Abstract:
A height-adjustable implant is designed to be inserted between vertebral bodies and includes a first and a second sleeve part. The second sleeve part carries an external thread and is inserted with a longitudinal section thereof in the first sleeve part in a rotationally fixed and axially movable manner. On its longitudinal section projecting from the first sleeve part, the second sleeve part is encompassed by a nut that engages with the external thread. The nut carries a toothed ring. The invention also relates to a tool for handling the implant.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a height-adjustable implant for insertion between vertebral bodies and a tool suitable for the manipulation thereof. 
     2. Present State of the Art 
     An implant known from patent specification DE 196 22 827 A1, for example, has a first and a second sleeve part, which second sleeve part has an external thread which is placed in the first sleeve part by means of a longitudinal portion so as to be prevented from rotating and axially displaceable whilst its longitudinal portion projecting out from the first sleeve part is enclosed by a nut engaging in the external thread. When the nut is rotated, the second sleeve part is moved out of the first sleeve part. In order to operate the nut, a rod-shaped manipulating tool is inserted by its free end in a recess on the external circumference of the nut. By pivoting the tool in a plane extending transversely to the longitudinal axis of the implant, the nut is turned by a further distance corresponding to the pivot angle of the tool. The tool is then extracted from the nut and the process described above is repeated until the implant is at the requisite height. During the operation of turning the nut, the first sleeve part must not turn as well and as a rule, it therefore has to be held still by means of another tool. The height adjustment of the known implant therefore requires extra time and technical equipment. Furthermore, a relatively large orifice is needed for the operation in order to perform the described manipulations unobstructed. 
     SUMMARY OF THE INVENTION 
     Against the background of the above, the objective of the invention is to propose an implant and a manipulating tool which facilitates insertion in the vertebral column. 
     The nut of the implant bears a toothed ring and is therefore designed as a gear. The height of the implant can be adjusted with the aid of a tool incorporating an appropriate complementary element, for example a driving gear, in which case there is no need to perform any pivoting movements with the manipulating tool. Furthermore, the tool does not have to be repositioned several times. Instead, it can be held in one and the same position during the entire process of making the height adjustment, which significantly simplifies the operation and reduces the time needed for the operation. 
     In order to guarantee that the first sleeve part is secured to prevent it from rotation, it is provided with a threaded bore, where the manipulating tool driving the nut can be secured. Unlike conventional implants, therefore, only a single tool is needed both to drive the nut and to immobilise the first sleeve part. 
     In the case of the implant known from patent specification DE 196 22 827 A1, the nut is supported on the end face of the first sleeve part directed towards it as the second sleeve part is moved out. However, the nut is not otherwise secured on the first sleeve part. Consequently, the height of the known implant can only be increased but not reduced, i.e. the second sleeve part can not be moved into the first sleeve part. In the case of the implant proposed by the invention, on the other hand, the nut is secured on the first sleeve part by means of an axially acting positive connection, in other words in both axial directions, as a result of which it is possible both to increase and reduce the implant height. The latter may be necessary if too big a height adjustment was made after inserting the implant, for example. 
     In a particularly preferred example of an embodiment of the invention, the two sleeve parts have axially extending windows opening in their mutually facing ends, in which case the peripheral portions disposed between two adjacent windows lie so as to be axially displaceable in the windows of the other respective sleeve part. The advantage of this compared with an arrangement in which the two sleeve parts engage concentrically one inside the other is that less material is necessary and the implant is therefore more lightweight overall. Furthermore, a significantly larger interior is available, which can be filled with bone material or similar. Due to the fact that the two sleeve parts mesh with one another like a comb, they are ultimately guaranteed to be fixedly secured, preventing mutual rotation. 
     A radially widened end plate is provided as a means of supporting the implant on a vertebral body. In a preferred embodiment, this is a separate, releasably fixed part. The appropriate end plate, for example one with a flat plane extending at an angle to the mid-longitudinal axis of the implant, may be used in each individual case. If the end plate is secured on the sleeve part by means of a snap-fit connection, a secure mount on the sleeve part can be guaranteed on the one hand, whilst making replacement easy on the other hand. In one embodiment which is simple from the point of view of production and assembly, an annular groove is provided in the internal wall of the sleeve part close to the end face, in which catch lugs integrally moulded on the underside of the end plate locate. 
