Abstract:
A spinal implant includes a hollow body having a distal end, a proximal end, and a pair of lateral walls extending from the distal end to the proximal end, the lateral walls having concave, non-threaded interior surfaces for defining an at least partially cylindrical internal space between the lateral walls. The spinal implant also includes an anchoring member having bone anchoring projections including a screw thread on an exterior surface thereof, wherein at least one of the lateral walls adjacent the proximal end of the hollow body includes a reentrant thread adapted to cooperate with the screw thread of the anchoring member when the anchoring element is rotated for enabling the anchoring member to be screwed into the internal space of the hollow body. The anchoring member has a proximal end, a distal end, a major axis extending between the proximal and distal ends, an interior space, and a fork surrounding the interior space, the fork including branches extending along a major axis of the anchoring member, the branches having a frustoconical exterior surface with a diameter that decreases from the proximal end toward the distal end of the anchoring member, and wherein the screw thread comprises a helical band connected to the fork and encircling the fork and the interior space of the anchoring member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present application is a divisional of U.S. patent application Ser. No. 09/403,396, filed Feb. 15, 2000, now allowed.  
           [0002]    The present invention relates generally to intersomatic implants which can be used in the surgical treatment of the spine.  
           [0003]    A great many intersomatic implants are already known.  
           [0004]    These include, in particular, implants having a more or less complex structure, made up of several parts, particularly to give them certain deformability characteristics. These known implants have the disadvantage that they are more expensive and difficult to manufacture, and that they are more awkward to fit. They can also suffer from a problem of long-term reliability.  
           [0005]    Implants are also known which, in order in particular to overcome all or some of the above disadvantages, being [sic] in the form or one-piece hollow bodies, or cages, provided with roughened areas on their upper and rear faces in order to ensure good initial immobilization relative to the overlying and underlying vertebral plateaus, their hollow character permitting bone to grow through them and, eventually, immobilize them definitively.  
           [0006]    Document FR-A-2,703,580 describes an example of such an implant.  
           [0007]    These known one-piece implants, despite the presence of roughened areas which become anchored in the vertebral plateaus when the intervertebral distraction necessary for fitting them is removed, may in some cases have inadequate stability, since the quality of the anchoring, which is effected by a simple translational movement, is dependent in particular on the hardness of the bones.  
           [0008]    Document DE-U- also discloses an implant which includes an outer body into which an inner anchorage reinforcement element can be engaged by screwing, the threads of the anchorage reinforcement element projecting above and below the upper and lower faces of this outer body.  
           [0009]    The object of the present invention is to improve this type of known implant.  
         SUMMARY OF THE INVENTION  
         [0010]    An implant for surgery of the spine comprises an essentially hollow body which can be inserted into an intervertebral space, the said body having a pair of lateral walls enclosing an internal space exposed to the overlying and underlying vertebrae which define the said intervertebral space. The implant additionally comprises an anchorage reinforcement member having, on its external surface, projections for bone anchorage which are inscribed within a diameter greater than the overall height of the body, the said member being able to be driven in rotation in the internal space of the body.  
           [0011]    To counter the reverse movement of the said  20  body out of the said intervertebral space, and hence to further improve the securing of the implant in position, the said hollow body has upper and lower surfaces provided 4th sharp-edged teeth which can be anchored in the said vertebrae.  
           [0012]    The said teeth preferably have a triangular cross-section.  
           [0013]    According to another aspect, in order to improve the compactness of the implant and to make it easier to put into place, the said lateral walls of the hollow body are partially cylindrical and coaxial with an axis of the said anchorage reinforcement member.  
           [0014]    According to yet another aspect, in order to promote the growth of bone outside the implant, in particularly laterally, the said lateral walls have through-openings permitting bone to grow through them.  
           [0015]    These openings advantageously comprise elongate slots extending essentially parallel to the direction of insertion of the said member into the said hollow body.  
           [0016]    In order to give the body a greater width, it is possible to use, for the lateral walls of the body, thick walls in which second through-openings are formed, extending between the upper and lower faces of the body. Bone growth can also be induced between the two vertebral plateaus via these second through-openings.  
           [0017]    The said first through-openings preferably bring the said internal space into communication with the said second through-openings.  
           [0018]    It is also possible to provide through-openings which bring the said second through-openings into communication with the outer sides of the body.  
           [0019]    According to another aspect of the invention, the hollow body has a distal end wall connecting the said lateral walls, and this distal end wall is rounded to facilitate insertion of the said hollow body into the said intervertebral space.  
           [0020]    The invention also proposes an implant such as has been defined above, in which the hollow body has a distal end wall connecting the said lateral walls, and this distal end all has a tapped hole for temporarily fixing the said hollow body o an instrument for inserting the body, in order thereby to make it easier for the surgeon to out it into place.  
           [0021]    According to another aspect, the said projections for bone anchorage comprise a self-tapping screw thread.  
           [0022]    This thread can have a generally square radial cross-section.  
           [0023]    This screw thread preferably has a radial cross-section which changes progressively from an essentially triangular radial cross-section to the said generally square radial cross-section starting from the distal end of the said thread, whilst the diameter of the screw thread increases progressively, starting from its distal end, up to a part of essentially constant diameter.  
           [0024]    According to the invention, an implant is also proposed in which the said projections for bone anchorage comprise a screw thread in the form of a helical band encircling an internal space of the said anchorage reinforcement member.  
           [0025]    This helical band is advantageously connected to a fork extending inside the said band in an axial direction of the said member, and this fork preferably comprises two branches extending from a proximal end wall of the said anchorage reinforcement member.  
