Patent Publication Number: US-2013253585-A1

Title: Surgical fixation system, spacer element for a surgical fixation system, use of an implant and method for stabilizing spinous processes

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of international application number PCT/EP2011/069895, filed on Nov. 11, 2011, and claims the benefit of U.S. application No. 61/412,825, filed Nov. 12, 2010, and the benefit of U.S. application No. 61/458,334, filed Nov. 22, 2010, which are incorporated herein by reference in their entirety and for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a surgical fixation system. 
     Furthermore, the invention relates to a spacer element for a surgical fixation system. 
     The invention also relates to a use of an implant. 
     Moreover, the invention relates to a method for stabilizing spinous processes. 
     SUMMARY OF THE INVENTION 
     In a first aspect of the invention, a surgical fixation system for stabilizing spinous processes of adjacent vertebral bodies relative to one another comprises at least one first fixing element and at least one second fixing element, which can be transferred relative to one another from an insertion position into an implantation position, wherein the fixing elements in the implantation position have a smaller spacing from one another than in the insertion position and in which implantation position the fixing elements are engageable laterally from different sides with at least one of the spinous processes in each case. It also comprises a securing device for securing the fixing elements relative to one another in the implantation position and at least one spacer element, which can be fixed by the fixing elements in the implantation position thereof in the intervertebral space between the spinous processes. 
     In a second aspect of the invention, a method is provided in which a sternal closure device described in the document DE 103 26 690 B4 or a fixing device described in DE 10 2006 021 025 B3 is used to stabilize spinous processes of adjacent vertebral bodies relative to one another, with at least one spacer element being positioned between two fixing elements of the fixing system in the intervertebral space. 
     In another aspect of the invention, a spacer element for a surgical fixation system is provided. 
     Another aspect of the invention relates to use of a sternal closure device described in the document DE 103 26 690 B4 or a fixing device described in the document DE 10 2006 021 025 B3 as a fixation system for stabilizing spinous processes of adjacent vertebral bodies relative to one another, with at least one spacer element can be positioned in the intervertebral space between fixing elements of the fixing device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The foregoing summary and the following description may be better understood in conjunction with the drawing figures, of which: 
         FIG. 1 : shows a perspective view of a first preferred embodiment of a fixation system in accordance with a first aspect of the invention; 
         FIG. 2 : shows a perspective view of a second preferred embodiment of a fixation system in accordance with a first aspect of the invention; 
         FIG. 3 : shows a perspective view of a third preferred embodiment of a fixation system in accordance with a first aspect of the invention; 
         FIG. 4 : shows a perspective view of a fourth preferred embodiment of a fixation system in accordance with a first aspect of the invention; 
         FIG. 5 : shows a perspective view of a fifth preferred embodiment of a fixation system in accordance with a first aspect of the invention; 
         FIG. 6 : shows the fixation system from  FIG. 1  when being fixed to two spinous processes; 
         FIG. 7 : shows the fixation system from  FIG. 2 , fixed to two spinous processes; 
         FIG. 8 : shows the fixation system from  FIG. 3  when being fixed to two spinous processes; 
         FIG. 9 : shows the fixation system from  FIG. 4 , fixed to two spinous processes; 
         FIG. 10 : shows a lateral-medial view of a plurality of vertebral bodies, the spinous processes of two vertebral bodies, in each case, being fixed relative to one another by a sixth preferred embodiment of a fixation system in accordance with a first aspect of the invention; 
         FIG. 11 : shows a schematic side view of a portion of an implantation tool during application on the fixation system from  FIG. 10 ; 
         FIG. 12 : shows a sectional view along the line  12 - 12  in  FIG. 11 ; 
         FIG. 13 : shows a sectional view along the line  13 - 13  in  FIG. 12 ; 
         FIG. 14 : shows a schematic sectional view of a portion of a further implantation tool, applied to the fixation system from  FIG. 10 ; 
         FIGS. 15A to 15C : show a perspective view of a seventh preferred embodiment of a fixation system in accordance with a first aspect of the invention when being fixed to two spinous processes, a spacer element being introduced between two spinous processes at the beginning ( FIGS. 15A and 15B ) and  FIG. 15C  showing the fixation system in the implantation position; 
         FIG. 16 : shows a perspective view of an eighth preferred embodiment of a fixation system in accordance with a first aspect of the invention when being fixed to two spinous processes; 
         FIG. 17 : shows a perspective view of a ninth preferred embodiment of a fixation system in accordance with a first aspect of the invention when being fixed to two spinous processes; 
         FIGS. 18A and 18B : show a perspective view of a tenth preferred embodiment of a fixation system in accordance with a first aspect of the invention when being fixed to two spinous processes, a spacer element firstly being introduced between the spinous processes ( FIG. 18A ) and  FIG. 18B  showing the fixation system in the implantation position; 
         FIG. 19 : shows a perspective view of an eleventh preferred embodiment of a fixation system in accordance with a first aspect of the invention; 
         FIG. 20 : shows a side view of an implantation tool when cooperating with the fixation system from  FIG. 19 ; 
         FIG. 21 : shows an enlarged partial view of the tool from  FIG. 20  when cooperating with the fixation system from  FIG. 19 ; 
         FIG. 22 : shows a perspective view of a twelfth preferred embodiment of a fixation system in accordance with a first aspect of the invention; 
         FIGS. 23A and 23B : show respectively a schematic plan view and a schematic side view of a fixing element of one of the fixation systems mentioned above; 
         FIGS. 24A and 24B : show respectively a schematic plan view and a schematic side view, partially sectional, of a further fixing element of one of the fixation systems mentioned above; and 
         FIGS. 25A and 25B  show a thirteenth preferred embodiment of a fixation system in accordance with a first aspect of the invention in an insertion position ( FIG. 25A ) and in an implantation position ( FIG. 25B ). 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 
     The present invention relates to a surgical fixation system for stabilizing spinous processes of adjacent vertebral bodies relative to one another comprises at least one first fixing element and at least one second fixing element, which can be transferred relative to one another from an insertion position into an implantation position, wherein the fixing elements in the implantation position have a smaller spacing from one another than in the insertion position and in which implantation position the fixing elements are engageable laterally from different sides with at least one of the spinous processes in each case. It also comprises a securing device for securing the fixing elements relative to one another in the implantation position and at least one spacer element, which can be fixed by the fixing elements in the implantation position thereof in the intervertebral space between the spinous processes. 
     A fixation system of this type solves the object to provide a fixation system for spinous processes having a structurally simple configuration. The at least one spacer element can be used to support the spinous processes relative to one another, and it can be fixed in a structurally simple manner by the fixing elements in the intervertebral space. In particular, it can further be provided that the fixing elements are engaged only by clamping with the spinous processes and are not screwed to them. The danger of a screw being pulled out, such as can occur in the fixation systems known from the prior art, can be thereby avoided. The spacer element, for example, allows for the fixing elements to take up a well-defined position relative to one another, and for the support of the spinous processes. The fixation system in accordance with a preferred embodiment of the invention also allows, in a structurally simple manner, a modular configuration of instruments for the fixation of the spinal column in accordance with an aspect of the invention, wherein it is possible for the at least one spacer element and the fixing elements to be available separately from one another, in each case, for example in different sizes. An individual adaptation to the size of the spinous processes to be stabilized with one another in each case can therefore be carried out in a simple manner by a suitable combination of one or more spacer elements with fixing elements. 
