Abstract:
So that a surgical instrument for inserting an intervertebral implant into an intervertebral space between two adjacent vertebral bodies of two vertebrae of a human or animal spinal column, wherein the intervertebral implant comprises a first abutment element for abutment against one of the two adjacent vertebral bodies as well as a second abutment element directly or indirectly supported in an articulated manner on the first abutment element for abutment against the other of the two adjacent vertebral bodies, wherein the instrument comprises an elongate shank, which defines a longitudinal direction and on the distal end of which at least two abutment-element holding elements are provided for detachable connection to the first and the second abutment element, and a spacer element, which projects from the distal end of the shank in extension thereof and which, when the abutment elements are connected to the instrument, engages between the abutment elements and holds them a defined spacing apart from one another, may be improved in such a way that with it a plurality of different implants, in particular of differing sizes, is insertable through different approaches into the intervertebral space, it is proposed that the spacer element is supported movably relative to at least one of the two abutment-element holding elements.

Description:
The present disclosure relates to the subject matter disclosed in German patent application 10 2004 043 996.6 of Sep. 8, 2004 which is incorporated herein by reference in its entirety and for all purposes. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a surgical instrument for inserting an intervertebral implant into an intervertebral space between two adjacent vertebral bodies of two vertebrae of a human or animal spinal column, wherein the intervertebral implant comprises a first abutment element for abutment against one of the two adjacent vertebral bodies as well as a second abutment element directly or indirectly supported in an articulated manner on the first abutment element for abutment against the other of the two adjacent vertebral bodies, wherein the instrument comprises an elongate shank, which defines a longitudinal direction and on the distal end of which at least two abutment-element holding elements are provided for detachable connection to the first and the second abutment element, and a spacer element, which projects from the distal end of the shank in extension thereof and which, when the abutment elements are connected to the instrument, engages between the abutment elements and holds them a defined spacing apart from one another. 
     Instruments of the initially described type are used to insert intervertebral implants with movable implant components, in particular to insert replacement intervertebral disks. In this case, a basic distinction is made between two types of instrument. On the one hand, there are instruments, with which first the abutment elements are disposed against the adjacent vertebral bodies and only in a next step is an articulated element inserted between the two abutment elements. With this procedure, spreading of the adjacent vertebral bodies is an absolute requirement. Known insertion instruments accordingly also have a spreading function. On the other hand, insertion instruments are known, with which an intervertebral implant may be inserted as a unit between adjacent vertebral bodies. Known insertion instruments are each individually adapted to the replacement intervertebral disk that is to be inserted. 
     SUMMARY OF THE INVENTION 
     It is an advantage of the present invention that with an instrument of the initially described type that is improved according to the invention a plurality of different implants, in particular of differing sizes, is insertable into an intervertebral space. 
     This is achieved in particular in that the spacer element is supported movably relative to at least one of the two abutment-element holding elements. 
     This development makes it possible to use the insertion instrument to hold intervertebral implants of differing size, in particular in different positions. By virtue of supporting the spacer element movably relative to at least one of the two abutment-element holding elements, the position of the spacer element may be adapted in a desired manner to the implant to be inserted in each case. In said case, it would in particular be conceivable for the spacer element to be rotated, displaced in a translatory manner within a plane of motion or displaced transversely of the plane of motion. It is therefore possible to act with the insertion instrument in different positions on the implant to be inserted and to move the spacer element into the position, in which the spacer element holds the abutment elements connected to the instrument a defined spacing apart from one another. Thus, intervertebral implants may be introduced in particular also through different approaches, i.e. from different directions, e.g. from an anterior or lateral direction, into the intervertebral space. 
     The spacer element is preferably supported movably transversely or substantially transversely of the longitudinal direction of the shank. It is therefore possible to act with the instrument not only centrally but also laterally on the intervertebral implant to be inserted, wherein owing to the transverse mobility of the spacer element in relation to the longitudinal direction a lateral offset in relation to a symmetrical basic position of the instrument is possible and the abutment elements connected to the instrument may be held in a desired manner a defined spacing apart from one another. 
