Abstract:
A surgical instrument for the introduction of an intervertebral prosthesis ( 10 ) including at least three components, namely, two prosthesis plates ( 14, 16 ) and a prosthesis core ( 12 ). The surgical instrument can include a U-shaped holder ( 30 ) at the distal end of a gripping element ( 20 ) into which the intervertebral prosthesis ( 10 ) with all the components can be detachably introduced, whereby the individual components are aligned with respect to one another in a fixed manner, wherein the two holder elements ( 50, 52 ) of the U-shaped holder ( 30 ) are connected via a parallel guidance, which can be opened as well as closed via an elbow or bell-crank lever ( 70 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation-in-part application of U.S. patent application Ser. No. 10/900,647, filed Jul. 28, 2004, the entirety of which is herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention concerns a surgical instrument for the introduction of a multi-component intervertebral prosthesis.  
       BACKGROUND OF THE INVENTION  
       [0003]     Various instruments are known for the introduction of multi-component, especially three-component, intervertebral prosthesis, which consist of two prosthesis plates, each of which is joined to a vertebral body, and a prosthesis core arranged between them.  
         [0004]     A surgical instrument for the introduction of intervertebral prosthesis is known from EP 0 333 990 A2 which consists of expanding tongs that have a holder for a prosthesis plate on the front end on each jaw. The two prosthesis plates can be first made to come very close to the expanding tongs in order to introduce them into the space between the neighboring vertebrae. Then the expanding tongs are spread out in order to be able to introduce the prosthesis core between the prosthesis plates.  
         [0005]     DE 299 16 078 U1 discloses a surgical instrument for the introduction of intervertebral implants, which has two guide tracks that are supported pivotably at the back end, and each of which has a holding device for a prosthesis plate on their free end. A longitudinal guide for the prosthesis core is arranged between the two arms. First the two prosthesis plates are introduced into the intervertebral space in the closed position, and then the two prosthesis holders are spread apart whereby, at the same time, the prosthesis core is pushed to the distal end of the instrument until it reaches the desired end position between the prosthesis plates.  
         [0006]     DE 102 25 703 A1 discloses an instrument for the introduction of an intervertebral prosthesis which has two prosthesis holders for a pair of prosthesis plates, the holders being joined through a parallel guide and can be separated from one another, where all parts joining the two prosthesis holders are arranged outside a middle entry opening running in the longitudinal direction of the instrument, the width of which corresponds at least to the transverse measurements of the prosthesis core to be introduced between the prosthesis plates and to the prosthesis core holder provided for this. Again, first the two prosthesis plates are introduced with the aid of the instrument, in order to then spread apart the prosthesis plates and introduce the prosthesis core.  
         [0007]     In particular, the known instruments respectively comprise two grip elements in the form of scissors or pliers grips, which must be pressed together under force, in order to bring about a spreading apart of the two prosthesis holders. This type of grip is cumbersome and can impede access to the operation area. Particularly, this type of grip elements can be urged together only under application of high force, in order to spread the prosthesis holders apart, wherein force must be exerted to counter that of the adjacent vertebra. A controllable moving together of the two prosthesis holders is generally not possible.  
         [0008]     On the surfaces facing each other, the prosthesis plates have concave recesses between which the prosthesis core is set, which has similarly formed convex protrusions. The bowed surfaces of the prosthesis plates and the prosthesis core can slide on one another within certain limits and thus permit tilting and rotation of the upper prosthesis plate with respect to the lower one, as a result of which the mobility of the spinal column section in which the intervertebral prosthesis is introduced, is ensured.  