           [0026]    The fork can also comprise branches having a frustoconical external surface, the diameter of which decreases from the proximal end towards the distal end of the member. This makes it possible to compress a substance promoting bone growth, placed beforehand in the anchorage reinforcement member, when the latter ins being screwed in.  
           [0027]    Alternatively, the fork comprises at least two branches, each having a cutting edge for attacking the bone, in order thereby to accumulate bone chips inside the member  20  and facilitate bone fusion.  
           [0028]    It is preferable for the fork and the helical band to be made in one piece.  
           [0029]    The invention also proposes an implant in which the projections for bone anchorage comprise a screw thread, and in which the said member has means for immobilizing the latter against reverse rotation. These immobilizing means preferably comprise a deformed part of the said thread in the region of its proximal end. This therefore improves the stability of the implant until fusion has taken place.  
           [0030]    According to another aspect, the projections for bone anchorage comprise a screw thread having an external diameter which decreases, in its distal region, towards its distal end, in order to make it easier for this thread to penetrate the vertebral plateaus.  
           [0031]    It is furthermore proposed that the said anchorage reinforcement member has a proximal end wall which ins able to essentially close a frontal opening of the said hollow body in such a way that a substance promoting bone growth, placed inside the said member, is compressed during the insertion of the said member into the said hollow body.  
           [0032]    In this case, the anchorage reinforcement member has at least one part whose external surface belongs to a truncated cone. Alternatively, the anchorage reinforcement member is substantially shorter than the body and has a generally conical point directed towards the said distal end wall of the body.  
           [0033]    It is advantageous in this case that the proximal end wall of the member has a tapped opening for temporarily fixing the said member to an instrument for inserting the member.  
           [0034]    According to yet another aspect, the invention proposes an implant such as has been defined above, inn which the anchorage reinforcement member has indexing means for fixing the said member, to an instrument for inserting the member, in a given angular relationship.  
           [0035]    According to another characteristic, the anchorage reinforcement member has a plug attached at its proximal end, which plug can, for example, be screwed into a tapped frontal opening of the anchorage reinforcement member, or else can be engaged by being clipped elastically into a frontal opening of the anchorage reinforcement member.  
           [0036]    It is advantageous that this plug has an arrangement which can cooperate with an instrument allowing the member to be driven in rotation, and/or arrangements for angular indexing of the anchorage reinforcement member with an instrument for positioning the said member.  
           [0037]    It is also proposed according to the invention that the projections for bone anchorage comprise a screw thread, and that at least one of the lateral branches of the body has a reentrant part forming a threading which is able to cooperate with the said thread.  
           [0038]    This reentrant part can be provided only on one of the branches and can then constitute the only part of the body cooperating, by screwing, with the screw thread.  
           [0039]    In addition, this reentrant part can have an essentially rectilinear free end edge.  
           [0040]    According to another aspect, the invention proposes an implant in which the said member is oriented obliquely, for example at about 450, in relation to a plane of the body corresponding to the sagittal plane.  
           [0041]    According to another aspect, it is proposed that through-openings be provided in the said member between the interior and the exterior thereof, the said openings being elongate in an essentially circumferential direction of the member.  
           [0042]    According to another different aspect, the body has a distal end wall, and the anchorage reinforcement member has a distal end part which can be screwed into an opening of the said distal end wall.  
           [0043]    The body can also in this case have a proximal end wall including an opening which is wider than the external dimension of the said anchorage reinforcement member and in which the said member can be engaged freely.  
           [0044]    The invention furthermore proposes an implant in which the body has a proximal wall, a distal wall and two lateral walls, the said walls defining between themselves an internal space which is larger than the said anchorage reinforcement member. This therefore increases the space designated for bone growth between the overlying and underlying vertebral plateaus.  
           [0045]    In this case, the anchorage reinforcement member can have a threaded part for screwing it into the proximal wall of the body, or else the said anchorage reinforcement member and the distal wall of the body can have threaded means cooperating with each other for fixing the said member to the body.  
           [0046]    In such a configuration, the projections for bone anchorage can comprise a screw thread having the same pitch as the said threaded part or the threaded means for fixing to the body.  
           [0047]    The shape of the body, in this case, is preferably such that the lateral walls and the proximal wall of the body extend essentially on the same arc of a circle, and that the said distal wall is essentially rectilinear.  
           [0048]    It is also advantageous that the upper and lower faces of the body have projections for bone anchorage which extend along its walls.  
           [0049]    According to the invention, an implant is also proposed which is provided with means for mounting the anchorage reinforcement member so that it can rotate in the internal space of the body, while at the same time preventing a relative translational movement between these.  
           [0050]    These mounting means advantageously comprise a cylindrical opening formed in a distal end wall of the said body, and a shaft provided on the said member and able to be engaged, by elastic deformation, in the said opening.  
           [0051]    In this particular case, the said anchorage reinforcement member preferably has the shape of a screw having two diametrically opposite flats, the said projections for bone anchorage being defined between the said flats, and cutting edges being provided at the transitions between the thread of the screw and the flats in order thereby to promote the bone fusion once the implant has been put into place.  
           [0052]    To facilitate the insertion of the implant, the distance between the opposite flats is not greater than the distance between the upper and lower faces of the said body.  
           [0053]    According to another aspect of the invention, an implant for surgery of the spine is proposed, comprising an essentially hollow body which can be inserted into an intervertebral space, the said body having a group of generally parallel walls defining at least two internal spaces situated side by side and exposed to the overlying and underlying vertebrae which define the said intervertebral space, the said implant additionally comprising at least two anchorage reinforcement members having, on their external surface, projections for bone anchorage which are inscribed within a diameter greater than the overall height of the body, the said members being able to be driven  ˜ n rotation in respective internal spaces of the said body.  