     It is further advantageous when the spacer element is supported movably parallel or substantially parallel to the longitudinal direction of the shank. In this way, an unwanted tilting of the two abutment elements relative to one another may be prevented, namely in that the spacer element is moved substantially in such a way that both abutment elements are supported over a large area against the spacer element, in particular around an edge thereof, and so a tilting of the abutment elements relative to the spacer element, in particular around an edge thereof, is prevented. 
     It is particularly advantageous when the intervertebral implant comprises an articulated element disposed between the first and the second abutment element. In this way, a lordosis angle formed between the articular surfaces of the vertebral bodies delimiting the intervertebral space may be reconstructed in an optimum manner. It moreover allows an almost natural mobility of the two abutment elements relative to one another. 
     In an advantageous manner, the articulated element can be encompassed at least partially by the spacer element. This results in a particularly good support of the two abutment elements against the spacer element. It may therefore be ensured particularly well that the articulated element maintains a desired position, equally that the two abutment elements may be held a desired spacing apart from one another. 
     The construction of the instrument becomes particularly simple when the spacer element is of a substantially U-shaped design. This moreover allows it to be easily displaced relative to the two abutment elements. 
     It would in principle be conceivable for the spacer element to be of a semicircular design. The spacer element preferably comprises two limbs directed in distal direction parallel or substantially parallel to the longitudinal direction of the shank. This allows a position of the spacer element to be readjusted in a desired manner in a direction parallel to the longitudinal direction of the shank. 
     It is advantageous when a spacing between the two limbs is greater than a width of the articulated element and when the spacing between the two limbs corresponds at most to the width of the first and second abutment element. By virtue of this dimensioning it is ensured that the spacer element is introducible on either side of the articulated element between the two abutment elements and may hold the two abutment elements a desired spacing apart from one another. 
     A height of the spacer element is advantageously equal to or greater than a minimum possible spacing of the first abutment element from the second abutment element. This prevents forces, which act upon the two abutment elements during insertion of the implant, in the direction of the other abutment element from being able to lead to damage of the articulated element. If the height of the spacer element is slightly greater than a minimum possible spacing of the first abutment element from the second abutment element in a finally inserted position of the implant in the intervertebral space, then the implant may be inserted without contact between parts of the implant that lie adjacent to one another in the inserted position. In this way, damage to the implant during insertion is avoided even more effectively. 
     In order to prevent damage being caused to the implant during insertion by an unintentional movement of the spacer element relative to the two abutment elements, it is advantageous when the spacer element is securable in at least one transverse movement position, which is defined or movable in a defined manner, relative to the shank. This at least one transverse movement position may be so selected that it corresponds to one or more special coupling positions of the instrument on the implant, for example mid-centre or laterally offset coupling positions of the instrument on the implant. 
     It would in principle be conceivable for the spacer element to be supported pivotably relative to the shank. Such a support becomes particularly stable when the spacer element is supported displaceably relative to the shank. 
     The stability of the instrument and the precision and reproducibility of the setting of a specific position of the spacer element may be increased when a displacement guide is provided for the spacer element. 
     Two independent setting options for the spacer element may be realized when the spacer element is supported movably on a holding element and when the holding element is supported movably relative to the shank in longitudinal direction thereof. This allows the spacer element to be displaced for example in a translatory manner in one plane. It would however also be conceivable to rotate the spacer element relative to the holding element. 
     It is advantageous when at least two corresponding locking elements are provided for locking a relative position of the spacer element and the holding element in a locking position, in which the spacer element and the holding element are secured such that they are immovable relative to one another or movable in a defined manner, and when the spacer element carries a first and the holding element carries a second of the at least two locking elements. In this way, a relative position of the spacer element and the holding element may be secured in a particularly simple manner. A position movable in a defined manner may be defined for example by means of an elongate indentation or opening, in which a projection is guided between two defined stops. 
     The construction of the instrument becomes particularly simple when the one first locking element is a locking receiver and the one second locking element is a locking projection. 
