Abstract:
An insert for a clamping element having two jaws for clamping a rod-shaped element comprises at least one jacket element. The jacket element can be inserted into one jaw each of the clamping element, thereby allowing the varying, especially reducing, the free space available for a rod. The insert also comprises at least one retaining section which fastens at least one part of the insert in or on at least one of the jaws of the clamping element. A clamping element can be provided with two jacket elements, interlinked via an undulated web, or two or three juxtaposed longitudinal grooves for receiving rods having different diameters.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention concerns an insert for a clamping element for clamping a rod-shaped element of a universal joint, particularly for a clamping element of a universal joint for stabilizing bone fractures. Furthermore, the invention concerns a universal joint with two clamping elements and with one locking element. 
     Prior Art 
     EP 1 184 000 describes a one-piece element that has two opposing jaws and one free space that opens to the side for receiving a rod-shaped element and a hinge placed opposite the free space, that connects the jaws to one another and by means of which these are movable, whereby each jaw has one bore, and which are aligned with each other. 
     This clamping element has the advantage that with two identical clamping elements placed one next to the other, a universal joint may be produced whereby through the said bores, a connecting screw may be inserted, which is screwed into an interior-threaded nut, in order to close the clamping jaws. 
     A disadvantage of the known device is that the rod-shaped elements may be inserted into the receiving free spaces only from their ends in a lengthwise direction. 
     Another clamping element is known from U.S. Pat. No. 6,277,069, which is open on the side. This permits the lateral insertion of a first rod-shaped element. A second rod-shaped element may be introduced into a closed casing connected to a tension lever. 
     A universal joint is known from both U.S. Pat. No. 6,616,664 and EP 0 700 664, that is composed of four individual clamping jaw elements and one central screw. With this universal joint it is possible to introduce one or two rod-shaped elements laterally into the corresponding free spaces. In EP 0 700 664 a spring is arranged between the two center clamping jaw elements, against the spring tension of which it is possible to clip in the rod-shaped elements and thus to hold the universal joint to the rod-shaped elements before locking it. In U.S. Pat. No. 6,616,664 narrow, laterally-placed lever arms are provided in order to hold laterally-inserted rod-shaped elements before locking of the universal joint. 
     A disadvantage of these devices lies in the fact that the clamping elements of such a universal joint must be designed for the diameter of the rod or pin to be inserted. Thus the surgeon must have available a series of different clamping elements, in order to take into account the conditions of a particular operation. 
     Starting with this prior art, it is the object of this invention to present an insert for a clamping element that allows the lateral insertion of rod-shaped elements of varying thicknesses. 
     It is further the object of this invention to present a clamping element for the simple insertion of such inserts that allows the lateral insertion of rod-shaped elements of varying thicknesses, in particular at least the insertion of two different rods in two clamping elements of a universal joint. 
     A further goal of the invention is to create a cost-effective single-use clamping element, in particular made of injection-molded plastic, which is subsequently adaptable for various different rod-shaped elements. 
     Starting from the known prior art, the invention also has the object of presenting an improved universal joint. 
     Abstract of the Invention 
     Pursuant to the invention, this problem is solved for an insert of the type described in the introduction with the characterizing features of claim  1 . A kit made up of such inserts is described in claim  10 . A corresponding clamping element is described by means of the features in claim  11 . A universal joint pursuant to the invention is described in claim  13 . 
     Through the fact that the clamping elements may subsequently be equipped with inserts, the size of the jaws of the two clamping elements may be adjusted to each other, in order to be designed in a simple manner for varying rod-shaped elements of an articulated element. 
     On the other hand, clamping elements that already have inserts, in one or more of the jaws, may be provided and supplied, which, upon actual use may easily be removed. If the inserts are formed from an isolating material, it is possible to avoid the formation of a conducting circuit through an external fixator and thus contribute to the MRI safety of such a fixator. 
