Abstract:
Disclosed is an implant for treating lumbar spinal canal stenosis, comprising a spacer that is proved with an elongate interior space into which an insert part can be inserted. A first retaining element is fixed in the spacer in the inserted state. Said first retaining part can be folded apart by inserting the insert part while a second rear retaining element that is molded onto the insert part simultaneously comes to rest on the vertebral processes, thus making it possible to insert the implant unilaterally while reducing the risk of having to undergo possible postoperative interventions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an implant for treating lumbar spinal canal stenosis, with a spacer which may be attached between spinous processes of two adjacent vertebral bodies. 
     BACKGROUND OF THE INVENTION 
     Spinal canal stenosis is to be understood as any form of narrowing of the spinal canal through which the spinal chord runs, whilst excluding inflammation, tumors and complete slipped disks. Most commonly, spinal canal stenosis takes place in the region of the lumbar spine, but it also occurs in the region of the thoracic spine and cervical spine. The most common cause of the acquired spinal canal stenosis is degenerative changes on the spinal column. Such degenerative changes of the bone-cartilage system occur more commonly with older patients. Therapeutically, one initially intervenes with anesthetic medication, such as non-steroid anti-rheumatics or by way of creating a lordosis correction by way of bandages or corsets. If this is inadequate, then one must intervene in an operative manner, for example with decompressive surgery. Since, as already mentioned, the stenosis patients are often older people and they often also suffer from co-morbid conditions, the risk of complications is considerable. Accordingly, one is interested in being able to perform minimal-invasive surgery which reduces the risk of complication. 
     In place of the very widespread stiffening of several vertebral bodies in the lumbar region, in recent years elements have been developed which may be inserted between two adjacent vertebra processes and are designed to be adjustable in height. Such implants are shown, for example, in U.S. Pat. No. 5,458,641 or U.S. Pat. No. 5,702,455. The use of these implants however requires the operator to largely open up the lumbar spinal region, in order to insert the respective element and in particular to carry out the required size adaptation. This problem has been recognized, and a corresponding solution has been suggested, which has a simplified implant which may be adapted in size in a self-regulating manner by an elastic intermediate element. The advantage of this solution is not only simpler adaptation to the bodily particularities, but also the simple construction of the element and its fixation on the vertebral processes. It would also be conceivable to apply such a solution using merely a unilateral access. However, one would not do this for safety reasons, since the element with the processes is screwed, and as a result one would operate on both sides of the spinal column for a secure control. 
     Further implants for dealing with lumbar spinal canal stenosis are known from EP-0,322,334 A and FR-2,724,554 A. The solution described in WO99/21501 is particularly advantageous. The implant disclosed therein operates with a central body on which a sleeve is rotatably mounted in an eccentric manner. As locking means, wings are provided on both sides of this sleeve which is oval in cross section, and these wings must bear on the central body on both sides of the vertebral processes. This size adaptation by way of the spacer which is oval in cross section, requires more space to be provided for this, and furthermore the design is set up such that the operator must have access to both sides of the vertebral column. 
     The main advantage of this solution is that one requires no type of screwing on the vertebral body, and the implant itself is relatively simple in its construction. There are differing opinions with regard to the requirements of an element which may be adapted in diameter to the respective situation. Certain operators are of the opinion that the size of the spacer to be inserted may be exactly defined by way of an exact diagnostic clarification and measurement. Thereby, one wishes to assume the smallest required diameter of the spacer. The smaller the implant and the smaller the operation, the lower the risk of post-operative complications. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to provide an implant for treating lumbar spinal canal stenosis which is as small and simple as possible, but which may in particular be inserted by way of unilateral intervention. 
     This object is achieved by an implant with a spacer which may be applied between spinous processes of two adjacent vertebrae, wherein the spacer is designed as a roller body, on which, on each of both sides, a first and a second retaining element may be brought to bear which hold the transversally running roller body bearing on the spinuous processes on both sides. The implant is designed such that it may be introduced in a unilateral manner and, in the introduced condition, the first retaining element which is distanced furthest from the introduction sides may be pivoted in position by the effect of force, so that, at the side distant to the introduction side, this comes to bear on the spinous processes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments are shown in a simplified representation in the drawing, and are explained by way of the subsequent description. 
