Abstract:
A method for securing neighboring bone plates by an implant includes the steps of resting an inner contact element of the implant on inner faces of the bone plates, resting an outer contact element of the implant on outer faces of the bone plates, connecting the inner contact element and the outer connecting element by a flexible tensioning element, forming a knot between free strands of the tensioning element, wherein the knot is a slip knot, and pushing the knot in a recess of the outer contact element with the knot being positioned at least partially below an outer surface of the outer contact element.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/702,258, filed Feb. 5, 2007, which is a continuation of International Application No. PCT/EP2005/005738, filed May 27, 2005, which claims the benefit of priority of German Application No. 10 2004 038 823.7, filed Aug. 4, 2004. All of the aforementioned applications are incorporated herein by reference in their entirety and for all purposes. 
    
    
     FIELD 
     The present invention relates to implants and methods for securing neighboring bone plates, and in particular, implants and methods for securing neighboring cranial bone plates. 
     BACKGROUND 
     The invention relates to an implant for securing neighboring bone plates, especially neighboring cranial bone plates, wherein each of the bone plates has an inner face and an outer face, comprising an inner contact element that is adapted to rest on the inner face of the neighboring bone plates, an outer contact element that is adapted to rest on the outer faces of the neighboring bone plates and in a linear manner a flexible tensioning element for connecting the inner contact element and the outer contact element in such a manner that they can no longer be separated from one another. 
     Such an implant is known from DE 199 52 359 C1 (wherein it is referred to as a surgical connecting element). 
     A further example of such an implant is known from DE 101 28 917 C1. 
     A procedure for the treatment of a broken bone is known from U.S. Pat. No. 5,921,986, wherein an anchor connected to a thread is fed through the bone on each side of the break, the thread is tensioned in order to transmit a force to a bone on the first side of the break, wherein the thread extends over the break, and wherein a force is transmitted from a second anchor to the bone on a second side of the break. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, an implant with improved properties is provided. 
     In accordance with an embodiment of the invention, an implant is provided with the outer contact element comprising at least one recess for at least partially accommodating a connection region between the free strands of the tensioning element or for feeding the connection region through into a separation gap between the neighboring bone plates. 
     The free strands of the flexible linear tensioning element which, in particular, is a thread or a wire are linked by means of the connection region. The resultant formation such as a knot for example, can lead to irritation of the surrounding tissue or there is a danger that this connection region is or will be felt by a patient. In accordance with the invention, there is provided at least one recess with the aid of which the connection region is adapted to be at least partially countersunk relative to the outer surface of the outer contact element. As a consequence thereof, protrusion of the connection region above the outer contact element can be prevented or at least reduced, and thus in turn, tissue irritations can be prevented or at least reduced. 
     In particular, the at least one recess is formed in such a way that the connection region is positionable at least partially below an outer surface of the outer contact element. In consequence, the connection region (and in particular a knot) can be at least partly sunk with respect to this outer surface. 
     In particular, the connection region is formed by means of a knot. The free strands can be permanently connected to each other by means of the knot and hence the contact elements are fixed together so that they can no longer be separated from one another. 
     It is particularly very advantageous if the knot is in the form of a slip knot. It can then be pushed into a desired position and pulled-together with the aid of a slip knot applicator in order to complete the securing process as is described in DE 101 61 724 A1 for example. 
     It is particularly very advantageous if, whether with or without the recess for the connection region, the connection region is formed by means of a prefabricated slip knot. It can then be supplied to the operating surgeon in the form of a finished manufactured implant which is utilizable in a simple manner. The operating surgeon then only has to position the slip knot at the correct position and tighten a loop. In particular, he does not have to produce a knot himself. 
     The free strands are preferably those regions of the tensioning element which emanate from the outer contact element. By permanently connecting these free strands, the contact elements can be fixed with respect to one another in such a manner that they cannot be moved apart. As a consequence thereof, the bone plates can then in turn be fixed relative to each other. 
     Provision may be made for the at least one recess to constitute a through hole. In consequence, a connection region and in particular a knot can be pushed through the recess into the separation gap between the bone plates and accommodated therein so that it will not project above an outer surface of the outer contact element. 