     An essential advantage of the clamping elements pursuant to the invention lies in the possibility, by using a clever combination of materials, of attaining a good grip on the rod-shaped elements. In particular, the insert may consist of a softer, more plastic material than the clamping element or the rod, so that an increased and improved static friction between insert and rod and insert and jaw of the clamping element occurs than would be possible in direct contact. 
     Additional advantageous embodiments are set forth in the subordinate claims. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
       The invention will now be described in greater detail, making reference to the drawings and using embodiments as examples. 
       The figures show: 
         FIG. 1  a perspective view of an articulated element with two clamping elements with one insert pursuant to the invention, 
         FIG. 2  a perspective view of the insert according to the first embodiment for a clamping element according to  FIG. 1 , 
         FIG. 3  a side view of the insert according to  FIG. 2 , 
         FIG. 4  a perspective representation of an articulated element according to  FIG. 1  in a locked position with two clamped rod-shaped elements and one insert according to  FIG. 2 , 
         FIG. 5  a perspective view of an insert according to a second embodiment for a clamping element according to  FIG. 1 , 
         FIG. 6  a side view of the insert according to  FIG. 5 , 
         FIG. 7  a side view of an articulated element according to  FIG. 1  with an insert according to  FIG. 5 , 
         FIG. 8  a perspective view of an insert according to a third embodiment for a clamping element according to  FIG. 1 , 
         FIG. 9  a side view of an insert according to  FIG. 8 , 
         FIG. 10  a perspective view of an insert according to a fourth embodiment for a clamping element, 
         FIG. 11  a side view of the insert according to  FIG. 10 , 
         FIG. 12  another perspective view of the insert according to  FIG. 10 , diagonally from below, 
         FIG. 13  a perspective view of another articulated element with an insert according to  FIG. 10  and a clamped rod, 
         FIG. 14  a side view of the articulated element according to  FIG. 13 , 
         FIG. 15  a perspective view of an insert according to a fifth embodiment for a clamping element, 
         FIG. 16  a side view of the insert according to  FIG. 15 , 
         FIG. 17  a top view of the insert according to  FIG. 15 , 
         FIG. 18  a detail from an external fixator with several articulated elements and various rods of differing configurations held by these 
         FIG. 19  a perspective view of an insert according to a sixth embodiment for a clamping element according to  FIG. 1 , 
         FIG. 20  a side view of the insert according to  FIG. 19 , 
         FIG. 21  a perspective view of an insert according to a seventh embodiment for a clamping element according to  FIG. 1 , 
         FIG. 22  a side view of the insert according to  FIG. 21 , and 
         FIG. 23  a sectional front view of the insert according to  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a perspective view of a first embodiment of an articulated element  100  with two clamping elements  10  with an insert  50  pursuant to the invention. Each clamping element  10  has two opposing clamping jaws  12  and  13  having a free space  11  to receive a rod-shaped element. The clamping jaws  12  and  13  on their free ends  15  each have a transverse groove  14 , which together span the free space  11 . On the free ends  15 , the outer edges  16  of the sides of the clamping jaws  12  and  13  that face each other are angled in order to simplify the pushing in of a rod-shaped element from the side. Opposite the free space  11  and the free ends  15 , a hinge  17  is provided, which connects the clamping jaws  12  and  13  into a single piece. A screw  103  that passes through the clamping elements  10 , closes the articulated element  100  and clamps rods to be inserted into it. This is a locking element, which may also be realized by means of levers and other elements. 
     The clamping elements  10  have in their center area a full material transverse cut, which form two lateral transverse ribs  21 , which are particularly pronounced in the upper area of clamping jaw  12 . The area between the transverse ribs  21  is hollowed out form the front edge  16  to a round screw mounting visible in the top view. The screw mounting may, for example, have a conical shoulder surface or a stepped shoulder and is graduated to receive the screw  103  in a through bore in the upper clamping jaw  12 . The ribs may also run entirely along the outer side of the clamping element. 
