Abstract:
An insertion instrument for a multi-part intervertebral endoprosthesis includes two closure plates and a sliding core arranged between these, said insertion instrument having a handgrip part, gripping members which hold the closure plates between them, and a force-receiving part for applying an insertion force to the intervertebral endoprosthesis, the gripping members being guided movably toward and away from one another via a hinge and being able to be tensioned against the intervertebral endoprosthesis, projections pointing in the tensioning direction or recesses for holding the intevertebral endoprosthesis with form-fit being provided on the gripping members, and a block guided in the longitudinal axis direction and with an abutment surface being provided which can be moved by means of an actuating device so as to bear on the intervertebral endoprosthesis and, in its forward position, secures the intevertebral endoprosthesis against the projections or recesses.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a continuation of Ser. No. 10/619,180, filed Jul. 15, 2003, now abandoned. 
    
    
     FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to an insertion instrument for a multi-part intervertebral endoprosthesis which comprises two closure plates and a sliding core arranged between these, said insertion instrument having a handgrip part, gripping members which hold the closure plates between them, and a force-receiving part for applying an insertion force to the intervertebral endoprosthesis. 
     For inserting intervertebral prostheses, an insertion instrument is known (EP-A-1 306 064) which, at its front end, has two prosthesis holders for receiving in each case a prosthesis plate and which consist of two gripping members which are connected rigidly to one another and which hold the plates between them by friction. For very small implants, of the kind which are used in the area of the cervical spine and which have to be positioned very precisely, this may be too unreliable. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to make available an improved instrument for implantation of intervertebral prostheses which is adapted in particular to the requirements of implantation in confined conditions, as apply in particular in the area of the cervical spine. 
     The solution according to the invention lies in an insertion instrument for a multi-part intervertebral endoprosthesis that includes two closure plates and a sliding core arranged between the closure plates, an insertion instrument that includes a handgrip part, gripping members which hold the closure plates between them, a hinge, a force-receiving part for applying an insertion force to the intervertebral endoprosthesis, either projections pointing in a tensioning direction or recesses for holding the intervertebral endoprosthesis with a form-fit that are formed on the gripping members, and a block guided in the longitudinal axis direction and provided with an abutment surface configured to be movable by an actuating device so as to bear on the intervertebral endoprosthesis and, in a forward position, so as to secure the intervertebral endoprosthesis against the projections or recesses. The gripping members are configured to be guided movably toward and away from one another via the hinge and to be tensioned against the intervertebral endoprosthesis. The preferred embodiments set forth other advantageous features of the invention. 
     In the case of an insertion instrument for a multi-part intervertebral endoprosthesis, in particular a cervical prosthesis, which comprises two closure plates and a sliding core arranged between these, said insertion instrument having a handgrip part, gripping members which hold the closure plates between them, and a force-receiving part for applying an insertion force to the intervertebral endoprosthesis, the invention provides that the gripping members are guided movably toward and away from one another via a hinge and are able to be tensioned against the intervertebral endoprosthesis, projections pointing in the tensioning direction or recesses for holding the intervertebral endoprosthesis with a form-fit are formed on the gripping members, and a block guided in the longitudinal axis direction and with an abutment surface is provided which can be moved to the intervertebral endoprosthesis by means of an actuating device and, in its forward position, secures the intervertebral endoprosthesis against the projections or recesses. When the forceps-like insertion instrument is closed, the gripping members connected to one another via a hinge move toward one another and engage with a form-fit via their projections (or recesses) in corresponding depressions (or elevations) of the intervertebral endoprosthesis and thus tension the latter in a direction transverse to the longitudinal axis of the insertion instrument. The longitudinally movably guided block can be moved toward the intervertebral endoprosthesis until its abutment surface bears on the intervertebral endoprosthesis and secures the latter against the projections (or recesses). In this way, the intervertebral endoprosthesis is also tensioned in the longitudinal direction. It is thus held by the insertion instrument in a manner free of play and in a precise position. By virtue of the block bearing firmly on the intervertebral endoprosthesis, considerable forces, such as arise when striking the intervertebral endoprosthesis into place, can also be safely transmitted. Since these considerable forces are transmitted via the block and its abutment surface, the projections (or recesses) do not have to take up these forces. They can be of fairly small dimension and therefore made very fine, as is desired for precise positioning, without having to take into consideration the high force transmission when striking the intervertebral endoprosthesis home. In addition, by bearing on the intervertebral endoprosthesis, the block ensures that the latter does not inadvertently turn and that its individual elements do not open. By virtue of the invention, the intervertebral endoprosthesis can thus be held easily, safely and with precise positioning on the insertion instrument and inserted. 