     “Vertebral body” in the present case designates both the vertebra as a whole and also the vertebral body in the narrower sense (“corpus vertebrae”). 
     “Adjacent vertebral bodies” primarily indeed means “directly adjacent vertebral bodies”, but, in the present case, is not restricted to directly adjacent vertebral bodies. 
     Anatomical position and direction details such as, for example “medial”, “lateral”, “cranial”, “caudal”, “dorsal”, “ventral”, “sagittal plane”, “anterior”, posterior” or the like, which relate to features of the fixation system, are to be understood, in the present case, as applied in the implantation position of the fixing elements, in which implantation position the fixation system is fixed to the spinous processes as intended. 
     It may, in particular, be provided that at least one spacer element can be fixed in positively-locking and/or force-locking manner. 
     For example, the at least one spacer element can be fixed by clamping, so the fixation system can be easily handled. 
     Furthermore, it is possible for the at least one spacer element to engage, in particular by latching, at least in the implantation position, with at least one fixing element. For this purpose it and/or the at least one fixing element can have engagement members. 
     The at least one spacer element may comprise or form at least one lateral contact face for at least one fixing element. 
     Furthermore, the at least one spacer element can comprise or form a cranial contact face for a spinous process, for example a planar, a saddle-shaped or a groove-shaped contact face. 
     The at least one spacer element can also comprise or form at least one caudal contact face for a spinous process, for example a planar, a saddle-shaped or a groove-shaped contact face. In combination with the last-mentioned implementation, the spinous processes can be supported against one another in the cranial-caudal direction. 
     It can be provided that the at least one spacer element comprises or forms at least one anterior contact face for at least one vertebral body, in particular dorsally for at least one lamina arcus vertebrae, the processus articularis superior and/or the processus articularis inferior at least of one of the vertebral bodies. A facet joint formed between adjacent vertebral bodies, for example, can be stabilized thereby. The contact face can be in the form of a strip. 
     Anterior and/or posterior to the at least one spacer element, a receiving space can be formed between the fixing elements, into which receiving space, for example, bone or a bone replacement material can be inserted for the supplementary stabilisation of the spinous processes relative to one another. 
     It is possible for at least one spacer element to form a receiving space for bone and/or bone replacement material. 
     Furthermore, it may be provided that at least one spacer element engages in the implantation position of the fixation system with at least one spinous process. For example, the spacer element comprises engagement members in the form of cutting edges, for example a thread. For this purpose, the spacer element can form a screw. 
     It may be provided that the at least one spacer element is rigid. 
     Alternatively, it may be provided that the at least one spacer element is deformable. 
     In particular, the at least one spacer element can be resiliently deformable, for example in the cranial-caudal, in the dorso-ventral and/or in the medial-lateral direction. 
     The at least one spacer element preferably acts upon the fixing elements in the implantation position with forces directed away from one another and is thereby reliably fixed between the fixing elements. 
     It may be provided that the size of at least one spacer element is variable, specifically in the cranial-caudal, in the medial-lateral and/or in the dorso-ventral direction. 
     In particular, an adjusting device for varying the size of the at least one spacer element may be provided. 
     The at least one spacer element is advantageously formed in one piece. 
     For example, the at least one spacer element is at least partially plate-like, it being possible for it to be plate-like overall, in particular. 
     With the plate-like portion, the at least one spacer element is oriented, for example, in a sagittal plane or parallel to a sagittal plane, with the fixation system being fixed to the spinous processes as intended. 
     The at least one spacer element may be lattice-shaped and thus have osteointegrative properties. 
     Furthermore, the at least one spacer element or a group of spacer elements, a “spacer package”, may be bellows-shaped. 
     The at least one spacer element may also be cushion-like and be formed as a gel-cushion or the like. 
     It may also be provided that the at least one spacer element is cuboidal and forms a hollow body, which, for example, can be filled with resilient elements. 
     It is possible for the at least one spacer element to comprise at least one engagement element for an engagement of the at least one spacer element with a further spacer element, so that the two spacer elements can adopt a defined position relative to one another. The at least one engagement element is, for example, a projection, in particular a strip or a rib. 
     A structurally simple fixation system comprises precisely one spacer element. 
     Another type of fixation system may comprise two or more spacer elements. These may together form an ensemble of spacer elements, a so-called “spacer package”. 
     The two or more spacer elements may be formed identically or at least two spacer elements may be formed identically. 
     In a corresponding manner, the two or more spacer elements may be formed differently, or at least two spacer elements may be formed differently. 
     It is possible for two or more spacer elements to abut against one another, wherein they can, in particular, rest flat on one another, for example in a sagittal plane, with the fixation system being fixed to the spinous processes as intended. 
     Furthermore, it is possible for two or more spacer elements to engage with one another, in particular in positively-locking manner. 
     For example, it is possible for two or more spacer elements to abut against one another or engage with one another with the medial-lateral direction, but it may also be provided that two or more spacer elements engage with one another or abut against one another in the cranial-caudal direction or in the dorso-ventral direction. 
     The at least one spacer element may be at least partially resorbable. 
     The at least one spacer element may be made at least partially from an osteointegrative material or be osteointegratively coated. 
     For example, the at least one spacer element is made from metal, for example from titanium. 
     The at least one spacer element may also be made from a plastics material, for example from PEEK. 
     It is also possible to make the at least one spacer element from bone material or a bone replacement material, such as, for example, hydroxyapatite. 
     The at least one spacer element may be at least partially coated, for example by vacuum-coating with high-purity titanium powder, which forms a rough microporous titanium layer for improved anchoring to the bone on the surface of the spacer element (so-called “Plasmapore” coating below). “Plasmapore” is a registered trademark of Aesculap AG and Aesculap Inc. 
     It is possible for at least one spacer element to be engaged or engageable with the securing device, in particular when the fixing elements adopt the implantation position. 
     In particular, the at least one spacer element can comprise or form at least one opening through which the securing device engages. 
     It is furthermore possible for the at least one spacer element to comprise or form at least one recess, in which the securing device engages. 
     Each fixing element in the implantation position is preferably engageable with two spinous processes in order to achieve a reliable stabilisation by the fixation system. 
     At least one fixing element can be planar. 
     Further, at least one fixing element can be adapted to be oriented in a sagittal plane or substantially in a sagittal plane when the fixation system is fixed to the spinous processes as intended. 
     It may be provided that at least one fixing element is rigid. 
     Furthermore, at least one fixing element may be deformable, in particular resiliently deformable. It may, for example, comprise defined deforming regions, for example bending zones, to allow an adaptation to the spinous processes. 
     It is possible for at least one fixing element to be rectangular. 