     In particular when a transverse movement of the spacer element relative to longitudinal direction of the shank is to be secured, it is advantageous when the locking projection is supported movably parallel or substantially parallel to the longitudinal direction of the shank. 
     So that the at least two locking elements may be secured in the locking position against unintentional detachment, it is advantageous when the locking projection is supported spring-biased in the direction of the locking receiver. The locking projection may then engage in a spring-actuated manner into the locking receiver. 
     The locking position may be secured in a particularly simple manner against unintentional detachment when the one of the at least two locking elements is designed in the form of a spherical thrust piece. The locking receiver is then preferably of a corresponding design to the spherical thrust piece, being designed in particular in the form of a hemispherical indentation or a corresponding elongate groove with lateral stops, which are used to limit the movement, for the spherical thrust piece. 
     In order to ensure that the spacer element may be secured in at least two locking positions, it is advantageous when the holding element and/or the spacer element carries at least two locking elements. These may be, for example, two locking receivers or two locking projections that can be brought in each case into engagement with a further locking element. 
     A connection of the spacer element to the remaining instrument becomes particularly stable when the displacement guide is formed by an opening, which is disposed transversely of the longitudinal direction of the shank and is at least partially open in the direction of the spacer element. In this way, it is possible to form, for example, a slot guide for the spacer element. 
     The intervertebral implant may be connected to the instrument in a simple manner when a stop device is provided for limiting a movement of the abutment-element holding elements away from another. In this way, in particular an unintentional detachment of an articulated element inserted loosely between the two abutment elements is additionally prevented. In said case, it may be advantageous when the stop device is variable, i.e. a maximum spacing between the abutment-element holding elements is definable in dependence upon the setting of the stop device. Thus, for example, abutment-element holding elements that are supported resiliently relative to one another may be moved away from one another to a differing extent, depending on how the stop device is set. 
     The construction of the stop device becomes particularly simple when the stop device comprises a stop element that encompasses both abutment-element holding elements in each case at least partially. 
     It would in principle be conceivable for the stop element to be of a clamp-like design. The construction of the instrument is however further simplified when the stop element is a sleeve supported movably in longitudinal direction of the shank. The sleeve may be displaced in longitudinal direction of the shank or moved in the manner of a screw, in which case a distal end of the sleeve is displaced in longitudinal direction of the shank. 
     According to a preferred embodiment of the invention it may be provided that the stop device comprises at least one slide surface for a distal end of the sleeve, that the slide surface is formed on one of the two abutment-element holding elements or adjacent thereto on the shank, and that the slide surface in distal direction relative to the longitudinal direction of the shank is inclined away from a longitudinal axis of the shank. This development allows the abutment-element holding elements to be moved towards one another by moving the sleeve in distal direction. Conversely, the abutment-element holding elements biased towards one another may spring away from one another when the sleeve is moved back in proximal direction. 
     The instrument may be connected to the intervertebral implant in a simple manner when the abutment-element holding element carries at least one holding pin, which projects in distal direction parallel to the longitudinal direction of the shank and is of a corresponding design to at least one holding-pin receiver of the abutment element. By moving the instrument parallel to the longitudinal direction of the shank towards the intervertebral implant a connection may be established. It is in particular advantageous when the abutment element has more than one holding-pin receiver so that the instrument is connectable in various positions to the intervertebral implant and may also be coupled, for example, laterally to the implant. 
     According to a further preferred embodiment of the invention it may be provided that at least the distal end of the instrument is of a forked design comprising two fork ends, which are movable relative to one another, and that the two fork ends form or carry the abutment-element holding elements. In particular, the fork ends may be spring-biased in such a way that they may be pressed together only after loading with a force. 
     A mechanical drive unit is advantageously provided for moving the spacer element in longitudinal direction of the shank. A user of the instrument may then bring about a movement of the spacer element in longitudinal direction of the shank by loading the drive unit with a force. In particular, it would be possible to provide an indicating device for indicating a relative position of the spacer element relative to the shank. 
