Abstract:
A fixation clamp for use in an external fixation system for holding bone fragments adjacent to each other with the help of fixation elements has at least one clamping assembly having a pair of jaws with at least two different size grooves to accommodate a bone fixation element such as a pin or rod. An alternate clamping assembly has at least three grooves wherein at least two of the grooves have a different size adapted to accommodate a correspondingly sized bone fixation element such as a bone pin. The longitudinal axes of the grooves define a polygon. The jaw pairs can be rotated about a central longitudinal axis to present different size reception cavities towards the pins or rocks depending on their diameter.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/780,231, filed May 14, 2010, which claims the benefit of European Patent Application No. 09160445.4, filed May 15, 2009, entitled Fixation Clamp, the disclosures of which are hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a fixation clamp and, more particularly, to a fixation clamp for use in an external fixation system for holding bone fragments adjacent to each other. 
         [0003]    External fixation systems are widely used to connect two or more bone fragments to each other. Such systems comprise bone screws, pins, wires which are inserted directly into the bone material and these systems use external structural elements as fixation rods, bars and rings. In order to connect the rods and bars to form a rigid frame, fixation clamps are used. Furthermore, fixation clamps are used to connect this screws and pins to the rigid frame to specifically hold bone fragments at an intended place. 
         [0004]    One adjustable fixation clamp is known from U.S. Pat. Nos. 5,752,954 and 6,080,153, the disclosures of which are incorporated herein by reference, comprising two pairs of jaws allowing clamping of a rod as well as of a pin. 
         [0005]    A clamp for multiple rod-shaped elements is known from U.S. Pat. No. 7,618,417, the disclosure of which is incorporated herein by reference, having one single pair of jaws. However, such a clamp allows clamping more than two, e.g. three or four rod-shaped elements such as pins with one single clamp, thus reducing the number of clamps. However, one further fixation clamp is necessary to fix the rod of said clamp to the frame of the fixation system. 
         [0006]    U.S. Patent Publication No. 20060287652 discloses that the usual fixation clamps as e.g. known from U.S. Pat. No. 6,080,153 allow clamping of one single screw or pin to the frame and that this way to attach pins or rods leads to bulky fixation systems. Therefore U.S. Patent Publication No. 20060287652 discloses a fixation clamp addressing this problem and comprises two pairs of jaws within which each pair of jaws allows the introduction and clamping of two rods or pins etc. at the same time. 
         [0007]    These clamps according to the prior art either provide different diameters of the reception cavities, such as grooves, provided by the jaws to introduce different sizes of rods, pins or wires, or they rely on additional inserts as e.g. disclosed in U.S. Patent Publication No. 20080065068. Such inserts reduce the diameter of the reception cavities to allow a secure fixing of differently sized rods, pins or wires. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Solutions according to the prior art providing different diameter reception cavities necessitate provision of either a variety of different clamps or additional inserts. 
         [0009]    It is one aspect of the invention to overcome this problem and to provide the practitioner with a fixation clamp, especially for use in an external fixation system, which clamp can directly be used with a variety of differently sized rods, pins, screws and wires. 
         [0010]    A fixation clamp for use in an external fixation system for holding bone fragments adjacent to each other with the help of fixation elements includes at least one clamping assembly, and a central locking shaft extending through the one or more clamping assemblies for blocking the position of the clamping assemblies in a defined angular position; wherein each clamping assembly comprises two jaws, wherein each jaw comprises three grooves. The longitudinal axis of each groove is perpendicular to the locking shaft. One groove of one jaw corresponds to one groove of the other jaw to form a cavity to accommodate a bone fixation element. The longitudinal axes of the grooves may span a triangle, and wherein at least two grooves have a different size adapted to accommodate a correspondingly sized fixation element. The fixation clamp groove may have a different size. The fixation clamp for use in an external fixation system for holding bone fragments adjacent to each other with the help of fixation elements also may include at least one clamping assembly having jaws mounted on a locking shaft, each jaw having four grooves forming a cavity to accommodate a bone fixation element along the longitudinal axis of the groove. The longitudinal axes of these grooves form a quadrilateral. At least two grooves have a different size adapted to accommodate a correspondingly sized fixation element. Each groove of the fixation clamp has a different size wherein two opposite grooves have the same size. The fixation clamp for use in an external fixation system for holding bone fragments adjacent to each other with the help of fixation elements may have at least one clamping assembly including at least one pair of jaws mounted on a locking shaft having five grooves to accommodate a bone fixation element along the longitudinal axis of the grooves. The longitudinal axes of the grooves form a pentagon, and in that at least two grooves have a different size adapted to form a cavity to accommodate a correspondingly sized fixation element. Each groove set forms a different size cavity. The grooves of all clamping elements may be circular or triangular in crossection and may comprise longitudinal ribs. Each clamping assembly preferably comprises an anti-rotation pin extending from a first jaw into a complementary recess in an opposite jaw. The grooves may be provided within outer side walls of each jaw in a way that the surface of a fixation element pointing away from the locking shaft when inserted into one groove is flush with the corresponding side wall. 
