vertebra. 
     It may for example be provided that the drive element comprises diverging locating faces for tension members, which are held in each case on a support element and/or locating element and, when the support elements and/or locating elements move apart from one another, slide along the locating faces in such a way that the drive element is displaced in the direction of the vertebral-body locating face. 
     In particular, the locating faces may be formed by the limbs of a triangular drive element. 
     Such a drive element may moreover take the form of a limiting element that allows adjacent support elements and/or locating elements to move up to a maximum spacing apart from one another, i.e. the function of the drive element for a fixing projection and the function of the limiting element may be combined in one component, which limits the movement of adjacent, support elements and/or locating elements apart from one another. 
     The following description of preferred embodiments of the invention serves in connection with the drawings to provide a detailed explanation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 : is a perspective view of a vertebral body implant with a swellable core and with support- and locating elements in the form of spheres embedded therein; 
         FIG. 2 : is a plan view of a vertebral body with an intervertebral implant according to  FIG. 1  prior to swelling of the core; 
         FIG. 3 : is a view similar to  FIG. 2  after swelling of the core; 
         FIG. 4 : is a perspective view of a further preferred embodiment of an intervertebral implant with a core made of a swellable material and with integral support- and locating elements embedded therein, which are movable apart from one another independently of one another; 
         FIG. 5 : is a side view of the intervertebral implant of  FIG. 4 ; 
         FIG. 6 : is a diagrammatic plan view of the intervertebral implant of  FIG. 4  prior to swelling of the core; 
         FIG. 7 : is a view similar to  FIG. 6  after swelling of the core; 
         FIG. 8 : is a view of a further preferred embodiment of a intervertebral implant similar to that of  FIG. 4  with limiting elements that limit the moving-apart of the support- and locating elements of in each case one row; 
         FIG. 9 : is a side view of the intervertebral implant of  FIG. 9 ; 
         FIG. 10 : is a perspective view of a further preferred embodiment of an intervertebral implant similar to  FIG. 8  with additional limiting elements for limiting the moving-apart of the support- and locating elements in adjacent rows; 
         FIG. 11 : is a side view of the intervertebral implant of  FIG. 10 ; 
         FIG. 12 : is a perspective view of a further preferred embodiment of an intervertebral implant with a swellable core having support elements embedded therein as well as locating elements, which are coupled to the support elements by eye-shaped connections; 
         FIG. 13 : is a side view of the intervertebral implant of  FIG. 12 ; 
         FIG. 14 : is a perspective view of a further preferred embodiment of an intervertebral implant with annular or eye-shaped locating elements; 
         FIG. 15 : is a side view of the intervertebral implant of  FIG. 14 ; 
         FIG. 16 : is a perspective view of a further preferred embodiment of an intervertebral implant with cube-shaped support elements and cube-shaped locating elements; 
         FIG. 17 : is a side view of the intervertebral implant of  FIG. 16 ; 
         FIG. 18 : is a view of an intervertebral implant similar to  FIG. 10  with mutually overlapping locating elements; 
         FIG. 19 : is a side view of the intervertebral implant of  FIG. 18 ; 
         FIG. 20 : is a perspective view of an intervertebral implant similar to  FIG. 18  with fixing projections raised above the vertebral-body locating face; 
         FIG. 21 : is a side view of the intervertebral implant of  FIG. 20 ; 
         FIG. 22 : is a side view of the intervertebral implant of  FIG. 21  in the direction of the arrow A in  FIG. 21 ; 
         FIG. 23 : is a perspective view of the intervertebral implant of  FIG. 20  in the non-swollen state of the core and the retracted state of the fixing projections; 
         FIG. 24 : is a side view of the intervertebral implant of  FIG. 23  and 
         FIG. 25 : is a side view of the intervertebral implant of  FIG. 24  in the direction of the arrow B in  FIG. 24 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The intervertebral implant  1  represented in the drawings has as a principal part a core  2  made of a swellable material. In the embodiments represented in the drawings the core is in the shape of a cuboid, with other shapes also being usable, wherein the core  2  will as a rule be of a plate-shaped design with a flat top and a flat underside, although the external contour might alternatively be adapted to the external contour of a vertebral body  3 . 
     The principal feature of the swellable material is that the volume of the swellable material in the dehydrated state, i.e. without a large liquid content, is small and increases considerably upon the absorption of liquid, in particular water. Thus, the core  2  expands when it is introduced into the body. 
