Patent Document

BACKGROUND OF THE INVENTION 
     The invention relates to a device for lining up and introducing multiple drilled channels in a bone. 
     Such a device is known from German Utility Model G 84 11 993.4. 
     Such devices serve the purpose of preparing drilled channels in a bone, implants being inserted into the drilled channels. 
     One broad field of use is the reconstruction of cruciate ligaments in the region of the knee. The anterior cruciate ligament extends from the upper plateau (tibial plateau) of the lower leg (tibia) and runs to the inner side of the lower end of the upper leg bone (femur). 
     In cases of serious injury, the cruciate ligament is completely removed and replaced by a tendon implant. 
     This tendon implant is often a tendon from the patient itself, for example the semitendinosus ligament, which has proven to be particularly useful for the reconstruction of cruciate ligaments in the knee. 
     To achieve an alignment of the tendon implant that is as close as possible to the natural alignment, it must be anchored securely in the bone. For this purpose, corresponding drilled holes have to be introduced into the bone. 
     Since, as mentioned above, the cruciate ligament extends in a quite specific direction from the lower leg bone to the upper leg bone, the drilled holes in these bones into which the tendon implant is to be inserted and anchored should as far as possible likewise extend in this direction. 
     This allows achievement of the effect that, proceeding from the anchoring site, the tendon implant already extends in the anatomically correct direction from the surface of the bone, for example from the tibial plateau. 
     For this purpose, exactly aligned drilled holes must be made in the bone. 
     Since such surgical interventions are carried out arthroscopically and the knee joint represents a complicated and confined joint, the surgeon has relatively little space available for properly lining up and making such drilled holes. 
     The device mentioned at the beginning has proven to be successful for lining up and introducing drilled channels. 
     The device of German Utility Model G 84 11 993.4 comprises a handle, which is formed like a bar or grip, and a single guiding sleeve, through which a so-called aiming wire can be pushed. Such aiming wires are relatively stiff, pointed metal wires with a diameter in the range from 2 to 3 mm. 
     In handling, for example the distal, relatively narrow end of the arm projecting from the device is pushed into the knee joint and placed on the tibial plateau. The distal end of the movable guiding sleeve is usually placed obliquely on an outer side of the lower leg. 
     If such an oblique drilled hole is to be introduced into the lower leg, the exiting of the drilled hole on the tibial plateau inside the knee joint should take place at a site and at an angle as close as possible to the attachment and alignment of the cruciate ligament to be replaced. 
     For this purpose, the distal end of the arm which has been pushed into the knee joint has an opening through which the aiming wire that is driven through the bone from the outer side can enter. 
     After setting the aiming wire, the devices is removed and the guiding sleeve is thereby removed from the aiming wire. 
     After that, the aiming wire is overdrilled with a hollow drill and this then produces the desired drilled channel in the bone, into which the tendon implant is then inserted and anchored. 
     With the device of German Utility Model G 84 11 993.4, a surgical technique in which two aiming wires can be set with one and the same device that has only a single guiding sleeve is described. For it, the guiding sleeve has more than one channel for guiding aiming wires. 
     It is possible to reconstruct the anterior cruciate ligament as anatomically replicating very closely the natural ligament. 
     In the reconstruction of ligaments, some tendon implants that do not have a circular cross section are used. One reason for this is, for example, that a tendon band of a specific length formed into a U-shaped loop, with legs of the U lying against each other, is used. Such a double strand has in cross section the form of an “8”, when provided with an approximate envelope curve an approximately rectangular form. 
     Transplants with an angular bone block, for example a patella with patellar tendon, or quadricep tendons, are also used. 
     There is therefore a need for devices with which drilled holes deviating from a circular geometry, in particular polygonal and rectangular drilled holes, can be prepared and produced. 
     Devices for preparing rectangular drilled holes are known from U.S. 2006/0161163 A, U.S. 2008/0097453 A1 and U.S. Pat. No. 6,022,356 A. Several circular drill holes can be provided close to another or intersecting one another. A dilator inserted into the drill holes shape the resulting opening into a rectangular hole. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to provide a device capable to accomplish multiple drilled channels lying next to one another, which can then be worked to form corresponding channels deviating from a round geometry. 