         [0011]    A fixation clamp for use in an external fixation system for holding bone fragments adjacent to each other with the help of fixation elements includes a first and a second jaw member. A central locking shaft extends through the first and second jaw members wherein each jaw member comprises at least three grooves. The longitudinal axis of each groove lies in a plane perpendicular to a longitudinal axis of the locking shaft. One groove of the first jaw member corresponds to one groove of the second jaw member to form a cavity to accommodate a bone fixation element. The longitudinal axes of the grooves are all non-parallel in the plane. The first and second jaw members have a face parallel to the plane containing the longitudinal axis of the at least three grooves. An anti-rotation pin extends perpendicular to the plane of the face of the first jaw extends into a bore in the planar face of the second jaw member. The pin and bore are located within a geometric shape formed by the grooves. The fixation clamp for use in an external fixation system for holding bone fragments adjacent to each other with the help of fixation elements may have first and second jaw members having four grooves to accommodate a fixation element along the longitudinal axis of the groove wherein the longitudinal axes of said grooves form a quadrilateral. At least two grooves have a different size adapted to accommodate a correspondingly sized fixation element. 
         [0012]    The fixation clamp for use in an external fixation system for holding bone fragments adjacent to each other with the help of fixation elements may include first and second jaw members having five grooves to accommodate a fixation element along the longitudinal axis of the grooves. The longitudinal axes of the grooves form a pentagon, and in that at least two grooves have a different size adapted to form a cavity to accommodate a correspondingly sized fixation element. 
         [0013]    The clamp according to the invention allows readily treating different types of fractures or connecting bones of different sizes to each other, since usually different pin diameters are required. The clamp provides a plurality of different couplings possibilities which is an advantage, avoiding mismatching of components, which can lead to insufficient connecting strength. The clamp according to the invention also allows for clicking in rods from the side. The clamp can be built based on the usual metallic components and can comprise non-magnetic and non conductive materials, which are safe for temporary exposition in a MRI scanner, and can furthermore comprise plastic or composite materials or have electrical insulating cover surfaces. 
         [0014]    It is an advantage of the clamp according to the invention that after having clamped a bone screw with one clamping assembly, a practitioner attaching subsequently a rod of an external fixator to the other clamping assembly can check the robustness of the external fixator, and if the practitioner finds that the rod used is not stiff enough, one simply opens the other clamping assembly, removes the thinner rod, turns the other clamping assembly e.g. 60 degrees into one direction or the other around the longitudinal axis to align a larger reception cavity with the new thicker rod and replaces said rod. This change does not necessitate the replacement of the clamp itself and is thus faster and more reliable since the clamping of the bone screw is not changed, and the use of a second sterile clamp at said time is avoided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Preferred embodiments of the invention are described in the following description with reference to the drawings, which are provided for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings, 
           [0016]      FIG. 1  is an exploded view of a first embodiment of the clamp of the present invention; 
           [0017]      FIG. 2  is a top view of the clamp according to  FIG. 1 ; 
           [0018]      FIG. 3  is a first side view of the assembled clamp of  FIG. 1 ; 
           [0019]      FIG. 4  is a second side view of the assembled clamp of  FIG. 1  from a different direction than  FIG. 3 ; 
           [0020]      FIG. 5  is a top view of an inner jaw portion of the clamp according to  FIG. 1 ; 
           [0021]      FIG. 6  is a top view of an outer jaw portion of the clamp according to  FIG. 1 ; 