     It can also be provided that at least one fixing element is step-like with two portions offset relative to one another in the cranial-caudal direction. This is advantageous if a plurality of spinous processes are to be stabilized relative to one another. The offset may, for example, be approximately one third or approximately half of the cranial-caudal extent of the fixing element. 
     For engagement in the spinous processes, at least one fixing element has, for example, projections in the lateral-medial direction. 
     No projections are advantageously formed in the region of the intervertebral space, for example in order to avoid damage to the at least one spacer element or injury to the patient. For this purpose, the fixing element can comprise sections having projections at opposite ends and a section without projections therebetween. 
     The projections are, for example, arranged at one edge of the fixing element. 
     It may furthermore be provided that the projections enclose an acute angle with a plane defined by the fixing element. 
     It is possible for the projections to be deformable in a defined manner. For example, they can be transferred into an engagement position, in that the angle, which they enclose with the fixing element, is increased. 
     At least one fixing element may be made from metal, for example from titanium. A resorbable fixing element, a fixing element made of a plastics material and an at least partially coated fixing element are also conceivable. 
     The securing device is preferably a latching device, having one or more latching elements. 
     At least one latching element can be, for example, be a clamp rod or tie rod. 
     The latching device can, in particular, be a self-locking latching device, which facilitates implantation of the fixation system. 
     The latching device may, for example, have at least one latching element, which is fixed to a fixing element and on which the other fixing element can be latched, so that it can be easily operated. 
     In addition or alternatively, separate locking members can be provided for latching to the latching elements, so that a fixing element can be fixed thereto. 
     The at least one latching element can engage through the at least one spacer element or engage therein, so that the at least one spacer element can be fixed on the securing device. 
     Furthermore, the at least one latching element can engage through at least one fixing element or engage therewith. 
     The latching device can comprise two or more latching elements, which can be formed identically or differently. 
     The present invention further relates to a method, in which a sternal closure device described in the document DE 103 26 690 B4 or a fixing device described in DE 10 2006 021 025 B3 is used to stabilize spinous processes of adjacent vertebral bodies relative to one another, with at least one spacer element being positioned between two fixing elements of the fixing system in the intervertebral space. 
     Moreover, as mentioned at the outset, the invention further relates to a spacer element. A spacer element in accordance with the invention can comprise one or more features which the at least one spacer element of the fixation system in accordance with the invention or one of the preferred embodiments of the fixation system has and is adapted to be used in a fixation system in accordance with the invention. 
     As mentioned at the outset, the invention further relates to a use. In accordance with the invention, a sternal closure device described in the document DE 103 26 690 B4 or a fixing device described in the document DE 10 2006 021 025 B3 can be used as a fixation system for stabilizing spinous processes of adjacent vertebral bodies relative to one another. These two documents are hereby incorporated in their entirety by reference. The sternal closure device or the fixing device does not need to agree in all its details with the sternal closure device known from DE 103 26 690 B4 or with the fixing device known from DE 10 2006 021 025 B3. For example, a difference is possible with regard to the size, ratio of the longitudinal side to the transverse side of the fixing elements, arrangement of the fixing projections on the fixing elements, arrangement of the securing pins relative to the fixing elements or the like. At least one spacer element can be positioned between the fixing elements in the intervertebral space. 
     When using the sternal closure device or the fixing device, a fixing element is advantageously transferred in each case into an implantation position and engaged laterally with at least one spinous process, the fixing elements being arranged on different lateral sides of the spinous processes. 
     A first preferred embodiment in accordance with an aspect of the invention of the fixation system  10  shown perspectively in  FIG. 1  comprises a first, rectangular fixing element  11  and a second fixing element  12 , which is of substantially identical configuration to the first fixing element  11 . Both fixing elements, on their edges carry engagement members directed towards the respective other fixing element and substantially projecting transversely from the planar fixing elements, in the form of tooth-shaped projections  13 . However, on their respective long sides, the two fixing elements  11 ,  12  have regions  14 , which are free of projections  13  and which in each case extend over approximately a central third of the length of the fixing elements  11 ,  12 . 
     By means of the projections  13 , the fixing elements  11 ,  12  can penetrate into bone material, for example into spinous processes  15  and  16  of vertebral bodies  17  or  18 , respectively. The vertebral bodies  17  and  18  may be human or animal vertebral bodies. “Vertebral body” in the present case designates both the vertebra as a whole and also the vertebral body in the narrower sense (“corpus vertebrae”). 
     By penetrating into the spinous processes  15  and  16 , the fixing elements  11  and  12  can secure them against a movement relative to one another in the cranial-caudal, dorso-ventral and lateral direction. The fixing elements  11 ,  12  are in this case applied laterally from different sides onto the spinous processes  15 ,  16 , each of the fixing elements  11 ,  12  being able to penetrate into both spinous processes  15 ,  16  and the fixing elements being oriented with their longitudinal direction in the cranial-caudal direction. 
     The fixation system furthermore comprises a securing device  19 , which is configured as a latching device and comprises two identical latching elements  20 ,  21 . The latching elements  20 ,  21  are tie rods  22 ,  23  which are fixed to the fixing element  12 , oriented perpendicular thereto and on which the fixing element  11  can be latched in a self-locking manner. For this purpose, the tie rods  22 ,  23  have peripheral ribs  24  into which resilient arm elements  25  on the fixing element  11  can latch. 
     By means of the securing device  19 , the fixing elements  12 ,  13  can be immovably fixed to the spinous processes  15 ,  16 , in that one of the fixing elements  12 ,  13  is placed on the spinous processes  15 ,  16 , with the tie rods  22 ,  23  engaging through an intervertebral space  26  from lateral to lateral. If the fixing elements  11 ,  12  are moved toward one another, the other one of the fixing elements  11 ,  12  also engages in the spinous processes  15 ,  16 . A renewed removal of the fixing elements  11 ,  12  from one another is not possible as they are secured by means of the latching securing device  19  against a movement increasing their spacing from one another. A position of this type of the fixing elements  11 ,  12  relative to one another defines an implantation position, in which the fixing elements  11 ,  12  have a smaller spacing from one another than in an insertion position ( FIG. 6 ), in which the fixation system  10  can be inserted into the body interior for implantation. 
     The fixation system  10 , as described up to now, is a fixation system in the manner of the sternal closure device described in document DE 103 26 690 B4 and in the manner of the fixing device described in the document DE 10 2006 021 025 B3. Reference is expressly made hereby to the aforementioned documents, and they are incorporated in the present application in their entirety by reference. The invention also relates to a use of a sternal closure device identical to that or in the manner of that, as described in DE 103 26 690 B4, and to the use of a fixing device identical to or in the manner of the fixing device described in document DE 10 2006 021 025 B3 for fixing the spinous processes of adjacent vertebral bodies relative to one another with at least one spacer element being positioned in the intervertebral space between the spinous processes. 