     The object is achieved by a device for preparing multiple channels in a bone comprising a handle, a single guiding sleeve mounted removable at said handle, a distal end of said single guiding sleeve being capable to be placed on a side on a bone, an arm projecting from said handle, a distal end of said arm being capable to be placed on another side of said bone, said single guiding sleeve comprises a central first guiding channel for receiving a first aiming wire, a second guiding channel for receiving a further aiming wire, a central longitudinal axis of said second guiding channel being at a distance from said central longitudinal axis of said first guiding channel and said axes running parallel to one another, at least one cannulation, a central longitudinal axis thereof runs at a distance and parallel to said central axis of said first guiding channel, said at least one cannulation being arranged offset, seen in an circumferential direction extending around said central longitudinal axis of said first guiding channel, at an circumferential angle to said second guiding channel, and a further aiming wire introduced into said second guiding channel can be transferred to said at least one cannulation by pulling off said guiding sleeve from said handle, turning said guiding sleeve about said first aiming wire received in said central first guiding channel up to an alignment of said further aiming wire with said at least one cannulation and reinserting said turned guiding sleeve into said handle. 
     These measures have numerous advantages. 
     Providing the second guiding channel, which runs at a distance A from and parallel to the central longitudinal axis of the first guiding channel, creates the basic precondition for setting two aiming wires lying next to each other and running parallel to each other. In this case, the distance A may be chosen such that, after overdrilling the aiming wires, the two resultant circular drilled holes overlap, so that this alone in principle allows a channel that already has approximately a rectangular circumferential profile to be accomplished. 
     Providing the cannulation at an outer side of the guiding sleeve, which, as far as its central longitudinal axis is concerned, likewise runs at the distance A from the central longitudinal axis of the central channel and likewise extends parallel to this axis, opens up the possibility of performing the following procedures. 
     After setting the first two aiming wires, the guiding sleeve may be pulled off from the handle to an extent that it is still but only located on the central, correspondingly longer, first aiming wire, but no longer holds the second aiming wire. Consequently, the second aiming wire has left the second guiding channel. Then, the guiding sleeve may be turned by an appropriate angle about the first aiming wire until the second aiming wire is in line with the cannulation in the outer side on the guiding sleeve. By advancing the guiding sleeve in the distal direction i.e. reinserting it into the handle, the second, or last-set, aiming wire is pushed into the cannulation. Since in this state the second guiding channel is no longer occupied, a third aiming wire can be pushed through it and introduced into the bone. 
     Depending on the number of these cannulations and the circumferential angular orientation, further aiming wires in addition to the two aiming wires that have been set through the first and second guiding channels can then also be set. If only one such cannulation is present, and if for example it lies diametrically opposite the second guiding channel, three aiming wires running parallel to one another can be set. After overdrilling the three set aiming wires with appropriate hollow drills, then a drilled hole which, seen in cross section, is relatively elongated and approximately rectangular is obtained. 
     If the cannulation is not offset in terms of the circumferential angle by 180° but by a different angle, correspondingly angled-away drilled hole profiles are obtained. 
     If there are multiple circumferentially angularly offset outer cannulations, other geometrical formations can also be achieved, such as “T”-shaped or “†”-shaped drilled holes. For the surgeon, handling can be carried out easily and safely, since the same course of action is always followed. 
     This involves aiming and setting the device in the known and accustomed way, as when only a single aiming wire is intended to accomplish the provision of only a single circular drilled hole. The provision of the second guiding channel allows the second aiming wire firstly to be set directly adjacent and parallel to the first aiming wire. Then, the removable guiding sleeve is pulled off to the extent that the second aiming wire is exposed, but the guiding sleeve is still pushed on the first aiming wire. By turning the guiding sleeve by the desired angle about the first aiming wire, a third aiming wire, or possibly multiple further aiming wires, can be set as desired. The aiming wires respectively set beforehand through the second drilled channel are then placed in the open cannulation or cannulations. 
