Abstract:
A connecting element is created for connecting two rods ( 6, 9 ) or screws used for bone or vertebra stabilisation. The connecting element has a connecting part ( 10 ), a first part connectable to one of the rods and a second part connectable to the other rod. The connecting part is adjustable in length in the direction of the connecting axis of the first part and the second part and can therefore be adapted to different rod distances.

Description:
The invention relates to a connecting element for connecting two rod-shaped elements used for bone or vertebra stabilisation with a connecting part, a first part connectable to one of the rod-shaped elements and a second part connectable to the other rod-shaped element. 
   BACKGROUND 
   A connecting part is known from WO 91/16020. The connecting part has two channels, constructed in the shape of cylindrical sections, which serve to receive two rods parallel to one another. Connection of rods inclined towards one another or running diagonally to one another is not possible with this. 
   Furthermore, a connecting part of this kind can be used only for a predetermined distance between the rods. 
   SUMMARY 
   The object of the invention is to create a connecting element which allows adaptation to the distance between the rods to be connected. 
   A connecting element of this kind has the great advantage that the length of the connecting element can be adjusted during the operation. 
   Further developments of the connecting element include the additional advantage that the surgeon has freedom in aligning the rods as a function of the desired alignment of the parts to be connected. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention emerge from the description of embodiment examples using the figures. 
       FIG. 1  shows a perspective illustration of a case of application. 
       FIG. 2  shows a sectional illustration through a first embodiment of a connecting element. 
       FIG. 3  shows a sectional illustration through a second embodiment of a connecting element. 
       FIG. 4  shows a sectional illustration through a modified embodiment. 
       FIG. 5  shows a horizontal projection on to the connecting part according to the invention of the connecting element according to a further embodiment. 
       FIG. 6  shows a sectional illustration of the connecting part of  FIG. 5  along line A—A. 
       FIG. 7  shows a perspective illustration of the elements of the connecting part of  FIG. 5 . 
   

   DETAILED DESCRIPTION 
   In  FIG. 1  two tubular bone parts  1 , 2  to be connected to one another and fixed in respect of one another are shown. A screw  3 ,  4 , known from vertebral column surgery as a pedicle screw, is screwed into each of the two parts. Each of the screws has a head  5  with a receiving orifice for receiving a rod  6 . The rod is rigidly connected to the head with the aid of a nut  7 . As can be seen from  FIG. 1 , a third screw  8 , constructed exactly like the first two screws and receiving a second rod  9  in its head, is screwed into the part  1 . 
   The second rod  9  is connected to the first rod  6  via a connecting element  10 . This provides additional stabilisation. 
   In the above embodiment example the two parts  1  and  2  to be connected are tubular bone parts. In the same way application of at least two rods with corresponding screws for receiving thereof takes place in vertebral column surgery, possibly with an internal fixator, as known, for example, from DE 38 23 737-C. 
   In the embodiment shown in  FIG. 2  the connecting element  10  has a shank  11  with a first part  12  on one of its ends and a second part  13  on its other end. 
   The second part  13  comprises two legs  15 ,  16 , limiting a U-shaped channel  14 . The two legs  15 ,  16  have a cylindrical shape externally and have an outer thread  17  on their open ends. The U-shaped channel  14  has a diameter which is substantially identical to or slightly larger than the diameter of a rod  18  to be received and is chosen as just large enough for the rod  18  to be inserted into the U-shaped channel  14  and to be guided thereby in the lateral direction. Further provided is a nut  19 , which is equipped with its inner thread in such a way that it cooperates with the outer thread  17 . The thread  17  is constructed in such a way that the distance from the thread to the floor of the U-shaped channel  14  is smaller than the diameter of the rod  18 , so the rod  18  placed in the U-shaped channel  14  can be fixed by screwing down the nut  19 . 
   As can be seen from  FIG. 2 , the other end of the shank  11  has a head  21  comprising a spherical section. The first part  12  has a cylindrically constructed mount  20 , the diameter of which is substantially identical to or slightly larger than the diameter of the head  21  and is dimensioned in such a way that the head can be inserted into the bore and guided thereby. 
   In the embodiment example shown the bore  22  has a floor  23  which is spherically constructed, its radius being identical to the radius of the head  21 . As can be seen from  FIGS. 2 and 3 , the shank  11  is constructed as separable from the spherical head via a screw connection. 
