Abstract:
A space keeper for insertion between two vertebrae which has a variable axial length is provided. The space keeper possesses a sleeve-like first member ( 2 ) and a second member ( 3 ) guided in the latter and movable relative to the first member in the axial direction for adjusting an overall length. In order that adjustability during operating is facilitated the two members ( 2, 3 ) are connected to one another by a lever ( 7, 8 ), wherein one centre of motion ( 16 ) of the lever is connected to one member ( 3 ) and the other centre of motion ( 18 ) is connected in terms of action to the other member ( 2 ).

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a space keeper for inserting between two vertebrae, the space keeper having an adjustable axial length and a sleeve-like first member and a second member guided in the latter and movable in the axial direction relative to the first member for setting an overall length. 
   A space keeper of this type is known from EP 0 977 528 A1. In this the two members in the telescoped position are inserted between two vertebrae and then pulled apart by hand to the desired length and then locked in the extended position. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to provide a space keeper of the type described at the outset in which the operating surgeon can manage the adjustment to the desired length in the most simple manner. 
   This task is solved by a space keeper of the type described at the outset which is characterized in that the two members are connected to one another by a lever one of whose centers of motion is connected to one member and whose other centre of motion is connected to the other member. 
   Refinements of the invention are identified in the subsidiary claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and functions of the invention emerge from the description of embodiments with reference to the figures. In the figures: 
       FIG. 1  a side view of the space keeper in the contracted position; 
       FIG. 2  a section along the line II/II in  FIG. 1 ; 
       FIG. 3  the same section as in  FIG. 2  but this time with the space keeper pulled apart to its maximum length; 
       FIG. 4  a plan view onto the object shown in  FIG. 1 ; 
       FIG. 5  a second embodiment in the extended position corresponding to the sectional illustration II/II; 
       FIG. 6  the second embodiment in the contracted position; 
       FIG. 7  a section through another embodiment. 
   

   DETAILED DESCRIPTION 
   As may be seen best in  FIG. 1  a space keeper  1  comprises a sleeve-like first member  2  and a sleeve-like second member  3  guided in the former. The two members can be pushed into one another to a maximum extent as shown in  FIGS. 1 and 2  and be moved apart to a maximum length as shown in  FIG. 3 . 
   As may be seen in  FIGS. 1 to 3  the inner second member  3  has on its outer wall facing towards the outer first member  2  a section with a catch  4  extending in the axial direction having a plurality of depressions  5  arranged adjacent to one another in the axial direction and bounding one another and the outer first member  2  has a fixing member  6  which can be brought into engagement with the catch. The fixing member serves the purpose of locking the two members in a desired position. 
   As may be seen best in  FIGS. 2 and 4  the spacer  1  has a lever device for adjusting the axial position of the two members relative to one another. In the first embodiment this comprises a first lever arm  7 , a second lever arm  8 , a setting screw  9  and a threaded sleeve  10 . As may be seen best in  FIG. 2  the outer first member  2  has a recess  11  on the side whose lateral extension is smaller than the diameter of the head  12  of the setting screw  9  as may be seen best in  FIG. 1 . The setting screw  9  is inserted in the manner shown in  FIG. 2  into the interior of the sleeve-like members at right angles to the axial direction. The threaded sleeve  10  is screwed onto the screw. On both sides extending in the axial direction of the sleeve it has shoulders  13 ,  14 . The shoulder  13  serves to connect to the first lever arm  7 . The lever arm is mounted pivotably about a shaft  16  by its first end  15  by means of this shaft mounted on two opposite points of the wall of the second member  3 . The shaft extends perpendicular to the longitudinal axis of the space keeper. At its second end  17  opposite the connection to the shaft  16  the first lever arm is connected pivotably about a shaft  18  to the shoulder  13  via a pin or shaft  18 . The pin or shaft  18  extends parallel to the shaft  16 . 
   As illustrated in  FIG. 2  the second lever arm  8  viewed about the setting screw  9  is constructed or arranged symmetrically relative to the first lever arm  7 . At its first end  19  correspondingly located opposite end  15  the lever arm is mounted via a shaft  20  to pivot about the latter. The shaft  20  is mounted on the side in the side walls located opposite one another of the first member  2  and extends parallel to the shaft  16 . At its end located opposite the end  19  the second lever arm is connected pivotably about a shaft  21  to the shoulder  14  by means of a pin or shaft  21 . 