     Provision may be made for the at least one recess to comprise a seating area for the connection region. This seating area can be trough-shaped for example. By virtue of such a seating area, the connection region can be positioned such that is sunken with respect to an outer surface of the outer contact element. 
     For example, a base is associated with the at least one recess. The connection region can be prevented from being pushed into the separation gap by means of this base. 
     It is expedient for the inner contact element to comprise at least two spaced feed-through recesses for the tensioning element. By virtue of the feed-through recesses, the tensioning element can be held on the inner contact element and a means for altering the direction of the tensioning element can be provided. 
     In particular, the tensioning element is placed on a surface of the inner contact element between the feed-through recesses. By virtue of the corresponding placement region, the inner contact element can be displaced relative to the outer contact element by means of the tensioning element and the two contact elements can be tensioned towards one another. 
     Provision is made, in particular, for the outer contact element to comprise at least two spaced feed-through recesses for the tensioning element. Thus, for example, the free strands of the tensioning element can thereby be fed through the outer contact element. 
     It is expedient for the at least one recess for the connection region to be formed at a feed-through recess or to form a feed-through recess. As a consequence thereof, only a minimized number of openings through the outer contact element need be provided, this thereby increasing the mechanical stability. Furthermore, the production process is simplified. 
     It is particularly very advantageous, if the tensioning element is guided on the inner contact element and the outer contact element in such a way that a pulley-block system is formed. On the one hand thereby, a secure tensioning arrangement between the contact elements can be achieved by means of the tensioning element and thus secure fixing of the neighboring bone plates is obtained. On the other hand, purposeful guidance of the outer contact element and the inner contact element relative to one another during a tensioning process can be achieved, this thereby facilitating the work for an operating surgeon. Furthermore, relatively large tensional forces can be applied, this thereby resulting in the contact elements exerting large clamping forces on the bone plates held therebetween. In consequence, the bone plates are held securely between the contact elements and hence secure fixing of the bone plates relative to one another is obtained. 
     It is expedient, if, in combination with the at least one recess for the connection region or even without such a recess, the inner contact element comprises a first pair of spaced feed-through recesses for the tensioning element between which the tensioning element rests on the inner contact element in a first placement region, if the inner contact element comprises a second pair of neighboring feed-through recesses for the tensioning element between which the tensioning element rests on the inner contact element in a second placement region, if the outer contact element comprises a first pair of neighboring feed-through recesses for the tensioning element between which the tensioning element rests on the outer contact element in a third placement region, and if the outer contact element comprises a second pair of spaced feed-through recesses through which the free strands of the tensioning element are fed. By virtue of such an arrangement of feed-through recesses, the tensioning element can be guided through a first turn on the inner contact element, then diverted towards the outer contact element, rest on the outer contact element in the course of a further turn and then be diverted back to the inner contact element and from there, after a further turn, be diverted yet again towards the outer contact element. A pulley-block-like system can thereby be formed, and this can be employed in an advantageous manner. For example, large clamping forces can be exerted and correct guidance of the outer contact element by means of the tensioning element is assured thereby simplifying the employment of the arrangement for an operating surgeon. 
     In particular, the first pair of feed-through recesses in the outer contact element is arranged between the feed-through recesses of the second pair. Thus, a turn of the tensioning element between the feed-through recesses of the first pair can be formed so as to enable a pulley-block system to be formed once again. 
     It is advantageous for the feed-through recesses of the inner contact element to be arranged in a line. They are then aligned. In consequence, the regions of the tensioning element which pass through the separation gap are parallel and aligned. The employment thereof is thereby simplified. For example, one or more contact elements (which are arranged on the inner contact element and/or on the outer contact element) can then be used in a simple manner in order to hold the oppositely located bone plates apart in the region of the separation gap between the contact elements so that the tensioning element cannot get trapped between the bone plates. Thus, for example, it is thereby ensured once again that, in the course of exerting a pulling force on the tensioning element, the contact elements will move relative to one another in order to hold the neighboring bone plates therebetween in a clamping manner. 
