Patent Publication Number: US-9402651-B2

Title: Fixation clamp

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 13/302,559, filed Nov. 22, 2011, which issued as U.S. Pat. No. 8,827,998 on Sep. 9, 2014, and claims priority from European Patent Application No. 10 194 945.1, filed Dec. 14, 2010, the disclosures of which are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     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 each other. 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 the screws and pins to the rigid frame to specifically hold bone fragments at an intended place. 
     One adjustable fixation clamp is known from U.S. Pat. No. 6,080,153 comprising two pairs of jaws allowing clamping of a rod as well as of a pin. 
     A clamp for multiple rod-shaped elements is known from U.S. Pat. No. 7,618,417 having one single pair of jaws. However, such a clamp allows clamping more than two, e.g. three or four rod-shaped elements 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. 
     U.S. Patent Application Publication No. 2006/0287652 mentions that 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. This way of attaching pins or rods leads to bulky fixation systems. Therefore 2006/0287652 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. 
     These clamps according to the prior art either provide different diameters of the reception openings 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. Publication 2008/0065068. Such inserts reduce the diameter of the reception cavities to allow a secure fixing of differently sized rods, pins or wires. 
     From U.S. Publication 2010/0298827 a further fixation clamp is known. The disclosure of U.S. 2010/0298827 is incorporated herein by reference. Users feel very comfortable with the fixation clamp according to this design. However, past use has shown that in some applications the jaws of the clamping assembly have been orientated in an erroneous manner which led to unsatisfactory results. Hence there is a need to have a fixation clamp with which erroneous alignment of the jaws is prevented. 
     SUMMARY OF THE INVENTION 
     It is one aspect of the present invention to provide a fixation clamp which overcomes the disadvantages of prior art. It is in particular one aspect of the present invention to provide a fixation clamp with which erroneous alignment of the jaws is prevented. Furthermore such a fixation clamp shall be adjustable during the mounting process to a large degree. 
     Such an aspect is achieved by the features of claim  1 . Accordingly a fixation clamp, more particularly for use in an external fixation system for holding bone fragments adjacent to each other with the help of fixation elements, comprises at least one clamping assembly having at least one reception provided by means of grooves to accommodate a fixation element along the longitudinal axis of the reception. At least one locking element extends through the clamping assemblies for blocking the position of the clamping assemblies in a defined angular position. This clamping assembly comprises a first jaw and a second jaw which are in contact with each other via respective contact surfaces. The clamping assembly comprises at least two, preferably exactly two, orientation devices that extend from and/or into the contact surfaces which at least two orientation devices serve to orient the first jaw with respect to the second jaw. 
     The arrangement of at least two orientation devices has the advantage that a misalignment of the jaws can be prevented. Furthermore the jaws will be positioned with an enhanced accuracy. In case the clamping assembly is designed such that a pivoting motion between the clamping assembly and the locking element becomes possible, the arrangement of the at least two orientation devices is also very advantageous to compensate possible misalignments during the mounting process. 
     The orientation device comprises preferably an opening extending from said surface into the respective jaw and a protrusion extending from said surface away from the respective jaw wherein said protrusion engages in the opening. Hence one of the jaws comprises the openings and the other jaw comprises the protrusions. Alternatively it is also possible to mix the openings with the protrusion on one of the jaws, namely to arrange a protrusion and an opening on a first jaw and an opening and a protrusion on a second jaw. 
     The openings have preferably the shape of a channel or slot extending along an axis which is substantially parallel to the plane of the surface. The slot or channel has the advantage that the width of the slot or channel can be varied for several purposes. 
     Preferably the protrusions extend in direction of the central axis of the locking element and the axis of the channel extends substantially perpendicular to the central axis, wherein the protrusion engages into the channel perpendicular to the axis of the channel. 
     Preferably the channel opens out into neighboring grooves. Thereby the channel is accessible from two sides which is advantageous for cleaning purposes. In this case the sidewalls of the channels serves as abutment element for the protrusion. Hence the protrusion engages with the sidewalls of the channels. 
     Alternatively the channel can also be limited on the opposite side of one of the grooves as viewed along the respective axis of the channel by an abutment element, which abutment element has a surface which is preferably curved around a central axis extending perpendicular to the respective surface. Here the abutment element as well as partly the sidewalls serve as abutment element for the protrusion. 