         [0009]     Therefore, in order to be able to introduce the prosthesis core between the two prosthesis plates, the prosthesis plates have to be spread apart relatively far so that the convex protrusions of the prosthesis core are able to slide in over the edge of the concave recesses in the prosthesis plates. Such a large spreading of the intervertebral space should, however, be avoided as much as possible in order to be able to exclude damage to the spinal column and to the vertebrae. Furthermore, the prosthesis core is usually introduced in such a way that the intervertebral space is not completely spread apart, in order to be able to introduce the prosthesis core without any expenditure of force, but that the prosthesis core is driven into a smaller intermediate space between the prosthesis plates, in which case the intervertebral space is spread especially widely only in the instant in which the convex protrusions of the prosthesis core slide over the edge of the concave recesses in the prosthesis plates. However, in this case, the prosthesis core is exposed to large loads since the force that spreads the intervertebral space acts on it so that the surface of the prosthesis core can become damaged.  
       SUMMARY OF THE INVENTION  
       [0010]     Therefore, the task of the invention is to provide a surgical instrument for the insertion of intervertebral prosthesis, an instrument which is easier to handle and at the same time permits as protective insertion of the intervertebral prosthesis as possible, protecting both the patient as well as the prosthesis core.  
         [0011]     The task according to the invention is solved by a surgical instrument as set forth herein.  
         [0012]     Advantageous embodiments and further developments of the invention are given forthwith.  
         [0013]     The surgical instrument for the introduction of an at least three-part intervertebral prosthesis according to the invention has a U-shaped holder at the distal end of a grip element into which the intervertebral prosthesis, consisting of two prosthesis plates and a prosthesis core, can be inserted removably with all the components, where the individual components are aligned to one another in a fixed manner.  
         [0014]     With the surgical instrument according to the invention, the intervertebral prosthesis is introduced together with all the components into the intervertebral space, which is held separated with the aid of another instrument and is kept open. The advantage is first of all that the prosthesis core is already introduced between the two prosthesis plates so that subsequent introduction of the prosthesis core between the prosthesis plates is not needed and thus increased spreading of the intervertebral space is avoided. Another advantage lies in the fact that all components of the intervertebral prosthesis are kept aligned with respect to one another so that it is ensured that, even when inserted into the intervertebral space, no tilting or twisting of the prosthesis plates against one another is possible. The U-shaped holder of the instrument according to the invention ensures that the intervertebral prosthesis is safely introduced between the vertebrae from the access side and then can be removed again, without twisting or unnecessarily moving the intervertebral prosthesis.  
         [0015]     The U-shaped holder comprises two components, wherein the two holder elements of the U-shaped holder are connected via a parallel guidance and are spreadable as well as closeable. A design of this type of the U-shaped holder makes it possible, with one and the same instrument, to insert and hold in place intervertebral prosthesis of varying heights. Therewith it is not necessary to utilize various surgical instruments adapted for the varying heights of intervertebral prosthesis as needed to fit the varying vertebral morphology of various patients.  
         [0016]     Further, the parallel guidance, which is actuated via an elbow or bell-crank lever, enables a controlled opening and closing of the parallel guidance, so that, in particular upon closing, both prosthesis plates are clamped under pressure between the two prosthesis holders and are securely held there.  
         [0017]     Preferably the elbow lever is associated with a threaded rod extending through the grip, which is operatable via a rotatable knob located at the proximal end of the grip element. Thereby a particularly space-saving arrangement of the actuating element for spreading and closing of the parallel guidance is made possible, since no grips in the manner of a scissors or pliers are required, rather actuation occurs via the rotatable knob and the threaded rod. This is possible in particular since with the present instrument it is not necessary to spread apart the two adjacent vertebrae with the instrument in inserted position, in order to be able to insert the intervertebral prosthesis, which spreading forces do need to be exerted in the case of the pliers type grip elements. In the present case it is merely necessary that the intervertebral prosthesis is securely clamped between the two holder elements, in order then to be inserted in the space between the two vertebra. For this it is however necessary, to be able to exercise a controlled force during closing, which is ensured by the threaded rod, which can exercise pressure on the elbow lever and therewith on the parallel guidance, depending upon the direction of rotation.  
