Abstract:
An instrument for inserting an intervertebral prosthesis, comprising two prosthesis holders which are connected by a parellel guide and can be spread apart from one another and are intended to receive a pair of prosthesis plates. The first prosthesis holder is arranged fixedly on an elongate instrument body. The second prosthesis holder is held from the instrument body by means of a parallel guide. The parts connecting the second prosthesis holder to the instrument body or to the first prosthesis holder delimit on both sides a central through-opening which extends like a channel in the longitudinal direction of the instrument body and whose width corresponds at least to the transverse dimensions of a prosthesis core, to be inserted between the prosthesis plates, and of the prosthesis core holder provided for this.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     To insert intervertebral prostheses consisting of two prosthesis plates, each to be connected to a respective vertebral body, and of a prosthesis core arranged between these plates, insertion instruments are known (EP-A-333 990) which, at their front end, have two prosthesis holders which each receive a prosthesis plate. The prosthesis holders are connected to one another via a parallel guide which makes it possible initially to bring the prosthesis plates very close to one another, so as to be able more easily to introduce them into the narrow intervertebral space, and then to spread them apart (with the adjoining vertebrae) in order to be able to insert the prosthesis core between them. Thereafter, the prosthesis holders are moved back toward one another so that the prosthesis plates receive the prosthesis core in its operational position, and the instrument is removed. The known instrument is designed as a forceps which is angled in relation to the direction of the prosthesis holders, which direction is intended to coincide with the median direction of the body, so as not to impede the introduction of the prosthesis core. Nevertheless, the introduction of the prosthesis core is difficult.  
         [0002]     An instrument for introducing a prosthesis of this kind is also known (DE-U-299 16 078) which is formed by a lower pair of guide rods and an upper guide rod, these rods being articulated on one another at the rear end and carrying prosthesis holders at their front ends. They form a guide track for a spreader element. When the latter is driven forward between them by means of a toothed rack, it spreads the rod ends apart and at the same time pushes the prosthesis core ahead of it until the latter has reached the desired end position. Thereafter, the spreader element is drawn back in order to bring the prosthesis plates toward the prosthesis core. In this case, the spreading movement is inextricably linked with the introduction of the prosthesis core, so that the spreading operation is not separate from the introduction of the prosthesis core and can be observed only with difficulty.  
       SUMMARY OF THE INVENTION  
       [0003]     The object of the invention is to make available an instrument which permits spreading of the prosthesis plates independently of the introduction of the prosthesis core, but which still facilitates said introduction of the prosthesis core.  
         [0004]     The solution according to the invention lies in the features of claim  1 .  
         [0005]     It relates to an instrument for inserting an intervertebral prosthesis, comprising two prosthesis holders which are connected by a parellel guide and can be spread apart from one another and are intended to receive a pair of prosthesis plates. The first of these prosthesis holders is arranged fixedly on an elongate instrument body so as to lie in the longitudinal direction of the latter. The second prosthesis holder is held on the instrument body by means of the parallel guide. All the parts connecting the instrument body and the second prosthesis holder are arranged outside a central through-opening which extends in the longitudinal direction of the instrument body and whose width corresponds at least to the transverse dimensions of the prosthesis core, to be inserted between the prosthesis plates, and of a prosthesis core holder provided for this. In this way, the prosthesis core can be easily introduced with the aid of a prosthesis core holder through the insertion instrument, whose elements on both sides form a guide for the prosthesis core or prosthesis core holder. To ensure that the operating surgeon, when introducing the prosthesis core, can easily detect the position of the prosthesis core holder at which the prosthesis core has reached the desired position between the prosthesis plates, the insertion instrument and the prosthesis core holder are expediently provided with interacting limit stops which determine this end position.  
         [0006]     For actuation, an oblique link arm can be provided whose first end is mounted on the instrument body so as to be movable in the longitudinal direction thereof. Its second end is mounted on the second prosthesis holder with a fixed axis. Its first end is connected to an actuating device which is movable in the longitudinal direction of the instrument body. When the actuating device is moved in the direction in which the first end of the oblique link arm is moved in the direction toward the hinge point of its second end, the oblique link arm straightens and thus spreads the second prosthesis holder away from the instrument body and the first prosthesis holder, and vice versa.  
         [0007]     The oblique link arm can be part of a scissor-type parallel guide. The oblique link arm is expediently provided in a pair symmetrically on both sides of the instrument body, in order to avoid a force transmission which is asymmetrical and tends to cause tilting.  