     In the lower clamping jaw  13 , said transverse ribs  21  lead into a ring flange  22 , which may, for example, have a flat ring-shaped base, which may be connected to a recess produced by injection molding, to save materials and weight, and in the center of which a bore is provided. This through bore is placed so as to be aligned with the aforementioned though bore in the upper clamping jaw  12 . It runs through the clamping element  10  perpendicular to the axis of the free space  11  and parallel to the back side of the hinge  17 . But it could also run diagonally. 
     In the representation in  FIG. 1 , the articulated element  100  is formed from two clamping elements  10 . The lower clamping element  10  is intended for a rod with a diameter of, for example, 12 millimeters. Then the opening on the free end has a diameter of, for example, 8 millimeters, at rest. If the upper clamping element  10  is to be intended for rod with a diameter of 4 to 6 millimeters, then the opening on the free end  15  should have a diameter of, for example, 2 millimeters at rest. 
     In the free space  11 , an insert  50  is inserted that consists of two curved surfaces  51  in the form of hollow quarter-circle cylinders, which are connected to each other by a web  52 . These sections may also be termed jacket elements  51 . The web  52  in its radial direction is specifically thinner than the curved surfaces  51 . The curved surfaces  51  with their outer surfaces  56  in the shape of the outer cylinder jackets touch the inner surfaces of the grooves  14 . The insert  50  used in  FIG. 1  includes two retaining tongues  53  and  54  that extend away from the interior space  58  of the insert  50  and that particularly with the insert with a clamping element  10 , extend between the said ribs  21 . Thus the insert  50  is held securely against axial displacement in the direction of the rod to be inserted. By means of the two tongues  53  and  54 , a twisting of the insert is also prevented. The rounded outer surfaces  55  of the tongues  53 ,  54  in the transition to the curved surfaces  51  of the insert  50  form the insert edges  16  for a rod. The retaining tongues or clips  53  may in general be termed retaining sections. 
       FIG. 2  shows a perspective view of the insert  50  according to the first embodiment for a clamping element  10  according to  FIG. 1 .  FIG. 3  shows a side view of said insert  50  according to  FIG. 2 . The insert  50  is provided with an upper clip  53  oriented in the direction of the connecting web  52 , whereby between the clip  53  and the outer surface  56 , there is a clamping space  57 , in which a portion of the upper clamping jaw  13  is inserted. The clip  53  may be so formed that at rest, i.e. placed in the direction of the outer surface, the insert  50 , after its insertion in the clamping element  10 , is held by the clip  53  under initial tension. The length of the upper clip  53  here is almost as long as the width of the quarter cylinder  51 . The lower clip  54 , on the other hand, is considerably shorter and is oriented perpendicular to the axis of the free space  11 . The material thickness of the clips  53 ,  54  corresponds to that of the quarter cylinder  51  (here elements  51  according to  FIGS. 2 and 3 ). The width of the clips  53  and  54  is advantageously between one-third and two-thirds of the width of the quarter cylinder  51 . The width of the quarter cylinder  51  is preferably of the longitudinal size of the groove  11  of the jaws  12  or  13 . 
     For other embodiments, not shown here, other clip forms are also possible. In particular, the upper clip  53  and/or the lower clip  54  may be made thinner and, in particular, complementary to a slot provided in the upper or lower clamping jaw  12  or  13 . Such a slot would then run parallel to the main axis of a rod  101 ,  102  to be inserted. In this way, the insert may be pressed into clamping element  10  without projecting elements and thus held under continuous tension. The insert  50  may, for example, be a one-piece plastic element. It may also include a co-extruded plastic element with two different types of material, or a metallic element (as or in the hinge). 
     The connecting web  52  here has the same radius of curvature as the surfaces  51 . It is only thinner and when subjected to stress, buckles forward into the free space  11  or backwards out of the free space  11 . 