         [0018]     Preferably the U-shaped holder has clamping elements for the intervertebral prosthesis. In this case, the intervertebral prosthesis can be introduced into the intervertebral space with the surgical instrument, whereupon the spreading of the intervertebral space is eliminated. The teeth arranged outside the prosthesis plates engage into the neighboring vertebrae. This engagement is sufficient to overcome the clamping of the intervertebral prosthesis in the U-shaped holder when the surgical instrument is removed so that no additional mechanism is needed for separating the prosthesis.  
         [0019]     In an advantageous further development of the invention, the clamping elements are designed as two leaf springs running on the inside along the leg of the U-shaped holder. The leaf springs are especially simple to manufacture and also can be molded in one piece against the U-shaped holder.  
         [0020]     Preferably the clamping elements hold the prosthesis core. Especially in combination with an aligning device for the prosthesis plates, this is sufficient to safely fix the intervertebral prosthesis.  
         [0021]     In an advantageous further development of the invention, the inner contour of the U-shaped holder is designed corresponding to the outside contour of the prosthesis core. In this way, it is ensured that the prosthesis core is held especially securely.  
         [0022]     Preferably, the inner contour of the U-shaped holder is designed as a circular arc of about 200°. The inner contour of the U-shaped holder thus surrounds slightly more than half of the circular prosthesis core, and has an opening between the legs of the U-shaped holder, which is smaller than the diameter of the prosthesis core. In this way, clamping of the prosthesis core is achieved reliably.  
         [0023]     In an advantageous further development of the invention, two guide tracks are formed in the plane of each of the U-shaped holders on the inside of the leg of the U-shaped holder for holding the prosthesis plates. The prosthesis plates can thus be inserted in the guide tracks as an individual element without resistance. Holding the intervertebral prosthesis is achieved by the fact that the convex protrusions of the prosthesis core engage in the concave recesses of the prosthesis plates and thus the prosthesis plates are also securely held in the U-shaped holder, although the prosthesis plates are not clamped. Furthermore, the guide tracks for holding the prosthesis plates provide alignment of the prosthesis plates with respect to the prosthesis core and to one another. For this purpose, preferably the guide tracks for holding the prosthesis plates are arranged parallel to one another. Preferably for this purpose, furthermore, the guide tracks are arranged on both sides of the leaf springs running along the legs of the U-shaped holder.  
         [0024]     Preferably, connected to the U-shaped holder a stop is present which can be moved along the axis of the grip elements. This stop serves to define when the intervertebral prosthesis has reached the desired end position as is introduced into the intervertebral space. As a rule, the intervertebral space, which is formed during surgery after removal of the defective disk, is probed with a control prosthesis in order to determine the preferred size of the intervertebral prosthesis and accurate positioning of it. In order to see, correspondingly, on the surgical instrument according to the invention for introduction of the intervertebral prosthesis, how far the instrument with the intervertebral prosthesis must be introduced into the intervertebral space in order to position the intervertebral prosthesis optimally, the value determined with the control prosthesis can be adjusted at the moveable stop. As soon as the stop encounters the outside contour of the neighboring vertebra, the optimum position for the intervertebral prosthesis is reached.  
         [0025]     For this purpose, the stop is arranged preferably perpendicularly to the plane of the U-shaped holder in order to provide a defined stop point.  
         [0026]     Preferably, the stop meets the grip element perpendicularly and projects on both sides of the grip element. In this way, it ensures that the operator can see the stop independently of whether the surgical instrument is rotated by 180° around the longitudinal axis or not.  
         [0027]     Preferably, a thread engages in the stop, this thread runs along the axis of the grip element and can be adjusted with the aid of a screw element. This makes it possible to move the stop simply along the longitudinal axis of the grip element and also ensures that when the stop reaches the vertebral body, the stop cannot be displaced along an axis parallel to the longitudinal axis of the grip element by a pressure on the stop.  