         [0008]     The actuating device expediently comprises a handle and a transmission device. The transmission device can, for example, be formed by a threaded spindle. It has proven expedient to design the actuating device as a grip lever which is connected to a shorter working lever forming the transmission device. It is expediently arranged in such a way that it at the same time converts the lateral movement of the grip lever into the actuating direction extending in the longitudinal direction of the instrument body.  
         [0009]     The oblique link arm can be mounted with its first end on a slide which is guided on the instrument body in the longitudinal direction thereof. Instead of this, it is also possible for the oblique link arm to be a member of a toggle lever pairing, in which case the actuating device acts directly or indirectly on the toggle point of the lever pairing.  
         [0010]     In another embodiment of the invention, an actuating device is provided which comprises an actuating lever which is mounted at its front end on the instrument body or the first prosthesis holder so as to pivot. The pivot axis extends transversely with respect to the longitudinal direction of the instrument body and to the direction of spreading. Behind this axis, the lever has a limit stop which acts directly or indirectly on the second prosthesis holder. At the rear end, the lever is designed such that it can be operated by hand. In the unspread state of the instrument, the lever is at a certain angular distance from the instrument body. If it is pulled by hand, or by suitable aids such as a threaded spindle, toward the instrument body, the limit stop moves the second prosthesis holder away from the first prosthesis holder and in this way spreads them apart. By virtue of the lever action, great spreading forces can be transmitted. In a preferred embodiment of the invention, the limit stop acts on an oblique link arm connected to the second prosthesis holder, which oblique link arm can also be part of the parallel guide. The lever is expediently not an integral part of the instrument body, and instead it is designed in such a way that it can be easily attached to the instrument body and released again from the latter during the operation. This has the advantage that the instrument body is not weighed down by the spreader mechanism, formed by the lever, in those stages of the operation when spreading does not take place or does not have to be maintained. This actuating device may merit protection independently of the features of the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention is explained in greater detail below with reference to the drawing which depicts an advantageous illustrative embodiment. In said drawing:  
         [0012]      FIG. 1  shows an overview of the instrument,  
         [0013]      FIG. 2  shows a perspective view of the front portion of the instrument, obliquely from above,  
         [0014]      FIG. 3  shows a side view of the front portion,  
         [0015]      FIG. 4  shows a bottom view of the front portion,  
         [0016]      FIG. 5  shows a bottom view of the rear part of the instrument,  
         [0017]      FIG. 6  shows a detail of the actuating device,  
         [0018]      FIG. 7  shows a second design of the spreader device,  
         [0019]      FIG. 8  shows a third design of the spreader device,  
         [0020]      FIG. 9  shows a variant of the third design of the spreader device, and  
         [0021]      FIG. 10  shows a detail of the actuating lever used for this. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     At the front end of the instrument body  51  there are two holders  52  for prosthesis plates  53 . The prosthesis holders  52  are fork-shaped and open at the end. Their side branches form guides for the edge of the prosthesis plates  53 . Their direction coincides with the longitudinal direction of the instrument body. They allow the prosthesis plates to overcome a frictional force and be inserted easily into the prosthesis holders  52 , and removed therefrom, in the longitudinal direction of the instrument. At the rear end, the prosthesis body  51  has a strike plate  54 . By striking this plate, the prosthesis plates  53  held by the prosthesis holders  52  can be driven in between two vertebral bodies.  
         [0023]     The lower prosthesis holder  52 A ( FIGS. 9 and 10 ) is fixedly connected to the instrument body  51 , and in the example illustrated is even made integral therewith. The upper prosthesis holder  52 B is connected to the instrument body  51  via a scissor arrangement consisting of scissor members  56 ,  57 . The scissor arrangement  56 ,  57  is provided as a pair on both sides of the instrument body and is designed in such a way that the upper prosthesis holder  52 B can move exclusively perpendicular to the lower prosthesis holder  52 A and parallel to it. The prosthesis holders can be brought very close to one another ( FIG. 1 ) so that it is easier to drive them into the intervertebral space. They can be spread apart ( FIGS. 2 and 3 ) together with the adjoining vertebral bodies in order to create space for introducing the prosthesis core  77  between the prosthesis plates  53 . They are then brought back toward each other in order to secure the prosthesis core in the desired position. The instrument can then be removed.  