     Furthermore, the fixation system  10  comprises two spacer elements  27  and  28 , which are positioned between the fixing elements  11  and  12  and are inserted into the intervertebral space  26  during the use of the fixation system and are fixed therein by clamping. In the longitudinal direction of the fixing elements  11 ,  12 , they adopt approximately the width of the free region  14 . The spacer elements  27 ,  28  in each case have cranial-caudally extending ribs  29  and grooves  30 , so the spacer elements  27  and  28  can positively engage in one another in the manner of combs, their spacing from one another being variable in the lateral-lateral direction, depending on to what extent they engage in one another. “Lateral-lateral” is to be understood as transverse to the cranial-caudal direction in the intervertebral region  26  substantially in the median plane, to a certain extent “lateral-medial-lateral” in the intervertebral region  26 . 
     The spacer elements  27  and  28  in each case have a cranial contact face  31  for the spinous process  15 , a caudal contact face, not shown in the drawing, for the spinous process  16 , an anterior contact face  32  for the laminae arcus vertebrae of the vertebral bodies  17  and  18  and a lateral contact face  33  for the fixing elements  11  and  12 . In the ventral direction they extend over the fixing elements  11 ,  12 . 
     By means of the cranial contact face  31  and the caudal contact face, the spinous processes  15  and  16  can be supported in the cranial-caudal direction, the contact face  32  is used for stabilisation in the dorso-ventral direction of the vertebral bodies  17  and  18 , and by means of the contact faces  33 , the spacer elements  27 ,  28  are fixed in force-locking manner by clamping in the intervertebral space  26  by the fixing elements  11 ,  12 . Overall, a well-defined position of the fixing elements  11 ,  12  relative to one another can be obtained. This makes possible a reliable stabilisation of the spinous processes  15  and  16  relative to one another. 
     The fixation system  10  furthermore proves to be usable in diverse ways, because the spacer elements  27  and  28 , depending on the width of the intervertebral space  26  in the lateral-lateral direction, can engage to different extents with one another. This makes it possible to reliably support spinous processes of different dimensions against one another by means of the spacer elements  27 ,  28 . 
     Formed posterior to the spacer elements  27  and  28 , between the fixing elements  11 ,  12 , is an intermediate space  34 , which can, for example, be additionally filled with a bone material or bone replacement material when the fixation system  10  is applied. 
     Furthermore, the spacer elements  27 ,  28  have recesses  35  and  36 , in which the tie rods  22  and  23  can engage. As a result, the spacer elements  27  and  28  are also fixed by clamping between the tie rods  22 ,  23  in the cranial-caudal direction. In the implantation position of the fixation system, they are particularly reliably fixed thereby in the intervertebral space  26 . 
     Despite the versatility already mentioned, the fixation system can additionally be constructed in a modular manner; it can comprise fixing elements  11 ,  12  of different dimensions here as well as spacer elements  27  and  28  of different dimensions, which can be combined with one another as required. This reduces the quantity of material to be stored by the user and, nonetheless, the most varied requirements predetermined by different vertebral bodies can be individually taken into account. 
     The spacer elements  27 ,  28  may be rigid, they may be deformable, they may be resiliently deformable, they may be resorbable, they may be made from a metal, such as for example titanium, they may be made from a plastics material such as, for example, PEEK, they may consist of bone or other bone replacement material such as, for example, hydroxyapatite, they may be at least partially coated, for example with a Plasmapore coating and they may be osteointegrative. Further advantageous properties of the spacer elements  27 ,  28  are conceivable. 
       FIGS. 2 to 5  show further preferred embodiments  37 ,  38 ,  39  or  40  respectively, of the fixation system in accordance with an aspect of the invention.  FIGS. 7 and 8  show the fixation systems  37  or  39  respectively, in each case in the implantation position fixed on the spinous processes  15 ,  16 , and  FIG. 8  shows the fixation system  38  in an insertion position, a fixing element  12  of the fixation system  38  already being engaged with the spinous processes  15 ,  16 . 
     All the fixation systems  10 ,  37 ,  38 ,  39  and  40  use the same fixing elements  11  and  12  and the same securing device  19 , and they only differ with respect to their spacer elements, so that reference will only be made to the spacer elements of the fixation systems  37  to  40  below and otherwise reference is made to the above statements on the fixation system  10 . 
     Identical and identically-acting features or components of the spacer elements of the fixation systems  10  and  37  to  40  have the same reference numerals. 
     The fixation system  37  ( FIGS. 2 and 7 ) comprises a plurality of a total of five spacer elements  41 ,  42 ,  43 ,  44  and  45 . The spacer elements  41  to  45  are in each case planar in a disc form, each being oriented approximately in a sagittal plane. In the lateral-lateral direction, adjacent spacer elements in the non-implanted state, abut against one another along contact lines. The spacer elements  41 ,  43  and  45  are planar, whereas the spacer elements  42  and  44  are convex or concave respectively, in the lateral-lateral direction. 
     The spacer elements  41  to  45  are preferably resiliently deformable, so that they form a resilient spacer package  46  in the lateral-lateral direction in their entirety. When transferring the fixing elements  11  and  12  into the implantation position ( FIG. 7 ), the spacer package  46  can be compressed in the lateral-lateral direction. On the one hand, this provides the possibility of using the spacer package  46  in a large number of spinous processes  15 ,  16  of different dimensions and nevertheless allowing a well-defined relative position of the fixing elements  11 ,  12  and a reliable support of the spinous processes  15 ,  16 . On the other hand, the spacer package  46  is reliably fixed relative to the fixing elements  11 ,  12 , which it in each case acts upon with a medial-lateral force counteracting the clamping force of the fixing elements  11 ,  12 . 
     The fixation system  37  can also be constructed in a modular manner, for example the number of spacer elements may be varied and selected depending on the size and type of spinous processes  15 ,  16 . Furthermore, it is possible for the spacer elements  41  to  45  to project anteriorly beyond fixing elements  11 ,  12 , so that they also form an anterior contact face  32  for the vertebral bodies  17 ,  18 . 
     Provided in the fixation system  38  are five spacer elements  47 ,  48 ,  49 ,  50  and  51 , which are formed identically and together form a spacer package  52 . Each of the spacer elements  47  to  51  is a disc spring constructed from two segments  53  and  54  abutting against one another at the edge, which is deformable in the lateral-lateral direction and can flex. Each segment  53  of a spacer element rests flat on the segment  54  of an adjacent spacer element, and the spacer elements  47  to  51  are in each case oriented substantially in a sagittal plane. 
     Because of the resilient effect of each of the spacer elements  47  to  51 , the spacer package  52  is also resilient in the lateral-lateral direction. The advantages mentioned as above in conjunction with the spacer package  46 , to which reference is made, can thus already be achieved. 
     The fixation system  37  is also constructed in a modular manner. Thus, for example, the size of the spacer elements  47  to  51  or their number can be varied in order to allow a particularly individual adaptation of the fixation system  38  to the spinous processes  15 ,  16 . A high level of diversity of the fixation system  38  as well is made possible purely because of the spacer package  52 . 
     The fixation system  39  comprises a one-piece spacer element  55 , which is lattice-shaped and can be made, in particular, from a metal such as, for example, titanium. Because of the lattice-shaped structure, the spacer element  55  is porous and therefore has particularly good osteointegrative properties. In particular, the spacer element  55  may be coated, for example with a Plasmapore coating. 