       There are shown in: 
         FIG. 1  the implant in its condition of installation, between two adjacent spinous processes of a vertebral body, 
         FIG. 2  the implant according to the invention represented alone in the assembled condition, in a longitudinal section. 
         FIG. 3  shows a spacer realized as a roller body, in a lateral view and 
         FIG. 4  the same spacer in a view from above. 
         FIG. 5  shows one variant of the spacer with a pointed head, again in a lateral view, whilst 
         FIG. 6  shows the same spacer with a view onto the pointed end, which is the end on the introduction side and 
         FIG. 7  shows the same spacer with a view onto the rear-side end, whilst 
         FIG. 8  again shows the same spacer in a view from above. 
         FIG. 9  shows one variant of the spacer with a first retaining element mounted thereon, in an introduction position, and 
         FIG. 10  the same spacer according to  FIG. 9  with the first retaining element in a slightly advanced position, as well as 
         FIG. 11  the spacer and the retaining element, wherein this is located in the retaining position. 
         FIG. 12  shows a first retaining element in a single-piece design in a perspective representation, with a push- and/or pull element connected thereto in a hinged manner. 
         FIG. 13  again in a simplified manner, shows a spacer with a partly led-through, first retaining element, wherein here it is the case of a two-part retaining element and 
         FIG. 14  shows the same element according to  FIG. 13  in the retaining position. 
         FIG. 15  shows an alternative first retaining element, again in a partly led-through condition, in a longitudinal section, whilst 
         FIG. 16  shows the same two-part element according to  FIG. 15  in the retaining position. 
         FIG. 17  shows a second retaining element in a simplest design, in a perspective view and 
         FIG. 18  a part of the spacer with a second retaining element which may be attached thereon, in a lateral view. 
         FIG. 19  symbolically and in a simplified manner, shows a spacer with two introduced clamping jaws of a forceps, which serve for introducing the spacer, in the lateral view, and 
         FIG. 20  the same situation in a view from the front. 
         FIG. 21  shows a similar spacer with a differently shaped introduction forceps, whose jaws are designed running past one another in a shearing manner. Finally 
         FIG. 22  shows the situation of  FIG. 21  in a view of the tip of the clamping jaws of the forceps, or of the introduction side of the spacer. 
         FIG. 23  shows an embodiment which is designed in a detailed manner, according to the variant according to the  FIGS. 15 to 17 , in a perspective representation in the introduction position, as well as 
         FIG. 24  in the lateral view. 
         FIG. 25  shows the embodiment according to  FIG. 23  in the introduced end position, again in a perspective representation and 
         FIG. 26  in a lateral view. Finally, a solution which is particularly preferably with regard to handling is shown in 
         FIG. 27  in the introduction position, in a perspective representation. 
         FIG. 28  shows the same solution as in  FIG. 27 , but in an intermediate position during the attachment, wherein the implant is shown in a phantom view. And finally 
         FIG. 29  shows the solution in the installed position. 
     
    
    
     DETAILED DESCRIPTION 
     The situation with regard to a patient is shown in  FIG. 1 . Two adjacent vertebral bodies or vertebrae are shown at A. Their spinous processes are indicated at B. The spinal canal C runs between the vertebral bodies A and the spinous processes B. E represents the exit locations of the nerve roots. The interspinal ligament D runs between two adjacent spinous processes B. A spacer  10  crosses through this ligament, and in its position is secured against transversal displacement by a first retaining element  20  on the one side, and by a second retaining element  30  on the other side. This securement is however hardly effective since the spacer  10  is designed in a waisted manner and thus centers between the two spinous processes B. 
     Implants of this type are required when signs of the so-called Baastrup/kissing spine syndrome appear. The Baastrup syndrome indicates the contacting of two adjacent spinous processes. In this situation, the supraspinal ligament is forwardly curved towards the spinal canal and affects the spinal canal stenosis. Additionally, it may lead to an invertebral disk protrusion which further narrows the spinal canal. The spinous processes are pressed apart with the implant according to the invention, and the compressed interspinal ligament is relieved, so that the supraspinal ligament recedes and the stenosis is cured. 