           [0054]    The said members are advantageously identical.  
           [0055]    The invention furthermore proposes that the hollow body can have different geometries, and in particular:  
           [0056]    upper and lower surfaces which are inclined in relation to one another, with a distance between them which decreases from the proximal end towards the distal end of the body; and/or  
           [0057]    upper and lower surfaces which are inclined in relation to one another, with a distance between them which decreases from a first lateral side of the body towards the opposite lateral side.  
           [0058]    The invention furthermore proposes a set of implants for forming a spinal implant intended to be inserted into an intervertebral space of the human vertebral column by being adapted to the geometry of the said intervertebral space. This set of implants comprises:  
           [0059]    a plurality of hollow bodies, each having a pair of lateral walls delimiting an internal space and each able to be inserted into an intervertebral space inn such a way that the said internal space  ˜ s exposed to the overlying and underlying vertebrae which define the said intervertebral space, each of the said bodies having a specific size and shape, at least one anchorage reinforcement member having, on its external surface, projections for bone anchorage which are inscribed within a diameter greater than the overall height of the bodies, the said member being able to be driven in rotation in the internal space of any one of the said bodies, in such a way that a specific hollow body appropriate to the particular configuration of a given intervertebral space can be chosen from among the said plurality of hollow bodies.  
           [0060]    The specific sizes and shapes of the bodies can result in particular from:  
           [0061]    different angles of inclination between their upper and lower surfaces;  
           [0062]    different widths; in this case, the widest hollow bodies advantageously have lateral walls in which through-openings are formed which extend between the upper and lower faces of the said bodies;  
           [0063]    different heights;  
           [0064]    different lengths.  
           [0065]    Preferably, a defined group of hollow bodies from the said plurality is able to receive a same type of anchorage reinforcement member.  
           [0066]    The invention finally proposes a method for positioning, in an intervertebral space of a human vertebral column, an implant comprising an essentially hollow body having a pair o ˜  lateral walls enclosing an internal space, and an anchorage reinforcement member having, on its external surface, projections for bone anchorage which are inscribed within a diameter greater than the overall height of the body, and able to be driven in rotation in the internal space of the body, the said method comprising the following steps:  
           [0067]    selecting from a set of hollow bodies, which have different shapes and dimensions, a hollow body which is adapted to the configuration of the said intervertebral space;  
           [0068]    filling the said selected hollow body with a substance which promotes bone growth;  
           [0069]    pushing the said hollow body into the said intervertebral space in such a way that the internal space thereof is exposed to the overlying and  
           [0070]    underlying vertebrae which define the said intervertebral space; and  
           [0071]    inserting the said anchorage reinforcement member into the said hollow body in such a way that the said projections for bone anchorage anchor in the said overlying and underlying vertebrae.  
           [0072]    In the case where the intention is to position an implant whose body has lateral walls provided with through-openings extending between the upper and lower faces of the said body, the method can additionally comprise, before the step of pushing the said hollow body into the said intervertebral space, a step in which the said through-openings are filled with a substance which promotes bone growth. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0073]    Other aspects, aims and advantages of the present invention will become more apparent on reading the following detailed description of preferred embodiments thereof, given by way of example, and with reference being made to the attached drawings, in which:  
         [0074]    [0074]FIG. 1 is a perspective view of an implant according to a first embodiment of the invention,  
         [0075]    [0075]FIG. 2 is a side view of the implant from FIG. 1, placed between two vertebral plateaus,  
         [0076]    [0076]FIG. 3 is a front view of the implant from FIG. 1,  
         [0077]    [0077]FIG. 4 is a plan view of the implant from FIGS. 1 and 3,  
         [0078]    [0078]FIG. 5 is a side view of an element of the implant from FIG. 1,  
         [0079]    [0079]FIG. 6 is an end view in the direction of arrow VI in FIG. 5,  
         [0080]    [0080]FIG. 7 is an end view in the direction of arrow VII in FIG. 5,  
         [0081]    [0081]FIG. 8 is a perspective view of the element from FIGS.  5  to  7 ,  
         [0082]    [0082]FIG. 9 is a perspective view of an implant according to a second embodiment of the invention,  
         [0083]    [0083]FIG. 10 is a front view of the implant from FIG. 9,  
         [0084]    [0084]FIG. 11 is a plan view of the implant from FIGS. 9 and 10,  
         [0085]    [0085]FIG. 12 is a plan view of a first element of the implant from FIGS.  9  to  11 ,  
         [0086]    [0086]FIG. 13 is a side view of a second element of the implant from FIGS.  9  to  11 ,  
         [0087]    [0087]FIG. 14 is an end view in the direction of arrow XIV in FIG. 13,  
         [0088]    [0088]FIG. 15 is an end view in the direction or arrow XV in FIG. 13,  
         [0089]    [0089]FIG. 16 is an exploded perspective view of an implant according to a third embodiment of the invention,  
         [0090]    [0090]FIG. 17 is a side view of the implant from FIG. 16, when assembled,  
         [0091]    [0091]FIG. 18 is a view in the direction of arrow XIIX [sic] in FIG. 17,  
         [0092]    [0092]FIG. 19 is a view in the direction of arrow XIX in FIG. 17,  
         [0093]    [0093]FIG. 20 is an exploded perspective view of an implant according to a fourth embodiment of the invention,  
         [0094]    [0094]FIG. 21 is a side view of the implant from FIG.  20 , when assembled,  
         [0095]    [0095]FIG. 22 is a view in the direction of arrow XXII in FIG. 21,  