   One of the two parts has a threaded bore while the other part has a screw part which can be screwed into the threaded bore. This connection is schematically indicated by the connecting point  24 . The threaded bore can also be provided directly in the head  21  and the shank  11  then has on its end facing the head a correspondingly constructed screw projection which can be brought into engagement with the threaded bore to screw together the two parts. 
   In the embodiment shown in  FIG. 2  firstly the shank  11  is unscrewed from the head  21 , so the head  21  can be inserted therein from the open end of the bore  22  into the position shown. The shank  11  is then screwed on, so the connection shown in the figure is produced. 
   As  FIG. 2  further makes clear, adjacent to the floor  23  is a second bore  25 , which is widened in a funnel shape, so the shank  11  can be swivelled about a solid angle relative to the mount  20 . 
   After the head  21  has been inserted, a pressure element  26 , which is constructed as spherical on its side facing the head, with a radius corresponding to the radius of the head  21 , is placed into the bore  22 . On its side facing away from the head  21  the pressure element has a cylindrical surface  27  in which the diameter of this cylinder is identical to the diameter of the rod  28  to be received, so the rod  28  can be placed into the recess  27 . As can be seen from  FIG. 2 , the recess is further constructed in such a way that a U-shaped channel  31 , coaxial to the bore  22 , is formed with legs  29 ,  30  limiting the channel. The two legs  29 ,  30 , like the second part  13 , have adjacent to their open ends an outer thread  32 , which extends to the other end of the mount  20  to such an extent that its distance from the floor of the cylindrical recess is smaller than the diameter of the rod  28 . Further provided is a nut  33 , the inner thread of which corresponds to the outer thread  32 . 
   In operation first the rod  18  is inserted into the monoaxially acting second part  13  or into its U-shaped channel  14 . Then the rod is fixed with the aid of the nut  19 . The mount  20  is subsequently aligned in such a way that it receives the second rod  28  into itself. After the rod  18  has been inserted, the nut  33  is screwed down. This not only fixes the rod  18 , but also exerts via the rod  28  and the pressure element  26  a pressure on the head  21  such that it is stabilised in its axial position. 
   In the embodiment shown in  FIG. 3  the mount  20 , the pressure element  26 , the head  21 , the rod  28  and the nut  33  coincide in all details with the first part  12  in  FIG. 2 . The embodiment differs only in that the second part is formed not as a monoaxial connection but also as a polyaxial connection. This second part  12 ′ is constructed as mirror symmetrical to the first part  12 . All parts of mount, head, pressure element, rod and nut coincide with the corresponding parts of the first part  12 . For assembly, as in the previously described embodiment example, the shank  11  is detachable by means of a screw connection along line  24 . After the heads  21  have been inserted the two parts of the shank  11  are rigidly connected to one another. 
   In operation the connection takes place as previously described using the first part  12 , wherein the mount is orientated in each case towards the rod to be received before fixing and the rod is then placed in and fixed via the nut. By exerting the pressure from the nut via the rod and the pressure element the head is then also finally fixed. 
   In a modified embodiment, not shown, the mount  20  or the second part  13  can have in each case, adjacent to its open end, another inner thread into which an inner screw can be screwed, in order in this way to achieve blocking of the screw connection in a manner known per se. 
   In the above-described embodiments the head  21  is inserted in each case from the open end of the U-shaped recess. In a modified embodiment the bore  22  can extend through the entire mount. The head is then inserted from the end of the bore  22  facing away from the legs and held in the bore by a detent ring or snap ring to be attached. It is decisive that the open edge which surrounds the head on the end facing the shank  11  is widened in the shape of a cone, in order to enable a polyaxial movement between mount and head or shank. 