     The mechanical drive unit may be realized in a particularly simple manner when it comprises a threaded spindle extending in longitudinal direction of the shank as well as a rotary knob supported on the shank and coupled to the threaded spindle. This allows the threaded spindle to be displaced in longitudinal direction of the shank through rotation of the rotary knob. 
     It is advantageous when the intervertebral implant is a replacement intervertebral disk. 
     It is advantageous when the articulated element and one of the two abutment elements are of an integral construction. This allows the number of parts of the implant to be minimized to two. 
     The articulated element and at least one of the two abutment elements preferably lie loosely adjacent to one another, in particular in the insertion position and also in an implanted position. In this way, it is possible to dispense with additional connection elements for connecting the abutment element to the articulated element and therefore reduce an overall height of the implant as a whole. 
     In order to guarantee that the implant parts are held together particularly well, it is advantageous when the articulated element and at least one of the two abutment elements are non-positively and/or positively connected to one another. 
     In order also to be able to vary distances between the abutment elements, it is advantageous when the spacer element is held in a detachably connectable manner on the instrument. Thus, for example, one or more further spacer elements may be provided, which may be connected to the instrument depending on the type and size of the implant to be inserted. Preferably, a set of different spacer elements is provided. 
     According to the invention the initially stated object is further achieved in that one of the previously described instruments is used to insert an intervertebral implant into an intervertebral space between two adjacent vertebral bodies of two vertebrae of a human or animal spinal column, wherein the intervertebral implant comprises a first abutment element for abutment against one of the two adjacent vertebral bodies as well as a second abutment element directly or indirectly supported in an articulated manner on the first abutment element for abutment against the other of the two adjacent vertebral bodies. 
     According to the invention the initially stated object is further achieved by an implant system comprising an intervertebral implant for insertion into an intervertebral space between two adjacent vertebral bodies of two vertebrae of a human or animal spinal column as well as an insertion instrument for inserting the intervertebral implant into the intervertebral space, wherein the intervertebral implant comprises a first abutment element for abutment against one of the two adjacent vertebral bodies as well as a second abutment element directly or indirectly supported in an articulated manner on the first abutment element for abutment against the other of the two adjacent vertebral bodies, wherein the insertion instrument is one of the previously described surgical instruments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed explanation is provided by the following description in connection with the drawings. The drawings show: 
         FIG. 1 : a partially broken-through and part-sectional side view of an insertion instrument; 
         FIG. 2 : an enlarged view of the region A in  FIG. 1 : 
         FIG. 3 : a perspective, part-sectional and/or partially broken-through view of the instrument of  FIG. 1  during connection to an intervertebral implant; and 
         FIG. 4 : a plan view of a distal end of the instrument with an intervertebral implant held thereon, in a laterally offset position of the spacer element. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an insertion instrument, which is provided as a whole with the reference character  10  and may be used to insert an intervertebral implant in the form of a replacement intervertebral disk  12  into a non-illustrated intervertebral space between two adjacent vertebral bodies of two vertebrae of a human or animal spinal column. 
     The replacement intervertebral disk  12  illustrated in  FIGS. 1 to 4  comprises a top end plate  14  and a bottom end plate  16 , which serve as abutment elements for abutment against the two non-illustrated adjacent vertebral bodies. The bottom end plate  16  is provided with a substantially cuboidal indentation  18 , which forms a receiver for a polyethylene core  20  serving as an articulated element. In the described embodiment of the replacement intervertebral disk  12  the polyethylene core  20  is seated immovably in the indentation  18  but might however alternatively be supported in a movable manner. A convexly curved surface of the polyethylene core  20  facing towards the top end plate  14  and forming part of a spherical surface forms an articulated surface  22  for producing an articulated connection between the top end plate  14  and the bottom end plate  16 . 
     The top end plate  14  is provided with a hollow-spherical sliding surface  24  facing towards the bottom end plate  16  and corresponding to the articulated surface  22 . This development allows, in accordance with a radius R of the articulated surface  22  and/or of the sliding surface  24 , a rotational movement of the top end plate  14  relative to the bottom end plate  16  about a centre of rotation  26 . 