     After that, the device can be removed and the aiming wires that are set and fixed in the bone can be overdrilled with appropriate hollow drills, in order then to produce the desired drilled hole with the desired cross-sectional profile in the bone. 
     In a refinement of the invention, there is a single cannulation, which is arranged angularly offset in relation to the second guiding channel by an angle of up to 180°. 
     As mentioned above, this measure has the advantage that three aiming wires can be set directly adjacently, to be precise between a linear alignment, as seen over a joining line of the central axes of the aiming wires, and an angled-away alignment. 
     In a further refinement of the invention, the single cannulation is angularly offset exactly by 180°. 
     This measure has the advantage that an exactly straight-aligned drilled hole with a rectangular cross section can be accomplished by this refinement. 
     In a further refinement of the invention, there are three cannulations, which are respectively arranged angularly offset in relation to the second guiding channel by 90°. 
     This measure has the advantage that it allows multiple different cross sections of drilled holes to be achieved. 
     For one thing, as mentioned above, if only the 180° angularly offset cannulation is occupied, it is possible to accomplish the straight-extending cross-sectionally rectangular opening. 
     If a cannulation which is angularly offset only by 90° is occupied, a correspondingly angled away drilled hole is achieved. 
     If two of these cannulations are occupied, an approximately “T”-shaped cross-sectional structure is achieved. 
     If all three cannulations are occupied, a “symmetrically cruciform” profile can be achieved. 
     In a further refinement of the invention, the guiding sleeve has an approximately bar-shaped body, in which the first guiding channel is centrally cut out, and the second guiding channel is set on the body. 
     This measure has the advantage that the two guiding channels can be produced very simply in terms of production technology and the surgeon is provided right away with an orientation feature in the form of the outer, set, second guiding channel, from which he knows in which position and orientation the second guiding channel is in relation to the first guiding channel. Thus, the guiding sleeve may consist of a bar-shaped body which centrally has a bore that represents the first circumferentially closed guiding channel. Joined or placed onto this body there may then be the second guiding channel in the form of a guiding tube. For this purpose, this guiding tube may be placed onto the outer side or inserted into a correspondingly cut-in depression and fastened therein, this being determined in part by the respective dimensions, in particular the distance A. 
     In a further refinement of the invention, the at least one cannulation is formed as a longitudinal laterally open groove along the body of the guiding sleeve. 
     This measure has the advantage that this groove can be easily produced exactly to size and in the correct position by milling out the body. This also facilitates the handling to the extent that, after setting the first two aiming wires and after pulling off the guiding sleeve and turning it about the longer central aiming wire, the guiding sleeve merely has to be advanced linearly again, the second aiming wire then entering this longitudinal groove. Due to the fact that the groove is laterally open to the outside, some minor misalignments of the second or further aiming wire which has to be transferred into the groove can be tolerated. 
     In a further refinement of the invention, cut out in the handle is an opening, which is adapted to the outer contour of the guiding sleeve such that the guiding sleeve can only be pushed into the opening in certain alignments only. 
     This measure also facilitates the handling to the extent that, after pulling off and turning the guiding sleeve, the handling person can only push said sleeve back into the opening in specific rotational positions, that is to say the rotational positions that correspond to the desired rotational angle or angles. 
     In a further refinement of the invention, at the distal end of the arm there is an opening through which an aiming wire pushed through the first guiding channel can be passed. 
     This measure, which is known per se, has the considerable advantage that the device is held on the first aiming wire at two opposite positions of the bone, to be specific on one side by way of the opening through which the aiming wire reaches through the distal end of the arm and on the opposite side also through the guiding sleeve resting on the first aiming wire. 
     In a further refinement of the invention, markings are provided at the distal end of the arm, adjacent to the opening, representing target points of the further aiming wires, which run through the second guiding channel and the at least one open cannulation. 