     For the same reason, it is expedient for the feed-through recesses in the outer contact element to be arranged in a line. 
     It is expedient if the feed-through recesses of the first pair in the outer contact element and the neighboring feed-through recesses of the first pair and the second pair in the inner contact element are mutually matched. In consequence, the tensioning element can be guided in such a way that a pulley-block system can be realized. 
     For the same reason, it is expedient if the feed-through recesses of the second pair in the outer contact element and non-neighboring feed-through recesses of the first pair and the second pair in the inner contact element are mutually matched. 
     It is expedient if the at least one recess for the connection region is arranged in a feed-through recess of the second pair of the outer contact element or forms such a feed-through recess. As a consequence thereof, the formation of the pulley-block system is not affected by the recess. Furthermore, through holes in the outer contact element, which could in principle affect the mechanical stability thereof, can be minimized. 
     Provision may be made for the at least one recess for the connection element to be arranged such that it is displaced relative to the first pair of feed-through recesses. In consequence, the position of a tensioning element region near a turn or a loop of the tensioning element, which rests on the surface of the outer contact element, can be displaced. 
     Provision is made for the first placement region and the second placement region to lie on a surface of the inner contact element that is remote from the outer contact element. The inner contact element can thereby be pulled against the outer contact element with the aid of the tensioning element. 
     Provision may also be made for the third placement region to lie on a surface of the outer contact element that is remote from the inner contact element. In consequence, a pulley-block system can then be formed. 
     In particular, the tensioning element is guided through the outer contact element in displaceable manner. A pulling force can then be exerted by means of which the spacing between the inner contact element and the outer contact element is reducible and a clamping force is adapted to be exerted on the bone plates located therebetween. The tensioning element tracks said decrease of the spacing so as to thereby enable a clamping force to be applied. 
     In particular, the inner contact element is displaceable with respect to the outer contact element when the tensioning element is tensioned. 
     It is expedient for the tensioning element to be provided for passing through the separation gap between the bone plates. This gap makes the appropriate space available for enabling the tensioning element to be accommodated in the region between the contact elements. 
     It is particularly very advantageous, if the inner contact element and/or the outer contact element comprises at least one spacer for the bone plates which is adapted to project into the separation gap. In consequence, the bone plates can be kept apart at the separation gap between the contact elements, namely, in such a manner that the tensioning element can penetrate freely through the separation gap. This in turn thereby prevents the tensioning element from getting jammed between the bone plates. By exerting a pulling force for example, the contact elements can then be moved relative to one another so as in turn to thereby enable bone plates to be clamped therebetween. Preferably, the at least one spacer is in line with the feed-through recesses for the tensioning element in order to ensure free guidance of the tensioning element in the separation gap. 
     Provision may be made for the inner contact element and/or the outer contact element to be curved in such a manner that an intermediary space is formed between a region of contact with a bone plate and the region holding the contact region. It is thereby possible for example, to change to a certain extent the height of the contact element itself by the application of force. For example, the height is reduced during the fixing process. When the force abates, then the height increases. This can provide for an additional tensioning effect which improves the securement of the bone plates between the contact elements. 
     It is then expedient if the inner contact element and/or the outer contact element is resilient taken with reference to a connection region. It is thereby possible for the clamping effect to be improved. 
     It is expedient for the inner contact element and/or the outer contact element to have a gripping area at a region of contact with a bone plate. This gripping area provides for an improved gripping effect on the bone plate. The gripping area can be formed by means of ribbing, a roughened area or a set of teeth for example. 
     In particular the gripping area is arranged in peripheral manner, i.e. it is arranged around the periphery of the corresponding contact element. This thus results in a symmetrical arrangement of the contact element which simplifies its employment. 
     It is expedient if the tensioning element is made of a resorbable material. 