     A first channel extends preferably along a first axis being parallel to the surface and a second channel extends along a second axis being parallel to the surface, wherein the first axis is angularly arranged to the second axis. 
     The protrusions have preferably the shape of pins preferably with a circular cross-section. The protrusions and the openings are arranged such that the first jaw and the second jaw are connectable in only one determined aligned position. 
     Preferably the orientation devices are provided such that rotation of the first jaw with respect to the second jaw is prevented. Alternatively the orientation devices are provided such that rotation of the first jaw with respect to the second jaw is permitted in a narrow field of rotation such as rotation angle in the range of 0.5° to 5° before blocking the clamping assemblies by means of the locking element. 
     Further embodiments of the invention are set forth in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings, 
         FIG. 1  shows a perspective view of a first embodiment of a fixation clamp of the present invention; 
         FIG. 2  shows a cross-section of the fixation clamp according to  FIG. 1 ; 
         FIG. 3  shows a top view of the fixation clamp for  FIG. 1 ; 
         FIG. 4  shows a perspective view of a washer that is used in the fixation clamp of  FIG. 1 ; 
         FIG. 5  shows a side view of a clamping assembly of the clamping element of  FIG. 1 ; 
         FIG. 6  shows a cross-sectional view along line X-X of  FIG. 5 ; 
         FIG. 6A  is the cross-sectional view of  FIG. 6  showing an alternate slot or channel design; 
         FIG. 7  shows a perspective view of a first jaw of the clamping assembly of  FIG. 5 ; 
         FIG. 8  shows a top view of the jaw of  FIG. 7 ; 
         FIG. 9  shows a side view of the jaw of  FIG. 7 ; 
         FIG. 10  shows a perspective view of a second jaw of the clamping assembly of  FIG. 5 ; 
         FIG. 10A  is the perspective view of  FIG. 10  showing the alternate slot or channel design of  FIG. 6A ; 
         FIG. 11  shows a top view of the jaw of  FIG. 10 ; and 
         FIG. 11A  is the top view of  FIG. 11  showing the alternate slot or channel designs of  FIGS. 6A and 10A . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show a preferred first embodiment of a clamping element or fixation clamp  10  pursuant to the invention. The clamping element  10  consists of a first clamping assembly  20  and a second clamping assembly  30  and a locking element or shaft  40  which is positioned through bores  21 ,  31  within the two clamp assemblies  20 ,  30  along the longitudinal axis M of shaft  40 . The shaft  40  is preferably a locking element adapted to allow closing the clamp assemblies  20  and  30 . Shaft  40  enters a first jaw  11  through a washer  41 . 
     The shaft  40  comprises a head portion  44 , a reduced diameter portion  43  which is followed by a shaft portion  42  and a thread portion  49 . The outer threaded portion  49  is adapted to be screwed into a complementary inner thread within the distal jaw  11   a  so that turning the head of the shaft  40  changes the longitudinal position of the shaft  40  against the lower jaw  11   a , which allows opening or closing the entire clamp  10  against the force of a spring  15  provided between the two clamp assemblies  20  and  30 . Spring  15  is preferably positioned in corresponding counter bores  16  and  16   a  in jaws  12  and  12   a  respectively. Instead of 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 ,  12   a  adjacent to the spring  15  can eventually come into contact and then the anti-rotation surfaced  55  which are provided in both surfaces of the jaws  12 ,  12   a  fix the angular orientation of each clamping assembly  20  and  30  against the other. 
     Preferably after having mounted the shaft  40  with the thread  49  within the lower jaw  11   a , the end portion of the thread  49  is 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. 
     Each clamping assembly  20  or  30  comprises two opposing clamping jaws  11 ,  12  and  11   a ,  12   a . These jaws  11 ,  11   a  and  12 ,  12   a  are essentially similarly shaped on the sides facing each other. Each of the jaws  11 ,  12 , and  11   a ,  12   a  comprises a respective contact surface  18 ,  19  and  18   a ,  19   a  facing the other surface of the jaw  11 ,  12  and  11   a ,  12   a.    
