Abstract:
An endoscopic insertion apparatus for a spinal column implant system is provided having a screwing-in tool and an elongated holding device for holding a bone plate. The implant system essentially comprises at least one anchoring element, a bone plate connected to the anchoring element and at least one connection element for connecting at least two bone plates. The holding device comprises an insertion sleeve and a centering element. The centering element and the insertion sleeve can be connected to one another in a screwing-in position by a coupling mechanism in the direction of a longitudinal axis of the holding device, and the centering element and insertion sleeve can be separated from one another in a centering position. The invention reduces the number of parts used as compared to prior art insertion apparatus and simplifies handling, particularly of the centering element, since the centering element is provided as part of the holding device.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an endoscopic insertion apparatus for a spinal column implant system. The spinal column implant system essentially comprises at least one anchoring element, a bone plate (also referred to herein as “vertebra plate”) connected to the anchoring element, and at least one connection element for connecting at least two bone plates. A screwing-in tool is provided for screwing the anchoring element into a bone part to secure the bone plate in place and an elongated holding device is provided for holding the bone plate. 
     Spinal column implant systems of the type mentioned in the introduction can be used to fix various bone parts relative to one another; in particular, such an implant can be used for fixing adjacent vertebrae of the spinal column. Such an implant system is attached to the bone parts using a plurality of insertion instruments. Particularly where restricted access points are involved, for example in endoscopic operations, endoscopic insertion apparatus of the type mentioned in the introduction is used. A holding device associated with the insertion apparatus is used to hold the bone plate and the connection element connected to the bone plate and to introduce them into the body. The screwing-in tool is then used to screw the anchoring element into the bone part, for example. A similar procedure is carried out with a second anchoring element and a bone plate associated therewith. A connection element, for example a connection rod or a connection plate, is then brought up to the bone plate. The connection element is then fixed relative to the bone plate. In particular, a clamp element can be used to fix the connection element to the bone plate. Such a clamp element is generally very small, and hence there is a risk of losing it in the operating area. It is also difficult to position the clamp element properly relative to the bone plate. In order to simplify positioning the clamp element, centering pieces are used. The centering pieces are arranged (for example screwed on or latched) on the unit comprising the bone plate, the anchoring element and the connection element before the clamp element is introduced. Only when the centering piece has been positioned properly is the clamp element introduced using the clamp element guide tool. 
     In this procedure, it is disadvantageous that the centering piece has to be introduced as an independent instrument after the anchoring element and the bone plate have already been fixed on the bone part. In addition, a separately attached centering piece requires at least one actuation unit with which it can be introduced and removed again. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to improve endoscopic insertion apparatus of the type described in the introduction in such a manner that the number of parts used in the apparatus is reduced and that handling, particularly of the centering piece, is simplified. 
     The invention achieves this object in endoscopic insertion apparatus of the type described in the introduction in that the holding device comprises an insertion sleeve and a centering element. The centering element and the insertion sleeve can be connected to one another in a screwing-in position by a coupling mechanism in the direction of a longitudinal axis of the holding device, and the centering element and the insertion sleeve can be separated from one another in a centering position. 
     Such a holding device makes it possible to hold the bone plate and the connection element and bring them to the bone part to which the spinal column implant system is to be attached. After the anchoring element has been attached to the bone part using the screwing-in tool, it is no longer necessary to remove the holding device completely and then to use a centering piece. According to the present invention, it is possible to separate the holding device after the anchoring element has been attached. The centering element remains on the unit which comprises the anchoring element and the bone plate and is attached to the bone part, while the insertion sleeve is detached from the centering element. The centering element and the insertion sleeve are connected by a coupling mechanism. This coupling mechanism ensures that the two parts cannot be separated from one another in the axial direction when the anchoring element is attached to the bone part, that is to say that when the holding device is in the screwing-in position. The centering position for introducing the clamp element and the connection element is obtained by separating the insertion sleeve from the centering element. The centering element remains on the spinal column implant system and, in this position, is used for centering of the connection element which is to be introduced and of the clamp element. 
     It is beneficial if the centering element is formed by an elongated sleeve, at one end of which there is a part of the coupling mechanism. In contrast to centering pieces which are already known, the fact that the centering element of the present invention is designed as a sleeve means that it can perform a centering function both internally and externally. For example, the screwing-in tool can be guided inside the centering element, whereas the clamp element can be guided in the axial direction along the outer peripheral wall of the sleeve in the direction of the spinal column implant. By arranging that part of the coupling mechanism which is located on the centering element at one end of the centering element, the physical size can be significantly reduced. At the same time, the accessibility and functionality of the coupling mechanism between the insertion sleeve and the centering element are simplified. 