           [0022]      FIG. 7  is a cross-section of the clamp shown in  FIG. 4 ; 
           [0023]      FIG. 8  is an exploded view of a second embodiment of the clamp of the present invention; 
           [0024]      FIG. 9  is a top view of the clamp shown in  FIG. 8 ; 
           [0025]      FIG. 10  is a cross-section of the clamp of  FIG. 8  along line X-X of  FIG. 9 ; 
           [0026]      FIG. 11  is a top view of the clamp of the present invention with two attached fixation elements; 
           [0027]      FIG. 12  is a front view of the clamp with two attached fixation elements according to  FIG. 11 ; and 
           [0028]      FIG. 13  is a right side view of the clamp of  FIG. 11  with two attached fixation elements. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Referring to  FIG. 1  there is shown a perspective exploded view of a preferred first embodiment of a clamp  10  pursuant to the invention. The clamp  10  consists of a first clamping assembly  20  and a second clamping assembly  30  and a shaft  40  which is positioned through bores  21 ,  31  within the two clamp assemblies  20 ,  30  along the longitudinal axis of shaft  40 . Each clamping assembly has a first jaw  11  and a second jaw  12 . Shaft  40  is preferably a locking element adapted to allow the closing the clamp assemblies  20  and  30 . Shaft  40  enters a first jaw  11  through a washer  41 . Washer  41  may have a part-spherical shape for receipt on a part-spherical surface of bore  21 . The shaft  40  comprises a proximal portion  42  and a reduced diameter portion  43  which is followed by a threaded portion  49 . The outer threaded portion  49  is adapted to be screwed into a complementary inner thread which may be formed within the distal most jaw  11  (bottom jaw of  FIG. 1 ) so that turning the head of the shaft  40  changes the longitudinal position of the shaft  40  against the bottom jaw  11 . This allows for opening or closing the entire clamp  10  against the force of a spring  15  provided between the two clamp assemblies  20  and  30 . Obviously a separate nut could be provided rather than threading the bore in lowermost jaw  11  of  FIG. 1 . Spring  15  is preferably positioned in corresponding reception cavities in jaws  12 . Instead of a spring  15 , provided around shaft  40 , it is possible to provide a different spring means as Belleville washers or an elastic compressible solid or foam. Upon closing of the clamp assemblies  20  and  30  the jaws  12  adjacent spring  15  can eventually come into contact and then the anti-rotation surface  44  which is provided in both surfaces of the jaws, fixes the angular orientation of each clamping assembly  20  and  30  against each other. 
         [0030]    Preferably after having mounted the shaft  40  with the thread  49  within the bottom jaw  11 , the end portion of the thread  49  is deformed or destroyed through pressure to ensure that the shaft  40  cannot be removed from the clamping assemblies  20 ,  30  to maintain the clamp as one single piece. 
         [0031]    As discussed above, each clamping assembly  20  or  30  comprises two opposing clamping jaws  11  and  12 . These jaws  11  and  12  are essentially similarly shaped on the sides facing each other except for a pin  13  which extends into a corresponding bore  14  in clamping jaw  12 . This pin-bore connection which is oriented along or parallel to the longitudinal axis of the clamping device is an anti-rotation device for jaws  11  and  12 . Once engaged jaws  11 ,  12  cannot change their mutual angular orientation. The plane surface of jaw  11  facing the plane surface of jaw  12  is provided with three spacers  17  arranged in the corners of the surface. The spacers  17  have a mostly triangular form and a height to allow the function of a counter bearing as explained below. Additionally, the spacers  17  result in the two plane surfaces of jaws  11  and  12  being spaced so that the open areas between these surfaces can be cleaned. 
         [0032]    The jaws  11  and  12  are provided with three grooves  51 ,  52  and  53 . Grooves  51 ,  52  and  53  are all provided in a same plane perpendicular to the longitudinal axis of shaft  40 . In that plane they are oriented perpendicular to the radial direction from the center of the bore  21  or  31 . As such the grooves  51 ,  52  and  53  are parallel to outer side wall  61 ,  62  or  63  of each pair of triangularly shaped jaws  11  and  12 . 