     Each of the two end plates  14  and  16  in plan view has a polygonal shape, namely having in each case a back edge  28 , two side edges  30  and  32  extending at right angles to the back edge  28 , a short front edge  34  extending parallel to the back edge  28 , and two holding edges  36  and  38  connecting the front edge  34  to the side edges  30  and  32  and inclined in each case by 30° relative to the front edge  34 . In other variants, angles of 45° would also be conceivable. For detachably connecting the replacement intervertebral disk  12  to the insertion instrument  10 , the two side edges  30  and  32 , the front edge  34  and the holding edges  36  and  38  of both the top and the bottom end plates  14  and  16  are provided in each case with blind hole bores  40 , which project at right angles from the respective edges. The blind hole bores  40  in the top end plate  14  and in the bottom end plate  16  are arranged in the identical edges so as to be aligned in each case parallel and above one another, so that in an insertion position of the replacement intervertebral disk  12  longitudinal axes of the mutually associated blind hold bores  40  in identical edges of both end plates  14  and  16  define in each case one plane. 
     The insertion instrument  10  comprises an elongate tubular sleeve  42 , which defines a longitudinal axis  44  in longitudinal direction of the insertion instrument  10 . At the proximal end, the sleeve  42  is connected in a rotationally fixed manner to a rotary sleeve  46 , which is provided with an internal thread  48 . The sleeve  42  penetrates a shank  50  that is provided with a central longitudinal bore  52 . A blind hole bore  54 , which at the distal end widens the longitudinal bore  52  in the shank  50 , is provided with an internal thread that is connected to an external thread of a threaded bolt  56 , which is directed integrally with a holding fork  58  in proximal direction. 
     The holding fork  58  adjoining the threaded bolt  56  is of a rod-shaped design but is provided along over half of its length at the distal end with a slot  60  for forming a top and a bottom fork end  62  and  64 . Both the threaded bolt  56  and the adjoining, non-forked portion of the holding fork  58  are provided with a bore  66  that is a continuation of the longitudinal bore  52 . To facilitate a springing of the fork ends  62  and  64 , these are provided in the interior adjacent to the non-forked portion of the holding fork  58  with a weakening in the form of an annular groove  68  facing towards the longitudinal axis  44 . 
     The, at the proximal end, substantially cylindrical holding fork  58  widens conically in the direction of its distal end, so that the two fork ends  62  and  64  each have run-on bevels  70  and  72  serving as slide surfaces. The run-on bevels  70  and  72  are adjoined by two substantially cuboidal regions of the fork ends  62  and  64 , which are provided in each case symmetrically to one another with at least one blind hole bore  74  and  76  each, which are aligned relative to one another parallel to the longitudinal axis  44  and open in distal direction and into each of which a holding pin  78  and/or  80  serving as an abutment-element holding element is inserted and connected firmly to the respective fork end  62  and/or  64 . The holding pins  78  and  80  are so designed that they are introducible into the blind hole bores  40  of the replacement intervertebral disk  12  for detachably connecting the insertion instrument  10  to the replacement intervertebral disk  12 . 
     At the proximal end, the shank  50  is equipped with an annular flange  84  that is provided with an external thread  82 , wherein the external thread  82  corresponds to the internal thread  48  of the rotary sleeve  46 . This allows the sleeve  42  to be moved in a defined manner relative to the shank  50 , wherein by means of the corresponding internal and external threads  48  and  82  a defined rotational/translational movement of the sleeve  42  is preset. 
     A distal end of the sleeve  42  forms an annular stop  86 , which limits an outward rotating movement of the fork ends  62  and  64  away from the longitudinal axis  44 . Together with the stop  86 , the run-on bevels  70  and  72  provided on the fork ends  62  and  64  therefore form a stop device. The further the sleeve  42  is slid forward in distal direction, the further the two fork ends  62  and  64  are moved towards one another. Conversely, an outward rotating of the fork ends  62  and  64  biased towards one another by the sleeve  42  is made possible when the sleeve  42  is rotated back in proximal direction. 