     A manipulating tool for the implant described above has a gear co-operating with the nut. A retaining mechanism is preferably provided on the manipulating tool as a means of holding the implant immobile. The gear is disposed so that its axis extends transversely to the axis of the toothed ring of the nut during the driving operation. As mentioned above, a deflection of the rotating movement of the drive axis is not necessary. In one arrangement that is particularly compact and easy to operate, the toothed ring is disposed on the end face of a tubular portion and the tubular portion has a rod extending through it, the free end of which projects out from the tubular portion and can be screwed into the threaded bore of the first sleeve part. The coaxial disposition of the tubular portion and the rod results in a compact manipulating tool that is easy to operate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in more detail with reference to the appended drawings. Of these: 
         FIG. 1  is a perspective view with a partially cut-away section of an implant comprising a first sleeve part and a second sleeve part lying inside it and axially displaceable therein, the second sleeve part being shown in its inserted position, 
         FIG. 2  shows the implant illustrated in  FIG. 1  with the second sleeve part partially extracted, 
         FIG. 3  is a perspective view of the first sleeve part, 
         FIG. 4  is a perspective view of the extractable second sleeve part, 
         FIG. 5  shows a nut used to drive the first sleeve part, 
         FIG. 6  shows an end plate which can be fixed on a sleeve part, 
         FIG. 7  shows a tool for manipulating the implant. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The implant illustrated in the drawings comprises a first sleeve part  1 , a second sleeve part  2  and a nut  3  as its main components. The sleeve part  2  is provided with an external thread  4  extending essentially across its entire length. Both sleeve parts  1 ,  2  have axially extending windows  6  which open into their mutually facing end face  5   a, b  in the assembled state. The peripheral portions  7   a, b  left between two adjacent windows lie so as to be axially displaceable in the windows  6  of the other respective sleeve part  1 ,  2 . This being the case, the clearance between the peripheral portions  7   a, b  is dimensioned so as to guarantee that the two sleeve parts will sit without wobbling but easily slide one inside the other. The sleeve parts  1 ,  2  have a more or less identical wall thickness and the same internal diameter, i.e. the peripheral portions  7   b  of the second sleeve part  2  do not project beyond the external circumference or beyond the internal circumference of the sleeve part  1 . The axial length of the windows  6  and peripheral portions  7   a, b  is dimensioned so that there is an axial distance  9  between the end face  5   a, b  of a peripheral portion  7   a, b  and the base  8  of a sleeve part  1 ,  2  when the sleeve part  2  is inserted to its maximum. 
     The nut  3 , which encloses both sleeve parts  1 ,  2 , is used to adjust the height and move the sleeve part  2  in and out. The nut  3  is connected to the first sleeve part  1  so as to be axially immobile and rotatable. The internal face of the nut  3  enclosing the two sleeve parts  1 ,  2  has an upper longitudinal portion provided with an internal thread  10  and a longitudinal portion  13  with no thread adjoining it. Incorporated in the longitudinal portion  13  is an annular groove  14 . The nut  3  is positioned on the sleeve part  1  so that only the thread-free longitudinal portion  13  is disposed enclosing the peripheral portions  7   a  of the sleeve part  1  and the internal thread  10  engages with the external thread  4  of the sleeve part  2 . Close to the end face  5   a  of the peripheral portion  7   a  of the sleeve part  1  is an integrally formed segment-shaped projection  15  extending across the entire width of the peripheral portion  7   a , which locates in the annular groove  14  of the nut. Consequently, although the nut  3  is able to rotate on the sleeve part  1 , it is immobilised on it in both axial directions. The side of the nut  3  facing the free ends of the peripheral portions  7   b  of the sleeve part  2  bears a toothed ring  17  extending coaxially with the mid-longitudinal axis  16  of the implant. The toothed ring  17  is integral with the nut  3 , formed by milling for example. Its purpose is to displace the nut  3  in rotation with the aid of a tool, which will be described in more detail below, and thus move the sleeve part  2  out of the sleeve part  1  or into it, in other words, to adjust the height of the implant. 