         [0033]    Each pair of grooves  51 ,  52  or  53 , respectively, in each jaw  11  and  12 , define one reception cavity, i.e. a first reception cavity  71 , a second reception cavity  72  and a third reception cavity  73 . The grooves  51 ,  52  and  53  are each formed as a rounded semi-spherical recess in section to provide reception cavities  71 ,  72  and  73  which accommodate cylindrical pins or rods  100  with a defined diameter (see  FIGS. 11 to 13 ), if the clamp is closed. The outer side walls  61 ,  62  or  63  can comprise an inclined sliding surface to allow for easy clipping or snapping in of such pins or rods  100  into the corresponding cavities. The grooves  51 ,  52 ,  53  are formed as rounded semi-spherical recesses in a section. This means that the recesses provided by the grooves  51 ,  52 ,  53  have a hollow cylindrical shape to accommodate rod-shaped elements. 
         [0034]    All three grooves  51 ,  52  and  53  have different sizes so that the corresponding reception cavities  71 ,  72  and  73  have three different sizes. In other words each reception cavities  71 ,  72  or  73  is adapted to accept a different fixation element, i.e. a rod, screw, pin or wire having a different diameter. One preferred embodiment of the first clamping assembly  20  has grooves to accept fixation elements having a diameter of 12 mm, 8 mm and 5 mm, respectively. A different embodiment may have a sequence of diameters of 8 mm, 6 mm and 4 mm, respectively. 
         [0035]    The second clamping assembly  30  according to the embodiment of  FIG. 1  also comprises two jaw portions  11  and  12  and these comprise three grooves  51 ,  52 ,  53 . These grooves  51 ,  52 ,  53  also comprise a sequence of different sizes. In the embodiment shown the inner jaws portion  12  have an identical structure as have the outer jaws  11 , especially in view of the anti-rotation device  44 , the second bore for a spring  15  as well as ribs  45  inside the grooves  51 ,  52 , and  53 . 
         [0036]    Within a preferred embodiment the first clamping assembly  20  may comprise a sequence of smaller size cavities, e.g. 7 mm, 5 mm and 3 mm; or 6 mm, 5 mm and 4 mm; and the second clamping assembly  30  may comprise a sequence of larger sizes, e.g. 13.5 mm, 12 mm and 10 mm. Different sizes are possible, usually for wires starting from 2 mm diameter up to thicker rods with a diameter of 30 mm are used within such a clamp  10 . Such a clamp  10  allows the use of one single versatile clamp, wherein the first clamping assembly  20  is used to fix a specific pin or screw or wire having a diameter for which one of the reception cavities  71 ,  72  or  73  is adapted. The user takes the clamp  10  and orients or rotates the first clamping assembly  20  into the correct alignment so that the pin or screw can be clipped into the corresponding reception cavity. 
         [0037]    Then the clamp  10  can be clamped on a rod of an external fixator with the help of the second clamping assembly  30 . The second clamping assembly  30  can be oriented in a way so that the rod can be clipped into the corresponding reception cavity. It is an advantage of the clamp  10  having two clamping assemblies  20  and  30  according to the invention, that a practitioner attaching such a clamp at a bone screw with one clamping assembly  20  and subsequently a rod of an external fixator to the other clamping assembly  30  can check the robustness of his external fixator, and if it is found that the rod used is not stiff enough, one simply opens the second clamping assembly  30 , removes the thinner rod, turns the second clamping assembly  30  e.g. 60 degrees in one direction or the other around the longitudinal axis, to align the larger reception cavity with the new thicker rod and replaces it. This change does not necessitate the replacement of the clamp  10  itself as necessary with prior art systems. The method to replace such a rod  100  is faster and more reliable since the clamping of the bone screw is not changed, and at the same time avoids use of a second sterile clamp. 
         [0038]    It is of course also possible that the second clamping assembly  30  is a traditional clamping assembly or even any other element known in the prior art with clamping elements. The object of a versatile clamping assembly is already achieved through one first clamping assembly  20 , since it allows clamping one of three different sizes of screws, pins of wires through simple reorientation of the first clamping assembly  20 . 
         [0039]      FIG. 2  shows a top view of the clamp according to  FIG. 1 . Since the embodiment of  FIG. 1  comprises three grooves  51 ,  52  and  53 , there are three side walls  61 ,  62  and  63 , which provide, when looked from above as in  FIG. 2  a triangular shape of each clamping assembly  20  or  30 . 
         [0040]      FIG. 3  shows a first side view of the clamp of  FIG. 1  and  FIG. 4  shows a second different side view of the clamp  10  of  FIG. 1  from a different direction. Identical reference signs are used for identical features within the same embodiment and are used for identical or similar features in further embodiments. 