     As swellable materials so-called hydrogels may be used. In this case, these may be in principle any non-degradable hydrophilic polymers, for example polyacrylic acid and its derivates such as polymethacrylic acid, polyacrylamide, polyacrylonitrile, polyacrylate, polyhydroxy ethylmethacrylates, polyvinyl pyrrolidone (PVP), polyurethanes, high-molecular weight polyvinyl alcohol. 
     Also conceivable are polymer blends (copolymers that are connected to one another by chemical bonds) of the above-mentioned polymers or interpenetrating networks (IPNS) of the above-mentioned polymers. IPNs consist of at least two different polymers, the polymer chains of which are interlocked and are connected to one another by physical interactions (van der Waals, electrostatic, hydrogen bridge bonds and/or ionic forces). 
     Further polymer blends that may be used are copolymers as well as IPNs of polyacrylates (polyacrylic acid and its derivatives such as polymethacrylic acid, polyacrylamide, polyacrylonitrile, polyacrylate) with polycaprolactone. 
     In the embodiment of  FIGS. 1 to 3 , a plurality of spheres  4  are embedded in the upper side of the plate-shaped or cuboidal core, namely in such a way that the greater part extends into the material of the core  2 , while a smaller part projects upwards from the core  2 . The drawings show such spheres  4  only at the top of the core  2  but it is easily possible for the intervertebral implant  1  to be of an identical design at the opposite, bottom side. This applies both to the intervertebral implant of  FIGS. 1 to 3  and to all of the other embodiments that are discussed below, for which in each case only the configuration at one side of the core  2  is shown and discussed in detail. At the opposite side too, the intervertebral implants  1  may be configured in the same way as is shown and described for the upper side of the intervertebral implant  1 . 
     In the embodiment of  FIGS. 1 to 3 , the spheres  4  with their parts embedded in the core  2  form in each case a support element  5 , by which the spheres  4  are supported in the core  2 , while the regions of the spheres  4  that project from the core  2  form locating elements  6 , which are positioned against and therefore support the adjacent vertebral body. 
     In the embodiment of  FIGS. 1 to 3  the spheres  4  are practically both a supporting element  5  and a locating element  6 , i.e. both functions coincide in one component. 
     In the dehydrated state, the core  2  has a low volume and hence also a small cross-sectional area, as is evident from the representation of  FIG. 2 . After being introduced into the body and after absorbing liquid from the area surrounding the site of the operation, the material of the core  2  swells and so the cross section of the core  2  also increases, in the manner illustrated in  FIG. 3 . Simultaneously with the increase of the cross-sectional area of the core  2 , the spheres  4  are moved apart from one another, i.e. their mutual spacing increases. In this way, after swelling of the core  2  the spheres  4  are also distributed substantially uniformly over the entire cross-sectional area of the core  2  and, there, form support points for supporting the adjacent vertebral body. 
     This principle is realized also in the embodiment of an intervertebral implant such as is shown in  FIGS. 4 to 7 . In this embodiment, rod-shaped feet  7  are embedded in the core  2  at right angles to the upper side thereof and carry on their free end a spherically widened portion  8 . The feet  7  project slightly from the core  2  and form there an annular and eye-shaped portion  9 , from which at the opposite end to the foot  7  a connecting rod  10  protrudes and runs into the underside of a locating plate  11 . In the embodiment shown in  FIGS. 4 to 7  the locating plates  11  have the shape of a cuboid, the locating plates  11  in the non-swollen state of the core  2  lying close together, without forming a gap, in a single plane extending parallel to the upper side of the core  2 , the locating plates  11  jointly forming a vertebral-body locating face. 
     The foot  7  with the widened portion  8 , the eye-shaped portion  9  and the connecting rod  10  correspond to the support element  5  in the embodiment of  FIGS. 1 to 3 , while the locating plates  11  correspond to the locating element  6 . 
     When the material of the core  2  absorbs liquid and swells, the core  2  expands laterally so that it occupies a larger area. In this case, the support elements  5  embedded in the core  2  and connected to the locating elements  6  are moved apart from one another, thereby producing gaps  12 ,  13  between the individual locating plates  11  ( FIG. 7 ). As a whole, the vertebral-body locating face is therefore enlarged without high shearing forces simultaneously being exerted on the core  2 , as is the case with integral known locating elements. The vertebral-body locating face in this case comprises individual elements, which are disposed adjacent to one another like scales and which during the swelling of the core  2  easily follow the movement of the core material and move apart from one another in accordance with the increase in the volume of the core  2 . 