         [0028]     Preferably the two elements of the U-shaped holder each have on the inside of the legs facing away from one another a guide track for holding the prosthesis plate. Since as a rule the height of the intervertebral prosthesis varies according to the height of the prosthesis core, it is ensured that the intermediate space between the clamped prosthesis plates in the U-shaped holder can be varied. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     The invention will be explained in detail with the aid of the following figures. The following are shown:  
         [0030]      FIG. 1   a  is a side view of a three-part intervertebral prosthesis,  
         [0031]      FIG. 1   b  is an axial section through the intervertebral prosthesis according to  FIG. 1   a,    
         [0032]      FIG. 1   c  is a top view onto the intervertebral prosthesis according to  FIG. 1   a,    
         [0033]      FIG. 1   d  is an axial section through a second practical example of an intervertebral prosthesis,  
         [0034]      FIG. 2   a  is a top view on a first practical example of a surgical instrument for introducing an intervertebral prosthesis,  
         [0035]      FIG. 2   b  is a view axially from the top onto the practical example according to  FIG. 2   a,    
         [0036]      FIG. 3   a  is a top view onto a second practical example of a surgical instrument for introducing an intervertebral prosthesis,  
         [0037]      FIG. 3   b  is a top view onto the practical example according to  FIG. 3   a  with the stop set back,  
         [0038]      FIG. 3   c  is a view axially from the top onto the practical example according to  FIG. 3   a,    
         [0039]      FIG. 3   d  is a side view of the practical example according to  FIG. 3   a,    
         [0040]      FIG. 3   e  is an axial section through the practical example according to  FIG. 3   a  in the spread-apart state,  
         [0041]      FIG. 3   f  is an axial section through the practical example according to  FIG. 3   a  in the closed state. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]      FIGS. 1   a ,  1   b  and  1   c  show an intervertebral prosthesis  10  consisting of a prosthesis core  12  and two prosthesis plates  14 ,  16 , which enclose the prosthesis core  12 . The prosthesis core  12  consists of a circular disk which has on both sides an axially arranged spherical segment  12   a  and a ring land  12   b  protruding axially and running at the outer edge.  
         [0043]     The two prosthesis plates  14  and  16  are designed identically and consist of an ellipsoidal disk, the main vertices of which are flattened and where a circular torus  14   a ,  16   a  is arranged on one side of the disk, and this torus has a recess  14   b ,  16   b  having the shape of a spherical shell. In the composed state of the intervertebral prosthesis  10 , the spherical segments  12   a  of the prosthesis core  12  lie in the recesses having the shape of a spherical shell  14   b ,  16   b  of the prosthesis plates  14 ,  16 . On the side of the prosthesis plates  14 ,  16  away from the prosthesis core  12  there are several teeth  18  arranged, in this case six, which anchor the prosthesis plates  14 ,  16  in the neighboring vertebra. In the present practical example, the sides of the prosthesis plates  14 ,  16  away from the prosthesis core  10  are designed to be flat. In order to be able to adapt the prosthesis plates  14 ,  16  to the slopes of the neighboring vertebrae, the side of the prosthesis plates  14 ,  16  facing away from the prosthesis core  10  can be inclined to the plane of prosthesis plate  14 ,  16 .  
         [0044]      FIG. 1   d  shows an axial section through another embodiment of the intervertebral prosthesis  10 , consisting of the two prosthesis plates  14 ,  16  and a three-part prosthesis core  13 . Here the prosthesis core  13  is designed so that a recess  13   b  having the shape of a spherical shell is formed in a disk-shaped middle element  13   a  on both sides and a sliding element  13   c  is set in each one of these, consisting of two spherical segments of the same diameter. The spherical segment of the sliding element  13   c  facing the middle element  13   a  is thus arranged so that it can slide in the recesses  13   b , having the shape of a spherical shell, of the middle element  13   a , while the spherical segment of the sliding element  13   c  facing away from middle element  13   a  lies in the spherical-shell-shaped recesses  14   b ,  16   b  of prosthesis plate  14 ,  16  and is arranged in these so that it can slide. A prosthesis core  13  made of several parts make additional degrees of freedom of the movement of the two prosthesis plates  14 ,  16  with respect to one another possible, as a result of which the mobility of the spinal column section into which the intervertebral prosthesis  10  was implanted is further enhanced.  