     Moreover, the spacer element  55  also has a cranial contact face  31 , a caudal contact face and an anterior contact face  32 . In the lateral direction, the spacer element  55  can rest virtually flat on the fixing elements  11 ,  12  by means of a large number of individual support points  56  and also be held, in the implantation position thereof in the intervertebral space  26  in a reliable manner by clamping. 
     The spacer element  55  is also fixed on the tie rods  22  and  23 , for example they engage through said spacer element. 
     A modular configuration of the fixation system  39  is also possible, for example in that a plurality of spacer elements with the properties of the spacer element  55  is made available, in order to allow a particularly individual adaptation of the fixation system  39  to the spinous processes  15  and  16 . 
     A spacer element  57 , which is cuboidal and can be formed as a hollow body having an interior  58 , is used in the fixation system  40 . The interior  58  may be hollow, the spacer element  55  preferably having resiliently deformable properties. As a result, it forms a resilient buffer in the lateral-lateral direction between the fixing elements  11  and  12 , so that the advantages which can be achieved by the spacer packages  46  and  52  can also be achieved with the spacer element  55 . This is even possible when further spacer elements, for example, are received in the interior  58 , for example spacer elements of the same type as the spacer elements  41  to  45  and/or of the same type as the spacer elements  47  to  51 . 
     It may be provided that the spacer element  57  comprises two segments  61  and  62  that can be spaced relative to one another in order to have access to the interior  58 . A particularly individual adaptation to the spinous processes  15 ,  16  can thereby be implemented, for example, in a modular configuration of the fixation system  40 . For example, depending on requirement, one or more spacer elements can be inserted into the interior  58 . 
     Furthermore, openings  59  and  60  for the tie rods  22  and  23  in the spacer element  57  are formed to allow particularly reliable fixing of the spacer element  57  in the implantation position of the fixation system  40 . Moreover, the spacer element  57  has a cranial contact face  31  and a caudal contact face as well as respective lateral contact faces  33  for the fixing elements  11  and  12 . 
     The spacer elements  41  to  45 ,  47  to  51  and  57  can have all the properties, which have already been mentioned above in conjunction with the spacer elements  27  and  28  of the fixation system  10 . 
       FIG. 10  shows in a lateral-medial view, four vertebral bodies  63 ,  64 ,  65  and  66  with spinous processes  67 ,  68 ,  69  and  70 , respectively. One fixation system  71  in each case of a sixth preferred embodiment fixes the spinous processes  67  and  68 ,  68  and  69  as well as  69  and  70  to one another. The fixation system  71  differs from the fixation system  10  in that its fixing elements, of which only one fixing element  72  is shown, do not have a rectangular configuration. The fixing element  72  instead comprises two, in each case rectangular portions  73  and  74 , which are offset relative to one another in the cranial-caudal direction. The offset is approximately one third of the length of the fixing element  72 , but it could also be greater, for example about 40% or about half of the length of the fixing element  72  (see, for example, the variants in  FIGS. 15C ,  17 ,  22  and  23 A to  24 B). The fixing element  72  thus receives an overall step-like construction. This is advantageous if a plurality of spinous processes  67  to  70  is to be stabilized. In this case, as shown in  FIG. 10 , projecting regions of the portions  73  and  74  of a fixing element  72  can in each case project into set-back regions of the portions  73  and  74  of an adjacent fixing element  72 . 
     Otherwise, the fixation system  71  is formed like the fixation system  10 , so reference can be made to the above statements. It is also possible for the fixing elements  72  to be used instead of the fixing elements  11  and  12  in each of the fixation systems  37  to  40 . 
     To implant the fixation systems  10 ,  37  to  40  and  71 , a tool  75  shown only schematically and in portions in  FIGS. 11 to 13  can be used. It is shown cooperating with the fixation system  71 , wherein apart from the fixing element  72 , a fixing element  76  formed mirror-inverted thereto, the tie rods  22  and  23  of the securing device  19  and a spacer element of the fixation system  71  are also shown. 
     The tool  75  comprises a first tool part  77  with end, cavity-shaped recesses  78  and  79  for end portions  80  or  81  of the tie rods  22  or  23 , respectively. Adjacent to the recesses  78  and  79 , the tool part  77  has exterior projections  82  or  83  with openings  84  or  85 , respectively. Guided through the openings  84  and  85  are angled fixing parts  86  or  87 , respectively, which run parallel to the tool part  77  and, at a right angle to the longitudinal direction thereof, comprise holding portions  88  or  89 . The holding portions  88  and  89  can engage below the end portions  80  and  81 . The fixing parts  86  and  87  are in each case rotatably mounted in the openings  84  and  85  about an axis defined by the longitudinal direction thereof. 
     A second tool part  90  of the tool  75  is substantially identically formed to the first tool part  77  and is used to handle the fixing element  76 . 
     To use the tool  75 , the end portions  80  and  81  can be introduced into the recesses  78  or  79  and the fixing parts  86  and  87  can be rotated relative to the tool part  77  in such a way that the holding portions  88  and  89  positively fix the end portions  80  and  81  in the recesses  78  or  79 , respectively ( FIG. 12 ). 
     The same applies to the ends of the tie rods  22  or  23 , which oppose the end portions  80  and  81 , respectively, and can also be held by means of the tool part  90  and fixing parts formed corresponding to the fixing parts  86  and  87 . The fixation system  71  is thus held on the tool  75  and can be introduced therewith into the body. By pivoting the tool parts  77  and  90  relative to one another about a pivot axis oriented perpendicular to the longitudinal direction of the tool parts  77  and  90  and perpendicular to the longitudinal direction of the tie rods  22  and  23 , the fixing elements  72  and  76  can be moved closer to one another and thereby transferred into an implantation position. A displacement of the tool parts  77  and  90  relative to one another along the tie rods  22  and  23  also allows a transfer of the fixing elements  72  and  76  into the implantation position. 
       FIG. 14  schematically shows a further tool  91 , in which the tool part  77  is to a certain extent divided in the transverse direction into two tool parts  92  and  93 , between which an intermediate space  94  is formed. An actuator  95  is displaceably mounted in the intermediate space  94  in the longitudinal direction of the tool  91 . The actuator  95  is tapered conically at the end. If the actuator  95  is displaced relative to the tool parts  92  and  93 , its conically tapered end portion  96  can displace blocking elements  97  and  98  in the form of balls transverse to the displacement direction, so that the end portions  80  and  81  are fixed in the recesses  78  or  79 , respectively. The tool  91  in this case, manages without the fixing parts  86  and  87 . 
       FIGS. 15A to 15C  partially or completely show a seventh preferred embodiment of a fixation system in accordance with an aspect of the invention having the reference numeral  99 . The fixation system  99  comprises, similar to the fixation system  71 , fixing elements  100  and  101 , which are mirror inverted with relative to one another, each with rectangular portions  102  and  103  offset with respect to one another in the cranial-caudal direction. The portions  102  and  103  approximately half overlap one another in each case. Furthermore, a securing device  104  in the manner of the securing device  19  of the fixation system  10  is provided. The above statements are referred to in this regard. 