     A number of terms are explained below: 
     The longitudinal axis of the forceps is understood as the center line which is the angle bisector between the handgrip parts of the forceps halves and the jaw parts of the forceps halves. 
     The tensioning direction is understood as the direction in which the gripping members move toward one another. The opposite direction is the spreading direction. These directions are generally approximately transverse to the longitudinal axis of the insertion instrument. 
     A form-fit hold is understood as meaning that the projections engage in correspondingly shaped receiving openings of the intervertebral endoprosthesis, or vice versa. Viewed in the direction of the longitudinal axis, the projections grip into an undercut. 
     The insertion instrument is preferably designed as a forceps, whose jaw parts form the gripping members. This permits a space-saving construction and easy handling, which is of advantage particularly in the confined conditions in the area of the cervical spine. 
     To make it simpler to use, the actuating device has a rod with a handle arranged in the rear area of the handgrip part. This allows the operating surgeon to use the actuating device without awkward maneuvering. Because of the small space available in the case of cervical prostheses, this is of particular importance when removing the insertion instrument after introduction of the intervertebral endoprosthesis, when the block has to be moved back. For this purpose, the rod is expediently provided with a screw thread and is guided in a counterthread which is fixed on the instrument and arranged preferably in the hinge. Thus, by turning in one direction, the block can be guided toward the intervertebral endoprosthesis and thus secure it, whereas, by turning in the opposite direction, the block is moved away and releases the intervertebral endoprosthesis for the purpose of removal of the insertion instrument. The screw device also has the advantage of being self-locking, with the result that a separate securing device for protection against inadvertent displacement is not necessary. However, a screw device is not absolutely necessary, and, instead, other preferably self-locking actuating devices can also be provided. 
     In a particularly advantageous construction, the actuating device is guided through the hinge. This is not only a particularly space-saving design, it also guarantees a near-center arrangement. This arrangement ensures that the insertion instrument does not deviate to the side even under high forces when struck. A high degree of positioning precision when inserting the intervertebral endoprosthesis is achieved in this way. 
     It is expedient for the actuating device to have a strike head at its handgrip end. In this way, via the actuating device and the block, it is possible to act directly on the intervertebral endoprosthesis so as to bring it to its implantation site. For this purpose, it is expedient for the handle itself to be designed as a strike head. This permits a space-saving construction, which is of considerable value particularly in the confined conditions in the area of the cervical spine. 
     In order to ensure that the insertion instrument does not inadvertently spring open, even when acted upon by considerable force, a locking device is expediently provided for securing the handgrip parts in the position when pressed together, said locking device having a guide for the actuating device. This ensures that the actuating device does not deflect outward under high loads, particularly when the strike head is arranged far to the rear. The locking device can be provided at the rear end of the handgrip parts in a manner known per se. It is important that it is sufficiently strongly dimensioned to withstand the loads which occur during striking but can nevertheless be easily released for removing the instrument. 