     The implant according to the invention is shown in its entirety in the assembled condition in  FIG. 2 , and is indicated at  1 . It consists of essentially four elements. The main element is a spacer  10  which is preferably designed as a roller body. This may basically be a cylindrical element. In the examples represented here, the spacer  10  is oval in cross section, whereby the spacer is seen to have two different sizes, depending on whether one represents the spacer  10  in a lateral view, as shown in  FIGS. 2 and 3 , or in a plan view from above, as shown in  FIG. 4 . The spacer  10  here has a continuous inner space  11 . This may not be rotationally symmetrical, and in the example represented here, is rectangular in cross section. Accordingly, in the lateral view according to  FIG. 3 , the inner space is seen to be larger, and in  FIG. 4  is seen to be smaller. The cross-sectional shape of the inner space  11  selected here is a shape which is preferred for reasons of manufacturing technology, but the inner space may in principle have practically any cross-sectional shape, as long as the cross-sectional shape is not round. The spacer or roller body  10  comprises a front side  12  and a rear side  13 . The surface which lies at the front on the introduction side is indicated as the front side, whilst the side lying opposite the introduction side is indicated as a rear side  13 . The outer peripheral surface of the spacer  10  has a waist  15 . This waist should effect a self-centering between the two adjacent spinous processes when the spacer is installed. 
     The two end-faces  12  and  13  of the spacer  10  may be formed in a plane manner. This results in an extremely inexpensive manufacture. Most preferably however, one would provide the side  12  at the front in the introduction direction with a head, as is displayed by most embodiments which are yet to be described hereinafter, and in particular as is represented in  FIGS. 5 to 8 . This head  17  is divided into two parts  18 . The division is effected by a transverse cut  18 ′. The transverse cut  18 ′ serves for the rotationally secured positioning of a first retaining element  20  which is yet to be described and which comes to lie at least partly in this transverse cut. In order to ensure that the retaining element  20 , on pulling-back towards the spacer  10 , does not again get into the inner space of the spacer, the transverse cut  18 ′ is preferably provided with rounded ramps  18 ″. 
     The spacer  10  may be designed on the rear side  13  as a simple plane surface, as shown in  FIGS. 3 and 4 , but it is possible to also provide the rear side with a groove-like recess  19  which serves for positioning a second retaining element  30  with a positive fit and in a rotational secure manner. Of course here too, the transverse cut  18 ′ as well as the groove-like recess  19  may have a differently designed shape when the retaining elements have been adapted accordingly. 
     The first or front retaining element  20  may also have different shapes. The shaping of the retaining element, in particular of the first retaining element, is determined mainly by the fact that this must be designed such that it may be led through the inner space  11  of the spacer  10 . Accordingly, the first retaining element  20  is designed at least approximately the same as the cross section of the inner space  11 . In the example represented here, the first retaining element  20  consists of one piece. It has essentially the shape of a flat rod and is connected to a push- and/or pull element  40  in a pivotally movable manner. The pivotally movable connection is realized by a pivot  41 . 
     A receiver groove  21  is integrally formed roughly centrically of the longitudinal axis of the first retaining element  20 . The push- and/or pull element  40  lies in the receiver groove  21  during the introduction phase, so that no projecting element exists which prevents the passage. The head  17  of the spacer  10  may, as shown in  FIG. 9 , be asymmetrical or, as shown in the  FIGS. 10 and 11 , be designed in a symmetrical manner. The first retaining element  20  comprises terminal, inclined end-faces  22 . These end-faces  22  run into cutting edges  23 . With the pushing of the first retaining element  20  through the inner space  11 , the inclined end-faces with their cutting edges  23  sever the interspinal ligament. Thereby, a torque is simultaneously created by the inclined end-faces  22 , whereby the first retaining element  20  tends to come into a certain pivot movement. This pivot movement only occurs when the first retaining element  20  is completely led through the spacer  10 . Thereafter, a pulling movement is applied onto the push- and/or pull element  40 , the first retaining element changes sides and comes to lie with its wide longitudinal surface onto the part surface, here shaped in a plane manner, in the transverse cut  18 ″ between the two parts  18 ′. As will be shown later, the actual spacer is previously introduced by way of a special forceps, and thereby simultaneously pushed through the interspinal ligament. The cutter  23  only simplifies the introduction when a certain back-deformation is affected by the elasticity. 