     The following description of preferred embodiments serves for a more detailed explanation of the invention when taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic perspective illustration of a first exemplary embodiment of an implant in accordance with the invention; 
         FIG. 2  is a sectional view of the implant in accordance with FIG. wherein the bone plates are secured and a knot is sunk in a recess; 
         FIG. 3  is the same view as  FIG. 2 , but wherein the knot is located in a separation gap between fixed bone plates; 
         FIG. 4  is a sectional view of a second exemplary embodiment; 
         FIG. 5  is a sectional view of a third exemplary embodiment; 
         FIG. 6  is a perspective illustration of a variant of a contact element and the implant in accordance with  FIG. 1 ; and 
         FIG. 7  is a schematic illustration of an exemplary embodiment of an implant and a slip knot applicator. 
     
    
    
     DETAILED DESCRIPTION 
     A first exemplary embodiment of an implant in accordance with the invention is shown in  FIGS. 1 to 3  and bears the general reference  10  therein. The implant serves for securing neighboring bone plates  12 ,  14 . The bone plates  12 ,  14  are, in particular, cranial bone plates; for brain operations, a cranial bone plate is sawn out in order to gain access to the brain. After completion of the brain operation, the cranial bone plate that had been removed (for example the bone plate  12 ) must be fixed back to the bone plates surrounding it (for example the bone plate  14  and further bone plates). This is effected with the aid of a plurality of implants  10 . 
     The bone plates  12 ,  14  each have an inner surface  16  and an opposite outer surface  18 . The inner surface  16  faces towards the interior of the body; in the case of a cranial bone plate, the inner surface  16  faces towards the brain. 
     The implant  10  comprises an inner contact element  20  that is adapted to rest on the inner surface  16  of the bone plates  12  and  14 . Furthermore, the implant  10  comprises an outer contact element  22  that is adapted to rest on the outer surfaces  18  of the bone plates  12  and  14 . 
     In the exemplary embodiment shown, the inner contact element  20  and the outer contact element  22  have a circular cross section. They are formed in a substantially identical manner insofar as their general shape is concerned. 
     The inner contact element  20 , similar to the outer contact element  22 , has an annular contact region by means of which it rests against the inner surface  16  of the bone plates  12 ,  14 . This contact region  24  comprises a gripping area  26  which is formed “non-smoothly”. This gripping area  26  serves the purpose of improving the bite of the inner contact element  20  on the inner surface  16  of the bone plates  12 ,  14  or of the outer contact element  22  on the outer surfaces  18  of the bone plates  12 ,  14  and in particular it serves to prevent slipping. For example, the gripping area  26  is formed by means of a set of peripherally extending teeth, ribbing or a roughened surface. 
     The inner contact element  20  (and, in the exemplary embodiment shown, the outer contact element  22  too) are curved, namely, in such a manner that an intermediary space  30  is formed between the contact region  24  and a region  28  holding it, in particular, in one-piece manner. 
     Provision may be made for the inner contact element  20  and/or the outer contact element  22  to be resilient taken with reference to a connecting direction  32  between the two contact elements  20  and  22 . This can improve the securement of the contact elements  20  and  22  together and thus the securement of the bone plates  12  and  14  located between the contact elements  20  and  22 . 
     For the purposes of connecting the inner contact element  20  and the outer contact element  22 , there is provided (at least) one linearly flexible tensioning element  34 . The tensioning element is, in particular, a surgical thread or a wire. The tensioning element serves for the purpose of connecting the two contact elements  20  and  22  together in such a manner that they can no longer be separated from one another (and thus to fix the bone plates  12  and  14  relative to one another), whereby the inner contact element  20  is displaceable with respect to the outer contact element  22  by pulling the tensioning element  34 . 
     The tensioning element  34  is made, in particular, of a material that is resorbable in the body. 
     The tensioning element  34  passes through a separation gap  36  between the neighboring bone plates for the purpose of securing the bone plates  12 ,  14 . 
     Hereby, provision may be made for the inner contact element  20  and/or the outer contact element  22  to comprise at least one spacer  38   a ,  38   b  ( FIG. 6 ) which serves to project into the separation gap  36 . The end face of the bone plate  12  then rests against a first contact face  40  of the spacer or spacers  38   a ,  38   b  and the end face of the neighboring bone plate  14  rests against an opposing second contact face  42  of the spacer or spacers  38   a ,  38   b . The spacer or the spacers  38   a ,  38   b  hold the bone plates  12 ,  14  apart so that the tensioning element  34  can pass freely through the separation gap  36  in such a manner that tension can be exerted and in order to prevent the tensioning element  34  from jamming against the bone plates  12 ,  14  in the separation gap  36 . 