       FIG. 4  shows a perspective representation of an articulated element  100  according to  FIG. 1  in a locked position with two clamped rod-shaped elements  101  and  102  and an insert  50  according to  FIG. 2 . 
       FIG. 5  now shows a perspective view, diagonally from above, of an insert  60  according to a second embodiment.  FIG. 6  shows a side view of an insert  60  according to  FIG. 5 . The same features are provided in each case with the same reference numbers. The two main differences between the two inserts  50  and  60  according to  FIG. 2  and  FIG. 5  are that the insert  50  according to  FIG. 2  is intended to receive a rod-shaped element of a larger diameter and the curved surfaces  51  of the insert  60  according to  FIG. 5  have a greater material thickness. After insertion of the insert  60 , however, the center axis of the free space  11  is still at the height of the slot. This is not true, for example, for an insert  80 , see  FIG. 14 . 
     Furthermore, the insert  60  according to  FIG. 5  has an undulated web  62 . This web begins to be elongated at the thicker quarter cylinder  51 , i.e. in a tangential direction, in order to form a cam bent inward toward the free space  58 . Thus a longer spring range is created for the web  62 . The two clips  53  and  54  are shaped as in the first embodiment. The web  82  could also be shorter than the longitudinal length of the insert  50  or be interrupted. 
     In an embodiment not represented in the drawings, an insert according to  FIG. 2  may consist of two separate parts, i.e. there is no web  52 . Then two inserts may be used, of which, for example, one consists of surface  51  and clip  53  and another of surface  51  and clip  54 . But two identical inserts are also possible. What is essential then is that these two inserts be clipped in above and below independently of each other. 
     The insert according to the embodiment of  FIG. 5  is designed using a smaller rod-shaped element. Instead of this one insert  60 , it is also possible, (according to an embodiment not represented in the drawings), to use two or more thin concentric shell inserts. Here it should be understood that in order to achieve the effect of a small opening  58  in an insert  50  according to  FIG. 2 , which is already inserted in  FIG. 1 , an additional shell insert is inserted, which is an insert that is placed concentric to the first insert  50 . The inner shell insert then has a surface  51  that leans with its upper side  56  onto the inner side of the insert  50  and it will preferably have a clip that on the outside lies on the first clip  53 . There may then also be a third shell insert, in order to reduce the opening  58  by one additional step. Thus a kit is formed, the different inserts of which form a sequence of jacket elements  51  which may be inserted concentrically into one another. 
     The embodiments described here are all designed concentrically with respect to the rod to be inserted. It should be noted already here—in anticipation of the embodiment according to FIG.  10 —that a corresponding eccentric embodiment of the insert  50  or  60  is possible. This means that the quarter-circle cylinders  51  are so termed only for their outer surface  56 , since these continue to touch a surface designed for a rod-shaped element. On the inner side, however, another asymmetric form may then be provided, which in cross section may, for example, be a triangular groove. This then allows the insertion of rods of various sizes, that are all positioned the same way with respect to one plane. 
       FIG. 7  shows a side view of an articulated element  100 , as represented in  FIG. 4 , with an insert  60  according to  FIG. 5  in the lower clamping element  10 . 
       FIG. 8  shows a perspective view, diagonally from above, of an insert  70  according to a third embodiment.  FIG. 9  shows a side view of the insert  60  according to  FIG. 5 . The sole difference between the two inserts  60  and  70  according to  FIG. 5  and  FIG. 8  is that the insert  70  according to  FIG. 8  has only one clip  53 . The clip  53  is provided for engagement in the area between the ribs  21  of the outer clamping jaw  12 . Thus there is no clip for the inner clamping jaw  13 ; but the outer impression surface  55  extends over the entire length of the insert  70 , while on the opposing side the impression surface  55  for a rod projects onto clip  53  and, as in the previously described embodiments, there is a back edge  75  to the right and left. 