         [0024]     The rear pins  58 ,  59  of the scissor members  56 ,  57  slide in oblong holes of the instrument body  51  or of the plate  73  which continues the upper prosthesis holder  52 B to the rear. The direction of the oblong holes coincides with the longitudinal direction of the instrument. The front pins  60  of the scissor members  56 ,  57  are rigidly connected to the prosthesis holders  52 . In order to spread the prosthesis holders, a device is provided which moves the rear pin  58  of the scissor member  57  in the longitudinal direction of the instrument. For this purpose, the grip lever  61  is provided which is pivotable on the instrument body about an axis  62  and has a working lever  63  acting on the rear end of a slide block  64 , which is part of a T-shaped slide  65  ( FIGS. 4 and 6 ) on whose crosshead the rear pins  58  of the scissor members  57  arranged on both sides are articulated. The slide  65  is guided in the longitudinal direction of the instrument body. It will be seen in  FIG. 4  that the parallel edges of the slide block  64  are guided between correspondingly parallel edges  66  of a cutout in the instrument body. It will be seen in  FIG. 3  that the ends  67  of the crosshead are guided in oblong holes  68 . When the grip lever  61  is pulled toward the instrument body, as when pressing together the levers of a forceps, its working lever  63  pushes the slide  64  in the arrow direction  70  ( FIG. 6 ). In this way, the rear end of the scissor member  57  is driven forward, as a result of which the prosthesis holders  52  are spread apart from one another. The working lever  63 , the slide  65  and the oblique link arms  57  thus form an arrangement for adjusting the distance between the prosthesis holders  52 . It will be appreciated that this arrangement can also be replaced by other designs. It will also be noted that the spreading force does not necessarily have to be exerted via parts of the scissor arrangement.  
         [0025]     If the angle between the oblique link arm  57  and the longitudinal direction of the instrument is too small for exerting a substantial spreading force, a separate member can be provided for the spreading. This alternative is illustrated in  FIG. 7 . The plate  73 , which at its front end supports the upper prosthesis holder  52 , is supported, as in the above-described illustrative embodiment, by means of a scissor arrangement  56 ,  57  on the instrument body  51 . In a departure from this design, the spreading device is made independent of the scissor arrangement. The link arms  100 ,  101  form a toggle lever arrangement. One end of these link arms is connected to the instrument body  51  or the plate  73 . Their other end forms the toggle  103 , on which the end of a link arm  102  engages whose other end  104  is connected to the actuating device. The connection can be configured as shown in  FIG. 6 . The spreading arrangement independent of the scissor arrangement  56 ,  57  has the advantage that the angles at which the link arms  100 ,  101  and  102  are stressed can be dimensioned solely for favorable force transmission and without taking into account a parallel guide function.  
         [0026]     Considerable forces arise when the prosthesis holders are spread apart. For this reason, the grip lever  61  is supplemented by a threaded spindle  71  with butterfly nut  72 , which makes the procedure easier and allows the instrument to be fixed temporarily in the spread position.  
         [0027]     In this position, a channel-like free space is formed between the instrument body  51  and the plate  53  continuing the upper prosthesis holder  52  rearward, on the one hand, and between the lateral scissor arrangements  56 ,  57  on the other hand. Using an instrument  76  guided between the link arms  56 ,  57 , the prosthesis core  77  can be guided through this free space between the prosthesis plates  52  ( FIG. 3 ). The instrument  76  has a limit stop  75  which bears on the rear edge  74  of the plate  73  when the prosthesis core  77  has exactly reached the intended position between the prosthesis plates  52 .  
         [0028]     A device is now described which is used to eject the prosthesis plates  53  from the prosthesis holders  52  and to force the instrument away from the prosthesis holders and the adjoining vertebrae. Behind the receiving area for the prosthesis plates  53 , the prosthesis guides  52  contain a guide groove  80  which extends in the longitudinal direction of the instrument and thus in the direction of sliding of the prosthesis holders  52 . It includes a slide  81  whose front end  82  strikes against the edge of the prosthesis plate located in the prosthesis holder and is therefore referred to as a prosthesis limit stop. The rear end (not visible in  FIGS. 2 and 3 ) of the slide  81  is rigidly connected to rods  83  likewise guided in the longitudinal direction of the instrument. The rear end of the rod  83  mounted in the instrument body  51  is, as shown in  FIG. 4 , secured on a limit stop element  84  whose nature will be explained later. It is also displaceable in the longitudinal direction of the instrument. The limit stop element  84  is in turn rigidly connected to a push rod  86  which is mounted so as to be longitudinally displaceable in the instrument body  51  and leads to a handle  87 . When the operating surgeon pushes the handle  87  forward in the direction of the arrow, the push rod  86 , the limit stop element  84 , the rod  83  and the slide  81  are moved forward in order to push the prosthesis plate  53  out of the prosthesis holder  52 . In doing so, the operating surgeon&#39;s hand can be supported on a projection  88  which is fixedly connected to the instrument body  51 .  