         [0096]    [0096]FIG. 23 is a view in the direction of arrow XXIII in FIG. 21,  
         [0097]    [0097]FIG. 24 is an exploded perspective view of an implant according to a fifth embodiment of the invention,  
         [0098]    [0098]FIG. 25 is a side view of the implant from FIG. 24, when assembled,  
         [0099]    [0099]FIG. 26 is a view in the direction of arrow XXVI in FIG. 25,  
         [0100]    [0100]FIG. 27 is a view in the direction of arrow XXVII in FIG. 25,  
         [0101]    [0101]FIG. 28 is an exploded perspective view of an implant according to a variant of the third embodiment of the invention,  
         [0102]    [0102]FIG. 29 is a perspective view of the implant from FIG. 28, in the assembled state,  
         [0103]    [0103]FIG. 30 is a view of the rear of the implant from FIG. 29,  
         [0104]    [0104]FIG. 31 is a side view of the implant from FIG. 29,  
         [0105]    [0105]FIG. 32 is a plan view of the implant from FIG. 29,  
         [0106]    [0106]FIG. 33 is a perspective view, before assembly, of an alternative design of the third embodiment of the invention,  
         [0107]    FIGS.  34  to  36  are three perspective views of the body of this alternative design,  
         [0108]    [0108]FIG. 37 is an end view, from the distal direction, of this same body,  
         [0109]    [0109]FIG. 38 is a perspective view of the anchorage reinforcement member of this alternative design,  
         [0110]    [0110]FIG. 39 is a side elevation of this same anchorage reinforcement member,  
         [0111]    [0111]FIGS. 40 and 41 are two perspective views of the implant according to this same alternative, in the assembled state,  
         [0112]    [0112]FIG. 42 is a plan view of this same implant when assembled,  
         [0113]    [0113]FIG. 43 is a side elevation of this same implant when assembled, and  
         [0114]    [0114]FIG. 44 is an end view, from the proximal direction, of this same implant when assembled. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0115]    First, it will be noted that, from one figure to another, identical or similar elements or parts are as far as possible designated by the same reference labels.  
         [0116]    It will also be noted that the terms “proximal” and “distal”, used throughout the present description correspond, respectively, to that end of the implant nearest the surgeon during the fitting operations, and that end of the implant furthest from the surgeon.  
         [0117]    Referring first to FIGS.  1  to  8 , a cage-type intersomatic implant is shown which is made up of two parts, namely a body  10  and an anchorage reinforcement member  20 .  
         [0118]    The body  10  has the general shape of a ring, with an upper face  11 , a lower face  12 , an inner face  13  and an outer face  14 .  
         [0119]    The contour of the body  10  has a circular shape truncated by a part of rectilinear contour, its width being equal, for example, to about four thirds of its depth.  
         [0120]    Along the rectilinear contour part, on the upper and lower faces  11  and  12 , roughened areas are formed to ensure that the implant is immobilized relative to the overlying V 1  and underlying V 2  vertebral plateaus (see FIG. 2) when the implant is compressed between these.  
         [0121]    These roughened areas are  ˜ n this case in the form of three upper ribs  11   b  and three lower ribs  12   b , of triangular cross-section and of circular trajectories concentric with the circular contour part of the body.  
         [0122]    Opposite the rectilinear contour part, the body has a thicker wall, produced by an upper land ha and a lower land (not labeled).  
         [0123]    Formed in this wall part there is a tapped through-orifice  18  whose axis extends obliquely, and preferably at about 450, relative to the vertical plane perpendicular to the plane distal wall of the implant, which vertical plane corresponds to the sagittal plane.  
         [0124]    In addition, the axis of this orifice  18 , which extends essentially horizontally, passes substantially through the center of the circular contour part, going towards the opposite region situated at the transition between the circular contour part and the rectilinear contour part.  
         [0125]    The implant according to the invention additionally comprises a member  20  intended to reinforce the anchoring on the vertebral plateaus.  
         [0126]    In this example, this member is in the form of a hollow cylindrical core  21 , on the outer surface of which there is a helical thread  22  which is complementary to the internal thread formed in the orifice  18 .  
         [0127]    Formed between the adjacent thread sections there are a plurality of openings  23 , oblong in the direction of the helical run of the thread, for reasons explained below.  
         [0128]    At its distal end, the member  20  is closed by a solid wall  25 . In the vicinity of its opposite face defining its proximal end, it includes a solid part  24  in which there ins formed a hollow recess  24   a , for example of hexagonal cross-section, for introduction of a screwing instrument (not shown).  
         [0129]    It is important to note, as is shown in particular in FIG. 3, that the overall diameter D within which the thread  22  of the member  20  is inscribed is slightly greater than the overall height H within which the body  10  is inscribed, this being for reasons which are explained below.  
         [0130]    It will be observed here that the length of the member  20  is such that it can be screwed into the orifice  18  of the body  10  until the outer face of its proximal solid part  24  is substantially aligned with the outer face  14  of the body  10  adjoining the said orifice.  
         [0131]    The use of an implant such as has been described above will now be explained. It will be observed that the same type of procedure, with the necessary adaptations, will be performed for the other embodiments, described below, of the implants according to the invention.  
         [0132]    Distraction having first been performed between two vertebrae to be treated, by means which are well known per se, the intervertebral disc is at least partially removed and the body  10  of the implant, without its member  20 , is put into place, by an anterior or posterior approach. The internal space of the body is advantageously first filled with bone grafts in order to ensure eventual intervertebral fusion by osteogenesis.  