     According to one preferred embodiment of the present invention, provision may be made for the coupling mechanism to be formed by a latch connection having at least one latching lug, formed as a projection, and at least one latching edge, formed as a projection. The latching lug is arranged on a first part of the holding device and the latching edge is arranged on a second part of the holding device. The refinement of the coupling mechanism as a latch connection significantly simplifies handling of the holding device. For release, all that is required is for the latching edge to be moved relative to the latching lug to enable the insertion sleeve to be removed from the centering element. On the other hand, connecting the two parts is particularly easy as they need merely be plugged together. Further the two parts can also be heard to latch when the latching lug slides past the latching edge and engages behind it. 
     It is particularly advantageous if the latching lug is arranged resiliently on a part of the holding device in the radial direction in relation to the longitudinal axis of the holding device. Although the latching edge could be arranged resiliently in the same way, it suffices if the latching lug is arranged resiliently. This reduces the number of moving parts and increases the lifetime of the instrument. 
     Although various types of resilient arrangements of the latching lug on the holding device are conceivable, it is particularly beneficial when the latching lug is arranged on a leaf spring, arranged in the peripheral wall of the insertion sleeve, so as to point in the direction of the longitudinal axis of the holding device. The latching lug is thus situated on the inner peripheral wall of the insertion sleeve. In this arrangement, it does not matter whether the leaf spring is integral with the insertion sleeve or is arranged on the insertion sleeve as a separate component, for example. 
     According to one preferred embodiment of the present invention, provision may be made for a part of the latch connection to be operationally connected to a release projection for releasing the latch connection. With the present invention, it is crucial that the centering element can be separated from the insertion sleeve. Separation can be induced particularly simply if a projection is provided which is operationally connected to the latch connection. This enables one or both moveable parts of the latch connection, for example the latching lug or the latching edge, to be moved relative to the other part. The release projection thus acts as an actuation element for the coupling mechanism. 
     In this case, it is particularly advantageous if the release projection is arranged on that surface of the leaf spring which points in the direction of the longitudinal axis, and if the release projection is provided with slide surfaces which rise and fall in the axial direction. Such a release projection can be actuated with a particularly low applied force. In addition, this makes it possible for the centering element to be detached from the insertion sleeve by an auxiliary means guided inside the holding device. This prevents inadvertent detachment as a result of the holding device unintentionally bumping into or sliding along an obstacle, for example within the operating area or when the holding device is inserted inside a patient&#39;s body. 
     It is beneficial if the latching edge is formed by an annular projection protruding in the radial direction on the centering element. With the annular projection arranged immovably on the centering element, the stability of the latter is markedly increased even though a resilient arrangement would be quite conceivable. A radial projection is particularly easy to produce on an essentially rotationally symmetrical component, for example using a double annular groove or using a fitted ring which can be permanently connected to the centering element in a variety of ways. 
     In principle, the invention can provide that the centering element and the insertion sleeve can be connected so as not to rotate. A non-rotating connection between the centering element and the insertion sleeve is particularly desirable if the holding device is intended to be used to transmit torques. This non-rotating connection enables the holding device to be used not only to perform pure holding functions, but also to function as part of a turning tool. 
     In this case, it is particularly advantageous if the non-rotating connection is formed by a positively locking connection, and if a first part of the positively locking connection is arranged at one end of the insertion sleeve and a second part of the positively locking connection is arranged at one end of the centering element. The positively locking connection provided enables the insertion sleeve and the centering element to be connected without any play therebetween. If the two parts of the positively locking connection are each arranged at one end of those parts of the holding device which can be connected to one another (e.g., the centering element and the insertion sleeve), assembly is simplified significantly. By way of example, it would be conceivable for the two parts to be provided in the form of a plug connection. 
     In this case, it can be particularly advantageous if the positively locking connection is formed by a polygonal connection having an inner polygon and an outer polygon, and if the axis of symmetry of the polygonal connection is formed by the longitudinal axis of the holding device. Fixing the axis of symmetry in the manner described enables the two parts forming the holding device to be plugged together in the axial direction. In other words, the inner polygon is fitted over the outer polygon or the outer polygon is inserted into the inner polygon. In addition, a polygonal connection affords a defined number of connection positions. 