     In an expedient embodiment, the projections or recesses are arranged on jaw inserts which are fastened releasably on the jaw parts. This means that, if necessary, it is easy to exchange the jaw inserts together with the projections or recesses arranged thereon, in order to adapt the insertion instrument to other types or sizes of intervertebral endoprostheses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained below with reference to the drawing in which an advantageous illustrative embodiment is shown, and where: 
         FIG. 1  shows an overall view of the insertion instrument according to the invention, seen from above, with an intervertebral endoprosthesis; 
         FIG. 2  shows an overall view of the insertion instrument according to the invention seen from below; 
         FIG. 3  shows an enlarged detail view of a jaw part of the insertion instrument, in a longitudinal axis section; 
         FIG. 4  shows a detail view of the other jaw insert; and 
         FIG. 5  shows a detail view of the insertion instrument with an intervertebral endoprosthesis arranged thereon. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrative embodiment, shown in the figures, of an insertion instrument according to the invention is a forceps, labeled as a whole by reference number  1 . It is used for inserting cervical prostheses  9  into the intervertebral space of two adjacent vertebral bodies of the cervical spine (not shown). 
     The forceps  1  is made up of two forceps halves  2 ,  3  which are connected to one another movably via a pivot hinge  4 . In their rear area, the forceps halves  2 ,  3  have a respective handgrip part  21 ,  31  and in their front area they have a respective jaw part  22 ,  32 . The pivot hinge  4  is arranged at the transition between the handgrip parts  21 ,  31  and the jaw parts  22 ,  32 . It is formed by a pin  42  on the forceps half  2  (in  FIG. 1  it extends upward from the plane of the drawing), which pin  42  is mounted in a matching opening  43  in the central area of the other forceps half  3 . The bearing pin  42  has a through-bore  44  which runs from the handgrip area of the forceps halves  2 ,  3  to the jaw area. It will be discussed in more detail later. The pivot hinge  4  allows the handgrip parts  21 ,  31  of the forceps halves  2 ,  3  to be moved toward one another so that the jaw parts  22 ,  32  close, and vice versa. 
     The jaw parts  22 ,  32  function as gripping members. In the front area, on their mutually facing inner surfaces, they each have two projections  51 ,  52  pointing in the tensioning direction  12 . These projections are not arranged directly on the jaw parts  22 ,  32 , but instead on jaw inserts  53  which are secured exchangeably, by means of a screw (not shown), in a corresponding recess on the outer surfaces of the jaw parts  22 ,  32 . Each jaw insert  53  has a projection  51  and a projection  52 . The projection  51  is formed like a pin and is located in the upper area of the jaw insert  53 , while the projection  52  is formed like a small plate and is located in the lower area of the jaw insert  53 . The dimensions and arrangement of the projections  51 ,  52  are adapted to corresponding receiving openings on the cervical prostheses  9  to be received. This will be explained in more detail later. 
     Arranged on the jaw part  22  there is a guide rail  60  which holds a block  61  such that the latter is longitudinally displaceable in the forward and rearward directions on the forceps half  2 . The guide rail  60  is designed as an elongate hole in the jaw insert  53  of the jaw part  32 . A grub screw arranged laterally in the block  61  engages in the oblong hole forming the guide rail  60  and guides the block in the longitudinal direction. Instead of the oblong hole, other guide elements can also be provided which allow the block  61  to be guided in forward and rearward movement in the longitudinal direction, for example a dovetail guide. At its front end, the block  61  is provided with an abutment surface  62  designed to cooperate with the cervical prosthesis  9 . 
     The block  61  is engaged by an actuating device  7  which extends from the rear area of the block  61  via the through-bore  44  and into the area between the handgrip parts  21 ,  31 . The actuating device  7  comprises a coupling element  70  for connection to the block  61 , which, in the illustrative embodiment shown, is a vertebra support suitable for transmitting shear forces, and it moreover comprises a rod  71  and a handle  72  for actuation. Provided in the front area of the rod  71  there is an external thread  73  which cooperates with a complementary internal thread (not shown) in the through-bore  44  of the pin  42  as an instrument-fixed guide. By turning the handle  72 , it is thus possible for the rod  71 , and with it the block  61  via the coupling element  70 , to be moved backward and forward along the guide rail  60 . The handle  72  is designed as a rotatable knob which, on its outer circumference  74 , has a suitable surface finish, for example a coarse ribbing  75 , to allow the operating surgeon a good grip. 