     The fixation system  99  also comprises a one-piece spacer element  105  formed, for example, from plastics material or metal. The spacer element  105 , with regard to the basic shape, has the shape of a hollow cylinder, from which axially extending arcuate segments have been removed, in each case, on mutually opposing lateral sides. As a result, planar lateral contact faces  106  or  107  facing the fixing elements  100  and  101 , respectively, are formed on the spacer element  105 . A slot-shaped recess  108  or  109  extending in an axially parallel manner is formed into each of the contact faces  106  and  107 , respectively. 
     Between the contact faces  106  and  107 , a plurality of cutting edges  110  sharply tapered in the radial direction and spaced apart from one another in the dorso-ventral direction run on the outside of the spacer element  105 . The cutting edges  110  may be segments of a spiral cutting edge extending over the surface of the spacer element  105 , to a certain extent individual threads of a screw formed by the spacer element  105 , which are interrupted in each case on the contact faces  106  and  107 . It is also conceivable for the cutting edges  110  not to arise from a spiral of this type, but to in each case be arranged in a plane oriented perpendicular to the dorso-ventral direction. This is the case in the embodiment shown in  FIGS. 15A to 15C , in which the cranially oriented and the caudally oriented cutting edges are offset relative to one another in the dorso-ventral direction, in other words “with a gap”. A caudal contact face, not visible in detail, and a cranial contact face, also not visible in detail, for the spinous process  16  or  15  are formed on the shell of the hollow-cylindrical spacer element  105  between the cutting edges  110 . 
     When implanting the fixation system  99 , the procedure can be as follows: 
     Firstly, the intervertebral space  26  is prepared, for example with a suitable thread cutter, in order to form slot-shaped recesses  111  to receive the cutting edges  110  on the spinous processes  15  and  16 . The spacer element  105  can then be screwed into the spinous processes  15  and  16  if it has screw-shaped cutting edges  110 . If this is not the case as in the variant shown, the spacer element  105  can be introduced into the intervertebral space  26  rotated through 90° compared to the configuration shown in  FIGS. 15A to 15C  and rotated therein through 90° such that the cutting edges  110  cooperate with the recesses  111  ( FIG. 15B ). In the cranial-caudal direction, the spinous processes  15  and  16  are thus resiliently supported relative to one another, the spacer element  105  being particularly reliably fixed on the spinous processes  15  and  16 . 
     The fixing elements  100  and  101  are then placed laterally on the spinous processes  15  and  16  and transferred to the implantation position, being secured therein by means of the securing device  104  ( FIG. 15C ). In the lateral-lateral direction, the spacer element  105  is dimensioned such that the fixing elements  100  and  101  in their regions engaged with the spinous processes  15  and  16  are slightly deformable in the lateral-medial direction. For example, this can be seen from the bending edges  112  and  113  of the fixing element  100 . As a result, the fixing elements  100  and  101  are additionally prestressed relative to one another so that the fixation system  99  is reliably fixed. 
     It can be provided in the hitherto mentioned further preferred embodiments of a fixation system in accordance with an aspect of the invention that the respective fixing elements, as with the fixing elements  100  and  101  of the fixation system  99 , are also to be deformed in the lateral-medial direction and, in particular, to be bent, for example in a spacer element or spacer package projecting out of the intervertebral space in the lateral direction. 
     It may further be provided in the fixation system  99  that the hollow space  114  enclosed by the spacer element  105  is filled with bone or bone replacement material in order to achieve still better cranial-caudal support properties. This may, for example, also be provided if, instead of the spacer element  105 , a hollow screw is used that is screwed to the spinous processes  15  and  16 . 
     The spacer element  105 , in manner corresponding to the spacer elements  27  and  28  of the fixation system  10 , can have a large number of different properties already mentioned above, to which reference is hereby made in order to avoid repetitions. These properties can also be fulfilled in the spacer elements of the fixation systems to be described below, so that these properties will not be listed again below either and reference is made to the above statements. 
     Likewise, the fixation system  99  and the fixation systems still to be described below, as with the fixation system  10 , can be modularly constructed. Depending on the type and size of the spinous processes  15  and  16  to be connected to one another, the operator can be provided with a set of surgical instruments which comprise a plurality of, for example, spacer elements of different sizes formed in the same manner as the spacer element  105 , and the same applies to the fixing elements  100  and  101 . As required, for example in accordance with the type of vertebral bodies  17  and  18 , and also the size of the patient or the like, the operator can take the fixing elements best suited for the respective use and the spacer element(s) from the instruments and implant them in combination with one another. 
     A variant of the spacer element  105  is formed as a coil spring, which can be inserted in the dorso-ventral direction into the intervertebral space  27  and projects laterally out of it in each case. By transferring the fixing elements  100  and  101  into the implantation position, this coil spring can be compressed in the lateral-lateral direction and thereby a cranial-caudal prestressing and therefore support between the spinous processes  15  and  16  can be achieved (not shown). 
       FIG. 16  shows an eighth preferred embodiment of a fixation system in accordance with an aspect of the invention which has the reference numeral  115 . The fixation system  115  comprises a one-piece spacer element  116  and a pair of fixing elements  117  and  118  formed mirror-inverted with respect to one another and furthermore also a securing device, not shown in the drawing, in the manner of the securing device  19 . 
     The spacer element  116  forms a groove-shaped cranial receiver  119  for the spinous process  15  with a corresponding contact face in the cranial direction and, furthermore, an also groove-shaped receiver  120  for the spinous process  16  with a corresponding contact face in the caudal direction. In the lateral-lateral direction, the spacer element  116  projects out of the intervertebral space  26 . 
     The fixing elements  117  and  118  are deformable and, in particular, bendable. They in each case comprise two portions  121  and  122  extending in the longitudinal direction. The portions  121  and  122  are each in the form of a strip. At the cranial end of the fixing element, the portions  121  and  122  are connected to one another by a bridge  123 , to a certain extent the “head” of the fixing element  117 . The portion  121  is arranged posterior with respect to the portion  122 , and it runs from the spinous process  15  laterally over the spacer element  116  to the spinous process  16  laterally, with which it engages, in each case, with it laterally fixing the spacer element  116  by clamping. 
     In contrast to this, the portion  122 , proceeding from the bridge  123 , is further bent over in the lateral direction, so that it extends both over the processus articularis inferior of the vertebral body  17  and also the processus articularis superior of the vertebral body  18 . In the implantation position of the fixation system  115 , the portion  122  is connected to the processus articularis superior of the vertebral body  18 , for example by means of an anchoring member  124  in the form of a screw, which can also engage in the processus articularis inferior of the vertebral body  17 . The same applies in a mirror-inverted manner to the fixing element  118 . This allows the vertebral bodies  17  and  18  to be particularly reliably fixed to one another. 