     In this case, it is beneficial if the polygonal connection is formed by a hexagonal connection. A hexagonal connection fixes the number of possible insertion positions at six. Hence, merely turning the insertion sleeve ensures that the insertion sleeve is seated onto the centering element in one of six different positions, even without direct visual contact. This is advantageous for endoscopic operations, in particular, in which there is no direct visual contact with the connection point. 
     According to a further embodiment of the present invention, provision may be made for the other end of the centering element to bear a mounting element for the bone plate. The centering element is part of the holding device, which, as described in the introduction, can be connected to the bone plate and the anchoring element. In contrast to known insertion apparatus, this refinement has the advantage that the centering element is already connected to the bone plate as part of the holding device and no longer has to be connected to the bone plate in an additional operation step after the holding device has been removed. It now suffices for the insertion sleeve to be removed from the centering element, with the result that the centering element is already fixed on the bone plate in the manner described. 
     In this case, it can be advantageous if the mounting element is formed by a screw thread which corresponds with a screw thread of the bone plate. That end of the holding device which is formed by the centering element can therefore be screwed into part of the bone plate. This can be done before the anchoring element is inserted. To remove the holding device, it is then removed again merely by unscrewing it from this part of the bone plate. 
     It is particularly advantageous in this case if the screw thread of the centering element is designed as an external thread and the screw thread of the bone plate is designed as an internal thread. The centering element is thus inserted into a part of the bone plate and screwed to this part. This means that this part of the bone plate can be provided with an external thread which corresponds with a thread of the clamp element. The central arrangement of the centering element on the bone plate then enables the clamp element to be brought to the bone plate externally over the centering element and screwed to said bone plate, for example. All other kinds of connections between the clamp element and the bone plate which are known to the person skilled in the art are also conceivable for use with the invention. 
     In principle, the invention can also provide that the other end of the insertion sleeve can be connected to the screwing-in tool in a screwing-in position, and that the insertion sleeve can be separated from the screwing-in tool in a separating position. Accordingly, the screwing-in tool and the insertion sleeve form an integral instrument in a screwing-in position. In this case, it should be taken into account that the centering element can be attached to the insertion sleeve, but is not required to be attached to it. 
     According to a particular embodiment of the present invention, provision may be made for the screwing-in tool to have a handle and a tool element. The handle makes the screwing-in tool easy to manage for the surgeon. The tool element can be used for screwing in the anchoring element, for example. 
     In this case, it is particularly beneficial if the handle can be detached from the tool element, and if the handle has a mount for the tool element. This refinement means that the tool element can be inserted into the handle and connected to it, for example. The detachable connection between the handle and the tool element makes it possible to combine different handles and also different tool elements with one another. In addition, the instrument can be cleaned more easily as a result. 
     It is particularly advantageous if the handle is formed by a ratchet grip. This means that the surgeon does not need to execute any full turns of the handle when using the screwing-in tool, but instead can move the screwing-in tool in steps in the desired direction by covering a limited rotary angular range, as is usual with ratchets. 
     In a preferred embodiment of the present invention, a part of the handle can be connected to the tool element so as not to rotate. The non-rotating connection enables direct force transmission in the direction of rotation from the handle to the tool element. 
     According to an advantageous embodiment of the invention, the screwing-in tool can be locked in the axial direction by a locking device having at least one resilient projection on the screwing-in tool and a corresponding recess on the holding device. In this manner, the screwing-in tool can be particularly easily connected to the holding device and locked. This connection can also be non-rotating, for example, so that torque transmission is possible from the screwing-in tool to the holding device. A resilient projection can be actuated particularly easily and with little applied force. In addition, the screwing-in tool is easily detached and connected to the holding device. 
     It is advantageous if the other end of the tool element is provided with a polygon which can be inserted in a positively locking manner into a tool mount of the anchoring element. This enables the screwing-in tool to engage in the tool mount of the anchoring element, which makes it possible to screw the anchoring element into the bone part using the screwing-in tool. In this case, the polygon can be designed in various ways, for example as a hexagon. 
     In addition, provision may be made for the other end of the insertion sleeve to be provided with a polygonal screw drive. In this case, the polygonal screw drive carries out at least two functions. First, the polygon screw drive can be operated using conventional open-ended wrenches. Second, the polygon screw drive can be part of the connection between the insertion sleeve and the screwing-in tool. In a similar way to that between the centering sleeve and the insertion sleeve, the polygonal screw drive and a corresponding polygon on the screwing-in tool can produce a non-rotating connection between the insertion sleeve and the screwing-in tool. 