     Apart from the preferred embodiment according to the  FIGS. 9 to 11  shown here, it is also possible to realize the retaining element  20  in a different shape, as shown in  FIG. 12 . Here too, a single-piece, first retaining element  20  is employed. This too has roughly a rod-like shape. The cross-section of this first retaining element is however smaller than the cross section of the inner space  11 . It only reaches the full cross section in the middle region, where the rod-like part  25  is provided with a plateau  26 . The plateau  26  here serves for mounting the already mentioned pivot pin  41 . The push- and/or pull element  40  in turn is integrally formed on this pivot pin  41 . In this embodiment, a torsion spring  42  is also attached on the pivot pin  41 , and rotates the rod-like part  25  of the retaining element  20  relative to the push- and/or pull elements after completely pushing through the inner space  11  of the spacer  10 , so that the first retaining element  20  is not pulled into the inner space again on retraction. 
       FIGS. 13 to 16  show two variants of a first retaining element  20  which is designed of two parts. Here, the rod-like part  25  is divided into two part rods  24 . In the embodiments according to  FIGS. 13 and 14 , the first retaining element is designed such that the two part rods  24  may be inserted with their freely movable ends at the front. The two part rods are held in a pivotally movable manner on the same pin  41  on which the push- and/or pull element  40  also engages. With this embodiment, the two part rods  24  must be spread apart by way of a relatively strong spring, which then permits a retraction only under relatively large tensile forces. The great advantage of such a solution lies in the fact that the unilateral installation is reversible, and as a result, if necessary, the complete implant may be unilaterally removed in a subsequent operation. 
     With the embodiment according to the  FIGS. 15 and 16  unilateral removal is no longer practical. Otherwise however, the first retaining element  20  is designed in a very similar manner. Whereas with the embodiment according to  FIGS. 13 and 14 , the pivot axis  41  follows the two part rods  24  in the push-through/piercing direction, here the hinge is displaced to the front, and thus lies at the front in the push-through direction. Otherwise, the element has the same parts and these are provided with the same reference numerals. The spacer  10 , although this is not represented here, may of course be provided with a somewhat rounded run-out stretch at the front side, so that a certain spreading may already be effected during the pushing-through of the folded-together, two-part retaining element  20  in the final phase of the pushing-through. The second retaining element  30  is usefully always designed as one piece. This too has a somewhat rod-like shape. The design of this second retaining element may be particularly simple since this is attached on the side which is freely accessible during the operation. In the present case, it consists of the rod-like body  31  with a plateau attachment  32 . The plateau attachment  32  is designed with regard to shape such that it may be attached with a positive-fit from the rearward side, wherein the plateau  32  is accommodated in the inner space  11  of the spacer  10  with a positive fit and secured against rotation. 
     A central bore  33  passes through the rod-like part  31  and the plateau  32 , and the push- and/or pull element  40  may be led through this bore. This situation may be clearly seen in  FIG. 2 . As  FIG. 2  clearly shows, the plateau  26  on the first retaining element  20  may also be designed such that it engages in the inner space  11  of the spacer with a positive fit and in a rotationally secure manner. The push- and/or pull element  40  as mentioned, passes through the second retaining element  30  with its rod-like part  43  and projects outwards on the rearward side. The rod-like part  43  comprises a thread  44  at the rearward end. A retaining nut  45  is screwed onto this thread  44 . A threaded bore which passes through the retaining nut  43  up to the center serves for the insertion of a securing screw  46 . When the nut  45  is secured by way of the screw  46 , thereafter one would then cut away the rod-like part  43  of the push- and/or pull element  40  as close as possible to the nut  45 . The arrow  47  indicates this separation. 