       FIG. 10  shows a perspective view of an insert  80  according to a fourth embodiment,  FIG. 11  a side view of the insert  80  according to  FIG. 10 , and  FIG. 12  another perspective view of the insert  80  according to  FIG. 10 , diagonally from underneath. This insert  80  may be most easily explained with a look at  FIG. 13 , in which a perspective view of another articulated element  110  with two other clamping elements  20  and with an insert according to  FIG. 10  and a rod  101 , here a so-called “pin” clamped securely, is represented. The clamping element  20  essentially corresponds to a clamping element pursuant to EP 0 700 664. 
     The insert  80  has a quarter cylinder  51  that is still recognizable by its outer surface  56 , but that has an underside that in section has a very reduced radius of curvature, and thus forms an upper boundary for a small free space  88 . The insert  80  has an oval recess  81 , going backwards in the top view, which thus forms a recess for the screw  103 . As guide grooves, two projections  83  are provided in the recess  81 . The thickened quarter cylinder  51 , which with its outer surface  56  engages an outer jaw  12 , passes over into a flat even web surface  82 , which comes to rest between the outer jaw  12  and the inner jaw  13  of a clamping element  20 . In this way the insert  80  is secured in its position in the articulated element  110 . 
     Through the existence of the backward recess  81 , two lateral webs  82  are created and the insert  80  may then be inserted sideways, as later a rod, into the articulated element  110 , whereby before securing of the elements, the projections  83  hold the insert  80  in the articulated element  10 . The front side  84  of the insert  80  then connects to the front side of the clamping element  20 . The webs  82  each have side slots  85 , which run in a radial direction to the main axis which runs transverse to it, and which corresponds to the orientation of the screw  103 . In this way, it is also possible to insert a metallic insert  80 , since if the screw  103  snaps onto the projections, the side webs  82  bend into the slots  85 . 
     In  FIG. 13  and  FIG. 14 , which represents a side view of the articulated element  120  according to  FIG. 13 , the application of insert  80  with a very thin rod or pin  101 , having a diameter of 4 to 6 millimeters, is shown. It may be seen that in the fourth embodiment of insert  80 , the pin  101  lies on one side on the inner jaw  13 , while on the other side, it touches the insert  80 . The insert  80  is shorter than the depth of the clamping element  20 , since for anti-twist protection, the two jaws  12  and  13  are provided with recess or complementary projection  86 . 
       FIG. 15  shows a perspective view of an insert  90  according to a fifth embodiment for a clamping element  20 ,  FIG. 16  a side view of the insert  90  according to  FIG. 15 , and  FIG. 17  a top view of the insert  90  according to  FIG. 15 . The insert  90  according to  FIG. 15 , in contrast to the insert  80  according to  FIG. 10 , has side ribs  92 , which may project next to the jaws  12  or  13  of the clamping element  20 . They may also be fitted into corresponding recesses in the jaws  12  or  13 . Thus, in addition to the anchoring deep inside the opening  81  around the screw  103 , the insert  90  is also protected against lateral displacement. The additional features of this insert  90  correspond to those of the insert  80  according to  FIG. 10 . 
     Finally,  FIG. 18  shows a detail from an external fixator with several articulated elements  100  and various rods  101 ,  102  held by these, with various inserts  50  and  60  in different configurations. The articulated elements  100  are each constructed out of two clamping elements  10 , with which a clamping of a thick rod, of 10 to 12 millimeters, is possible. The rod  102  of medium thickness used here has a diameter of between 6 and 8 millimeters and requires an insert  50  for the reduction and adaptation of the diameter of the rod to be clamped by, for example, 2 millimeters. In the other clamping element  10 , an insert  60  is used for the reduction and adaptation of the diameter of the rod  101  to be clamped to, for example 4 millimeters, since the thinner rod  101  used here has a diameter of between 6 and 8 millimeters. It is thus clear that in using the clamping element  10  with no insert, with an insert  50  or with an insert  60 , three possible rod thicknesses may be used. 