     Since in the embodiment of  FIGS. 8 and 9  a similar structure to that of the intervertebral implant of  FIGS. 4 to 7  is selected, parts that correspond to one another bear the same reference characters. In addition to the constructional features of the intervertebral implant of  FIGS. 4 to 7 , in the embodiment of  FIGS. 8 and 9  each two mutually adjacent support elements  5  in a row are connected to one another by an annular limiting element  14 , which engages through the eye-shaped portions  9  of two mutually adjacent support elements  5  in a row. When the core  2  prior to swelling has a small cross section, the limiting elements  14  are mounted loosely in the eye-shaped portion  9  but, when the support elements  5  move apart from one another as a result of the liquid absorption of the core  2 , the limiting elements  14  are positioned tightly on the eye-shaped portions  9  and limit their movement apart from one another, i.e. during the swelling of the core  2  the gaps  12  between mutually adjacent locating plates  11  in a row reach a maximum width that is not exceeded ( FIG. 9 ). From the representation of  FIG. 9  it is also evident that the eye-shaped portions  9  and the annular limiting elements  14  as a whole form a construction similar to a chain, wherein the eye-shaped portions  9  on the one hand and the annular limiting elements  14  on the other hand act as chain links. The overall effect is to limit the moving-apart of the support elements  5  disposed in a row, while in the embodiment of  FIGS. 8 and 9  no such limiting of the moving-apart occurs transversely thereof. 
     Such an additional limiting of the expansion of the support elements  5  from adjacent rows is however achieved in the embodiment of  FIGS. 10 and 11 , which is of a substantially similar construction to the embodiment of  FIGS. 8 and 9 . In this case, however, additional limiting elements  15  are provided, which engage through the limiting elements  14  of the mutually adjacent support elements  5  of parallel, mutually adjacent rows of support elements  5 . The result is a two-dimensional interlinking of the eye-shaped portions  9  of all of the support elements  5 , the limiting elements  14  and  15  in this case being disposed in a plane between the core  2 , on the one hand, and the locating plates  11 , on the other hand. In this way, the increase of the spacing of the support elements  5  and hence of the locating elements  6  within a row and transversely thereof between adjacent rows is limited. 
     In the embodiments of  FIGS. 4 to 10  the support elements  5  and the locating elements  6  are combined in one component. In contrast to this, in the embodiment of  FIGS. 12 and 13  the support elements  5  and the locating elements  6  are separate components. The support elements  5  in their construction fully correspond to the support elements  5  of the embodiment of  FIGS. 4 to 11 , except that the connecting rod  10  opposite the foot  7  is absent in this case. The support elements  5  terminate at their upper side, i.e. at their side remote from the core  2 , in the eye-shaped portion  9 . 
     The locating plates  11  carry on their underside, i.e. on their side facing the core  2 , a short connecting rod  16  that merges into a circular, eye-shaped portion  17 . The eye-shaped portions  9  and  17  of the support element  5  on the one hand and of the locating element  6  on the other hand engage through one another, so that the spacing of the locating plates  11  from the core  2  is also variable. 
     Both the eye-shaped portions  17  and the eye-shaped portions  9  are connected to one another within a row and transversely thereof by means of annular limiting elements  14  and  15  and by means of these annular limiting elements  14 ,  15  upon an increase in the volume of the core  2  the expansion of the core  2  is limited in directions lying at right angles to one another. 
     In the construction of  FIGS. 12 and 13 , between the locating plates  11  on the one hand and the core  2  on the other hand two layers of two-dimensional chain surfaces are therefore situated one above the other, i.e. surfaces, the individual elements of which are connected to one another in a chain-like manner in two directions extending at right angles to one another. 
     In the embodiment of  FIGS. 14 and 15  a similar construction to that of the embodiments of  FIGS. 12 and 13  is selected, except that the locating plates  11  with the connecting rod  16  and the eye-shaped portions  17  have been omitted. This leaves only the limiting elements  14  and  15  of the upper layer of the chain surface, wherein these limiting elements  14  and  15  are disposed in the manner of a chain in the space between two adjacent rows of support elements  5  above these rows. The limiting elements  14  of this upper plane with their outer sides remote from the core  2  then form the locating elements  6 , i.e. they rest against an adjacent vertebral body. 
     During the expansion of the core  2  the individual links of this chain are spread, with the result that the locating points are moved apart from one another, this expansion however being limited by the remaining limiting elements. 