       FIG. 17  shows a ninth preferred embodiment of a fixation system in accordance with an aspect of the invention and designated by the reference numeral  125 , which is shown in the implantation position. The fixation system  125  comprises fixing elements  126  and  127 , which are formed substantially identically to the fixing element  72 , and a spacer element  128  fixed between them by clamping, substantially identically to the spacer element  116 . The fixation system  125  further comprises a schematically shown securing device  129  with two securing elements in the form of latching tie rods  130  and  131 . 
     Spring elements  132  and  133  cover the fixing elements  126  or  127  laterally, and they are formed in a similar manner to these from two portions offset relative to one another in the caudal-cranial direction. The spring elements  132  and  133 , caudally and cranially at the end, have respective recesses  134  and  135 , respectively, into which projections  136  arranged at the end side on the fixing elements  126  and  127  can engage from medial to lateral. The length of the spring elements  132  and  133  in the caudal-cranial direction is greater than that of the fixing elements  126  or  127 , respectively, and they are further resiliently deformable. As a result, a preload, which can be transmitted to the spinous processes  15  and  16  for improved fixing of the fixation system  125 , can be exerted by the spring elements  132  and  133  on the fixing elements  126  and  127  both in the lateral and in the cranial-caudal direction. 
     So that the spring elements  132  and  133  do not give way laterally, they can also be fixed relative to one another by means of the securing device  129 , in particular, the tie rods  130  and  131  can be fixed to the spring element  133 , this is not shown in the drawings. They engage through the fixing element  127 , the spacer element  128 , the fixing element  126  and the spring element  132 , which can be fixed to them by latching relative to the spring element  133 . 
     The fixing elements of all the fixation systems can also be connected to one another to form a frame, for example made of metal. A frame of this type can be used to incorporate bone or a bone replacement material in the intervertebral space  26 , in addition to the spacer element being used in each case. For example, in the fixation system  125 , the fixing elements  126  and  127  can be connected to one another posterior to the spinous processes  15  and  16  and together form a frame. 
       FIGS. 18A and 18B  show a tenth preferred embodiment of a fixation system in accordance with an aspect of the invention designated by the reference numeral  138 . The fixation system  138  comprises fixing elements  139  and  140 , which are substantially identically configured to the fixing element  72 , a securing device  141  of the same type as the securing device  19  and a spacer element  142 , which can, in particular, be formed in one piece and is constructed in substantially three portions, of which only portions  143  and  144  are shown in the drawing. 
     The first portion  143  is inserted in shape-locking manner into the intervertebral space  26  between the spinous processes  15  and  16 , with it forming a cranial contact face  145  and a caudal contact face  146  for these. 
     The third portion, not shown, of the spacer elements  142  is mirror-inverted with respect to the second portion  144 , so only the second portion  144  will be dealt with below. The second portion  144  is arranged anterior to the first portion  143 , so a shape-locking connection is also achieved in the dorso-ventral direction between the spacer element  142  and the vertebral bodies  17  and  18 . In particular, the second portion  144  is in the form of a strip and projects laterally from the first portion  143 , in a way, as a “wing” thereof, and has an approximately sinusoidal profile in the lateral-medial transverse sectional direction. The second portion  144  can therefore rest flat on the laminae arcus vertebrae both of the vertebral body  17  and the vertebral body  18  and bring about a reliable dorso-ventral fixing. 
     In the cranial-caudal direction, the second portion  144  can, for example, extend from the processus articularis inferior of the vertebral body  17  to the processus articularis inferior of the vertebral body  18 . It is even conceivable for the second portion  144  to extend in the cranial direction up to the processus articularis superior of the vertebral body  17 . In a plan view from the dorsal direction, the spacer element  142  thereby receives approximately the profile of a large H. 
     When adapting the spacer element  142 , it may be advantageous to prepare the laminae arcus vertebrae of the vertebral bodies  17  and  18  in advance, for example by punching. This provides the possibility of further increasing the shape-locking connection between the spacer element  142  and the vertebral bodies  17  and  18 . If the spacer element is osteointegrative, the adhesion is thereby improved. 
     In the implantation position, the fixing elements  139  and  140  can laterally overlap the spacer element  142  in the manner already mentioned and be secured to one another by means of the securing device  141  ( FIG. 18B ). 
     An eleventh preferred embodiment of a fixation system in accordance with an aspect of the invention is perspectively shown in  FIG. 19  and has the reference numeral  147 . It comprises fixing elements  148  and  149  in the manner of the fixing element  72  and a spacer element  150 , which can be latched by means of latching arm elements  151  on at least one of the fixing elements  148 ,  149 . 
     The fixation system  147  further comprises a securing device  152  for securing in the implantation position, which, is substantially identical to the securing device  19  of the fixation system  10 . Accordingly, the securing device  152  comprises latching elements  153  and  154  in the form of tie rods  155  or  156 , each with peripheral ribs  157 . The tie rods  155 ,  156  are fixed to the fixing element  148 . 
     For cooperation with the tie rods  155  and  156 , the securing device  152  has locking members in the form of latching discs  158  or  159 , respectively. The latching discs  158 ,  159  are slotted cross-wise and can be latched onto the tie rods  155 ,  156 . In contrast to this, a latching of the fixing element  149  to the tie rods  155 ,  156  is not provided. This is nevertheless also possible. 
     At least the side of the latching discs  158 ,  159  facing the fixing element  149  can be concavely curved and thereby, for example, have a spherical contour. In practice, the latching disc  158 ,  159  can be oriented in an improved manner relative to the tie rod  155 ,  156  when the fixing element  159  tilts because of the anatomic circumstances of the spinous processes  15  and  16  and adopts an oblique orientation with respect to the fixing element  148 . 
     Although the securing device  152  was initially described in the fixation system  147 , it is obviously possible for the securing device  152  to be used instead of the respective securing device of each of the above-described fixation systems. It is furthermore conceivable for the spacer element  150  to be used instead of the respective spacer element(s) in one of the fixation systems mentioned above. 
       FIGS. 20 and 21  show a further tool  160  for the implantation of one of the above-described fixation systems. The fixation systems, shown in  FIGS. 20 and 21  using the example of the fixation system  147 , can be transferred by means of the tool  160  from the insertion position into the implantation position. 
     The tool  160  comprises two tool parts  162  and  163 , which can be pivoted about a pivot axis  161  relative to one another, of which each has a handle element  164  or  165  and a jaw part  166  or  167 , respectively. A groove-shaped recess  168  running transverse to the longitudinal direction of the tool  160  is formed at least on the jaw part  167  at the end. A comparable recess can also be formed at the end on the jaw part  166 . 
     To transfer the fixation system  147  from the insertion position into the implantation position, the jaw part  166  can be placed on the fixing element  148  and the jaw part  167  can be placed on one of the latching discs  158 ,  159 , the tie rod  155  or  156  associated with these latching discs  158 ,  159 , respectively, in each case being able to engage in the recess  168 . If the tool parts  162 ,  163  are pivoted relative to one another about the pivot axis  161  while moving the jaw parts  166 ,  167  towards each other, the respective tie rod  155 ,  156  can be guided through the recess  168 —optionally through the recess also formed on the mouth part  166 —for the reliable transfer of the fixation system  147  into the implantation position. 