         [0133]    It will be observed here that the contour of the body  10 , with the flat in the proximal part, is such that it is easily inscribed within the surface area of a vertebral plateau. If necessary, it is possible to offer the surgeon different sizes of body  10 , to be selected as a function of the spinal anatomy of the patient, as will be seen in greater detail below.  
         [0134]    The two vertebrae are then released, and an initial immobilization of the body between the vertebral plateaus V 1  and V 2  is ensured with the aid of the ribs  11   b ,  12   b.    
         [0135]    The member  20  is then screwed into the orifice  18  with the aid of an instrument. During this movement, the crest of the thread  22 , which projects slightly upwards and downwards in relation to the crest parts of the ribs  11   b ,  12   b , cuts into the opposing faces of the overlying and underlying vertebral plateaus in the manner of a self-tapping screw, and thus affords a supplementary anchoring which will firmly immobilize the implant relative to these plateaus.  
         [0136]    In addition, the rotation of the member  20  as it penetrates the internal space, filled with bone grafts, of the body  10  ensures that some of these grafts will migrate through the openings  23  and into the internal space of the hollow member  20 . The bone growth ill therefore also be obtained through the member  20 , and this will advantageously immobilize the member  20  in terms of any rotation, particularly reverse rotation, that risks affecting the stability of the implant in the long term. Alternatively, it is also possible for the member  20  to be filled beforehand with bone grafts.  
         [0137]    FIGS.  9  to  15  illustrate a second embodiment of the present invention.  
         [0138]    In these figures, elements or parts which are identical or similar to those in FIGS.  1  to  8  are designated by the same reference labels, and only the differences between this second embodiment and the first will be described.  
         [0139]    It will first be noted that the body  10 , which has the same contour as in the case of FIGS.  1  to  8 , here has a wall of essentially constant thickness over its whole periphery.  
         [0140]    Instead of the tapped orifice  18  in the first embodiment, this body includes a smooth through-orifice  19 .  
         [0141]    Moreover, a cylindrical rod  16  provided with a thread  16   a  extends along the axis of the orifice  19  starting from the opposite region of the body  10 , situated essentially at the transition between its circular contour and straight contour parts.  
         [0142]    In addition, the member  20 , which has substantially the same external contour as inn the case of the first embodiment, is solid, except for a central bore  28  which opens out on its rear face and in which there is formed an internal thread  28   a  complementary to the thread  16   a  formed on the protruding rod  16  of the body.  
         [0143]    It will be observed here that the helical pitch of the thread  16   a  and of the associated internal thread  28   a  is chosen substantially or exactly equal to the helical pitch of the thread  22  which is still present on the outer surface of the member  20 .  
         [0144]    A frustoconical part  27  is provided around the mouth of the bore  28 .  
         [0145]    It will be observed, finally, that the member  20  has, on its front face, a screwing arrangement which in this case consists of a projecting head  26 , for example of hexagonal cross-section.  
         [0146]    The implant according to this second embodiment is used essentially in the same way as that explained above.  
         [0147]    The essential difference lies in the fact that the member  20  is screwed onto the rod  16  in the manner of a nut, the size of the orifice  19  being chosen so as not to form an obstacle to this screwing. In this respect it suffices to choose an orifice  19  with a diameter slightly greater than the overall diameter of the thread  22 . It will be noted that the frustoconical part  27  of the member  20  makes it easier to introduce the rear end of the said member into the orifice  19  prior to screwing.  
         [0148]    As the pitch of the thread  16   a  is the same as that of the thread  22 , the advance of the member  20  into the body  10 , at the same time as the member is being driven in rotation,  ˜ s such that the thread  22  here once again bites into the vertebral plateaus in the manner of a self-tapping screw.  
         [0149]    In particular, it is possible for the upper and lower annular faces  11  and  12  of the body  10  to extend in planes which are slightly oblique in relation to each other, so as to adapt to the shape of the intervertebral space in question. Thus, as will be seen below, the surgeon can be offered bodies  10  having different inclinations in order to adapt to the anatomy of the vertebrae which are to be treated.  
         [0150]    In this case, the embodiment in FIGS.  9  to  15  is advantageous in that the external contour of the member  20  can be given a slightly frustoconical shape in such a way that the amount by which the thread  22  projects relative to the crests of the ribs ha and lib remains essentially constant from the front to the rear of the implant, and that as the vertebral faces concerned are substantially parallel to the upper and lower faces of the body  10 , the anchoring afforded via the thread is essentially of the same magnitude from the proximal end to the distal end.  
         [0151]    Referring now to FIGS.  16  to  19 , an implant according to a third embodiment of the invention has been shown, which implant comprises a body  10  which, in horizontal section, has the general shape of a U, with a bottom  101 , or distal wall, and two essentially parallel lateral walls or branches  102 ,  103 . This body includes upper and lower U-shaped faces,  104  and  104 ′ respectively, on which there are formed bone anchorage teeth  105 ,  105 ′ respectively, in this case sharp-edged teeth of triangular profile, which fulfill a role analogous to that of the ribs  11   b  in the preceding embodiments. It will be observed in particular from FIG. 17 that the upper and lower faces  104 ,  104 ′ converge slightly towards one another in the direction towards the region of the bottom  101 .  
         [0152]    Formed in the distal wall  101  there is a tapped bore  1010  which permits temporary fixing of an instrument, which is not shown and is conventional per Se, for fitting the body in the intervertebral space.  