         [0029]     The movement of the handle  87  acts directly only on the slide  81  which is arranged in the lower part of the instrument, namely in the instrument body. To ensure that the slides  81  of both prosthesis holders move in synchrony, a movement-transmitting device is provided. The rod  83  controlling the slide  81  of the upper prosthesis holder is fixedly connected at its rear end to a limit stop element  85  which, like the limit stop element  84  of the lower prosthesis holder, is guided movably in the longitudinal direction of the instrument. The lower limit stop element  84  has, on both sides, upwardly extending limit stop branches  90  which lie behind and adjacent to the branches  91  which extend downward on both sides from the upper limit stop element  85 . When the prosthesis plates  53  are located in their rearmost position in the prosthesis holders  52 , and the prosthesis limit stops  82  touch them, the mutually adjacent end faces of the limit stop branches  90 ,  91  also bear on one another. If, by means of actuation of the handle  87 , the lower limit stop element  84  is now pushed forward with the limit stop branches  90 , the cooperation of these with the limit stop branches  91  of the upper limit stop element means that the slide  81  of the upper prosthesis holder is also pushed forward. The two slides  81  thus move in synchrony. Since the interacting limit stop surfaces  90 ,  91  are perpendicular to the longitudinal direction of the instrument, the synchronous movement of the slides  81  is ensured independently of the respective distance of the prosthesis holders from one another.  
         [0030]     Each slide  81  carries a shoulder  95 , rigidly connected to it, and also a small block  96  which is guided on the slide, in the longitudinal direction thereof, and whose front face forms the vertebral limit stop. When the prosthesis holders, with the prosthesis plates  53  contained in them, are driven into the intervertebral space between two vertebrae, the front faces of the vertebral limit stops  96  finally bear on the ventral margins of the vertebral bodies. The distance of the front faces of the vertebral limit stops  96  from the prosthesis plates thus determines the depth to which the prosthesis plates reach into the intervertebral space. This depth can be changed by adjusting the vertebral limit stops  96  on the slides  81 . This is done by means of a threaded spindle  97  which is guided in a threaded bore of the shoulder  95  and whose end is rotatable, but connected fixedly to the vertebral limit stop  96  in the longitudinal direction. By turning the threaded spindle  97 , the operating surgeon can thus predetermine the depth of insertion of the prosthesis plates  53  in relation to the ventral margin of the associated vertebral bodies. Scale markings  98  help him to do this.  
         [0031]     In the alternative design according to  FIG. 8 , the instrument body  51 , near its front end, is connected via a pivot axis  30  to the front end of an actuating lever  31  which extends approximately parallel to the instrument body  51  and can be gripped at its rear end  32  in the manner of a forceps lever so as to be pressed toward the instrument body  51 . It has a limit stop projection  33 , or a pair of limit stop projections  33 , located on both sides of the instrument body and extending toward an opposite limit stop surface  34  on the second prosthesis holder or on a plate  73  connected to the latter. When the prosthesis holders  52 A,  52 B are not spread apart, the actuating lever  31  runs at an acute angle away from the instrument body  51 . When it is pressed toward the instrument body  51 , the limit stop projection  33  lifts the prosthesis holder  52 B in order to spread it apart from the prosthesis holder  52 A.  
         [0032]     A similar design is shown in  FIGS. 9 and 10 . The same reference numbers designate identical parts. For their description, reference can be made to the above example.  
         [0033]     The limit stop projection  33  does not engage directly on the plate  73 , but instead on the link arm  52  which carries a limit stop pin  35  cooperating with a groove  36  at the end of the limit stop projection  33 . For cooperation with the axis  30 , an open receiving bore  37  is provided at the end of the actuating lever  31 . The function is the same as that of the illustrative embodiment of  FIG. 8 . The difference lies in the fact that the engagement of the limit stop projection  33  on the oblique link arm  57  provides for a transmission, the order of which can be freely determined by the selection of the point of engagement. The design according to  FIG. 9  also differs from that of  FIG. 8  in that the actuating lever  31 , by virtue of the open groove  36  and the open receiving bore  37 , can be easily removed from the instrument body and can be easily coupled to it. As will be seen in  FIG. 10 , the limit stop projection  33 , the limit stop pin  35 , the axis  30  and the open receiving bore  27  are provided in pairs, in order to permit a secure connection to the instrument body and to ensure that the space between the parallel guides  56 ,  57  which serves for insertion of the prosthesis core is kept free from construction parts.  
         [0034]     At the rear end  32 , the actuating lever  31  can of course be operated by hand. In addition, however, a threaded spindle  38  is provided on which the actuating lever  31  can be brought close to the instrument body  51  with considerable force by means of a nut  39  and with the aid of which the spread position of the instrument can be secured. The actuating lever  31  can also be released from the instrument body in the area of the spindle  38 .