     A twelfth preferred embodiment of a fixation system in accordance with an aspect of the invention is partially shown in  FIG. 22  with a spacer element schematically depicted and has the reference numeral  169  therein. It comprises fixing elements  170 ,  171  with the shape of the fixing element  72  and a securing device  172  of the same type as the securing device  152 . 
     The special feature of the fixation system  169  is that engagement members for anchoring the fixing elements  170 ,  171  to the spinous processes  15 ,  16  are not projections arranged at the edge of the fixing elements  170 ,  171 , as in the fixation systems mentioned until now. Instead, projections  173  are arranged in the face of the fixing elements  170 ,  171 , and they to a certain extent can be “extended” from the planes defined thereby, in each case. 
     For example, the fixing element  170  comprises four centres of projections  173 , which, during insertion of the fixation system  169 , can be arranged in the plane defined by the fixing element  170  or can adopt a small acute angle relative to this plane. This is shown in  FIG. 22 , for example. Arranged in a circle on each of the four centres of projections are projections  173 , which are tapered and form engagement lugs to engage in the spinous processes  15 ,  16 . By acting upon the projections  173  with a force directed onto the respective other one of the fixing elements, the projections  173  can be transferred to a larger angle with respect to the plane defined by the fixing element  170 . If the fixing element is manufactured from metal, the projections  173  are, for example, bent over, perhaps with crimping pliers. 
     If the projections  173  in an engagement position of this type adopt a larger angle with respect to the fixing element  170 , they can be anchored on the spinous processes  15 ,  16  in an improved manner. If the projections  173  adopt the insertion position, in which they are arranged in the plane defined by the fixing element  170  or only adopt an acute angle relative to it, the fixation system  169  can be inserted into the intervertebral space  26  in a simpler manner. In addition, a risk of injury to the patient can be reduced as the projections  173  can be extended not until during the final transfer of the fixation system  169  into the implantation position. 
     It can be provided that the further fixation systems described above comprise engagement members in the manner of the projections  173 , in addition to the projections  13  or instead of the projections  13 . 
       FIGS. 23A and 23B  show a plan view and a side view respectively of a fixing element  174 , as can be used in each of the fixation systems described here. The fixing element  174  has a carrier  175 , which is provided at least on one side with a coating  176 . The coating  176  is, for example, a Plasmapore coating, in which high-purity titanium powder is applied to the carrier  175  by a vacuum method. This improves its osteointegrative properties in that a rough, microporous titanium layer is formed on the carrier  175 , which leads to improved adhesion to the intervertebral bodies  17 ,  18 . At least the side of the carrier  175  facing the spinous processes  15 ,  16  is coated. 
     The fixing element  174  can have at least one defined deformation region, as was described above with the aid of the fixing element  100 . 
     The deformation region is, for example, a bending zone  177  in order to facilitate an adaptation of the fixing element to the spinous processes  15 ,  16  and the spacer element(s) of the respective fixation system. The bending zones  177 , of which the fixing element  174  has four bending zones  177  running in parallel relative to one another in pairs, are for example formed as grooves  178  running in the carrier  175 , in particular with a round cross section. 
     The carrier  175  is advantageously not coated in the region of the bending zones  177 . This can reduce the danger of the coating  176  being detached from the carrier  175  during the deforming of the fixing element  174 . 
     A further fixing element  179  is shown in plan view and in side view respectively in  FIGS. 24A and 24B . The fixing element  179  can be used in each of the fixation systems described here. It comprises a carrier  180 , the base form of which is the same as that of the carrier  175 , and a plurality of coating members  181 . The coating members  181  are manufactured separately from the carrier  180  and fixed thereon, for example by gluing, screwing, latching, welding etc. 
     In the present case, each coating member  181  comprises an anchoring portion  182  for fixing in the plate of the carrier  180  and a coating portion  183  on the upper side of the plate of the carrier  180 , on which the actual coating  184  is applied. The coating  184  may, for example, be a Plasmapore coating. The cross section of the coating portion  183  may, for example, be circular ( FIG. 24A ). It may be provided that coating members  181  with a different size, cross section of the coating portion  183  and different type and extent of the respective coating  184  can be used in the fixing element  179 . 
     The coating  184  faces the vertebral bodies  17  and  18  and, in particular, the spinous processes  15  and  16  in order to improve the osteointegrative properties of the fixing element  179 . The use of coating members  181  allows the osteointegrative properties of the fixing element  179  to be improved in a targeted manner at a defined position of said fixing element. For example, no coating member  181  is present in the region of the intervertebral space  26 , in the present case. 
     A thirteenth preferred embodiment of the fixation system in accordance with an aspect of the invention is shown schematically in  FIGS. 25A and 25B  in the insertion position and the implantation position, respectively. The fixing elements, the securing device for the securing thereof in the implantation position of the fixation system  185  and the spacer element are, in this case, those of one of the fixation systems described above. The special feature of the fixation system  185  is that the fixing elements in each case have engagement members in the form of projections  186  which have an angle  187  with respect to the planes defined by the fixing elements. 
     The angle  187  is, for example, approximately more than 45°, measured on the side of the respective projection  186  remote from the intervertebral space  26 . The use of projections  186  running obliquely with respect to the fixing elements makes it possible to exert a tensile force in the cranial-caudal direction bringing the spinous processes  15  and  16  closer to one another during the transfer of the fixation system  185  from the insertion position into the implantation position. This results in the intervertebral space  26  shortening, it being possible for the spinous processes in the insertion position of the fixation system  185  to have a spacing D E  from one another and a spacing D I  from one another in the implantation position. 
     It can be provided that the projections  186  enclose the same angle  187  in each case with the fixing elements. It is also conceivable, however, for different projections  186  to enclose different angles  187  with the fixing elements. 
     If the projections  186  are inclined relative to the fixing elements in a counter direction, i.e. proceeding from the respective fixing element in the direction of the intervertebral space  26 , a spreading apart of the spinous processes  15  and  16  can also be achieved in the cranial-caudal direction. 
     The arrangement of the projections  13 ,  173  or  186  on the fixing elements can be “staggered,” i.e. projections of the fixing elements lying on mutually opposing lateral sides of the spinous processes  15 ,  16  have a spacing from one another in the cranial-caudal and/or dorso-ventral direction. This can prevent the spinous processes  15 ,  16  being weakened from both sides by engagement of the projections, so that the loading of the spinous processes  15 ,  16  is distributed more uniformly. This allows an even more reliable fixing of the fixation system on the spinous processes  15 ,  16 . 
     The above-described concept, although described with respect to the spinous processes  15 ,  16  of the vertebral bodies  17 ,  18 , can also be used to fix transverse processes adjacent to one another. Likewise, combinations of a spinous process fixing and a transverse process fixing are conceivable. 
     Individual components or features of the embodiments described above of a fixation system in accordance with the invention can obviously, if not already expressly mentioned above in any case, form independent fixation systems in accordance with the invention with other features or components of further preferred embodiments of a fixation system in accordance with the invention.