     In order to prevent rotation between jaw  11 ,  11   a  and jaws  12 ,  12   a  as well as in order to prevent a misalignment of the jaws  11 ,  12  and  11   a ,  12   a  at least two orientation devices or anti-rotation devices  13 ,  14  is arranged on the surfaces  18   a ,  19   a . In the present embodiment in the second clamping assembly  30  the jaw  11   a  comprises an opening  14  extending into surface  18  and the jaw  12   a  comprises a pin  13  extending from surface  19 . The pin  13  extends into the opening  14 . This pin-opening connection prevents therefore a possible rotation between the jaws  11   a ,  12   a  and a possible misalignment between the jaws  11   a ,  12   a . This will further be outlined in more detail with  FIGS. 5 to 11 . 
     The jaws  11  and  12  are provided here with three grooves  51 ,  52  and  53 . Jaws  11   a ,  12   a  have similar grooves  51   a ,  52   a  and  53   a  however only the grooves of jaws  11  and  12  will be described. 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 substantially parallel to outer side wall  61 ,  62  or  63  of each pair of jaws  11  and  12 . 
     Each pair of grooves  51 ,  52  or  53 , respectively, in each jaw  11  and  12 , define one reception, i.e. a first reception  71 , a second reception  72  and a third reception  73 . The grooves  51 ,  52  and  53  are each formed as a rounded semi-spherical recess in section to provide receptions  71 ,  72  and  73  which accommodate cylindrical pins or rods with a defined diameter, if the clamp is closed. The outer side walls  61 ,  62  or  63  can comprise an inclined sliding surface to allow an easier clipping of such pins or rods  100  into the corresponding reception. The grooves  51 ,  52 ,  53  form 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. Some or all of the grooves  51 ,  52 , and  53  are also provided with friction enhancing elements such as ribs  56 . 
     All three grooves  51 ,  52  and  53  have different sizes so that the corresponding receptions  71 ,  72  and  73  have three different sizes. In other words each reception  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. 
     The second clamping assembly  30  according to the embodiment of  FIG. 1  also comprises two jaw portions  11   a  and  12   a  and these comprise three grooves  51   a ,  52   a ,  53   a . These grooves  51 ,  52 ,  53  also comprise a sequence of different sizes. These grooves four receptions  71   a ,  72   a  and  73   a  having outer walls  61   a ,  62   a  and  63   a . In the embodiment shown the inner jaw portions  12 ,  12   a  have an identical structure as have the outer jaws  11 ,  11   a  especially in view of the anti-rotation device  55 , the counter bore  16  for a spring  15 . 
     Within a preferred embodiment the first clamping assembly  20  may comprise a sequence of smaller sizes, 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 until thicker rods with a diameter of 30 mm are used within such a clamp  10 . Such a clamp  10  allows using 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 receptions  71 ,  72  or  73  is adapted. The user takes the clamp  10  and orients the first clamping assembly  20  into the correct alignment so that the pin or screw can be clipped into the corresponding reception. 
     Then the clamp  10  can be clamped on a rod of an external fixator with the help of the second clamping assembly  30 . Second clamping assembly  30  can be oriented in a way so that the rod can be clipped into the corresponding reception. 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 to 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 he finds that the rod he has used is not stiff enough, he simply opens the second clamping assembly  30 , removes the thinner rod, turns the second clamping assembly  30  e.g. 60 degrees into one direction or the other around the longitudinal axis to align the larger reception 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 is faster and more reliable since the clamping of the bone screw is not changed, and avoids use of a second sterile clamp at said time. 
     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 . 
       FIG. 2  shows a cross-section of the clamp according to  FIG. 1 , 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 washer  41  against a flange  45  of the head of shaft  40 . The bore  21  which accommodates part of the shaft portion  42  and the reduced diameter portion  43  is provided with a larger diameter than the respective diameter of the shaft  40  so that an angular or pivoting movement of the first clamping assembly  20  against the shaft  40  is possible. This is in particularly advantageous during the mounting process of the fixation clamp. With this regard it has to be noted that also bore  31  can be provided with a larger diameter than the respective section of the shaft  40  such that jaw  12  of the second clamping assembly becomes pivotable to the shaft  40 . 