     In this case, it is beneficial if the polygonal screw drive is a hexagon. This means that conventional open-ended wrenches can be used for screwing. 
     In principle, provision can be made for the insertion apparatus to have an actuation member for detaching the insertion sleeve from the centering element. An auxiliary means is required to actuate the coupling mechanism. This is provided by the actuation member, which can be used to act on the coupling mechanism. 
     In this case, it can be particularly advantageous if the actuation member is formed by a projection which is arranged on the screwing-in tool and interacts with the release projection when the screwing-in tool located in the holding device is withdrawn from the holding device. This refinement allows the screwing-in tool to have a dual function. On the one hand, it can be used for screwing-in and hence as a tool per se. On the other hand, it can be used for detaching the insertion sleeve from the centering element. This is particularly easy if the screwing-in tool is designed such that it can interact with the release projection of the coupling mechanism. This is ensured if the screwing-in tool has a projection. The refinement of the holding device as a sleeve means such that the insertion sleeve can be detached from the centering element by moving the screwing-in tool in the axial direction simplifies operation of the device. 
     In this case, it is particularly advantageous if the actuation projection is formed by a section of the screwing-in tool whose diameter is larger than the adjacent sections of the screwing-in tool. The diameter of the screwing-in tool can be varied particularly easily. Furthermore, the position for actuating the coupling mechanism can be defined easily and precisely. 
     It is particularly advantageous if a clamp element guide tool is provided, one end of which has a mount for a clamp element, into which mount the clamp element can be placed symmetrically in a positively locking manner. For finally fixing the connection element of the spinal column implant system on the bone plate and the anchoring element, a clamp element is required. The clamp element guide tool ensures that the clamp element can be brought reliably to the bone plate and the anchoring element without being lost anywhere. The positively locking configuration of the mounting element enables a torque to be transmitted reliably from the clamp element guide tool to the clamp element. The symmetrical configuration of the mount facilitates insertion of the clamp element, which is therefore possible in a variety of ways and in a variety of positions. 
     In this case, it is particularly beneficial if the clamp element guide tool is designed as a sleeve and the centering element can be inserted into the clamp element guide tool provided with a clamp element from a first end which is provided with the mount. This refinement allows the surgeon to fit the clamp element guide tool with the inserted clamp element over the centering piece and to bring the clamp element guide tool reliably to the bone plate using the centering element. 
     The clamp element guide tool can be shaped to have no grip, but it is particularly advantageous if a second end of the clamp element guide tool is provided with a handle. The handle considerably facilitates manipulation, and, in addition, the special configuration of the handle makes it possible to limit any torque which may be exerted. 
     In principle, it is particularly beneficial if the centering element has an axial stop for the bone plate and/or the insertion sleeve. This enables the centering element to be brought to the bone plate in a defined manner and allows the insertion sleeve to be connected to the centering element in a defined manner. In particular, this ensures reliable operation of the coupling mechanism between the insertion sleeve and the centering element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description below of a preferred embodiment of the invention serves for more detailed explanation in conjunction with the drawing, in which: 
     FIG.  1 : shows a longitudinal section through a screwing-in tool connected to a holding device when an anchoring element is being screwed into a bone part; 
     FIG.  2 : shows a cross-section along line  2 — 2  in FIG. 1; 
     FIG.  3 : shows a sectional view similar to FIG. 1, but after the screwing-in tool has been separated from the holding device; 
     FIG.  4 : shows a perspective view of a clamp element being fixed using a clamp element guide tool and of the centering element being removed from the bone plate; and 
     FIG.  5 : shows a perspective view of a screwing-in tool when the anchoring element is being fixed in the bone part and of a turning tool when the anchoring element is being finally fixed relative to the bone plate by means of a clamp screw. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The endoscopic insertion apparatus shown in FIGS. 1 to  5  essentially comprises a holding device  1 , a screwing-in tool  2 , a socket wrench  3  and a clamp screw key  4 . 
     FIG. 1 shows a possible use for the holding device  1  in conjunction with the screwing-in tool  2 . 