     The spacer or the spacers  38   a ,  38   b  are located, in particular, in line with feed-through recesses for the tensioning element  34  as will be described in more detail hereinbelow. 
     The spacer or the spacers  38   a ,  38   b  is or are formed, in particular, in one-piece manner with the associated contact element  20 ,  22 . 
     The inner contact element  20  of the implant  10  comprises a first pair  44  of spaced neighboring feed-through recesses  46   a ,  46   b  and comprises a second pair  48  of spaced neighboring feed-through recesses  50   a ,  50   b . The feed-through recesses  46   b  and  50   a  are inwardly located feed-through recesses and the feed-through recesses  46   a ,  50   b  are outwardly located feed-through recesses. The feed-through recess  46   b  neighbors the feed-through recess  50   a . The distance between the feed-through recesses  46   a  and  50   b  corresponds to the largest distance between feed-through recesses. The feed-through recesses  46   b  and  50   a  are located between the feed-through recesses  46   a  and  50   b.    
     The feed-through recesses  46   a ,  46   b ,  50   a  and  50   b  are arranged, in particular, along a line (in common with the spacer or the spacers  38   a ,  38   b ) so that those tensioning element regions of the tensioning element  34  that are located in the separation gap  36  between the inner contact element  20  and the outer contact element  22  can be positioned so as to be orientated in parallel with one another and aligned with one another. 
     The outer contact element  22  comprises a first pair  52  of spaced neighboring feed-through recesses  54   a ,  54   b . Furthermore, the outer contact element  22  comprises a second pair  56  of spaced feed-through recesses  58   a ,  58   b . Hereby, the first pair  52  of the feed-through recesses  54   a  and  54   b  are located between the feed-through recesses  58   a  and  58   b . The feed-through recesses  58   a ,  58   b  of the second pair  56  are outwardly located feed-through recesses; the feed-through recesses  54   a ,  54   b  of the first pair  52  are inwardly located feed-through recesses. The feed-through recesses  54   a  and  58   a  are neighbors and the feed-through recesses  54   b  and  58   b  are neighbors. The distance between the feed-through recesses  58   a  and  58   b  of the second pair  56  corresponds to the maximum distance between feed-through recesses in the outer contact element  22 . 
     The feed-through recesses  54   a ,  54   b ,  58   a  and  58   b  of the outer contact element  22  are matched to the arrangement of the feed-through recesses  46   a ,  46   b ,  50   a ,  50   b  of the inner contact element  20 . In particular, neighboring feed-through recesses ( 58   a  and  54   a;    54   a  and  54   b;    54   b  and  58   b ) in the outer contact element  22  have the same spacing as the corresponding feed-through recesses ( 46   a  and  46   b ;  46   b  and  50   a ;  50   a  and  50   b ) in the inner contact element  20 . Furthermore, the feed-through recesses  54   a ,  54   b ,  58   a ,  58   b  in the outer contact element  22  are preferably located in a line. 
     Due to the matched formation of the feed-through recesses of the inner contact element  20  and those of the outer contact element  22 , a parallel and aligned guidance of the tensioning element  34  between the contact elements  20  and  22  can be achieved. 
     The tensioning element  34  is formed in one-piece manner in the exemplary embodiment shown in  FIGS. 1 to 3 . (It is also fundamentally possible for separate tensioning elements to be provided.) The tensioning element  34  is fed through the feed-through recess  54   a  in the outer contact element  22  and through the feed-through recess  46   a  in the inner contact element  22 . From the feed-through recess  46   a , it is then fed to the feed-through recess  46   b  and passed through the latter. Between the feed-through recesses  46   a  and  46   b , the tensioning element  34  is located in a first placement region  60  and rests on an outer surface of the inner contact element  20  that is remote from the outer contact element  22 . From the feed-through recess  46   b , the tensioning element  34  is fed to the feed-through recess  54   a  of the outer contact element  22  and passed therethrough. 