     The diameter D 1 , D 2  of bore  21  of the first clamping assembly  20  is larger than the diameter of the locking element  40  extending through the bore  21 . Thereby a pivoting movement or displacement between the locking element  40  and the first clamping assembly  20  during positioning the clamping assemblies  20 ,  30  and the pins or rods becomes possible. In the present embodiment the bore  21  in the first jaw  11  is a bore  21  having an abutment surface  86 . The abutment surface  86  is provided by means of a step-like bore  21  having a first section with a first diameter D 1  and a second section with a second diameter D 2 . The first diameter D 1  is larger than the second diameter D 2 . The abutment surface  86  serves as abutment element for the locking element  40  in particular for the flange  45  in case washer  41  is removed. Hence the abutment surface  86  together with the flange  45  prevents that the first clamping assembly  20  from the second clamping assembly  30  when the washer is removed. Particularly during a cleaning or sterilization process the prevention of such a separation is very advantageous. 
     Alternatively the bore  21  can be provided with a conical section  32  as shown with bore  21  in the jaw  12  of the first clamping assembly. In the present embodiment there are two conical sections arranged, whereby the diameter of the bore  21  decreases with increasing length of the bore as seen from outside of the jaw  12 . In case two conical sections  32  are present the degree of pivoting motion can be increased. 
     The shaft  40  as part of a locking element is threaded into the lower jaw  11   a  of the second clamping assembly  30 . Hence the lower jaw  11  comprises a threaded opening. 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. 
     Therefore the two clamp assemblies  20 ,  30  can be opened and closed through turning the head of shaft  40  and thus turning said shaft  40  in the jaw thread. 
     In the cross-sectional view of  FIG. 2  it can also be seen that the locking element  40  extends through the first clamping assembly  20  and is in contact with the second clamping assembly  30  by means of the threaded portion  49 . In mounting position in which the rods or pins will be positioned in the receptions  71 ,  72 ,  73  the first clamping assembly  20  is moveable along the middle axis M of the threaded portion  49 . Upon actuation of the locking element  40  the first clamping assembly  20  will be moved against the spring pressure towards the second clamping assembly  30  such that the anti-rotation surface  55  of the first clamping assembly  20  comes into contact with the respective anti-rotation surface  55  of the second clamping assembly  30 . Once the locking element  40  is firmly tightened the first clamping assembly  20  and the second clamping assembly  30  are in contact with each other via the anti-rotation surface  55 . 
     In  FIG. 2  the mounting position of clamping assemblies  20 ,  30  is shown. Thereby the clamping assemblies  20 ,  30  are positioned at the distance to each other with regard to the middle axis M. The second clamping assembly  20  is in contact with the locking element  40  and the spring  15  pushes the first clamping assembly away from the second clamping assembly  20  towards the washer  41  which is contact with the flange  45  of the locking element. 
     To summarize: The clamping assemblies  20 ,  30  will be moved due to actuation of the locking element  40  from a mounting position to a locking position and afterwards when fixation shall be cancelled from the locking position to the mounting position. After use the washer  41  will be removed as explained below in order to sterilize the clamping element  10  for further use. 
       FIG. 3  shows a view from above on the clamp according to  FIGS. 1 and 2 . 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 . 
     With the aid of  FIGS. 5 to 11  the at least two orientation devices or anti-rotation elements  13 ,  14  will now be explained in the following. While described in connection with clamping assembly  30  they may be also provided on clamping assembly  20 . In principle the orientation devices serve to provide a help for the user to align a first jaw  11  with respect to a second jaw  12 . Once the orientation devices  13 ,  14  engage with each other they also serve as anti-rotation devices to prevent unwanted rotation between the jaws  11 ,  12 . In the following the term “orientation device” is used for the sake of simplicity. 
     The orientation device  13 ,  14  comprises an opening  14  extending into said surface  18   a ,  19   a  and a protrusion  13  extending from said surface  19   a ,  18   a  wherein said protrusion  13  engages in said opening  14 . Since at least two of the orientation devices  13 ,  14  are arranged there are at least two protrusions  13  and at least two openings  14 . Preferably the number of protrusions  13  is equal to the number of openings  14 . In the present embodiment exactly two orientation devices  13 ,  14  are arranged. 
     In the present embodiment the protrusions  13  extend from the surface  18   a  of the first jaw  11   a  and the openings  14  extend from the surface  19   a  of the second jaw  12   a  into the latter. It is also possible to arrange the protrusions on the surface  19   a  of the second jaw  12   a  and the openings  14  from the surface  18   a  in the first jaw  11   a . It is further possible to arrange one protrusion  13  and one opening  14  on/in the first jaw  11   a  and to arrange one protrusion  13  and one opening  14  on/in the second jaw  11   a.    