     To connect bone parts, for example two vertebrae, a bone anchoring element, for example a hollow screw  5 , is screwed into the vertebra  6 , which is shown purely schematically in dashed lines. The hollow screw  5  is essentially formed by three support pins  7  of equal length which run parallel to one another. The support pins  7  are arranged in cross-section at the corners of an equilateral triangle and are surrounded by a screw thread  8  over their whole length and are connected to the screw thread  8 . One end of the essentially cylindrical hollow screw  5  is provided with a cylindrical termination plate  9  which bears a ball head  10  extending in the axial direction. The ball head  10  contains an internal hexagon  11  in the axial direction, said internal hexagon  11  ending in the manner of a blind hole in the direction of the screw thread  8 . The ball head  10  is essentially rotationally symmetrically surrounded by a vertebra plate  12  which has a socket-like ball head mount  13 , in which the ball head  10  is mounted. This allows the vertebra plate  12  to turn around the ball head  10  and to be inclined away sideways from the common axis of symmetry. The outer edge of the vertebra plate  12  has spikes  14  pointing in the direction of the hollow screw  5 . In addition, the vertebra plate  12  has a sleeve section  15  which extends in the axial direction as an extension of the ball head mount  13 . Sleeve section  15  is provided with a clamp screw thread  16  on the outside and with a holding thread  17  on the inside. 
     To screw in the hollow screw  5 , the vertebra plate  12  is connected to the two-part holding device  1 . The holding device  1  comprises two parts, a guide sleeve  18  and a sleeve-like centering piece  19 . One end of the centering piece  19  of the holding device  1  has a screwing-in holding thread  20  which can be screwed into the holding thread  17  of the vertebra plate  12 . The screwing-in holding thread  20  has a somewhat smaller external diameter than the centering piece  19 , which forms a stop shoulder  21 . The screwing-in holding thread  20  then extends over a length of the centering piece  19  in such a manner that the ball head  10  is still free to move inside the ball head mount  13  when the stop shoulder  21  encounters an end edge  22  of the sleeve section  15 . 
     The internal diameter of the centering piece  19  broadens out after approximately one quarter of its length, starting from the end provided with the screwing-in holding thread  20 , such that the wall thickness of the centering piece is reduced to approximately two thirds. The outer surface of the centering piece  19  is completely smooth, starting from the stop shoulder  21  in the axial direction to approximately three quarters of the length of the centering piece  19 . This is adjoined by a coupling outer hexagon  23  produced in the outer peripheral wall, the largest external diameter of said coupling outer hexagon  23  being somewhat smaller than the largest external diameter of the centering piece  19 . The coupling outer hexagon  23  is adjoined by a further smooth centering sleeve section  24 , whose external diameter is reduced somewhat towards the other end of the centering piece  19 . The centering piece  19  also has a centering end  26  which is surrounded by an annular bead  25  projecting outwards radially. This annular bead  25  has a latching edge  27  pointing in the direction of the hollow screw  5 . 
     The guide sleeve  18  is connected to the centering piece  19  so as not to rotate and so as to be immovable in the axial direction. The end of the longitudinal guide sleeve  18  which faces the centering piece  19  is provided with a coupling inner hexagon  28  which surrounds the coupling outer hexagon  23  of the centering piece  19  in a positively locking manner. The end of the guide sleeve  18  seated on the centering piece  19  then encounters a coupling stop  29  of the centering piece, which is formed by the transition between the longest smooth section of the centering piece  19  and the coupling outer hexagon  23 . 
     Extending in the axial direction of the guide sleeve  18  are two spring windows  30  which are arranged so as to be staggered by 180° and whose longitudinal edges run parallel to the longitudinal axis of the guide sleeve  18 . The spring windows  30  are almost completely filled by a leaf spring  31  which supplements the sleeve wall and is connected to the guide sleeve  18  at one window edge  32  which extends in the circumferential direction of the guide sleeve  18 . The free end of the leaf spring  31  has a semi-annular spring bead  33  which extends radially inwards and forms a latching lug  34  being arranged away from the centering piece  19 . The thickness of the springs in the radial direction increases in steps, starting from the latching lug  34 , which forms an unlocking surface  35 . After a maximum wall thickness, this thickness in turn decreases continually and thus forms a locking surface  36 . Adjacent to the locking surface  36 , the wall thickness of the leaf spring  31  remains essentially constant up to the window edge  32 . 
     The guide sleeve  18  extends over approximately two thirds of its length with a constant internal and external diameter. In the end region of the guide sleeve  18 , the outer diameter tapers a little at a taper edge  37 . Further towards the end an annular groove  38  is formed in the guide sleeve  18 . Directly adjacent to the sleeve end  39 , the guide sleeve  18  is provided with a removal hexagon  54  which has the same external diameter as the annular groove  38 . This forms an annular coupling projection  40 . 