     This measure has the advantage that, after forcing through the second and further aiming wires, the surgeon can check on the basis of the markings whether these aiming wires are set exactly. 
     In a further refinement of the invention, the first guiding channel is formed as a circumferentially closed guiding channel. 
     This measure has the advantage that, as a result, the pulled-off guiding sleeve can be turned in an exactly guided manner about the set first aiming wire, without a radial displacement or positional change of the guiding sleeve being possible. 
     It goes without saying that the features mentioned above and those still to be explained below can be used not only in the respectively specified combinations but also in other combinations or on their own without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described and explained in more detail below on the basis of several selected exemplary embodiments in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows an exploded view of a first exemplary embodiment of a device according to the invention, 
         FIG. 2  shows the device of  FIG. 1  in the assembled state, it being shown that a first aiming wire has already been pushed through the guiding sleeve, 
         FIG. 3  shows a representation corresponding to  FIG. 2 , it being shown that a second aiming wire has been pushed through the second guiding channel, 
         FIG. 4  shows a representation of the device in a state during handling in which the guiding sleeve has been pulled from the second aiming wire but is still located on the first, longer aiming wire, 
         FIG. 5  shows a representation corresponding to  FIG. 4 , after the guiding sleeve has been turned about the first aiming wire by 180°, 
         FIG. 6  shows a state after the guiding sleeve has been pushed in again from the position of  FIG. 5 , the second aiming wire has entered the first cannulation and a third aiming wire has already been set through the second guiding channel, 
         FIG. 7  shows a cross section through the guiding sleeve, approximately half-way along, of the exploded representation of  FIG. 1 , 
         FIG. 8  shows a corresponding cross section in the state of  FIG. 2 , 
         FIG. 9  shows a corresponding cross section in the structural state represented in  FIG. 3 , 
         FIG. 10  shows a cross section of the structural state of  FIG. 5 , after the guiding sleeve has been pushed in again, 
         FIG. 11  shows a corresponding cross section of the structural state of  FIG. 6 , 
         FIG. 12  shows a sectional representation through a bone into which the three aiming wires have been set, after overdrilling by hollow drills, 
         FIG. 13  shows a perspective representation of a lower leg bone into which the three aiming wires have been set, that is to say after pulling off of the device from the structural state of  FIG. 6 , 
         FIG. 14  shows a state of the bone corresponding to  FIG. 12 , after overdrilling and pulling off of the three aiming wires, 
         FIG. 15  shows the bone of  FIG. 14  after a possible reworking by a bone spatula to form an exactly rectangular drilled-hole cross section, 
         FIG. 16  shows a cross-sectional representation comparable to  FIG. 7  of a second exemplary embodiment of a guiding sleeve, with three open cannulations on the outer side, 
         FIG. 17  shows a structural state corresponding to  FIG. 9 , 
         FIG. 18  shows a structural state comparable to that of  FIG. 10 , although here the guiding sleeve has been turned only by 90°, 
         FIG. 19  shows a structural state comparable to  FIG. 11 , with three set aiming wires, 
         FIG. 20  shows a structural state after a further turning by 90°, with four set aiming wires, and 
         FIG. 21  shows a representation comparable to the representation of  FIG. 12 , with a drilled hole after overdrilling of the four aiming wires of  FIG. 20  to achieve an opening with a “T” profile. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A first exemplary embodiment of a device according to the invention that is represented in  FIGS. 1 to 11  is denoted overall by the reference numeral  10 . 
     The device  10  has a handle  12 , which has an approximately bar-shaped grip  14 . 
     Provided at one end of the handle  12  is an opening  16 , which serves for removably receiving a guiding sleeve  18 . 
     As can be seen in particular from the sectional representation of  FIG. 7 , the guiding sleeve  18  is formed approximately in the form of a tube  20 , the distal end  22  of which is provided with a serrated rim  24  ( FIG. 1 ). At the opposite end, the guiding sleeve  18  is provided with a rotatable clamping sleeve  26 . 