     The shank  50  extends at the proximal end beyond the annular flange  84  and is screwed into a handle  88 , which is provided with a receiving bore  90  for a proximal end of the shank  50 . Transversely of the longitudinal axis  44  the handle  88  is provided with a securing bore  92 , into which a threaded pin  94  may be screwed to secure the shank  50  in a rotationally fixed manner on the handle  88 . The threaded pin  94  for this purpose engages into a small recess  96  of the shank  50 . 
     On a proximal end of the handle  88  a rotary knob  98  is rotatably supported. The rotary knob  98  forms part of a spindle mechanism and for this purpose is provided with an internally threaded blind hole bore (not illustrated in detail), which is open in distal direction. The rotary knob is used to move a threaded rod  102 , which is provided at its proximal end with an external thread corresponding to the internal thread of the rotary knob  98 . The threaded rod  102  penetrates a longitudinal bore  100  of the handle  88  that is a continuation of the receiving bore  90  of the shank  50  in proximal direction, and also penetrates the longitudinal bore  52  that penetrates the shank  50  along the entire length thereof. A distal end of the threaded rod  102  is designed with a single-stage taper in the form of an externally threaded bolt  104 . 
     The threaded bolt  104  is screwed into an internally threaded blind hole bore  106  of a cuboidal holding element  108 . Adjacent to its distal end the holding element  108  is provided, parallel to top and bottom sides  110  and  112  forming largest lateral faces thereof, with a cuboidal transverse opening  114 , which by means of a parallel-running slot  116  is open in distal direction. In other words, the transverse opening  114  and the slot  116  form a groove, which is open in distal direction and widens in a single stage in proximal direction. Disposed on the top side  110  and the bottom side  112  are laterally offset, narrow, cuboidal longitudinal ribs  118  and  120  respectively, which extend parallel to the longitudinal axis  44  and are of a corresponding design to longitudinal grooves  126  and  128 , which are formed parallel to the longitudinal axis  44  in mutually opposing inner faces  122  and  124  of the fork ends  62  and  64 . They form longitudinal guides for the holding element  108  when it is displaced parallel to the longitudinal axis  44  in distal or proximal direction by rotating the rotary knob  98  on the proximal end of the insertion instrument  10 . 
     A substantially U-shaped stirrup spacing member  130 , which comprises two limbs  132  extending in distal direction parallel to the longitudinal axis  44 , is connectable to the holding element  108 . At the proximal end, the limbs  132  are formed integrally with a holding plate  134 , which is provided with a slot  136  extending parallel to a plane defined by the two limbs  132 . A plate-shaped end of a cuboidal connection element  138  is inserted into the slot, namely in such a way that the connection element  138  is insertable transversely of the longitudinal axis  44  into the transverse opening  114 , wherein the plate-shaped end in said case penetrates the slot  116 . The transverse opening  114  and the slot  116  form a transverse guide for the stirrup spacing member  130 , so that the stirrup spacing member  130  is displaceable in a defined manner transversely of the longitudinal axis  44 . 
     For securing defined positions of the stirrup spacing member  130  relative to the holding element  108 , a wall surface of the connection element  138  facing in proximal direction is provided with three symmetrically arranged, hollow-spherical indentations  140 . Alternatively, only two indentations may be provided, wherein one may be hollow-spherical and the other elongate. Provided in the holding element and extending from the transverse opening  114  in proximal direction and parallel to the longitudinal axis  44  are three blind hole bores  142 , into which spherical thrust pieces  144  spring-biased in distal direction are inserted. These are formed by a helical spring  148 , which is supported at the proximal end against the blind hole bore  142  and at the distal end against a detent element  146 , wherein only a hemispherical end  150  may project from the blind hole bore  142  and engage into one of the indentations  140 . 