     The rear end of the handle  72  is provided with a convex bulge  76 . It serves as a strike head for the actuating device  7 . Impulses acting on the bulge  76  of the strike head are transmitted by this via the rod  71  of the actuating device  7 , the shear-resistant vertebral support  70  and the block  61 , to the latter&#39;s abutment surface  62 . 
     A locking device  8  for the handgrip parts  21 ,  31  is provided in the rear area of the forceps  1 . This locking device  8  comprises a pivotably movable catch element  83  and a locking pawl  84  (which are arranged opposite one another on the handgrip parts  21 ,  31 ), a release device  81 , a base  82  and a spring  87 . The rear end of the handgrip part  21  is designed as a fork, the locking pawl  84  being formed by a beveling of the base of the fork. The catch element  83  is mounted by the base  82  in the plane enclosed by the handgrip parts  21 ,  31 . The spring  87  is designed as a leaf spring and acts on that end of the catch element  83  mounted in the base  82  in such a way that it is pressed forward to the locking pawl  84 . Starting from the base  82 , the catch element  83  has a wide area and a narrow area. In its narrow area, the catch element  83  has, on its front face, a toothing  86  into which, when the forceps  1  is closed, the locking pawl  84  engages and is locked, so that the handgrip parts  21 ,  31  cannot move away from one another and, as a result, the insertion instrument  1  is safeguarded against inadvertently springing open. In this way, it is possible for even substantial loads, for example hammer strikes, to be applied to the bulge  76  on the forceps  1  without any fear of inadvertent opening and without the operating surgeon needing to secure the handgrip parts  21 ,  31  by manual force against undesired opening. To open the forceps  1  after implantation has been carried out, the catch element  83  is pivoted rearward by applying rearward pressure on the release element  81 , by which means the locking pawl  84  is freed from the catch element  83 , and the handgrip parts  21 ,  31  thus move apart from one another under the action of the spring  11 . With the forceps  1  in the opened state, the catch element  83  is pivoted rearward counter to the force of the spring  87 . Provided in the wide area of the catch element  83  there is a guide  85  which is designed as an oblong hole and which is used to hold the rod  71 , even when the forceps  1  is open, in a defined position in the longitudinal axis  10  and to avoid deflection of the rod  71  even under high loads. 
     Also fixed on the handgrip part  31  there is a leaf spring  11  which is guided round the rod  71  to the other handgrip part  21 . With the forceps  1  closed, this leaf spring  11  is tensioned and has the effect that, after release of the catch elements  82   83 , the insertion instrument  1  automatically opens to permit removal. 
     The cooperation with the cervical prosthesis  9  will be described now with reference to  FIGS. 3 and 5 . The cervical prosthesis  9  consists of an upper closure plate  91  and a lower closure plate  92 , with a pivot [sic] element  93  arranged between them. The cervical prosthesis  9  is intended for implantation in the interspace between two adjacent vertebrae of a human cervical spine. The top closure plate  91  is secured to the upper vertebra and the bottom closure pate  92  is secured to the lower vertebra. To arrange the cervical prosthesis  9  securely on the forceps  1  for insertion into the intervertebral space, the top and bottom closure plates  91 ,  92  have receiving openings on their lateral flanks in the area of their front flange  94 ,  95 . The receiving opening on the top closure plate  91  is designed as a bore  97  with an additional countersink. The receiving opening on the bottom closure plate  92  is designed as a slit  96 . In its flange-side area, the sliding core  93  is likewise provided with a slit  96 ′ which is arranged in such a way that it is flush with the slit  96  of the bottom closure plate  92 . The slits  96 ,  96 ′ thus result in a continuous groove. 