     In the actual body  28  of the guiding sleeve  18  there is a first, central continuous guiding channel  30 , which in the present case is formed as a central bore passing through the body  28 . The clear inside diameter of the first guiding channel  30  is such that a first aiming wire  32 , as represented in  FIG. 1 , can be pushed snugly through it. The aiming wire  32  has an outside diameter of 2.4 mm. Laterally offset in relation to the first guiding channel  30  there is a second guiding channel  34 , which represents the inner lumen of a guiding tube  36 . The guiding tube  36  is fitted in a recess (not designated any more specifically here) on the outer side of the body  28  of the guiding sleeve  18  and fastened therein, for example adhesively bonded or welded or soldered. 
     It is evident from the sectional representation of  FIG. 7  that the central longitudinal axis  38  of the first guiding channel  30  runs parallel to and at a distance A from the central longitudinal axis  40  of the second guiding channel  34 .  FIG. 1  and the sectional representation of  FIG. 7  also reveal that on the outer side of the body  28  there is also a cannulation  42 , to be precise in the form of a cross-sectionally semicircular longitudinal groove  44 . The cannulation  42  is open to an outside laterally to the central longitudinal axis  38 . 
     It can again be seen from the sectional representation of  FIG. 7  that a virtual central longitudinal axis  46  of the longitudinal groove  44  likewise lies at a distance A from the central longitudinal axis  38  of the first guiding channel  30 . 
     Furthermore, the central longitudinal axis  46  or the longitudinal groove  44  lies exactly diametrically opposite the second guiding channel  34 . In other words, the cannulation  42  or the central longitudinal axis  46  thereof is arranged offset in relation to the second guiding channel  34  or the central longitudinal axis  40  thereof in terms of the circumferential angle by 180°. 
     Returning to the representation of  FIGS. 1 and 2 , it is evident that an arm  48 , which is held in a mounting  50 , projects from the handle  12  at a distance from and approximately parallel to the guiding sleeve  18 . 
     A clamping lever  54  keeps the arm  48  in the position represented; pressing of the clamping lever  54  allows the removal of the arm  48 , and it can correspondingly be cleaned or replaced by a new or differently formed arm. 
     The arm  48  has distally a bent region  54 , the distal end  56  of which has an opening  58 . The position of the opening  58  is such that it is in line with the first guiding channel  30  when the guiding sleeve  18  has been pushed into the opening  16  on the handle  12 , as is evident in particular from  FIG. 2 . 
     This means that, if a first aiming wire  32  is pushed through the guiding sleeve  18  from proximally, that is a say in the region of the clamping sleeve  26 , it meets the opening  58  and can pass through it. 
     As described and explained in more detail in particular by DE 10 2007 057 075.0 A1, the device  10  is set laterally inclined onto the outer side of a bone, for example onto the lower leg bone  64  represented in  FIG. 13 . The serrated rim  24  thereby facilitates the setting and holding of the guiding sleeve  18  at this site of the bone  64  or on the skin covering this bone. 
     The distal end  56  of the bent arm  48  is thereby introduced into the opened knee joint and positioned on the tibial plateau  60  such that a first aiming wire  32  pushed through the bone  64 , as is evident in  FIG. 13 , passes through the tibial plateau  60  and is passed through the opening  58 . 
     For the sake of overall clarity, the bone is not represented in  FIG. 2 , since this first working step is known per se from DE 10 2007 057 075.0 A1 which is incorporated by reference. 
     The handling and setting of the further aiming wires will now be described and explained in more detail on the basis of the sequence of images of  FIG. 3  to  FIG. 6  and the sectional representations of  FIG. 8  to  FIG. 11 . 
     After setting of the first aiming wire  32 , as represented in  FIG. 2 , a further or second aiming wire  68  is set through the second guiding channel  34 , as is evident in  FIG. 3  or  FIG. 9 . 