     The holding device  1  is formed from the centering piece  19  and the guide sleeve  18  as a unit which is connected together so as to be non-rotating. In the connected state, the coupling inner hexagon  28  of the guide sleeve  18  surrounds the coupling outer hexagon  23  of the centering piece  19 . The arrangement of the annular bead  25  on the centering piece  19  is provided such that the latching lug  34  on the leaf spring  31  of the guide sleeve  18  engages behind the latching edge  27  when the guide sleeve  18  encounters the coupling stop  29  of the centering piece  19 . In this manner, the centering piece  19  and the guide sleeve  18  are connected to one another with virtually no play. 
     The vertebra plate  12 , and hence also the hollow screw  5  which is connected to it, can be held, guided and positioned by the holding device  1 . 
     To screw the hollow screw  5  into the vertebra  6 , the screwing-in tool  2  is required. 
     The screwing-in tool  2  comprises a grip unit  41  and a tool insert  42 . The tool insert  42  essentially comprises a cylindrical rod having an external diameter chosen such that the tool insert  42  can be inserted into the guide sleeve  18  and is free to move in it. That end of the tool insert  42  which is remote from the grip unit is shaped as a hexagon  43  which can be inserted in a positively locking manner into the inner hexagon  11  of the ball head  10  of the hollow screw  5 . Starting from the hexagon  43 , the tool insert  42  merges into the cylindrical rod, which has the smallest diameter over this section. This diameter broadens out continuously to the maximum diameter of the tool insert  42 . In this way, a slide surface  44  in the form of a truncated cone is formed. This is adjoined by a tool section  45  having the maximum diameter of the tool insert  42 . Further along the tool insert  42 , the diameter is reduced over a rod section  46 , specifically such that oblique slide surfaces are formed in the transitional regions  47  and  48 . 
     The other end of the tool insert  42  is connected to the grip unit  41  via a coupling device  50  shown schematically by the annular projection  49 . 
     The grip unit  41  is essentially rotationally symmetrical and comprises a mounting unit  51 , which can be connected to the tool insert  42  so as not to rotate, and a T-shaped handle  52 . The handle  52  is arranged on the mounting unit  51  via a ratchet mechanism which is known to the person skilled in the art. The mounting unit  51  has a rotationally symmetrical cylindrical recess  53  into which the tool insert  42  can be inserted. The recess  53  is additionally prepared to receive that end of the guide sleeve  18  which is provided with the annular groove  38 , so that the coupling projection  40  can slide in the recess  53  in the axial direction. 
     The external diameter of that end of the grip unit  41  which faces the guide sleeve  18  broadens out towards the end. Starting from the maximum diameter, this diameter is reduced in a single step, which forms a slide bearing surface  55  running transversely with respect to the longitudinal axis of the grip unit  41 . In this region of the grip unit  41 , there is a spring-actuated locking unit  56 , as shown in cross-section in FIG.  2 . In the region of the single-step reduction in the diameter of the grip unit  41 , part of the sleeve-like region of the grip unit  41  is removed, so that a C-shaped mounting guide  57  remains on the grip unit  41 . Transversely to the longitudinal axis, a blocking slide  58  is inserted directly adjacent to the slide bearing surface  55 . The bottom end of the C-shaped mounting guide  57  is provided with a securing thread  59 . A securing nut  60  is screwed onto this securing thread and forms the termination of the grip unit  41 . The blocking slide  58  thus slides between the slide bearing surface  55  and the securing nut  60 . 
     The C-shaped region of the mounting guide has a hole  61  formed radially opposite the open section, and a spring  62  is supported in this hole  61  so as to project radially outwards. The other end of the spring  62  is supported in a spring hole  63  provided for it in the blocking slide  58 , the axes of symmetry of the hole  61  and the spring hole  63  coinciding. The blocking slide  58  is perforated parallel to the longitudinal axis of the grip unit  41 . In the spring-loaded state, the blocking slide  58  locks the guide sleeve  18  located in the recess  53 . The blocking slide  58  then encounters one side of the annular groove  38  in the guide sleeve  18  with a semicircular inner edge  66  of the perforation  64 . In this position, a semicircular outer edge  67  of the blocking slide  58  is matched to the diameter of the grip unit  41 . Two further side edges  65  of the blocking slide  58  run parallel to the axis of symmetry of the spring  62 . The pressure edge  68  opposite the outer edge  67  has a significantly larger radius of curvature and serves to actuate the blocking slide  58  by pressing onto the pressure edge  68 . 