     In the embodiment according to  FIG. 14 , as a guide for the thin rod  101 , in addition to the insert  80  on the opposite side on the bottom of the groove  14  of the lower clamping jaw  13 , the two serrated elevations (not visible in the drawings) on both sides of groove  14  symmetrical to the center line, may be used. These support a thin rod that has been inserted each from the respective side. 
     The materials of the clamping elements  10 ,  20  and the inserts  50 ,  60 ,  70 ,  80 ,  90  may respectively be chosen from among plastic, fiber-reinforced plastic, metal and particularly titanium or a steel. It is also possible, as noted above, to use mixtures, in particular co-extruded elements. Interestingly, inserts  50 ,  60 ,  70 ,  80 ,  90  are of a softer plastic, which effectively prevents a longitudinal slippage or twisting of the rods  101 ,  102  in the insert. This also makes the use of thinner inserts practical, which are inserted not for reduction of thickness, but primarily or exclusively to improve the bond. Then the aforementioned quarter cylinders  51  are very thin and no thicker than the aforementioned web  52 ,  62 . 
     The clips  53 ,  54  are not only guide- and fixing elements, but also operating elements. The clips  53  and  54  should be able to be gripped by the user in order to engage the inserts  50 ,  60  etc. and to take them out or insert them into a clamping element  10 . 
       FIG. 19  shows a perspective view of an insert  140  according to the sixth embodiment for a clamping element  10  according to  FIG. 1 .  FIG. 20  shows a side view of said insert  140  according to  FIG. 19 . The insert  140  has an upper clip  53  oriented in the direction of the connecting web  52 , whereby between the clip  53  and the outer surface  56 , there is a clamping space  57 , into which a portion of the upper clamping jaw  13  intrudes. For these a groove  63  that runs lengthwise is provided in this latching space  57 , which may be shaped complementary to a corresponding elevation in the clamping element  10 . Furthermore, this thinning may enable an easier grip by the clip  53 , as will be seen below. 
     The clip  53  may be shaped so that at rest, i.e. oriented in the direction of the outer surface, the insert  50 , after its insertion in the clamping element  10  is held under initial tension by the clip  53 . The length of the upper clip  53  is here almost as long as the width of the quarter cylinder  51 . It has a base  73  at a slight distance from the clamping element  10  for easier gripping. 
     The lower clip  54 , in contrast, is significantly shorter and is oriented perpendicular to the axis of the free space  11 . The material thickness of the clips  53 ,  54  may be modified and other clip forms are possible. For this, reference may be made to the features of the descriptions of the other embodiments. 
     The connecting web  52  here shows a smaller radius of curvature than the jacket surfaces  56  of the elements  51 . It is designed to be much thinner and when subjected to stress, buckles forward into the free space  11  or backwards out of the free space  11 . 
     Particularly advantageous in this embodiment is the provision of several (two or more), here three, recesses  141 ,  142 , and  143 . These, identified as small, medium and large receiving grooves  141 ,  142 , and  143 , running in a transverse direction in the upper and lower portions of the inserts  140 , permit the versatile insertion of the clamping element  10 . In addition to the insertion of a rod of, for example, 15 millimeters in the clamping element  10  per se, by using a single insert  140 , one can work with this clamping element with rods of, for example, 4, 5 or 6 millimeter diameters in the free spaces formed by grooves  141 ,  142  or  143 . 
     The clamping is thus also advantageous in that in closing, the halves of the inserts generally become too displaced against each other, and less tilting of the insert halves  51  must take place. There is a smaller clamping distance than previously. 