     In the embodiment of  FIGS. 14 and 15  the chain links of the chain surfaces are of a circular shape. In contrast to this, in the embodiment of  FIGS. 16 and 17  there are disposed on each foot  7  of a support element  5  cube-shaped support bodies  18 , which each consist of rods  19  running along the edges of a cube, wherein the lateral faces are open. On one of the rods the foot  7  is disposed as an extension of the rod, and the support bodies  18  are disposed adjacent to one another in a plurality of parallel rows. A likewise cube-shaped locating body  20  engages in each case through four support bodies  18 , wherein each of the vertical rods of the locating body  20  penetrates an open upper lateral face of one of four support bodies  18 . This produces between two rows of cube-shaped support bodies  18  a row of cube-shaped locating bodies  20  that are at a greater distance from the core  2  than the support bodies  18 . 
     During swelling of the core  2  the support bodies  18  may move apart from one another in two directions lying at right angles to one another, this expansion being limited by the abutment of the edges of the locating body  20  with the edges of the support bodies  18  ( FIG. 17 ). 
     The locating bodies  20  are positioned with their upper side against an adjacent vertebral body and therefore form the locating elements  6 . 
     The arrangement of  FIGS. 18 and 19  corresponds substantially to the arrangement of  FIGS. 10 and 11 . Unlike the embodiment of  FIGS. 10 and 11 , in which the locating plates  11  in the non-swollen state of the core  2  lie closely adjacent to one another, in the embodiment of  FIGS. 18 and 19  the locating plates  11  mutually overlap when the core  2  prior to absorbing liquid has not yet swollen. The edge regions  21 ,  22  of adjacent locating plates  11  are bevelled so that the mutually overlapping locating plates  11  slide on one another along the bevelled edge regions  21 ,  22 . Thus, when the locating plates  11  during swelling of the core  2  move apart from one another, no gaps or only very narrow gaps are formed between adjacent locating plates  11 , whereas in the previously described embodiments the width of the gaps arising correspond to the displacement movement of the support elements  5  as a result of the swelling. 
     In  FIGS. 20 to 25  there is shown an intervertebral implant that is substantially identical in construction to that of  FIGS. 18 and 19 . However, in contrast to the embodiment of  FIGS. 18 and 19  the limiting elements  15  disposed between adjacent rows are not annular but triangular, wherein two limbs  23 ,  24  of the limiting element  15  converge in the direction of the locating plates  11 . The limiting elements  14  that connect adjacent support elements  5  of a row to one another pass through the triangular limiting element  15  so that, when the core  2  expands and these limiting elements  14  are pulled apart, the limiting elements  14  slide along the oblique limbs  23 ,  24  and therefore raise the triangular limiting element  15 , i.e. displace the limiting element  15  in the direction of the locating plate  11 . 
     At the apex the triangular limiting elements  15  carry a pointed projection  25 , which remains below the locating plates  11  while the support elements  5  in the non-swollen state of the core  2  are not pulled apart from one another ( FIG. 25 ), and which projects upwards from the locating plates  11  when the support elements  5  during the swelling of the core  2  are pulled apart from one another. These projections  25  may then penetrate into the vertebral body lying adjacent to the locating plates  11  and therefore fix the intervertebral implant  1  relative to the vertebral body. 
     With this construction, therefore, the increase in the volume of the core  2  is utilized on the one hand to increase the mutual spacing of the individual locating elements  6  and on the other hand to displace the triangular limiting elements  15  transversely of the plane of the locating plates  11  and therefore dig the projections  25  into the adjacent vertebra. 
     The described features of the various embodiments may optionally be combined and interchanged with one another, thereby producing a plurality of possible constructions, the basic principle of which is that individual support elements and locating elements may be moved independently of one another when the core  2  swells and therefore increases in size. 
     In all of the constructions the locating elements may be provided with a bony substance-friendly surface, thereby facilitating the growth of bony material thereon and therein. This applies in particular also to the arrangements according to  FIGS. 14 to 17 , in which chain-shaped elements or three-dimensional rod bodies form the locating elements. An effect achievable in these cases is that bony material grows into the open spaces of the locating elements and so a strong connection is achieved between the vertebral body on the one hand and the upper layer and hence the locating elements of the intervertebral implant  1  on the other hand.
In order, in an intervertebral implant having a core made of a swellable material and having a vertebral-body locating face on its top and/or bottom side, which is connected to the swellable core, to reduce the shearing forces between the swellable core and the vertebral-body locating face during swelling of the swellable core, it is proposed that the vertebral-body locating face comprises a plurality of support elements, which are respectively anchored adjacent to one another and individually in the core, and a plurality of mutually separate locating elements, which are disposed adjacent to one another and outside of the core and which are carried by the support elements and are movable relative to one another in the plane of the vertebral-body locating face.