     The openings  14  according to  FIGS. 6 and 10 to 11  have the shape of channels or slots  14  extending along respective axes  140 ,  142 . The axes  140 ,  142  extend substantially parallel to the plane of the contact surface from which the channels  14  extend into the jaw, here to the contact surface  19   a.    
     The protrusions  13  have the shape of pins  13  preferably with a circular cross-section. Pins  13  then engage into channels or slots  14 . 
     The protrusions  13  according to  FIGS. 6 to 9  extends in a direction of the middle axis M of the locking element  40 . The axis  140 ,  141  of channels  14  extends substantially perpendicular to middle axis M since the contact surfaces  18   a ,  19   a  extend also substantially perpendicular to the middle axis M. The protrusions  13  engage into channels  14  perpendicular to said axis  140 ,  141  of the channels  14 . 
     In the present embodiment there are arranged at least two, (exactly two are shown), channels  14 . A first channel  140  extends along a first axis  141  being substantially parallel to surface  19   a  and a second channel  142  extends along a second axis  143  being substantially parallel to surface  19   a . The first axis  141  is arranged angularly to second axis  143 . Preferably the angle between the first axis  141  and the second axis is in the range of 60 to 120°, more preferably the angle is substantially a right angle of 90°. 
     The first axis  141  or the channel  140  extend substantially perpendicular to the direction of a neighboring groove  51   a . The term direction of a groove is to be understood as the direction of a middle axis that extends along the groove. 
     The second axis  143  or the channel  142  extends angular, preferably with an angle in the range of 30° to 60°, in particular with an angle of 45°, to the direction of a neighboring groove  51   a.    
     At least one of the channels, here both channels  140 ,  142  open out into a neighboring groove  51   a ,  52   a  and are limited on the opposite side of the groove  51   a ,  52   a  as viewed along the respective axis  140 ,  142  preferably by an abutment element  144 . In other embodiments as shown in  FIGS. 6A, 10A and 11A , it may also be possible to omit the abutment element such that a channel is provided which extends from a first groove to a second groove. Hence such a channel then opens out in two grooves. However, the abutment element  144  has advantages in view of the accuracy of the orientation between the jaws  11   a ,  12   a . Nevertheless it has to be noted that an open channel  140 ,  142 , even if it is open on one end only has advantages concerning the sterilization process as the fluid enters the channel also via grooves  51   a ,  52   a.    
     The abutment element  114  has a surface which is preferably curved around a middle axis extending perpendicular to the respective surface  18   a ,  19   a.    
     With regard to the arrangement of the pins  13  and the channels  14  it has to be mentioned that they are arranged such that the first jaw  11   a  and the second jaw  12   a  are connectable in only one determined aligned position such that a misalignment becomes impossible. 
     Furthermore the orientation devices  13 ,  14  are provided such that rotation of the first jaw  11   a  with respect to the second jaw  12   a  is prevented. 
     Alternatively the orientation devices  13 ,  14  are provided such that rotation of the first jaw  11   a  with respect to the second jaw  12   a  is permitted in a narrow field of rotation. A narrow field of rotation can be defined as a rotation angle in the range of 0.5° to 5°. However such a rotation shall only be permitted during the mounting process of the fixation clamp, i.e. before blocking said clamping assemblies  20 ,  30  by means of the locking element  40 . In order to allow such a rotation, the channels  14  and pins  13  are provided with respective tolerances. Hence the channel  14  can be provided with a larger width such that the pin  13  is able to move with respect to the channel  14 . The pin  13  then abuts at the sidewalls limiting the channel  14 . The sidewall are the walls limiting the channel this extending from the surface  18   a ,  19   a  into the jaw. 
     The depth of the opening  14  from the surface  18   a ,  19   a  along the middle axis M of the locking element is preferably larger than the length of the protrusion  13  in the same direction. This configuration ensures that the surfaces  18   a ,  19   a  are always in full contact with each other. 
     The protrusion  13  can also be provided with a chamfered edge  130  allowing a better insertion of the protrusion into the opening. 
     Furthermore the orientation device  13 ,  14  allows better positioning of the jaws  11   a ,  12   a  with respect to each other. In particular the jaws may move slightly in a floating manner with respect to each other which enables a self-centering function once the pin or rod has been introduced into the respective reception  71   a ,  72   a ,  73   a.    