     A variant of the second or rear-side retaining element  30  is represented in  FIG. 18 . This again has a rod-like body  31  and likewise a plateau attachment  32  which is accommodated in the inner space of the spacer  10 . With this solution, a guide head  34  is additionally integrally formed on the rearward side opposite the plateau attachment. This guide head may guide the rod-like part  43  of the push- and/or pull element  40 . The through-bore  33  in this case may also be designed as a threaded bore. This however is not absolutely necessary. Since in this embodiment greater guidance for the securing screw  46  is provided, the securing screw  46  may be designed as a grub screw which is provided with a tip which penetrates into the rod-like part  43  with a positive fit. Thereby, in practice, a cold-welding may occur. An extremely secure connection may thus be realized. 
     The invention likewise includes a forceps preferred for placing the implant.  FIG. 19  illustrates the jaws  50  of the forceps. The forceps jaws  50  are designed such that, when lying completely on one another, they may be guided through the inner space  11  of the spacer  10 . The jaws  50  also have jaw tips  51 . These jaw tips  51  supplement the head  17  of the spacer when the forceps jaws are introduced, and are spread apart. 
     Once the spacer has been placed on the forceps jaws, one then guides the spacer with the forceps from one side between and through two adjacent spinous processes, and thereby penetrates the intraspinal ligament. For simplifying the leading-through, the operator creates the guide-through opening by way of a scalpel, at least in a slot-like manner. Retaining beads  52  are furthermore formed on the jaws  50 , to prevent slipping of the spacer on the jaws  50 . The forceps jaws  50  however also hold the spacer  10  with a non-positive fit and thereby bear on the inner surface of the inner space  11  with their outer surfaces. 
     One possible variant of the forceps is represented in  FIGS. 21 and 22 . Here, the two jaws of the forceps slide over one another in the manner of a scissors. The two jaws  50  again have jaw tips  51  which complement the head  17  of the spacer  10  into a tip. The jaw tips  51  thereby may be perfectly adapted to the head shape. This permits a shape which is more closed in the penetration direction, than with the previously mentioned embodiment of the forceps. Although the forceps represents a preferred embodiment for application of the implant, it is of course also possible to realize differently shaped introduction means. The embodiment described here merely serves for disclosure of the complete implementation of the invention, thanks to which it is possible to only carry out an opening of two adjacent spinous processes in the region of the lumbar vertebral channel stenosis from only one side, whereupon the implant may be placed thanks to the unilateral manner of installation. 
     A version which is modified with respect to the previously described embodiments is represented in  FIGS. 23 to 26 , wherein this implant for treating lumbar spinal canal stenosis achieves the same object of the invention, specifically of providing an implant which may be applied by way of a unilateral intervention. However, whereas with all previous embodiments, the first retaining element  20  was led through the spacer  10 , here a solution is shown, with in which the first, front retaining element  20 , is designed of two parts. The two parts of the retaining element  20  are here indicated with the reference numerals  121  and  122 . The surface which lies at the front during the introduction of the spacer  10  between the two spinous processes B is represented here as a head  117 . The head  117  here has a roof-like design. The head  117  has a crossing incision  118 . This incision  118  likewise has a roof-like shape, whose tip however is ground-off. Accordingly, a plane part surface  112  remains. The two parts  121  and  122  of the first, two-part retaining element  20  are held on the tensile- or compressive element  40  in a pivotally movable manner via a pivot  123 . The pivot  123  passes through the pull and/or push element  40 , and the two parts  121  and  122  engage around the tensile- or compressive element  40  designed as a rod. Since in this case, the first retaining element  20  thus no longer needs to be guided through the spacer  10 , it is also not necessary for the inner space  11  to have a design which differs from the round shape. The rotational securement results from the positive-fit mounting of the two-part first retaining element, which lies integrally in the head  117  of the spacer  10  already on applying the implant, thus in the introduction position. After the implant has been correctly placed between the two adjacent spinous processes, it is then sufficient to pull on the push- and/or pull element  40 , by which means the two parts  121  and  122  automatically come out of the position as shown in  FIG. 23 , into the end position as shown in  FIG. 25 . In this position, the two parts  121  and  122  then lie on the plane part surface  112  and now remain in this position. Thereafter, as a locking element, one then slides the second rearward retaining element  30  over the push- and/or pull element, until the second retaining element  30  bears on the spacer  10 . Thereby, it is not at all the case that the first retaining element and the second retaining element bear laterally on the spinous processes, but these processes serve merely as a securement in order to prevent a displacement out of this position. If the two elements were to bear flush on the spinous processes, then this would in practice be equal to a partial stiffening of the backbone, and this is not necessary in most cases of lumbar spinal canal stenosis. 