         [0153]    The branches  102 ,  103  define a generally cylindrical internal space, for reasons explained below.  
         [0154]    The two lateral branches  102 ,  103  of the body each include a longitudinal through-slot,  106  and  107  respectively, these slots being intended to permit lateral bone growth.  
         [0155]    At the open end of the body  10 , remote from its bottom  101 , there is a generally circular opening delimited by a reentrant thread  108  provided at the proximal free ends of the two branches  102 ,  103 .  
         [0156]    The implant includes an anchorage reinforcement member  20  provided with a hollow core whose outer surface is slightly frustoconical, tapering from its proximal end towards its distal end. A continuous thread  22  is formed on the outer surface of the core  21 .  
         [0157]    This thread  22 , in the form of a helically configured flat band, is able to cooperate with the reentrant thread  108  of the body  10  so as to allow the member  20  to be screwed inside the said body.  
         [0158]    As can be seen in particular from FIG. 16, the core  21  is made up of three angularly offset longitudinal branches which are separated by longitudinal empty spaces  23 .  
         [0159]    Each of these branches includes a leading edge (that is to say the front edge in the direction of screwing of the member  20 ) which is a cutting edge at  21   a , in such a way as to constitute a member for scraping the bone material from the overlying and underlying vertebrae. In this way, screwing in the member  20  will allow the internal space of the implant to be filled with bone chips, something which will help the graft to take and which will finally fuse the two vertebrae by means of bone growth.  
         [0160]    It will be observed here that the external diameter of the thread  22  is preferably very similar to the internal diameter of the body  10 , so that when the member  20  is being screwed in, it is guided inside the body.  
         [0161]    Finally, in its proximal part  24  forming a bushing, the member  20  includes an opening which is delimited by a plurality of bosses  24   b  separated by recessed zones  24   c . The bosses  24   b , which constitute the start of the branches  21  of the core, have an internal thread on their inner surface.  
         [0162]    The implant finally includes a generally cylindrical plug  30  having, on its outer surface, a thread  31  which is able to cooperate with the internal thread defined by the bosses  24   b . The rear face  32  of this plug is provided with a recessed socket  32   a  for a screwing instrument.  
         [0163]    The implant, such as it has been described above, is used in the following way:  
         [0164]    the body  10 , without the member  20 , is put in place between the vertebrae to be treated;  
         [0165]    the member  20 , without its plug  30 , is filled with bone grafts via its rear opening, and the plug is then put into place in this opening in order to prevent the grafts from escaping;  
         [0166]    the member  20 , provided with its plug, is then screwed into the body  10 , already in place, with the aid of a screwing instrument which is engaged in the socket  32   a ; during this operation, the thread  22  of the member  20  anchors in the opposing surfaces of the overlying and underlying vertebrae, possibly cutting off bone chips; in addition, the cutting edges  21   a  of the three branches  21  of the core of the member  20  attack the vertebrae so as to cut off chips which will complete the filling of the internal space of the member  20 ; finally, as the core  21  of the member  20  advances, its frustoconical shape ensures compression of some of this bone material against the walls of the vertebrae, in order to assist the grafting.  
         [0167]    FIGS.  20  to  23  illustrate a fourth embodiment of the invention in which the body  10  is similar to that in FIGS.  16  to  19  and will not be described again in its entirety. It will be observed, however, that in this example only the branch  102  of the body is provided with a through-slot  106 , while the other branch does not nave one. This type of body is advantageously used when two implants according to the invention are being used in one and the same intervertebral space. In this case, the implants are arranged side by side in such a way that the respective slots of the two bodies are situated on the inside, this being in order to promote fusion with bone grafts placed in the region of the intervertebral space situated between the two implants.  
         [0168]    In this case, the anchorage reinforcement member  20  is in the form of a threaded plug which is substantially shorter than the body  10  in the axial direction. This member has a solid cylindrical core  21  provided with a thread  22  which is able to cooperate with the thread  103  of the body  10 , in the same way as before.  
         [0169]    The rear face of the member  20  has a recessed socket  24   a  for a screwing instrument, whilst its front face  25  is in the form of a cone with a rounded apex.  
         [0170]    The implant according to this embodiment is intended to be used when the body  10  is being filled relatively densely with bone grafts. In this way, the penetration of the member  20  as it is being screwed in, in addition to reinforcing the anchorage obtained with the aid of the thread  22 , compresses the bone grafts situated in the body  10 , so as to stress these bone grafts in particular in the direction of the overlying and underlying vertebral plateaus and to improve the fusion.  
         [0171]    FIGS.  24  to  27  illustrate a fifth embodiment of the invention. The body  10  of the implant differs from that of the third and fourth embodiments essentially in that the bottom Dart  101  has a cylindrical through-opening  101   a  arranged on the axis of the body, and in that the entry opening situated opposite the bottom  101  does not have the thread  103  of the preceding embodiments.  
         [0172]    Here, the anchorage reinforcement member  20  is in the form of a screw which has a wide thread and which, at its front end, has a shaft-like extension made up of two essentially semicylindrical axial lugs  29   a ,  29   b  which, at their free ends, have an added thickness,  291   a ,  291   b  respectively.  
         [0173]    These two lugs have an external diameter which is slightly smaller than the diameter of the opening  101   a  of the body  10 , and they are thinner so that their elastic deformability allows the member  20  to be snapped into the body  10  before it is fitted by the surgeon, the said member  20  thus being immobilized against any translation, but being free in rotation and being guided, on the one hand, by the opening  101   a  and on the other hand, by the inner faces of the two branches  102 ,  103  of the body  10 .  