     A further component of the endoscopic insertion apparatus which is provided is the socket wrench  3 , as shown in FIG.  4 . This essentially comprises an elongated socket sleeve  69 . One end of the socket sleeve  69  has a key grip  70  which runs transversely with respect to the longitudinal axis and is formed by two radially projecting grip rods  71 . At the opposite end, the socket sleeve  69  is extended by a rotationally symmetrical nut mount  72  whose inside is shaped such that it can surround a clamp nut  73  in a positively locking manner. The clamp nut  73  is therefore situated in a rotationally symmetrical arrangement with respect to the longitudinal axis of the socket sleeve  69 . 
     A further instrument of the insertion apparatus which is provided is the clamp screw key  4 . This essentially resembles the screwing-in tool  2  and accordingly comprises a handle  74  and a screwing tool  75 . The screwing tool  75  and the handle  74  are connected to one another detachably. This connection can be designed in a similar manner to the connection between the tool insert  42  and the grip unit  41  of the screwing-in tool  2 . Similarly, the handle  74  can be designed as a ratchet grip. That end of the screwing tool  75  which is remote from the handle  74  has a taper  76  which merges into a cylindrical end section  77 . The end of the end section  77  bears a shaping tool  78  (not shown in further detail). This is shaped, for example as an outer hexagon, such that it can engage in a complementary recess in a clamp screw  79  having a clamp thread  80  on the outside which can be screwed into the holding thread  17  of the sleeve section  15  of the vertebra plate  12  of the hollow screw  5 . 
     The use of the endoscopic insertion apparatus will now be described below with the aid of FIGS. 1 to  5  for the case of relative fixing of two vertebrae  6 . 
     For this, the holding device  1  and the screwing-in tool  2  must first be prepared. In a first step, the hollow screw  5  is screwed to the centering piece  19  using the holding thread  17  provided for this. The screwing-in holding thread  20  of the centering piece is screwed into the holding thread  17  until the centering piece  19  encounters the end edge  22  of the sleeve section  15  with the stop shoulder  21 . 
     Next, the guide sleeve  18  is connected to the centering piece  19 . For this purpose, that end of the guide sleeve  18  which has the leaf spring  31  is guided in the axial direction over that end of the centering piece  19  which has the annular bead  25 . The configuration of the ends of the centering piece  19  and of the guide sleeve  18  with a coupling outer hexagon  23  and a coupling inner hexagon  28  produces six angle dependent coupling positions. Accordingly, the guide sleeve  18  needs to be turned relative to the centering piece  19  such that the coupling inner hexagon  28  engages completely around the coupling outer hexagon  23 . In the course of this axial movement of the guide sleeve  18  towards the centering piece  19 , the spring bead  33  of the leaf spring  31  slides on the annular bead  25 , which causes the leaf spring  31  to open outwards in the radial direction. As soon as the end of the guide sleeve  18  encounters the coupling stop  29  of the centering piece  19 , the leaf spring  31  relaxes because the latching lug  34  slides back behind the latching edge  27  and is latched there. The holding device  1  is thus completely assembled, and the guide sleeve  18  is connected to the centering piece  19  so as not to rotate and so as to be fixed in the axial direction. 
     The screwing-in tool  2  can now be inserted into the holding device  1 . This holding device was previously assembled from the grip unit  41  and the tool insert  42  using the coupling device  50 . The screwing-in tool  2  is now pushed into the holding device  1  until the blocking slide  58  encounters the sleeve end  39 . The exertion of pressure onto the pressure edge  68  of the blocking slide  58  moves the blocking slide  58  transversely with respect to the longitudinal axis of the screwing-in tool, and this means that the screwing-in tool  2  can now be pushed further forward into the holding device  1 . If an axial position as shown in FIG. 1 is reached, the pressure on the blocking slide  58  is reduced and the inner edge  66  of the blocking slide  58  slides forward into the annular groove  38 . In this way, the grip unit  41  is connected to one end of the guide sleeve  18  and is fixed in the axial direction. While the screwing-in tool  2  was being inserted into the holding device  1 , which already has the hollow screw  5  screwed onto it, the hexagon  43  slid into the inner hexagon  11  of the ball head  10  of the hollow screw  5 . 