   As may be seen in  FIGS. 1 and 2  the recess  11  is constructed as an oblong hole extending in a direction parallel to the longitudinal axis of the spacer. The oblong hole is positioned in such a way that the setting screw  9  is movable back and forth therein to such an extent that the screw is movable back and forth in the oblong hole from the compressed position shown in  FIG. 2  to the extended position shown in  FIG. 3 . 
   In operation the space keeper in the contracted position shown in  FIG. 2  with minimal length in the axial direction is inserted between the vertebrae. The length is then set to a desired length by engaging by means of a screwdriver in a corresponding slit or hexagonal opening of the head  12  of the setting screw  9  in that the setting screw  9  is turned in such a way that the threaded sleeve  10  is moved from the most extreme position shown in  FIG. 2 , in which the threaded sleeve is located at the free end of the setting screw  9 , towards the head. In doing so the two levers  7 ,  8  are moved from their retracted position into a maximum extended position shown in  FIG. 3 . In this way the two sleeve-like members  2  and  3  are moved from the contracted position shown in  FIG. 2  into the expanded position shown in  FIG. 3  or any intermediate position. Due to the screw guidance between the setting screw  9  and threaded sleeve  10  the two members remain initially in the position reached by turning the setting screw  9 . As soon as this position is regarded as final complete locking ensues by tightening the locking screw forming the fixing member  6  which for this purpose engages in a depression  5  of the catch  4 . 
   In the embodiment described above the length of the setting screw  9  is chosen so that the setting screw reaches by its free end into the hollow interior of the second member  3  without coming into engagement with the opposite wall of the second member  3  so that there is no hindrance to the movement of the second member  3 . As shown in the figures the second member  3  preferably has a recess  22  constructed in the form of an oblong hole which extends in its longitudinal direction parallel to the longitudinal axis of the space keeper and whose length and width are so constructed that the free end of the setting screw  9  with the threaded sleeve sliding thereon and the two shoulders  13  and  14  and the ends of the two lever arms  7  and  8  connected thereto in the back-and-forth movement shown in  FIGS. 2 and 3  can move freely back and forth in the oblong hole. In this way it is achieved that the setting screw  9  may have a greater length by which means the travel of the threaded sleeve  10  is increased and hence the expandability of the two members or the space keeper is increased. 
   In a modified embodiment shown in  FIGS. 5 and 6  the second member  3 , the setting screw  9 , the first lever arm  7 , the shoulder  13  and the two shafts  16  and  18  are constructed in the same way as the corresponding elements in the first embodiment. 
   In the second embodiment, instead of the oblong hole  11  a round hole  23  guiding the setting screw in the wall of the first member  2 ′ is provided whose diameter is chosen so that the setting screw is guided rotatably in this hole. The threaded sleeve  10 ′ has only one shoulder  13 . 
   In operation adjustment between the compressed position shown in  FIG. 6  and the expanded position shown in  FIG. 5  is done as in the first embodiment by turning the setting screw  9  in such a way that the threaded sleeve  10 ′ is screwed so far out of the most extreme position at the free end shown in  FIG. 6  towards the head until expansion to a desired size has occurred or the lever  7  has moved almost into the vertical position. The concluding locking is done as in the first embodiment by tightening a fixing screw  6  in cooperation with the depressions  5  of the catch  4 . 
   As may be seen in the figures the two walls of the first and second members are each constructed in such a way that they exhibit in the circumferential direction a plurality of diamond-shaped apertures  24 . The free ends  25 ,  26  located opposite one another are as shown in the figures each of serrated construction whereby engagement in the adjoining vertebrae walls stabilizing against rotation is facilitated. The apertures in the wall facilitate ingrowing after the operation. 
   In the embodiments described above the adjusting device of the setting screw  9 , threaded sleeve  10  and lever arms  7 ,  8  or  7  is constructed in each case in such a way that the maximum extension occurs when the threaded sleeve  10  is moved to the maximum towards the head  12  and compressed to the furthest possible when the threaded sleeve  10  is at its greatest possible distance from the head  12 . It is also possible, however, to reverse this device to the effect that the greatest extension possible is reached when the threaded sleeve  10  is at its greatest distance from the head  12 . At the smallest distance from the head  12  the height has its lowest possible value. Such an embodiment is described in  FIG. 7 .