         [0045]      FIGS. 2   a  and  2   b  show two views of a first practical example of a surgical instrument for introducing a multi-component intervertebral prosthesis  10 , consisting of a grip element  20  which has a U-shaped holder  30  on its distal end. The axis of the grip element  20  lies in the plane fixed by the U-shaped holder  30 . The U-shaped holder  30  has two legs  30   a ,  30   b  and a leaf spring  32  is arranged on the inside of each of these parallel to legs  30   a ,  30   b . The inner contour  36  of the U-shaped holder  30 , formed essentially by the two leaf springs  32 , is designed as a circular arc of about 200°. In this way, the opening between the distal ends of the leaf springs  32  is slightly smaller than the maximum diameter of the circular arc. Thus, when the disk-shaped prosthesis core  12  with its circular outer contour is introduced between the two leaf springs  32 , the leaf springs  32  first slightly relax and lie against the outer contour of prosthesis core  12 . In this way, secure clamping of the prosthesis core  12  between the leaf springs  32  is ensured.  
         [0046]     On the inside of legs  30   a ,  30   b  of the U-shaped holder  30 , on both sides, along the leaf springs  32 , guide tracks  34  are made to hold prosthesis plates  14 ,  16 . Here, the distances between the two legs  30   a ,  30   b  corresponds to the length of the main axis of the essentially ellipsoidal disk of the prosthesis plates  14 ,  16 . The guide tracks  34  run on each leg  30   a ,  30   b  parallel to one another, in order to provide a parallel alignment of the prosthesis plates  14 ,  16 . The distance between the guide tracks  34  on each of legs  30   a ,  30   b  corresponds to the distance of the prosthesis plates  14 ,  16  in the assembled state of the intervertebral prosthesis  10 . When the intervertebral prosthesis  10  is placed into the U-shaped holder  30 , only the prosthesis core  12  is held by clamping. In principle, the prosthesis plates  14 ,  16  can move in the guide tracks without any resistance. However, due to the insertion of the spherical segments  12   a  of the prosthesis core  12  into the spherical-shell-shaped recesses  14   b ,  16   b  and the exact parallel alignment of the prosthesis plates  14 ,  16  to one another, they are also held safely in the U-shaped holder  30 .  
         [0047]     Following the U-shaped holder  30 , in grip element  20 , a stop  40  is arranged which can be moved along the axis of grip element  20 . The stop  40  goes through the grip element in a radial opening  22  and protrudes out of the grip element  20  on both sides. The stop is perpendicular to the axis of the grip element and perpendicular to the plane of the U-shaped holder  30 . A thread  24  goes through stop  40  along the axis of grip element  20  and this thread can be rotated with the aid of a screwing element  26 . Since stop  40  cannot be rotated in the radial opening  22 , stop  40  moves along the axis of grip element  20  when the screwing element  26  and thus thread  24  are turned. When stop  40  is moved as far as possible in the direction of the distal end of the surgical instrument, the intervertebral prosthesis  10  is not introduced as far into the intervertebral space as when the stop  40  is removed as far as possible away from the distal end of the surgical instrument, and thus, when introducing the instrument into the intervertebral space, it will meet the neighboring vertebra later.  
         [0048]      FIG. 2   b  shows an axial top view onto the first practical example in which especially the parallel guide tracks  34  intended for holding the prosthesis plates  14 ,  16  can be seen clearly. Furthermore,  FIG. 2   b  shows the intermediate space between the leaf springs  32  and the guide tracks  34  into which the prosthesis core  12  can be inserted and in which it is fixed by the leaf springs  32  removably.  