     The arrangement of the three possibilities next to each other allows the surgeon to concentrate on the selection of the best pin-/rod material with respect to its size, and not to have to concern himself with questions of compatibility of the clamps. Naturally, it is also possible to provide only two alternative clamping grooves, which may also have diameters other than those mentioned. The smallest groove  141  is here the farthest away from the lateral insertion opening, so that the positions for laterally-inserted rods from the lateral opening through the groove  143  and on to groove  141  become smaller in each case. In principle, a reversed arrangement of the grooves is also possible, so that the grooves  141  for the smallest rod diameter are nearest to the entry areas  55 . 
       FIG. 21  shows a perspective view of an insert  150  according to a sixth embodiment for a clamping element  10  according to  FIG. 1 .  FIG. 22  shows a side view of said insert  150  according to  FIG. 21 , and  FIG. 23 , a sectional front view of the insert  150 . 
     The seventh embodiment has in common with the sixth embodiment described in  FIGS. 19 and 20  the fact that there are three receiving grooves  141 ,  142  and  143 , which extend along the main axis of the insert  150 . The receiving grooves  141 ,  142  and  143  form in cross-section a sector with a radius of 4, 5 or 6 millimeters, the center of which lies on the median axis of insert  150 . The smallest groove  141 , which is the farthest from the lateral insertion opening, in fact fills in a three-quarters circle in cross section. This means that the web  52  is designed here as remaining material between the inner radius of the grooves  141  and the outer radius of the outer jacket surfaces  56 . 
     Instead of a clip oriented toward the opening, a flange  153  is provided here on the one side, which is designed in a C-shape. It has free ends  154 , which fit into complementary recesses in a clamping element. In particular, the free ends  154  each have a cam  155 , which with its projecting step hooks in, and at the same time may form a gripping element. The connecting section  156  of the flange  153  that is opposite the free ends may in other embodiments also be made thinner or left out entirely, in order not to hinder the flexible movement of the web  52  in clamping. The front- and back-side openings in the grooves  141 ,  142  and  143  have bevels  159 , in order to allow a longitudinal insertion of rods. 
     Thus this insert  150  has two opposing jacket elements  51  that define, across the lengthwise direction of the rod-shaped elements to be inserted, a sequence of here three longitudinal receiving grooves  141 ,  142 ,  143  for rod-shaped elements of varying diameters. For reasons of space, the distance of the midpoint of the circle of the receiving grooves  141 ,  142 ,  143  lying on the median axis of the insert is smaller than the diameter of the rod determined by it. The medium receiving groove  142  thus is concentric to the jacket surface  56  of the insert  150 . The distance from this to the smaller receiving groove  142  next to the web is smaller than the distance to the larger receiving groove  143  next to the opening. 
     For an embodiment of a clamping element not shown in the drawings, the edge  158  that runs around the flange, particularly on the portions leading to the free ends  154 , is essential. In this clamping element, which is not depicted, complementary outer surfaces of the clamping jaws  11  and  12  surround these edges  158  and full cams extend from the clamping jaws  11  and  12  and lie between the areas of the free ends  154 , which are indicated by the reference number  157 . Thus the clamping jaws  11  and  12  when clamped press the free ends  154  onto one another and onto the cams that are provided in the area  157 . The clamping effect that is produced prevents the lengthwise displacement of the insert  150  and strengthens the holding quality, as the flange  153  itself is pressed by the clamping jaws  11 ,  12 . 
     It should be stressed that the term embodiment in the aforementioned description does not mean that only the elements of the respective insert, clamping element or articulated elements are the subject of the invention. There are, in particular, also combinations of features that are possible, that are described in the subjects of various figures. Thus, the slots  85  can also be provided in the webs  52 ,  62 ; the clips  53 ,  54  may have the entire width of the inserts and may also be slotted, in order to go around the ribs  21 ; the clip  53  may also, like the side rib  92 , be used in inserts  80 ,  90 , and the side ribs  92  can form a side border to inserts  50 ,  60 ,  70 . The scope of protection is thus not limited to the embodiments represented in the drawings, but may be taken only from the attached claims.