     Although the push- and/or pull element  40  in the embodiment represented here is realized as a round rod, for example as a threaded rod, this is not absolutely necessary. The push- and/or pull element may indeed, as previously mentioned, have a non-round shape and accordingly the inner space  11  would in turn have a non-round shape. The embodiment represented here is relatively simple in handling and design. The spacer  10  may be introduced in the position as is shown in the  FIGS. 23 and 24 , whilst simultaneously the second, rearward retaining element  30  is held secured on the push- and/or pull element  40  such that the relative positions are as shown in the  FIGS. 23 and 24 . Accordingly, the implants may be supplied in this preassembled condition. On introduction, pressure may be applied directly onto the push- and/or pull element  40 . Once the end position is reached, one may then exert tension on the push- and/or pull element, while compression is simultaneously exerted on the second retaining element  30 . This causes elements  30  and  40  to displace relative to one another, and only the securing part, for example a locking nut then needs to be rescrewed to the new position. 
     Whilst, in the embodiment shown here, the spacer  10  essentially has the shape of an octagon rounded at the corners, this is of course not absolutely necessary. Here too, the spacer  10  may in principle have the shape of a roller body. Likewise, as in the previously described examples, the spacer  10  may have a waist in order to exert a self-centering effect. In principle, a roller body is to be understood as a spacer which is axially symmetrical, but not rotational symmetrical. The term roller body merely expresses the fact that the spacer in its condition of use also serves for the spinous processes to be able to roll along thereon given movement. 
     The preferred embodiment represented in  FIGS. 27 to 29  utilizes the idea of designing the complete implant, which here is indicated at  201 , such that in an introduction position, the implant  201  in the longitudinal direction is larger than in the installed condition. By way of this, one creates additional space, in order during the introduction phase to accommodate the first, front retaining element  220  in the spacer  210  in a simpler manner, by which means this may also be designed in a more optimal manner. The spacer  210  now comprises an inner space  211  which has a longitudinal slot which extends over the whole length of the roller body  210  with the exception of the end region which forms the head  217 . Now the first, front retaining element  220  may be arranged in this free space which represents the inner space  211 , without any problem. The first, front retaining element  220  again is divided into two here, and the two parts  221  and  222  of the first retaining element  220  are held in a pivotable manner about a pivot  223 . Thereby, the pivot  223  is attached from the middle of the spacer  210 , so that the first, front retaining element is divided into a long retaining element part  221  and a short retaining element part  222 . 
     Furthermore, the implant  201  comprises a push- and/or pull element which is indicated here at  240 . This push- and/or pull element comprises an insert part  241 . Connected as one piece to this is the second, rearward retaining element  230  which consists of an upper retaining element part  231  and of a lower retaining element part  232 . Both parts are integrally formed on the insert part  241  as one piece. They are diametrically opposite one another. The insert part  241  is held in an extended position in the introduction phase of the implant  201 , as is represented in  FIG. 27 . The insert part  241  at the bottom and top in each case has a saddle-like waist  242  which in shape corresponds to a same type of waist  212  on the spacer  210 . In the extended condition, these two waists are separated from one another by the push-out distance. A central elongate hole  243  is integrally formed in the insert part  241 . The shank of a crossing clamping screw  244  projects through this elongate hole  243 . The clamping screw  244  serves for the securing of the insert part  241  in a desired retraction or extension position of the insert part  241  in the spacer  210 . The spacer  210  in the end region where the clamping screw  244  is arranged, may be pressed together slightly, thanks to the inner space  211  being designed as an elongate slot. During the introduction phase, the insert part  241  is clamped in the extended position by way of the screw  244 . 