     From the feed-through recess  54   a , the tensioning element  34  is fed to the neighboring feed-through recess  54   b  and passed therethrough. Between the feed-through recesses  54   a ,  54   b , the tensioning element  34  is located in a third placement region  62  and rests on an outer surface of the outer contact element  22  which is remote from the inner contact element  20 . 
     The tensioning element  34  is fed through the feed-through recess  54   b  up to the feed-through recess  50   a  and is passed therethrough. From the feed-through recess  50   a , the tensioning element  34  is fed to the feed-through recess  50   b  and passed therethrough. Between the feed-through recess  50   a  and  50   b , the tensioning element is located in a second placement region  64  on the outer surface of the inner contact element  20 . 
     From the feed-through recess  50   b , the tensioning element  34  is fed to the feed-through recess  58   b  and passed therethrough. 
     Starting from the feed-through recesses  58   a  and  58   b , the tensioning element  34  has free strands, namely, a first free strand  66   a  (outgoing from the feed-through recess  58   a ) and a free strand  66   b  (outgoing from the feed-through recess  58   b ). 
     When the neighboring bone plates  12  and  14  are secured to one another by means of the implant  10 , those regions of the tensioning element  34  that are fed between the feed-through recesses  58   a  and  46   a ,  46   b  and  54   a ,  54   b  and  50   a  and also  50   b  and  58   b  are then, for the greater part, located in the separation gap  36 . The tensioning element  34  is guided by the first pair  44  of feed-through recesses  46   a ,  46   b  in the inner contact element  20  into the form of a first loop or turn and, outgoing from the inner contact element  20 , the direction of the tensioning element  34  is diverted towards the outer contact element  22 . 
     The tensioning element  34  is guided by the first pair  52  of feed-through recesses  54   a ,  54   b  into the form of a second loop or turn in order to divert the tensioning element  34  from the outer contact element  22  towards the inner contact element  20 . 
     The tensioning element  34  is guided by the second pair  48  of feed-through recesses  50   a ,  50   b  in the inner contact element  20  into the form of a third loop or turn in order to divert the tensioning element  34  yet again from the inner contact element  20  towards the outer contact element  22 . 
     The free strands  66   a ,  66   b  are then fed out from the outer contact element  22  via the second pair  56  of feed-through recesses  58   a ,  58   b  therein. 
     A pulley-block system is formed by virtue of this form of guidance of the tensioning element  34  on the contact elements  20  and  22  and between the contact elements  20  and  22 ; when, for example, the free strands  66   a ,  66   b  are pulled (in the direction  32  for example), then the inner contact element  20  is thereby displaced in the direction of the outer contact element  22 . In consequence, a clamping force can be exerted on bone plates  12 ,  14  lying between the contact elements  20 ,  22  in order to secure them together. 
     For the purposes of establishing this clamping effect in such a manner that the bone plates  12 ,  14  can no longer be separated from one another, i.e. the inner contact element  20  and the outer contact element  22  can no longer be separated from one another, provision is made for the free strands  66   a ,  66   b  of the tensioning element  34  to be connected. This connection, which, in particular, is formed by means of a knot  70 , is effected in a connection region  68 . 
     The knot  70  is preferably in the form of a slip knot which, for example, is adapted to be pushed onto the outer contact element  22  by means of a slip knot applicator ( FIG. 7 ; an operative tip  72  of such a slip knot applicator is indicated in  FIG. 1 ). 
     An example of a usable slip knot is a Roeder knot. 
     In the case of the implant  10 , provision is preferably made for the knot  70  and in particular a slip knot to be prefabricated, i.e. the implant  10  is implemented with the inner contact element  20 , the outer contact element  22  and the tensioning element  34  guided in the manner described above. Furthermore, the free strands  66   a ,  66   b  are already connected together by means of a slip knot. 
     The (slip-) knot  70  can be displaced on the outer contact element  22  by means of the slip knot applicator and the two contact elements  20  and  22  can be fixed relative to one another by, for example, tightening the knot via a free end of the tensioning element  34 . 