   The embodiment shown in  FIG. 4  coincides completely in respect of shank  11 ′, head  21 , rod  18  or  28  and nut  19  or  33  with the embodiment described in  FIG. 3 . The mount  34  is differently constructed. It has a first end  35  and a second end  36  opposite this. A bore  38  coaxial to the symmetrical axis  37  of the mount is provided. A U-shaped recess  39  is further present, issuing from the first end  35  and extending crosswise to the symmetrical axis  39 . The U-shaped recess is limited by two legs  40 ,  41 . Adjacent to the first end  35  the two legs  40 ,  41  have an outer thread  42 . The diameter of the U-shaped recess  39  is identical to or slightly larger than the diameter of the rod  18  or  28  and just large enough for the rod to be inserted into the recess and guided laterally by the sides of the U-shaped recess. The outer thread  42  is constructed, as with the previously described embodiments, at a distance from the floor of the U-shaped recess such that the space between it and the U-shaped floor is smaller than the diameter of the rod to be received. Further provided, as in the previously described embodiment example, is a nut  33  which cooperates with the outer thread  42 . 
   Differing from the previously described embodiment examples, the cylindrical section  43  of the coaxial bore extends to a predetermined distance from the second end  36  and from there onwards is conically tapered towards the second end  36  at a conical angle. A pressure element  44  is further provided, the outer face of which is constructed conically towards the second end  36  in a region  45  laterally encircling the head  21 , wherein the conical angle corresponds to that of the conical region of the bore. The conical region has a slit  46  directed towards the second end  36  and running open towards this end. By adapting the conical faces between bore  38  and pressure element  44 , in the fully inserted state self-catching follows. The pressure element has in the way known from EP 0 732 081 B a first end  47  and a second end  48  opposite this. Adjacent to the first end is provided a substantially cylindrical section, the outer diameter of which is chosen in such a way that the pressure element can slide in the cylindrical section  43 . As can be seen from the figure, the pressure element has in its second region a recess, shaped like a spherical segment and open to the second end, for receiving the screw head. Otherwise the mount  34  and the pressure element  44  coincide with the disclosure in the mentioned EP 0 732 081, which is herewith made part of the description. 
   The device shown in  FIG. 4  is constructed as mirror symmetrical, so the other end of the shank  11 ′ with its head, the mount and the pressure element is constructed as identical to that previously described. 
   In operation the pressure element is inserted into the mount  34  from the first end  35 . The head  21  is inserted or pressed into the region  45  from the second end  36 . The rod  28  is then placed into the remaining U-shaped slot and via the screwing down of the outer nut  33  pressure is exerted on the rod  28  and via this on the pressure element  44  encircling the head  21  in such a way that rod  28  and spherical head  21  are fixed. The process is carried out correspondingly on the opposite side. 
   This version also allows swivelling of the shank  11 ′ about a predetermined framing angle and the symmetrical axis  37 , so alignment or adaptation to the rods or rods with screws to be connected becomes possible. 
   Alternatively, the device can also be constructed in such a way that a head with mount is constructed in the manner shown in  FIG. 4  and the other head is formed in the monoaxial manner described in  FIG. 2 . 
   The embodiment example shown in  FIGS. 5 to 7  differs from the embodiment shown in  FIGS. 3 and 4  in the construction of the shank  111 , the length of which can to a certain extent be adapted to the distance between the rods. Otherwise this embodiment coincides in all details in respect of the heads, and parts  12 ,  12 ′, the rods  18 ,  28  and the nuts  19 ,  33  with the embodiment according to  FIG. 3  and in respect of the mounts  34 , the rods  18 ,  28  and the nuts  19 ,  33  with the embodiment according to  FIG. 4 . 
   As can be seen in particular from  FIG. 7 , the shank  111  consists of three elements. A first shank part  211  is formed from a pin-shaped section with an open end  212  and connected to one of the heads  210 . The diameter of the pin-shaped section is such that the pin-shaped section can be guided through the bore  22  of the mount  12 . A second shank part  213  is substantially cylindrically constructed adjacent to the other head  210 ′ and has a coaxial bore  215 , extending from the open end  214  to a distance from the head  210 ′ for receiving the first shank part  211 . To fix the connection between first and second shank part a nut  216 , described in detail later, is provided. The second shank part  213  has adjacent to the head  210 ′ a first cylindrical section  217  with a first outer diameter which is dimensioned in such a way that the shank part  213  can be guided through the bore  22  of the mount  12 ′. On its end facing away from the head  210 ′ the first cylindrical section  217  has an outer thread  218 , indicated in  FIGS. 5 and 6 . Adjacent to the first cylindrical section  217  the second shank part has a second cylindrical section  219  with an outer diameter which is smaller than that of the first cylindrical section. Adjacent to the second cylindrical section  219  the second shank part has a third section  220 , the outer wall of which tapers conically towards the open end  214  at a conical angle. Further provided in the second shank part  213  are at least two, in the embodiment example shown, four longitudinal slots  221 , extending from the open end  214  as far as into the first cylindrical section  217  and beyond the region of the outer thread  218 , but not as far as the floor of the bore  215 . In each case two longitudinal slots  221  are opposite one another. On the second shank part the longitudinal slots form tongues which are to a certain extent elastic, so with the nut  216 , described below, a clamping effect on to the inserted first shank part  211  is achievable. 