     A longitudinal groove  245  is formed below the elongate hole  243  parallel to this. A plunger  250  is mounted in this longitudinal groove  245 . The plunger  250  has a lug  251  and a press surface  252 . By way of the lug  251 , the plunger, on collision of the insert part  241  into the spacer  210  which here are represented in a transparent manner, pushes the two retaining element parts  221  and  222  apart, whilst in the end position, the front press surface  252  lies in a flat manner on both retaining element parts  221  and  222  engaging into one another in the hinge region. The longitudinal groove  245  has a locking flute  246  which is arranged in the front region, whilst the plunger  250  comprises a bead  253  which in the position according to  FIGS. 27 and 28  (i.e. in the introduction position) and in the intermediate position of the pushing together, is mounted in locking flute  246 . The plunger  250  furthermore at the end has a longitudinal slot  254  which extends beyond the region on which the bead  253  is attached. By way of this, the end region of the plunger  250  may be pressed together in a resilient manner, so that the bead  253  may be pressed out of the locking flute  246  when the insert part  241  is pushed into the spacer  210 . This inserted condition which corresponds to the installation position of the implant, is represented in  FIG. 29 . In this position, the plunger  250  is completely inserted in the longitudinal groove  245 . This is evident in  FIG. 29  because here too the spacer  210  is represented in a transparent manner. The bead  253  now lies in a rear position, at which a locking flute may be present. However, the flocking flute is not absolutely necessary, and is not shown in the other Figures. 
     The solution shown in  FIGS. 27 to 29  for a post-operative intervention may also be unilaterally disassembled again. For this, the locking screw  244  fixed in the end position is released again, and thereafter is introduced through two insert bores  247  incorporated from the end side, by way of a tool which comprises two parallel round rods connected to one another. Whilst pressing on the tool, one simultaneously pulls the insert part  241  by way of tension on the rearward, second retaining element  230  which now lies free, so that, while the insert part  241  is being pulled out, the plunger  250  remains in its rearward position whilst pressure by the tool through the upper bore  247  onto the upper part of the two-part first retaining element part  221 , permits the two parts  221  and  222  to be folded back, so that finally again the position according to  FIG. 27  is reached. In this position, one may of course remove the complete implant without any problem. 
     LIST OF REFERENCE NUMERALS 
     
         
         A vertebrae 
         B spinous processes 
         C spinal canal 
         D interspinal ligament 
           1  implant, entirety 
           10  spacer, roller body 
           11  inner space 
           12  surface on the introduction side, plane, front side 
           13  rear side 
           14  wall 
           15  waisting 
           16  longitudinal axis of the roller body 
           17  head of the spacer 
           18  part crest 
           18 ′ crossing incision 
           18 ″ ramps 
           19  groove-like groove 
           20  first, front retaining element 
           21  receiver groove 
           22  inclined end surface 
           23  cutting edges 
           24  part rods 
           25  rod-like part 
           26  plateau 
           30  second, rearward retaining element 
           31  rod-like body 
           32  plateau attachment 
           33  through bore 
           34  guide head 
           40  push- and/or pull element 
           41  pivot 
           42  torsion spring 
           43  rod-like part 
           44  thread 
           45  retaining nut 
           46  securing screw 
           47  separation 
           50  forceps jaws 
           51  jaw tips 
           112  plane part surface 
           117  head 
           118  crossing incision 
           121  part of retaining element  20   
           122  part of retaining element  20   
           123  pivot 
           201  implant 
           210  spacer 
           211  inner space 
           212  waisting 
           217  head 
           220  first, front retaining element 
           221  long retaining element part 
           222  short retaining element part 
           223  pivot 
           230  second, rearward retaining element 
           231  upper retaining element part 
           232  lower retaining element part 
           240  push- and/or pull element 
           241  insert part 
           242  saddle-like waisting 
           243  elongate hole 
           244  clamping screw 
           245  longitudinal groove 
           246  locking flute 
           247  insert bore 
           250  plunger 
           251  lug 
           252  press surface 
           253  bead 
           254  longitudinal slot