         [0041]    It is clear from  FIG. 3  that the first reception cavity  71  is identical in size and allows for insertion of a large rod. From  FIG. 4  it can be seen that the third reception cavity  73  are small cavities, e.g. for a pin. In this embodiment, second cavities  72  have an intermediate size. From  FIG. 4  it can be seen that the depicted embodiment has a decreasing size sequence of reception cavities  71 ,  72  and  73  in the upper first clamping assembly  20  in clockwise direction whereas the depicted embodiment has a decreasing size sequence of the reception cavities  71 ,  72  and  73  in the lower second clamping assembly  30  in counter-clockwise direction. 
         [0042]    Referring to  FIG. 5  there is shown a top view of an inner jaw portion  12 , whereas  FIG. 6  shows a similar view on a corresponding outer jaw portion  11 . It is clear that each jaw portion  11  or  12  of any clamping assembly  20 ,  30  according to the invention comprises three differently sized grooves  51 ,  52  and  53 , respectively. The longitudinal axes of these grooves  51 ,  52  and  53  are oriented in an angle of 60 degree one to another. However, these angles of 60 degree are not mandatory. It is only necessary that the total internal angle of the triangle provided by these three grooves  51 ,  52  and  53  is 180 degrees. The grooves are also in the same median plane which indicates that only one pin, screw or rod can usually be introduced in one of the grooves  51 ,  52  or  53  and such an introduction blocks the other empty grooves. It is an aim of this orientation to provide a simpler mounting of a fixation device, since based on the chosen pin or screw a clamp of the invention can be chosen and through rotation of the clamping assembly the correct sized reception cavities  71 ,  72  or  73  is usable for a well clamped connection, wherein the clipping of the pin or screw from the open side further facilitates their introduction. 
         [0043]    It is clear from  FIGS. 5 and 6  that the grooves  51 ,  52  and  53  mutually intersect. The inner jaw portion  12  shown in  FIG. 5  comprises ribs  45  which are oriented in the longitudinal direction of the grooves  51 ,  52  and  53 . Each groove is provided with two lines of ribs  45 , which are arranged one behind the other and thus can also be described to be a single line interrupted in the middle part. Of course there may be one or no ribs  45 , or there may be more than two lines, and these lines can be provided uninterrupted, although the embodiment with interrupted ribs  45  as well as two lines of these ribs  45  is preferred. 
         [0044]    It is possible to deviate from the correct triangular orientation of the grooves; especially the angle between the largest groove  51  and the neighboring grooves can be less than 60 degree, so that the angle between the longitudinal axes of the grooves  52  and  53  is greater then 60 degrees. 
         [0045]    It is also possible, in different embodiments, not shown in the figures, to provide four, five or more grooves. If four grooves are provided, then the form of such a clamping assembly  20  seen from above is a square and each jaw comprises four grooves joining in the corners in at preferably a right angle. Then a sequence of four sizes of the reception cavities is possible as 12 mm, 8 mm, 6 mm and 4 mm. If five grooves are provided, then the form of such a clamping assembly  20  seen from above is a pentagon and each jaw comprises five grooves joining in the corners, preferably at an angle of around 108 degrees. Then a sequence of five sizes of the reception cavities is possible as 12 mm, 20 mm, 8 mm, 6 mm and 4 mm. Of course deviations from such a symmetrical polygon are possible. 
         [0046]    It is noted that the spacers  17  and thus the counter bearings as well as the corners of the jaw planes are not symmetrically positioned in view of the central bore  21  of a jaw. The deviation from the symmetric form is smaller for the largest reception cavity  71  and larger for the smallest reception cavity  73 . However, this is not problematic, since the largest reception cavity  71  with the smallest deviation accepts the largest rod and thus the largest forces, wherein the largest deviation occurs for the smallest reception cavity and the function of such a small reception cavity resides in accepting a limited force. 