         [0174]    Another important feature of this embodiment is that the member  20  is delimited by two flats  201 ,  201 ′, respectively, which confer upon the member, in its angular position as illustrated in FIG. 24, a thickness which is substantially equal to the thickness of the body  10 , all along the length of the latter.  
         [0175]    It will also be observed that at the transition between the thread  22  (of square cross-section) and the flats  201 ,  201 ′, the threads each form a sharp angle  22   a.    
         [0176]    Furthermore, as in some of the preceding embodiments, the proximal part  24  of the member  20  is provided with a recessed socket  24   a  for a screwing instrument.  
         [0177]    The surgeon fits the implant in place in the following way:  
         [0178]    the complete implant, that is to say the body  10  enclosing the member  20  which has first been clipped on, and which has been given the angular orientation in FIG. 24, is engaged by impaction into the intervertebral space, this operation being made easier by the fact that the member  20  does not protrude beyond the limits of the body  10 ;  
         [0179]    the member  20  is then turned about its axis with the aid of an appropriate instrument engaged in the socket  24   a , so that the sharp edges of the threads  22  attack the bone material of the overlying and underlying vertebral plateaus, in this way tearing off bone chips that will fill the free spaces existing between the body  10  and the member  20 , so as to contribute to the bone fusion.  
         [0180]    Because the member  20  is immobilized against any translation relative to the body  10 , and cannot therefore be screwed into the latter o into the vertebral plateaus, the threads  22  are advantageously given a wide helical pitch so that the screwing action favors a reciprocal sliding of the threads  22  relative to the vertebral plateaus, without inducing an axial force sufficient to displace the implant in this direction.  
         [0181]    Referring now to FIGS.  28  to  32 , a description will be given of a first variant of the third embodiment of the invention which was described above with reference to FIGS.  16  to  19 . In the description which follows, those elements already described with reference to FIGS.  16  to  19  will not be discussed again, but only the essential differences brought forth by the variant.  
         [0182]    According to this variant, the body  1  [sic] is made wider and is designed to receive two anchorage reinforcement members,  20   a  and  20   b  respectively. To this end, the body  10  is widened and has two lateral branches  102  and  103  as well as an intermediate middle branch  109  extending between the branches  102  and  103 .  
         [0183]    The branches  102  and  109  define a first seat for the member  20   a , while the branches  103  and  109  define a second seat for the member  20   b , the axes of these two seats here being mutually parallel, but being able, if appropriate, to adopt a certain inclination. These two seats preferably have the same configuration as the single seat of the third embodiment, and the members  20   a  and  20   b  are preferably similar to the member  20  of this same embodiment.  
         [0184]    Likewise, the body  10  is provided with bone anchorage teeth  105 ,  105 ′.  
         [0185]    It will be observed here, as shown particularly in FIGS. 30 and 31, that the upper and lower faces  104  and  104 ′ of the body  10  have a dual inclination, one corresponding to these faces coming closer together in the direction towards the bottom of the seats, and the other corresponding to these faces coming closer together in a lateral direction (from right to left in FIG. 30), but the opposite can be obtained simply by turning the body  10  around.  
         [0186]    This dual inclination allows the body  10  to be implanted at a slant while re-establishing the lumbar lordosis in the sagittal plane.  
         [0187]    Furthermore, the increased width of the implant ensures a more stable support between the two vertebral plateaus, whilst the presence of two anchorage reinforcement members  20   a  and  20   b  reinforces the resistance to slipping relative to these plateaus.  
         [0188]    Of course, this variant of the invention can be applied to all the other implants described in the present document, with a simple adaptation of the body  10 , within the ability of a person skilled in the art, being all that is needed.  
         [0189]    Referring now to FIGS.  33  to  44 , a description will be given of another variant of the implant which was described with reference to FIGS.  16  to  19 .  
         [0190]    According to this variant, the outer body  10  of the implant comprises, in the same way as before, a general U shape with two lateral branches  102  and  103  connected via a distal end wall  101 , with rounded transitions.  
         [0191]    To increase the width of the implant, and hence to improve its stability, the lateral branches  102  and  103  have, in the lateral direction, a thickness which is substantially greater than that of the branches  102  and  103  described with reference to FIGS.  16  to  19 .  
         [0192]    This thickness is preferably chosen in such a way as to give the overall width of the implant a value which is, for example, equal to about 1.S to 2.5 times the diameter of the anchorage reinforcement member  20 .  
         [0193]    In addition, to further improve the bone fusion between the overlying and underlying vertebral plateaus, oblong through-openings  110  and  111  are provided which extend, for example, vertically between the upper face  104  and the lower face  104 ′ of the body, in such a way that the lateral branches  102  and  103  each have a double wall. Also formed in each of these walls there is a generally horizontal oblong opening  106 ,  106 ′, and  107 ,  107 ′, respectively, which allow the internal space of the body  10  to open out laterally to the outside of the body, by passing through the two double walls and the through-openings  110 ,  111 , respectively.  
         [0194]    It will also be observed, as shown in FIGS. 43 and 44, that the upper and lower faces  104  and  104 ′ of the body have a dual inclination relative to each other, on the one hand in the lateral direction, and on the other hand from the proximal end towards the distal end.  
         [0195]    The anchorage reinforcement member  20  has a construction similar to that which was described with reference to FIGS.  16  to  19 . It essentially comprises an internal fork having two branches  21 , to which a helical band  22  forming a bone anchorage thread is attached, the parts  21  and  22  preferably being made in one piece.  