   The nut  216  is a spigot nut or tensioning nut. It is constructed as elongated and has adjacent to one of its ends an inner thread  222  which cooperates with the outer thread  218  of the second shank part  213 . Adjacent to its opposite end the nut has a section  223 , the inner wall of which tapers conically towards the second end of the nut. The length in the direction of the longitudinal axis of the nut and the conical angle correspond to that of the second shank part. The length of the nut is dimensioned in such a way that in the state screwed on to the second shank part  213  the conical region  223  of the nut cooperates with the conical region  220  of the second shank part. 
   To secure against twisting of the first shank part  211  in respect of the second shank part  213  the first shank part  211  has at a distance from its open end  211  a bore  224 , extending crosswise to the shank axis through the pin-shaped section, for receiving a corresponding securing pin  280 ,. The diameter of the bore corresponds to the diameter of the slots  221  in the crosswise direction. The securing pin to be inserted has a length which is larger than the diameter of the first shank part  211  and a maximum of the size of the core diameter of the nut  216 . 
   In operation first the first shank part  211  is inserted through the bore  22  of the mount  12 , shown in  FIG. 3 , until the head  210  is resting on the floor  23 . Then the second shank part  213  is guided through the bore  22  of the other mount  12 ′ until the head  210 ′ is resting on the floor  23 . The nut  216  is subsequently screwed by a small amount on to the second shank part  213 , so the conical sections of nut and second shank part do not yet cooperate and the first shank part can be inserted. The first shank part  211  is now inserted into the bore  215  of the second shank part  213  until a desired total length of the shaft is produced. However, the nut  216  is still not tightened, so adjustment in length is possible. To secure against twisting, the above-described securing pin  280  is subsequently guided through the longitudinal slots  221  and the bore  224 . All the time the nut  216  has not been tightened the length of the shank  111  can still be changed, even with inserted securing pin  280 , as the securing pin  280  can be displaced in the slots  221  with the first shank part  211 . Thus length adjustment can take place without twisting of the heads  210  or  210 ′. 
   Connection of the mounts  12 ,  12 ′ to the rods  18 ,  28  then takes place as in the manner described in connection with the embodiment according to  FIG. 3 . 
   Finally the nut  216  is tightened. By tightening the nut until the conical sections of nut and second shank part cooperate, the above-described tongues formed in the second shank part  213  by the longitudinal slots  221  are pressed together and thereby clamp the first shank part in a similar way to that with a collect chuck. If it emerges that another length adjustment of the shank  111  is required, only the nut  216  has to be loosened, in order to remove the clamping effect of the tongues. In practice the surgeon first screws the screws into the bone at the desired positions and then places the rods in. The connecting part  10  is usually already pre-mounted before being inserted, i.e. the heads are in the respective mounts and the shank part  211  is inserted into the second shank part  213 , so the shank has a predetermined length. The surgeon then places the connecting part between the rods to be connected and adapts the desired length of the shank part as described above. In this way, for example, one rod can also be pulled towards the other. 
   If the embodiment of the shank  111  shown in  FIGS. 5 to 7  is used with the embodiment of the mounts  34  shown in  FIG. 4 , connection of the shank parts can take place before the heads  210 ,  210 ′ are connected to the mounts  34 , because the shank parts are inserted into the mounts with the head side. 
   The embodiment shown in  FIGS. 5 to 7  can also be applied in the embodiment shown in  FIG. 2 , wherein one of the heads is then replaced by part  13  and the connecting element then has a monoaxial and a polyaxial connection. 
   In the above-described embodiment examples the connecting elements are always explained for connecting rods. Two shanks of two screws or one shank of one screw and one rod can also be connected to the connecting element and fixed in the same way.