     The preparations described above have now produced a unit comprising the holding device  1 , the screwing-in tool  2  and the hollow screw  5 . The hollow screw  5  can now be attached to a vertebra  6  and can be screwed into the vertebra  6  by turning the hand grip  52  of the screwing-in tool  2 . For this, the hand grip  52  has to be turned clockwise out of sight of the surgeon, as indicated in FIG.  1 . The hollow screw  5  is now screwed into the vertebra  6  to an extent such that the spikes  14  have not yet penetrated the vertebra  6 . 
     In a subsequent step, the guide sleeve  18  is separated from the centering piece  19 , specifically by withdrawing the screwing-in tool  2  from the holding device  1 . To detach the screwing-in tool  2  from the guide sleeve  18 , the blocking slide  58  must first be released from its locked position. This is done, in turn, by exerting pressure onto the pressure edge  68 . The screwing-in tool  2  can now be withdrawn from the guide sleeve  18  in the axial direction. During this movement, the transitional region  48  slides on the unlocking surface  35  of the tool insert  42 , which stretches the leaf spring  31  radially outwards. This causes the latching lug  34  to move out from its latching position behind the latching edge  27  and release the latter, as shown in FIG.  3 . The guide sleeve  18  and the centering piece  19  are now unlocked and can be separated from one another in the axial direction. The centering piece  19  remains on the hollow screw  5 . 
     A further centering piece  19  is once again assembled using the withdrawn unit comprising the screwing-in tool  2  and the guide sleeve  18  in the manner described, after it has been connected to a further hollow screw  5 . Using the procedure which is already known, the further hollow screw  5  is screwed into an adjacent vertebra  6 . The guide sleeve  18  is then separated from the centering piece  19 , in the manner which is already known, by withdrawing the screwing-in tool  2 . 
     The two centering pieces can now be used to thread a connection plate  81  and thus place it into the connection plate mounts  82  so as to connect the two hollow screws  5 . Instead of a connection plate  81 , two connection rods  83  can also be provided. 
     To fix the connection plate  81  or the connection rods  83  to the vertebra plates  12  of the hollow screws  5 , a clamp nut  73  is placed into the nut mount  72  of the socket wrench  3 . The socket wrench  3  is now guided, together with the clamp nut  73 , over the centering piece  19 , and the internal thread of the clamp nut  73  is screwed onto the clamp screw thread  16  and firmly tightened. The socket wrench  3  is then withdrawn and fitted with another clamp nut  73 . The socket wrench  3  is inserted over the further centering piece  19  in a similar way and the clamp screw  73  is first screwed loosely to the vertebra plate  12 . 
     If appropriate, a traction apparatus (not shown) can be used at this stage to set the distance between the two vertebrae  6  as desired. As soon as the desired distance has been achieved, the socket wrench  3  is used to screw the other clamp nut  73  firmly to the second vertebra plate  12  as well. The two vertebrae  6  are now firmly connected to one another via the connection plate  81 . 
     To bring the hollow screws  5  into their final position, the centering piece  19  must first be removed. For this, the guide sleeve  18  is fitted over the centering piece  19  and latched to it, as described further above. The guide sleeve  18  and the centering piece  19  are thus connected to one another so as not to rotate. An open-ended wrench (not shown) can be used to remove the holding device  1  from the hollow screw  5  by means of the removal hexagon  54  by turning the holding device  1  anticlockwise. 
     If the two centering pieces  19  are removed from the hollow screws  5  in this way, the screwing-in tool  2  can be engaged in the inner hexagon  11  of the ball head  10  of the hollow screw  5  again. The hollow screw  5  is now screwed into the vertebra  6  until the spikes  14  penetrate the vertebra  6  and the vertebra plate  12  bears against the vertebra  6 . 
     To prevent further rotation of the vertebra plate  12  relative to the ball head  10 , a clamp screw  79  is placed onto the shaping tool  78  of the clamp screw key  4  and  15  screwed to the vertebra plate  12 . A clamp thread  80  of the clamp screw  79  then engages in the holding thread  17  of the sleeve section  15  of the vertebra plate  12 . The two vertebrae  6  are finally fixed when the two hollow screws  5  are provided with a clamp screw  79  which is tightened so firmly that relative movement of the vertebra plate  12  and the ball head  10  becomes impossible. The clamp screw key  4  can then be removed from the patient&#39;s body again.