     To receive the cervical prosthesis  9  with the forceps  1 , the cervical prosthesis  9  is brought into the area between the jaw parts  22 ,  32  and the forceps  1  is closed, as a result of which the jaw parts  22 ,  32  move toward one another. In so doing, the projections  51 ,  52  engage in the corresponding receiving openings of the two closure plates  91 ,  92 , the pins  51  engaging in the bore  97  and the small plates  52  engaging in the slits  96 ,  96 ′. In this way, the cervical prosthesis  9 , in the tensioning direction, is held free from play on the forceps  1 . The different design of the projections  51 ,  52  and of the receiving openings configured as bores  97  and slits  96  ensures that the cervical prosthesis  9  can be held on the forceps  1  only with the correct orientation. If, as in the illustrated embodiment, the forceps  1  is additionally provided with a marking  14  for the top, this virtually eliminates the possibility of incorrect implantation as a result of incorrect orientation of the cervical prosthesis  9 . After the cervical prosthesis  9  has in this way been received in the correct orientation on the forceps  1 , the rod  71  can be moved forward via the actuating device  7  by turning the handle  72 , with the result that the block  61  comes to lie, from the rear, with its abutment surface  62  on the flange  94 ,  95  of the cervical prosthesis  9 . In doing so, the block  61  tensions the cervical prosthesis  9  against the projections  51 ,  52  and thus orients the cervical prosthesis  9  in a defined position. Any play existing in the longitudinal axis direction between the projections  51 ,  52  and the bores  97  and the slits  96  is compensated in this way. The cervical prosthesis  9  is thus held securely and in a precise position on the forceps  1 . In addition, the fact that the block  61  bears on the flanges  93 ,  94  of the two closure plates  91 ,  92  ensures that the two closure plates  91 ,  92  do not move away from one another at their front end. This eliminates the possibility of the cervical prosthesis  9  opening, which would prevent successful introduction into the intervertebral space. 
     It is furthermore made possible to implant cervical prostheses of different height without making changes to the forceps  1 .  FIG. 3   b  shows a cervical prosthesis  9 ′ which has a thicker sliding core  93 ′. Like the sliding core  93 , it is provided with a slit  96 ″ which is flush with the slit  96  of the bottom closure plate  92 . This configuration of the receiving opening on the bottom closure plate  92  as a slit  96  and its continuation as slit  96 ″ in the sliding core  93 ′ ensure that the thicker cervical prosthesis  9 ′ can be gripped and securely held with the same forceps  1  without changing the arrangement of the projections  51 ,  52 . The positioning precision is in this case guaranteed by the pin-like projections  51  which engage in the bores  97 . 
     If necessary, however, it is also possible to provide other jaw inserts  53 ′ which have a different arrangement of the projections  51 ′,  52 ′, as is shown in  FIG. 4 . In this way, the forceps  1  can be adapted to other intervertebral endoprostheses, for example to particularly small ones for treatment of children. 
     With its abutment surface  62 , the block  61  affords a sufficiently large force transmission surface for transmitting to the cervical prosthesis  9  the impulses applied to the bulge  76  acting as the strike head. The great advantage of this is that the projections  51 ,  52 , which have been finely dimensioned in the interest of precise positioning, do not have to transmit the strike forces, so that the risk of bending or even breaking of the projections  51 ,  52  as a result of overloading is excluded, by virtue of the block  61  and its abutment surface  62  assuming the role of force transmission. 
     The forceps  1  according to the invention allows the cervical prosthesis  9  to be arranged with precise positioning and without any risk of its being the wrong way round on the forceps  1 , thereby preventing any undesired opening of the cervical prosthesis  9 . Moreover, by virtue of the block  61  with the abutment surface  62 , it also permits transmission of forces even in the case of forceps  1  of small dimensions. In this way, reliable implantation of the prosthesis is guaranteed. The small dimensions of the forceps  1  also has the advantage that it gives the operating surgeon good access to and a good overall view of the implantation site.