     The end faces  18  remote from the free ends of the peripheral portions  7   a, b  bear an end plate  19  standing radially out beyond the periphery of the sleeve parts  1 ,  2 . The end plates  19  can be releasably secured on the sleeve parts  1 ,  2  with the aid of a snap-fit connection. To this end, an annular groove  20  is provided on the internal face of the sleeve parts  1 ,  2 , close to their end faces  18 , in which catch projections  23  provided on the side of the end plate facing the end faces  18   a, b  locate. The catch projections  23  are integrally formed on an apron  24  bounding a central orifice  21  in the end plate  19 . Provided in the edge  25  of the apron  24  are several recesses  26  distributed uniformly in the circumferential direction. The circumferential portions  27  disposed between the recesses  26  support the catch projections  23 . The circumferential portions  27  can be elastically deflected radially, slightly towards the interior, thereby facilitating the fitting or removal of the end plate  19 . Projecting out from the external faces  28  of the end plates  19  in the direction of the longitudinal axis  16  is a toothed ring  29 . It is used to anchor the implant on a vertebral body. 
     Disposed in the peripheral portions  7   a  are two orifices  30 . The orifices  30  and the central orifice  21  in the end plates  19  are used for filling with bone material, bone cement or similar. A radially oriented threaded bore  33  is provided in one of the peripheral portions  7   a , close to the nut  3 . It is used as a means of securing the manipulating tool described below. 
     As may be seen from  FIG. 7  the manipulating tool essentially consists of a rod  34 , one end of which bears a handle  35  and the other end of which bears a threaded portion  36 . The region of the rod  34  extending away from the threaded portion  36  is coaxially enclosed by a rotating sleeve  37 . The end of the rotating sleeve  37  facing the handle  35  bears a knurled wheel  38  and the oppositely lying end a toothed ring  39 . The toothed ring  39  is produced, like the nut  3 , by milling the sleeve end face. An axial displacement of the sleeve  37  in the direction towards the handle  35  is restricted by means of a stop flange  39 . 
     In order to adjust the height of the implant, for example starting from the situation illustrated in  FIG. 1 , the manipulating tool is turned in the threaded bore  33  by means of its threaded portion  36 . As this takes place, the toothed ring  39  engages with the toothed ring  17  in the manner of a crown gear, i.e. the axis of the toothed ring  39  extends essentially perpendicular to the axis of the toothed ring  17 . This being the case, the knurled wheel  38  lies in abutment with the stop flange  29 . 
     Once the implant has been inserted through an operation orifice in the vertebral column with the aid of the manipulating tool, the rotating sleeve  37  is displaced by rotating the knurled wheel  38  in order to set the implant at a bigger height. If the external thread  4  of the sleeve part  2  and the internal thread  10  of the nut  3  are right-hand threads, the nut  3  must be turned in the direction of arrow  40  and the knurled wheel turned in the direction of arrow  43 . In order to release the manipulating tool from the implant, its threaded portion  36  is removed from the threaded bore  33  by turning the handle  35 . Since the sleeve  37  is able to rotate about the rod  34 , there is no need to hold the rotating sleeve immobile during turning for removal from the threaded portion  36 . Once the two sleeve parts  1 ,  2  have been positioned relative to one another, the position can be fixed in various ways. One simple option is to screw a screw (not illustrated) into the threaded bore  33  more or less by a tip. 
     LIST OF REFERENCE NUMBERS 
     
         
           1  First sleeve part 
           2  Second sleeve part 
           3  Nut 
           4  External thread 
           5   a,b  End face 
           6  Window 
           7   a,b  Peripheral portion
       (a=first sleeve part;   b=second sleeve part)     
           8  Base 
           9  Axial distance 
           10  Internal thread 
           13  Longitudinal portion 
           14  Annular groove 
           15  Projection 
           16  Mid-longitudinal axis 
           17  Toothed ring 
           18  End face 
           19  End plate 
           20  Annular groove 
           21  Orifice 
           23  Catch projection 
           24  Apron 
           25  Edge 
           26  Recess 
           27  Circumferential portion 
           28  External face 
           29  Toothed ring 
           30  Orifice 
           33  Threaded bore 
           34  Rod 
           35  Handle 
           36  Threaded portion 
           37  Rotating sleeve 
           38  Knurled wheel 
           39  Stop flange 
           40  Arrow 
           43  Arrow