     The spherical thrust pieces  144  together with the indentations  140  form a securing device for securing the stirrup spacing member  130  in defined transverse movement positions. In principle, it would be conceivable to provide more or fewer than three spherical thrust pieces and/or indentations  140  in order to achieve further defined securing positions. If an indentation is designed in the form of an elongate hole, then a transverse movement position movable in a defined manner may be preset, wherein the spherical thrust pieces may move freely between two defined end stops in the elongate indentation. 
     The previously described insertion instrument  10  may be used to insert the replacement intervertebral disk  12  into an intervertebral space. For this purpose, first the stirrup spacing member  130  is moved into its most distal position by rotating the rotary knob  98  accordingly. The sleeve  42  is moreover moved into its most proximal position by rotation at the rotary sleeve  46 . The insertion instrument  10  is connected to the replacement intervertebral disk  12  by introducing the holding pins  78  and  80  into a blind hole bore  40  of the top and bottom end plate  14  and  16  respectively. The stirrup spacing member  130  is chosen in accordance with the selected replacement intervertebral disk  12 . This means that, for larger or smaller replacement intervertebral disks  12 , different stirrup spacing members  130  are connectable to the holding element  108 . What is crucial in each case is that the limbs  132  of the stirrup spacing member  130  may be supported both against the top end plate  14  and against the bottom end plate  16  while at least partially encompassing the polyethylene core  20 . It should further be ensured that the stirrup spacing member  130  is advanced far enough in distal direction to prevent a rotation of the two end plates  14  and  16  with the back edges  28  towards one another. 
     In a subsequent step, the replacement intervertebral disk  12  may be secured by clamping on the insertion instrument by moving the sleeve  42  in distal direction by rotating the rotary sleeve  46 . The stop  86  sliding along on the run-on bevels  70  and  72  forces the two free fork ends  62  and  64  to execute a movement in the direction of the longitudinal axis  44 , which leads to a jamming of the holding pins  78  and  80  in the blind hole bores  40 . In this way, the replacement intervertebral disk  12  is held securely on the insertion instrument and may be introduced into the intervertebral space. As soon as the replacement intervertebral disk  12  has been implanted in the desired shape, either the stirrup spacing member  130  between the two end plates  14  and  16  may first be withdrawn or a jamming of the holding pins  78  and  80  in the blind hole bores  40  may be cancelled by rotating the sleeve  42  back in proximal direction. The insertion instrument  10  is easily detachable in the described manner from the replacement intervertebral disk  12 . 
     The special development of the connection between the stirrup spacing member  130  and the holding element  108  allows the insertion instrument  10  to be connected to the replacement intervertebral disk  12  also in the manner illustrated in  FIG. 4 . If the holding pins  78  and  80  are namely introduced into blind hole bores  40  of the holding edges  36  and  38 , or alternatively of the front edge  28  or of the side edges  30  or  32 , the longitudinal axis  44  no longer always extends symmetrically through the polyethylene core  20 . The result of this would be that the stirrup spacing member  130  might not encompass the polyethylene core  20  solely by moving in distal direction. The lateral offset of the longitudinal axis  44  may however be compensated by lateral displacement of the stirrup spacing member  130  relative to the holding element  108 . The spherical thrust pieces  144  and the corresponding indentation  140  are disposed in such a way that in a displaced position only two spherical thrust pieces  144  engage into two corresponding indentations  140 . If only one spherical thrust piece  144  is provided, then it engages in different transverse movement positions into different indentations  140 . The lateral offset of a bisector of the stirrup spacing member  130  from the longitudinal axis  44  therefore corresponds precisely to the distance between two indentations  140 . 
     As already indicated, for replacement intervertebral disks  12  of differing size, stirrup spacing members  130  of differing size are connected to the holding element  108 . In said case, a height  152  of the limbs  132  as well as the distance  154  between them may in particular vary extremely from one another in different stirrup spacing members. 
     The insertion instrument  10  is preferably designed so that it may be completely disassembled for sterilizing purposes, i.e. the sleeve  42  and the threaded rod  102  may be fully detached from the shank  50 .