     If the inner contact element  20  and/or the outer contact element  22  is resilient, then a force can be exerted during the fixing process which reduces the distance between the outer surfaces of the inner contact element  20  and the outer contact element  22  due to the resilient deformation thereof. When this force is removed, then this distance readily increases. A kind of pre-tensioning process can thereby be effected. 
     The outer contact element  22  comprises a recess  74  which serves for accommodating or pushing through the connection region  68  of the tensioning element  34 , i.e. for the accommodation or the through passage of the knot  70 . The recess  74  is formed in such a way that the connection region  68  is positionable at least partly below an outer surface of the outer contact element  22 . As a consequence thereof, the connection region  68  (and in particular, the knot  70 ) does not project above this surface or does so to only a small extent. Irritation of the surrounding tissue due to a knot  70  lying on the implant  10  can then be prevented since the knot  70  is adapted to be “countersunk” due to the recess  74 . Furthermore, the danger that a patient will become aware of the knot  70  (in the form of the connection region  68 ) after a certain period of time is overcome. 
     The recess  74  is preferably arranged at an outer region of the outer contact element  22  whereat the outer contact element  22  is strengthened. This thereby ensures that the recess  74  will not impair the mechanical stability of the outer contact element  22 . 
     Preferably, the recess  74  is located at or forms the feed-through recess  58   b . The recess  74  can be then used directly as a feed-through recess. The complexity of the manufacturing process is thereby reduced. Furthermore, mechanical stability is ensured. 
     It is also possible for the outer contact element  22  to comprise a plurality of such recesses  74 . This may be necessary for example, when two separate tensioning elements are provided for connecting the two contact elements. 
     In principle, it is also possible for the inner contact element  20  to be provided with such a recess  74  or several recesses. Provision may be made for the inner contact element  20  and the outer contact element  22  to be of identical construction. A recess  74  in the inner contact element  20  has no functional purpose, but nevertheless it is not harmful to the securement of the neighboring bone plates  12  and  14 . If only one type of contact element has to be manufactured, then the manufacturing costs can be reduced and the production process is simplified. 
     In the exemplary embodiment shown in  FIGS. 1 to 3 , the recess  74  constitutes a through hole, i.e. it goes from an upper surface  76  of the outer contact element  22  to a lower surface  78  of the outer contact element  22 . A passage  80  extending through the outer contact element  22  is then formed through which the knot  70  can be pushed. 
     An intermediate position is shown in  FIG. 2  whereat the knot  70  is located in the passage  80 . The knot  70  can be moved from there into the separation gap  36  ( FIG. 3 ). The knot  70  does not thereby project above the upper surface  76  of the implant  10 . 
     The implant  10  functions as follows: 
     The contact elements  20  and  22  are connected “loosely” together by the tensioning element  34 , a slip knot  70  having preferably been prefabricated in the free strands  66   a ,  66   b . When the neighboring bone plates  12 ,  14  are to be secured together, the inner contact element  20  is then placed under the bone plates  12 ,  14  or a free bone plate is placed on the positioned inner contact element  20 . 
     The tensioning element  34  then runs in the separation gap  36 . 
     The free strands  66   a ,  66   b  are pulled in order to reduce the distance between the outer contact element  22  and the inner contact element  20 . The inner contact element  20  can thereby be pressed against the inner surfaces  16  of the bone plates  12 ,  14  and the outer contact element  22  against the outer surfaces  18  of the bone plates  12  and  14 . 
     For the purposes of securing this position, the slip knot  70  is pushed onto the outer contact element  22  by means of a slip knot applicator for example, and it is thereby pushed into the recess  74 . From there, the knot  70  can be pushed into the separation gap  36  so that it does not project above the outer contact element  22 . 
     The knot  70  is tightened by pulling on a free end of the tensioning element  34 . 
     Protruding portions of the tensioning element  34  can then be cut off. 