         [0047]      FIG. 7  shows a cross-section of the clamp according to  FIG. 4 , wherein the clamp  10  is shown in a premounted state, i.e. the spring  15  is under tension. The upper jaw  11  of the first clamping assembly  20  is therefore pushing the rounded counter piece  41  against a flange  40   a  of the head of shaft  40 . The jaw  11  has around its bore  21   a  rounded part-spherical recess to accommodate the washer  41 . This enables a pivoting movement of the upper jaw  11  against the axis of the shaft  40 , since the shaft  40  comprises a reduced diameter portion  43  extending over the whole length of the jaws  11  and  12  in both assemblies. It is also possible that there is no play between shaft  40  and jaw  11 ; the bore  21  just allows the introduction of the shaft  40 . Then jaw  11  and jaw  12  can only effect a translatory movement. 
         [0048]    The pin  13  of the upper jaw  11  is lodged in a recess  16  in the bore  14 . It is possible but not necessary that the pin  13  or the recess  16  receives an elastic fitting piece allowing elastic movements of the pin within the recess  16 . 
         [0049]    The shaft  40  as part of a locking element is threaded into the lower jaw  11  of the second clamping assembly  30  and is further connected with a counter nut  46 , which is fixedly lodged on shaft  40 . Therefore the two clamp assemblies  20 ,  30  can be opened and closed through turning the head of shaft  40  and thus turning shaft  40  with the blocking counter nut  46  and in the jaw thread. The counter nut  46  can then be used to lock shaft  40  from further rotation 
         [0050]    The combination of shaft  40  and counter nut  46  can also be replaced by a single screw to be screwed into the lower jaw  11  of the second clamping assembly  30 . Threading may be provided in the bore or the screw may exhibit self-tapping threading. Quite generally, a locking element may be provided which may be a lever locking element or a bayonet lock. Among these locking elements may also be supporting disks or toothed disks, which, for the sake of simplicity, are not shown in the drawings. 
         [0051]      FIG. 8  shows an exploded view of a second embodiment of a clamp  10   a  of the present invention;  FIG. 9  shows a top view of the clamp and  FIG. 10  shows a cross-section of the clamp along line X-X in  FIG. 9 . The sequence of sizes for the first clamping assembly  20   a  is 13.5 mm, 8 mm and 5 mm. The choice of this sequence depends on the intended application (e.g. which limb is to be treated) of the external fixator set and follows the needs of the application. 
         [0052]    The clamping assemblies  20   a ,  30   a  of the embodiment have a triangular form, as can be seen from  FIG. 9 , having defined straight side walls  61 ,  62  and  63  and identically curved transitory portions. For a description of features which are identical to the clamp of  FIG. 1  reference is made to that description. 
         [0053]    Instead of spacers  17  in the corners of the plane surface of the jaws  11   a  there are provided two flattened semi-spherical spacers  27  on the surface. As mentioned above, the first clamping assembly  20   a  comprises a sequence of larger sized reception cavities  71 ,  72 ,  73 . The lower second clamping assembly  30  comprises a different sequence of smaller sized reception cavities  71 ,  72 ,  73 . The corresponding grooves  51 ,  52  and  53  within the lower jaw  11   a  are not semi-spherical as with the clamp of  FIG. 1  but are triangular or v-shaped grooves  51 ,  52 ,  53  having a bottom line  54  of a v-shaped groove. The corresponding groove portion in the opposite jaw  12   a  is a rounded groove, in  FIG. 10  receiving the numeral  55 , so that slightly different sizes of elements can be clamped. However, the sizes of the grooves  51 ,  52  and  53  are nevertheless different one from the other. 
         [0054]    Usually the rounded grooves are intended to be used especially with carbon rods and allow high precision clamping under all circumstances, whereas the triangular grooves are more flexible. They usually provide two sizes with one groove, e.g. 4-5 mm, 5-6 mm and 7-8 mm for three grooves. 
         [0055]    Element  47  is a steel helicoil inserted into an aluminum jaw  11   a  to provide a better counter thread for the thread  49  of shaft  40 . The end portion  49  of shaft  40  is hollow with an additional inner thread to accommodate the outer thread  58  of a counter nut  48 . 
         [0056]      FIG. 11  shows a top view of the clamp  10   a  of the present invention with two attached fixation elements  100  and  101 .  FIG. 12  shows a front view of the clamp according to  FIG. 11 ; and  FIG. 13  shows a view from the right. 
         [0057]    The fixation elements shown here are small-sized rods. Fixation element  100  is introduced in the smallest size reception cavity  73  of the first clamping assembly  20  leaving the middle-sized reception cavity  72  and the large-size reception cavity  71  empty. From  FIG. 12  it can be seen that the introduction of rod  100  blocks the section of reception cavity  72 . From  FIG. 13  it can be seen that the introduction of rod  100  also blocks the section of reception cavity  73 . Therefore a clamping assembly  20  is usable for one single rod or pin at the same time, here rod  100 . 