         [0049]      FIGS. 3   a  to  3   f  show a second practical example of a surgical instrument for the introduction of the intervertebral prosthesis  10 . The second practical example of the surgical instrument according to the invention has a U-shaped holder consisting of two holding elements  50 ,  52 . Each element  50 ,  52  is essentially identical to the U-shaped holder  30 , but only one guide track  34  is arranged in each of holding elements  50 ,  52 . The two holding elements  50 ,  52  are arranged at the distal end of grip element  20  in such a way that the sides of the holding elements  50 ,  52 , which have the guide tracks  34 , lie on the sides away from one another, while the sides of the holding elements  50 ,  52  which have no guide tracks are facing one another. When the two holding elements  50 ,  52  lie directly on one another, as shown in  FIG. 3   d , essentially the U-shaped holder  30  is obtained, which was symmetrically separated by the plane placed through the U.  
         [0050]     The two holding elements  50 ,  52  are connected through a parallel guide  60  and can be spread apart.  FIGS. 3   e  and  3   f  each show an axial section through the second practical example of the instrument according to the invention with two different positions of the parallel guide  60 .  
         [0051]     In the known manner, the parallel guide  60  is designed as a pair of scissors with two scissor members  60   a ,  60   b , which are connected to one another so that they can be rotated against one another around their axis of symmetry through an axis  65 . The holding elements  50 ,  52  are arranged on the free end  61  of scissor members  60   a ,  60   b , these free ends lying on the side of axis  65  facing the distal end of the instrument. The free ends  62  of scissor members  60   a ,  60   b  lying on the other side of the axis are engaged with a device, a elbow lever  70 , designed in the known manner, which can move these free ends  62  towards and away from each other. The elbow lever  70  includes two lever arms  71 ,  72  with respective first ends  71   a ,  72   a  and second ends  71   b ,  72   b , which are mounted rotatably relative to each other on a rotation mount  75 , and of which the second end rotatbly engages a free end  62  of the scissors elements  60   a ,  60   b.    
         [0052]     This elbow lever can be operated via a knob  66  arranged at the proximal end of the instrument. For this, the elbow lever  70  is connected at it&#39;s rotation axis with a threaded rod  76 . This connection could be in the form of, for example, that the rotation axis  75  is a not-shown bolt, which can be rotated in a not-shown transverse bore hole extending through the threaded rod  76 . The threaded rod  76  extends in the longitudinal direction through the grip element  20  and protrudes from the grip element  20  at the proximal end of the grip element  20 . The rotatable knob  66  is located at the proximal end of the threaded rod  76 , via which the threaded rod  76  can be rotated about it&#39;s longitudinal axis. The threaded rod  76  has an external threading  76   a , which engages in an internal threading  20   a  of the grip element. Upon rotation of the rotatable knob  66  the threaded rod  76  rotates within the internal threading  20   a  and is screwed further into or out of the grip element  20  depending upon direction of rotation. Since there is a connection between the distal end of the threaded rod  76  and the elbow lever  70 , upon movement of the threaded rod  76  the elbow lever  70  is actuated. In  FIG. 3   e  the threaded rod  76  is screwed comparatively far into the grip element  20 , so that the rotation axis  75  is displaced in the direction towards the distal end of the instrument, whereupon the elbow lever  70  is spread apart and presses apart the two scissors elements  60   a ,  60   b . In  FIG. 3   f  a further position of the elbow lever  70  is shown. The threaded rod was rotated out of the grip element  20  with the help of the rotatable knob  66 , whereupon the rotation axis  75  of the elbow lever had become displaced in the direction of the proximal end of the instrument and the elbow lever  70  has been urged together, wherein via the rotatable connection between the lever arms  71 ,  72  to the scissors elements  60   a ,  60   b  the parallel guidance also is again closed.  
         [0053]     The arrangement of the rotatable knob  66  at the proximal end of the instrument is advantageous because in this way it is outside the surgery area and thus can be operated easily even when the distal end of the instrument is introduced into the surgery area. In particular, the threaded rod  76  in combination with the elbow lever  70  permits the exercising of a force upon the holder elements  50 ,  52  during opening as well as during closing of the parallel guidance.  