     In a second exemplary embodiment  81  which is shown in the form of a schematic sectional view in  FIG. 4 , a recess  82  which is not a through hole is provided in the outer contact element  22 . (The same reference symbols as were used for similar elements in the exemplary embodiment in accordance with  FIGS. 1 to 3  are used here.) The recess  82  comprises a seating area  84  for the knot  70 . The knot  70  is adapted to be inserted into this, for example, trough-shaped seating area  84  so that it does not project above the upper surface  76  of the outer contact element  22  or at most, only partly projects thereabove. 
     Associated with the recess  82  and thus the seating area  84 , there is a base  86  which closes the seating area  84  at the lower surface  78  of the outer contact element  22 . 
     In the base  86 , there is formed a feed-through recess  88  through which the tensioning element  34  is fed although the knot  70  cannot enter it. (The feed-through recess  88  corresponds to the feed-through recess  58   b  in the exemplary embodiment of  FIGS. 1 to 3 .) Starting from the second placement region  64 , the tensioning element  34  is fed through the feed-through recess  88  and thus through the outer contact element  22  towards the inner contact element  20 . 
     In other respects, the implant  81  in accordance with this exemplary embodiment functions as described above. 
     In a third exemplary embodiment of an implant which is shown in the form of a schematic sectional view in  FIG. 5  and bears the general reference  90  therein, there is provided an inner contact element  92  and an outer contact element  94 . The inner contact element comprises a first feed-through recess  96   a  and a second spaced neighboring feed-through recess  96   b . A flexible linear tensioning element  98  such as a thread or a wire for example is again provided as the connecting element. This tensioning element  98  is located between the feed-through recesses  96   a  and  96   b  on an outer surface of the inner contact element in a placement region  100  when the contact elements  92  and  94  are tensioned towards one another. 
     The outer contact element  94  comprises a first feed-through recess  102   a  and a second spaced neighboring feed-through recess  102   b  which are matched to the arrangement of the feed-through recesses  96   a ,  96   b  in the inner contact element  92 . 
     The tensioning element  98  is fed from the feed-through recess  102   a  of the outer contact element  94  to the feed-through recess  96   a  of the inner contact element  92  and then guided through this feed-through recess  96   a . It is fed on further between the feed-through recesses  96   a  and  96   b  in the form of a loop or a turn and rests against the inner contact element  92  in the placement region  100 . It is diverted towards the outer contact element  94  at the feed-through recess  96   b  through which it is fed. It is fed through the feed-through recess  102   b  in said outer contact element. 
     Free strands  104   a ,  104   b  of the tensioning element  98  are led out from the respective feed-through recesses  102   a  and  102   b . They are connected together by a connection region  106  and in particular, a knot  108 , in order to connect the free strands  104   a ,  104   b  together and thus secure the mutually fixed position of the two contact elements  92  and  94 . 
     An, in particular, trough-shaped recess  110  is formed in the outer contact element  94  between the feed-through recesses  102   a  and  102   b . The knot  108  can be inserted into this recess  110  so that it does not project above an upper surface  112  of the outer contact element  94  or at most, projects only partially thereabove. 
     In other respects, the implant  90  functions in the same manner as in the exemplary embodiments described above. 
     The use of a slip knot applicator  114  is indicated schematically in  FIG. 7 . This comprises a flange  116 . Furthermore, it comprises an applicator tip  118  with the aid of which a force can be exerted on a slip knot  120  in order to shift the latter towards an outer contact element  122  of an implant  124 . 
     Basically, the implant  124  is constructed in the manner described above. 
     For example, the applicator tip  118  is seated on a sliding member  126  of the slip knot applicator  114 . A handle element  128  is connected to the sliding member  126 . In one exemplary embodiment, the connection is such that the connection between the handle element  128  and the sliding member  126  will release when a certain displacement force is exceeded. Such a slip knot applicator (a device for pushing together a loop of a thread which is in the form of a slip knot that is formed by the distal free end of the thread and is displaceable along the thread) is described in DE  101   61   724  Al to which reference is expressly made. 
     With the aid of the slip knot applicator, it is possible to hold the tensioning element  34 , which is threaded through the handle element  128  below the sliding member  126 , at a proximal end thereof and to pull a slip knot  120  together by means of the applicator tip  118  (i.e. to form a firm knot by pulling a loop together).