         [0196]    The thread  22  is in this case preferably a self-tapping thread, which makes it possible to screw directly into the overlying and underlying vertebral plateaus without having to form a tapping in these vertebral plateaus prior to fitting. To this end, the thread  22  has, in its distal end region, a radial section  22   b  in the form of an outwardly turned point, and this section varies progressively, for example by about a fraction of a turn, up to a rectangular radial section  22   c . In addition, the diameter of the thread  22  increases progressively from its distal end up to the said part of rectangular section, which is here of constant diameter.  
         [0197]    It will also be observed that the outer faces of the branches  21  have a tapered form, the diameter decreasing from the proximal end towards the distal end, for reasons which are explained below.  
         [0198]    The two branches are joined at the area of a bushing  24  which is in the form of a cylindrical ring, formed preferably in one piece with the said branches.  
         [0199]    A plug  30  having a series of flexible locking tabs  33 , in this case two pairs of tabs, can be mounted in this bushing  24  by being clipped in elastically from the outside, which tabs engage in the central opening of the bushing  24 , and the ends of which tabs, in the form of teeth  33   a , can catch onto the internal edge of the bushing  24 .  
         [0200]    The member  20  and its plug  30  are made integral in terms of rotation by means of the fact that each pair of tabs  33  tightly encloses the start of a respective branch  21  of the fork.  
         [0201]    The plug  30  also has a tapped bore  34  arranged centrally and able to receive the threaded rod-shaped end of an instrument, which is known per se and is not shown, for fitting the member  20 .  
         [0202]    It will also be observed in FIGS. 40 and 44 that two diametrically opposite notches  35 , formed on either side of the tapped bore  34 , permit angular indexing of the abovementioned instrument, in this case equipped with complementary arrangements, relative to the plug  30  and, thus, to the whole of the anchorage reinforcement member  20 .  
         [0203]    It will then be observed, in particular in FIG. 44, that the thread  108  permitting screwing cooperation between the outer body  10  and the member  20  is provided only on one of the lateral branches  102  of the body, in the form of a reentrant flange ending in a generally rectilinear edge  108   a.    
         [0204]    Finally, it will be observed, in particular in FIGS. 33, 38 and  40 , that the end of the thread  22  on the proximal side is deformed, as indicated at  22   d , this deformation being obtained in the direction of the adjacent thread turn, that is to say towards the distal end.  
         [0205]    This deformation makes it possible to give the thread  22  an immobilizing function against reverse rotation, and thus to prevent any risk of the anchorage reinforcement member  20  coming loose from the body  10  after fitting, but before bone fusion.  
         [0206]    The implant described above with reference to FIGS.  33  to  44  is fitted in place using the following successive steps:  
         [0207]    first, the openings  110  and  111  of the body  10  are filled with material promoting bone growth, such as bone grafts;  
         [0208]    the body is then inserted into the intervertebral space, if necessary after distraction;  
         [0209]    the anchorage reinforcement member  20  is filled with a material promoting bone growth, and this member  20  is then closed at its proximal end by the plug  30  being clipped in;  
         [0210]    by means of screwing, the said member is engaged in the already fitted body; it should be noted here that the tapering shape of the two branches  21  of the fork of the member  20  makes it possible, as the member  20  advances, to compress the bone growth material and thus to ensure good contact on the one hand with the overlying and underlying vertebral plateaus and on the other hand with the bone growth material placed beforehand in the openings  110  and  111 , via the openings  108  and  109 .  
         [0211]    The implants according to the invention are of course made of a biocompatible material of suitable strength, such as a titanium alloy or stainless steel.  
         [0212]    The surgeon is advantageously offered implants according to the invention in the form of a set of implants of different shapes and dimensions, and this makes it possible to choose the implant, and in particular the body  10 , best suited to the anatomy of the implantation site.  
         [0213]    In particular, implants can be provided:  
         [0214]    in which the bodies  10  have different heights, with, in this case, anchorage reinforcement members  20  whose diameters can vary in order to adapt to these different heights,  
         [0215]    in which the bodies have different widths; thus, in the particular case of the third embodiment, it is possible to provide a range of implants whose widths vary progressively between a minimum width (case in FIGS.  16  to  19 ) and a maximum width (for example as represented in FIGS.  33  to  44 ), by varying the thickness, in the lateral direction, of the lateral branches  102  and  103  of the body, while at the same time maintaining the same size of internal space and also being able to use the same member  20  in all cases; these lateral branches  102 ,  103  advantageously vary from a single wall (FIGS.  16  to  19 ) to a double wall (FIGS.  33  to  44 ) once the thickness of the said branches  102 ,  103  has become sufficient to allow the vertical through-openings  110  and  111  to be made;  
         [0216]    in which the bodies have upper and lower faces of different mutual inclinations, both from the front towards the rear and also laterally, with members  20  of identical or different diameters;  
         [0217]    in which the bodies  10  and/or the anchorage reinforcement members  20  have different lengths;  
         [0218]    in which the anchorage reinforcement members have different anchorage projections, and in particular of greater or lesser depth and greater or lesser spacing, depending on the mechanical characteristics encountered in the vertebral plateaus; etc.  
         [0219]    Of course, the present invention is in no way limited to the embodiments described above and illustrated in the drawings, and the person skilled in the art will be able to vary or modify them in accordance with the spirit of the invention, and in particular will be able to combine the particular features of the various embodiments described.  
         [0220]    Furthermore, the bone anchorage projections such as have been described above can consist of any means permitting mechanical anchorage and/or of bone connection with the overlying and underlying vertebral plateaus. In particular, this can be a porous coating or hydroxyapatite.