         [0054]     In addition, the free end  61  of the scissor member  60   a ,  60   b  is connected to the free end  62  of the other scissor member  60   b ,  60   a  through a connecting element  63   a ,  63   b ; the holding elements  50 ,  52  are arranged in the extension of these to the distal end of the instrument, beyond the free ends  61  of scissor member  60   a ,  60   b . When the free ends  62  are moved away from one another, in particular by screwing in of the threaded rod  76  into the grip element and spreading apart of the elbow lever  70 , the holding elements  50 ,  52 , which are rotatably supported at the opposite free ends  61  of the scissor members  60   a ,  60   b , are moved away parallel from one another. With such design of the U-shaped holder  30 , it becomes possible to introduce intervertebral prosthesis  10  of different thicknesses into the intervertebral space with the same instrument.  
         [0055]     Thus, having a number of surgical instruments for intervertebral prosthesis  10  with different heights becomes unnecessary.  
         [0056]     In this embodiment of the instrument, no clamping elements are needed which run parallel to the legs of the U-shaped holder and clamp the prosthesis core along its outside contour. The intervertebral prosthesis is held sufficiently by the fact that the two prosthesis plates  14 ,  16  are inserted in the guide tracks  34 , each in a holding element  50 ,  52 , placing the prosthesis core  12  between them and by bringing the holding elements  50 ,  52  together, thus providing a clamping action.  
         [0057]      FIGS. 3   a  and  3   b  show the second practical example in a top view with two different positions of stop  40 . The second practical example differs from the first practical example also in the design of stop  40 , since the mechanism for displacing the stop  40  is arranged not inside the grip element  20 , but outside the grip element  20 , since the mechanism of the parallel guide  60  is arranged within the grip element  20 .  
         [0058]     The stop  40  of the second practical example has a contact contour  42  which corresponds to the ellipsoidal arc around a conjugate vertex of the essentially ellipsoidal prosthesis plates  14 ,  16 . If the stop  40  is moved as far as possible in the direction of the distal end of the surgical instrument, as shown in  FIG. 3   a , the contact contour  42  lies on the outside contour of prosthesis plates  14 ,  16 . If the surgical instrument with the stop  40  adjusted in this way is introduced into the intervertebral space, the contact contour  42  contacts the intervertebra[sic] as soon as the outside contour of the prosthesis plates  14 ,  16  coincides with the outside surface of the vertebra.  
         [0059]     In addition, stop  40  has a marking which can be brought into coincidence with a marking arranged in a fixed manner on grip element  20 . The marking gives the distance from the contact contour  42  to the conjugate vertex of prosthesis plates  14 ,  16 , which forms the distal end of the surgical instrument. Here the distance is 30 mm.  
         [0060]      FIG. 3   b  shows the stop  40  which is moved back as far as possible from the distal end of the surgical instrument, where the marking shows a clearly larger value, namely 45 mm.  
         [0061]      FIG. 3   c  is a view axially from the top onto the second practical example, in which especially the parallel guide tracks  34  for holding the prosthesis plates  14 ,  16  can be seen clearly. The prosthesis core  12  is positioned in the intermediate space between the guide tracks  34  and held in a fixed manner by bringing together the two holding elements  50 ,  52 .  
         [0062]     In a surgical procedure, the surgical instrument according to the invention is used as follows: after the access to the spinal column is made and the intervertebral space is freed from the diseased disk and is cleaned out, first the size of the intervertebral space is probed with a control prosthesis. Here, the size of the intervertebral prosthesis to be used, that is, the length of the main axis of the essential ellipsoidal prosthesis plates  14 ,  16  and the thickness of the intervertebral prosthesis  10 , that is, especially the thickness of the prosthesis core  12 , are determined. Furthermore, the slope of the vertebral surfaces to one another is determined. This will show if prosthesis plates with a plane or an inclined back surface will be used.  