     Reference is now made to  FIGS. 1 to 4 . In the present embodiment the first clamping assembly  20 , here jaw  11 , comprises a first contact surface  80  which is in contact with a second contact surface  81  of the washer  41 . The washer  41  and the first clamping assembly  20  are in contact via contact surfaces  80 ,  81 . The contact surfaces  80 ,  81  are spherical having the same curvature radius such that the washer  41  is enabled to slide with respect to the first clamping assembly  20  on the contact surface  80  when it comes to the above mentioned pivoting motion of the first clamping assembly  20  with respect to the locking element  40 . The curvature is at least the same over an overlapping surface which here is defined as the surface which encompasses the maximal gliding motion of the washer  41  on the contact surface  80 . 
     In the present embodiment the first contact surface  80  has a convex shape, whereas the second contact surface  81  has a concave shape. Such a configuration is particularly advantageous as it allows a pivoting motion as mentioned above while providing a very compact structure of the fixation clamp in terms of axial and radial dimension. Furthermore the surfaces which are shaped as explained allow that the washer  41  as explained in detail below is removable from the clamping element  10 . Thereby the first clamping assembly  20  and the second clamping assembly  30  become loose such that the parts are slightly moveable along middle axis M and sterilization of the clamping element  10  is possible without demounting or disassembling the clamping element  10  completely. This is very advantageous since during sterilization the parts remain together and re-assembly of the parts afterwards is not necessary. Hence the parts of the clamping element  10  remain loosely together such that the sterilization fluid is able to enter clearances between the respective parts. As mentioned above providing the diameters D 1  and D 2  accordingly, the abutment surface  86  serves as element which holds the parts loosely together. 
     The first contact surface  80  of the first clamping assembly  20  extends from a section point  82  between the middle axis M of the locking element  40  and said first contact surface  80  towards the first clamping assembly  20 . 
       FIG. 3  shows the clamping element from above. In  FIG. 3  the overlapping surface with limiting edges  54  can be recognized. 
       FIG. 4  shows the washer  41  in a perspective view and in  FIG. 2  a cross-sectional view of the washer  41  is shown. In the following the structure of the washer  41  will be explained. 
     The washer  41  comprises as mentioned above the contact surface  81  and an upper surface  88  which is arranged at a distance from the contact surface  81 . A central through opening  84  having a middle axis M 1  that is at least partly circumvented by means of a sidewall  85 . Said through opening extends from contact surface  81  to the upper surface  88 . The locking element  40  extends through the through opening. 
     The sidewall  85  is interrupted by cutout  87  which extends radially to the middle axis M 1  through the sidewall  85  to the opening  84  such that the sidewall  85  becomes interrupted. The cutout  87  has a width which is slightly larger than the reduced diameter portion  43  of the locking element  40  such that the washer  41  can be moved radially to the locking element  40  in order to remove the washer  41  after the use of the clamping element  10 . The width is defined as the clearance of the cutout  87  from the surfaces  89  of the sidewall limiting the cutout. 
     Furthermore the washer  41  comprises a recess  83  extending along middle axis M 1  from an upper surface  88  which is arranged opposite the contact surface  81 . The recess  83  is designed to accommodate the flange  45  of the locking element  40 . The recess  83  can also be designated as abutment element since it prevents the washer from being radially displaced to the middle axis M of the locking element  40 . In order to demount the washer  41  it is necessary to push the first clamping assembly  10  towards the second clamping assembly, such the washer  41  can also be moved along the middle axis M of the locking element  40 . Thereby the flange  45  will be moved out of the recess  83 . Once the flange  45  has been moved such that there is no connection between the flange  45  and the recess  83 , the washer  41  can be moved radially to the locking element  40  whereby the shaft of the locking element will pass the cutout  87  of the washer. 
     Recess  83  extends from the upper surface  88  along the middle axis M 1  of the through opening  84  into the washer  41 . The washer is preferably made out of a metallic material. 
     To summarize the arrangement of the contact surfaces  80 ,  81  has the advantage that during the mounting process of the fixation clamp  10  a pivoting motion of the first clamping assembly becomes possible with a large deflection. Furthermore the removable washer  41  has the advantage that the clamping assemblies  20 ,  30  become moveable along the interlocking element  40  such that an effective sterilization becomes possible. 
     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.