         [0058]    The same is true for rod  101  used in connection with the second clamping assembly  30   a . In this embodiment, the two clamping assemblies have an identical sequence of reception cavity sizes, i.e. there are three sizes of reception cavities twice in the clamp  10   a . As mentioned above it is possible to provide different reception cavity sizes in the two clamping assemblies  20 ,  20   a  and  30 ,  30   a . Therefore it is possible to have up to six different sizes of reception cavities within one clamp consisting of two clamping assemblies according to the invention, e.g. 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, and 10 mm. It has to be noted that the sequence is not necessarily distributed according to size. One clamping assembly can have sizes 3 mm, 5 mm and 8 mm, whereas the complementary assembly has the sizes 4 mm, 6 mm and 10 mm, showing a mixed sequence. 
         [0059]    It is also possible to use two rods  100  and  101  with one single clamping assembly  20 ,  20   a , if the rods are shorter so that the rods  100 ,  101  cannot intersect behind the clamp  10 . This allows providing a so-called Y-frame with one single clamping assembly, wherein the two rods or bone screws are oriented within an angle of 60 degrees. 
         [0060]    It is noted that the grooves  51 ,  52  and  53  are preferably provided at a distance from the center of the clamp  10  so that the rods, pins or screws which are to be inserted in the created reception cavities are flush with the side walls  61 ,  62  or  63  as it can be seen in  FIG. 11 . 
         [0061]    The single clamping assemblies  20 ,  20   a  or  30 ,  30   a  can be combined in different ways. If a clamping assembly having round grooves is called a rod clamping assembly and a clamping assembly having triangular grooves is called a pin clamping assembly then several clamps having two single clamping assemblies  20 ,  20   a  or  30 .  30   a  are possible, i.e. pin-pin, rod-pin or rod-rod. 
         [0062]    The clamp or articulation element according to the invention has at least two opposing first and second clamping jaws  11 ,  11   a  and  12 ,  12   a , providing one lateral open free space for laterally receiving a rod-shaped element  100 . The lateral open free space is formed through grooves and is in the form of an open slot. It is also possible to accommodate inserts, i.e. a jacket element adapted to be inserted in one jaw of the clamp to modify the space available for the rod-shaped element. Such an insert can be built according to e.g. U.S. Patent Publication No. 20080065068 and introduced into the reception cavities to have additional versatility. On the other side it is also possible that a triangular clamp  10 ,  10   a  according to the invention comprises a clamping assembly  20 ,  20   a  or  30 ,  30   a  having two identical grooves within the three grooves. This is especially true, if according to a different embodiment, four, five or more grooves are provided. 
         [0063]    For four grooves it is possible to combine the advantage of using two sizes of reception cavities which are provided one opposite to the other. Then—in clockwise direction—the four cavities may be: small, large, small, large; which allows the parallel introduction and fixation of two small pins or two large rods, since the square disposition do not hinder the simultaneous introduction of two pins or rods. The same is true, if five grooves/reception cavities are provided, since an angle of around 108 degrees, two out of the five reception cavities can be used. 
         [0064]    Within a preferred embodiment it is contemplated that at least the lower jaw  11 ,  11   a  of the second assembly  30 ,  30   a  has a different color then the other jaws to indicate that there is a specific sequence of sizes. It is e.g. possible that said lower jaw is green, indicating that said clamping assembly  30 ,  30   a  provides a sequence of larger reception cavities (13.5 mm, 10 mm, 8 mm) whereas the other clamping assembly  20 ,  20   a  provide smaller reception cavities (e.g. 6 mm, 5 mm and 4 mm). It is also possible to provide the upper most jaw  11 ,  11   a  of the first clamping assembly  20 ,  20   a  with a different color, e.g. blue to indicate that said clamping assembly  20  provides the smaller reception cavities. Then of course, blue-blue, blue-green and green-green combinations of clamps  10 ,  10   a  would provide a high usability of use with direct indication for the user, which clamp he should choose. This color model can be extended to a third of fourth color according to the above mentioned sequences of reception cavity sizes. 
         [0065]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.