         [0063]     Using the control prosthesis, it is also determined how far the intervertebral prosthesis  10  has to be introduced into the intervertebral space. The distance between the outside contour of the vertebra and the desired position of the outside contour of the intervertebral prosthesis  10  is adjusted correspondingly at stop  40 .  
         [0064]     Then the intervertebral prosthesis  10  is composed from the selected components, namely the desired prosthesis core  12  and the optimized prosthesis plates  14 ,  16  and is clamped into the third practical example of the surgical instrument according to the invention according to  FIGS. 3   a  and  3   b . The prosthesis core  12  is then held by the leaf springs  32 , while the prosthesis plates  14 ,  16  are placed in the guide tracks  34  and are held by the cooperation of the spherical segments  12   a  of the prosthesis core  12  and the spherical shell-shaped recesses  14   b ,  16   b  of prosthesis plates  14 ,  16 . In order to be able to insert the intervertebral prosthesis  10 , the intervertebral space must be made wider with another spreading instrument in such a way that the intervertebral prosthesis  10  including the protruding teeth  18  can be introduced into the intervertebral space. Here the spreading instrument is designed so that the surgical instrument for inserting intervertebral prosthesis according to the invention can be introduced into the intervertebral space without any problems, the valves [sic, “Valven”]of the spreading instrument not causing any disturbance.  
         [0065]     The surgical instrument with the inserted intervertebral prosthesis  10  is now introduced into the intervertebral space until stop  40  contacts the vertebra. The spreading elements are now lowered until the vertebra comes into contact with teeth  18 . Then the surgical instrument can be removed without any danger without changing the position of the intervertebral prosthesis  10  since this is held at the vertebrae through teeth  18 .  
         [0066]     The advantage of this surgical method lies in the fact that a smaller spreading of the intervertebral space is needed since the introduction of the prosthesis core  12  between the prosthesis plates  14 ,  16 , where the spherical segments  12   a  have to be pressed over the toruses  14   a ,  16   a  in the spherical-shell-shaped recesses  14   b ,  16   b , is omitted. Furthermore, exact positioning of the prosthesis plates  14 ,  16  and of the prosthesis core  12  to one another is provided automatically. Especially, damage to the surface of the prosthesis core  12  is avoided, since the prosthesis core  12  is introduced simultaneously with prosthesis plates  14 ,  16  into the intervertebral space and not subsequently into the intermediate space between the two prosthesis plates  14 ,  16 .  
       REFERENCE LIST  
       [0000]    
       
           10  Intervertebral prosthesis  
           12  Prosthesis core  
           12   a  Spherical segment  
           12   b  Ring land  
           13  Prosthesis core  
           13   a  Middle element  
           13   b  Spherical-shell-shaped recess  
           13   c  Sliding element  
           14  Prosthesis plate  
           14   a  Torus  
           14   b  Spherical-shell-shaped recess  
           16  Prosthesis plate  
           16   a  Torus  
           16   b  Spherical-shell-shaped recess  
           18  Teeth  
           20  Grip element  
           20   a  Internal threading  
           22  Radial opening  
           24  Thread  
           26  Screwing element  
           30  U-shaped holder  
           30   a  Leg  
           30   b  Leg  
           32  Leaf spring  
           34  Guide tracks  
           36  Inside contour  
           40  Stop  
           42  Contact contour  
           50  Holding element  
           52  Holding element  
           60  Parallel guide  
           60   a  Scissor member  
           60   b  Scissor member  
           61  Free end  
           62  Free end  
           63   a  Connecting element  
           63   b  Connecting element  
           65  Axis  
           66  Rotatable Knob  
           70  Elbow lever  
           71  Lever arm  
           71   a  First end  
           71   b  Second end  
           72  Lever arm  
           72   a  First end  
           72   b  Second end  
           75  Rotation axis  
           76  Threaded rod  
           76   a  External threading