     It is evident that the first aiming wire  32  is significantly longer than the further, second aiming wire  68 . In its maximum advanced position, the distal tip (not represented any more specifically here) of the second aiming wire  68  reaches up to the marking  60  at the distal end  56  of the curved arm  48 . Once it has reached this point, that is an indication to the surgeon that the second, further aiming wire  68  has been set in the correct position and in the correct line. 
     Then the clamping sleeve  26  is turned, so that the guiding sleeve  18  can be pulled off in the proximal direction (see arrow  19 ) until the second, further aiming wire  68  has left the second guiding channel  34 , this structural state being represented in  FIG. 4 . The length of the pulling-off distance is intended to be represented by the arrow  19 . 
     It is then possible to turn the guiding sleeve  18  about the first aiming wire  32 , as represented in  FIG. 4  by the arrow  21 . The turning is carried out through 180°, so that then the cannulation  42  on the outer side of the guiding sleeve  18  lies in an alignment in which the second aiming wire  68  can enter the cannulation  42  during advancement of the guiding sleeve  18 . This situation is represented in  FIG. 5 . 
     If the guiding sleeve  18  is then displaced in the distal direction in a way corresponding to the arrow  32 , the aiming wire  68  enters the cannulation  42  (see  FIG. 10 ). Subsequently, the guiding sleeve  18  is pushed through the opening  16 , this opening being designed such that the guiding sleeve  18  can be pushed through either in this position or in the position turned by 180°. After fixing by the clamping sleeve  26 , a third aiming wire  70  is then pushed through the second guiding channel  34  or the guiding tube  36 , lying on the underside in the representation of  FIG. 5 . 
     This situation is represented in  FIG. 6  and in  FIG. 11 . 
     The third aiming wire  70  can also be advanced until it reaches the corresponding marking  62  at the distal end  56  of the arm  48 , so that again the surgeon can check whether this third aiming wire  70  also protrudes from the tibial plateau  66  at the correct site. 
     Subsequently, the guiding sleeve  18  is pulled off and the arm  48  is detached from the handle  12 , so that the entire device  10  is removed from the three set aiming wires  32 ,  68  and  70 . 
     This situation is represented in  FIG. 13 , that is to say the three aiming wires  32 ,  68  and  70  have been pushed through into the lower leg bone  64  from “below” by means of the device  10  such that they all three stand up from the tibial plateau  66  aligned parallel to one another. 
     The distance A between the three central longitudinal axes of the three aiming wires  32 ,  68  and  70  is chosen such that they can be overdrilled with a 4.5 mm drill. This initially involves overdrilling the two outer aiming wires  68  and  70  and subsequently likewise overdrilling the middle aiming wire  32 . 
     This then results in a drilled hole  72 , as represented in  FIGS. 12 and 14 . 
     If an exactly rectangular channel  74 , as represented in  FIG. 15 , is to be achieved, a correspondingly rectangular dilator may be pushed into the drilled hole  72 , in order to detach the protruding regions of bone remaining in the region of intersection. 
     In the reconstruction of an anterior cruciate ligament, a rectangular tendon transplant, for example, with the correct fit and form can then be inserted into the channel  74  and anchored. 
     In  FIGS. 16 to 21 , a second exemplary embodiment of a device according to the invention is represented, the difference merely being that the guiding sleeve  78 , and correspondingly the opening into which the latter can be pushed into the handle  12 , are formed differently. 
     It can be seen from the sectional representation of  FIG. 16 , which corresponds to the sectional representation of  FIG. 7 , that here too there is a central, first guiding channel  80 . At the previously described distance A and running parallel to it there is a second guiding channel  82 . Here, too, in the outer side of the guiding sleeve  78  there is a first cannulation  84 , the central longitudinal axis of which again runs parallel to and at the same distance A from the central longitudinal axis of the first guiding channel  80 , as described above in conjunction with the first exemplary embodiment. 
     As a departure from the first exemplary embodiment, in the case of the second exemplary embodiment a second and a third cannulation  86  and  88  are also cut out on the outer side of the guiding sleeve  78 . These cannulations again take the form of longitudinally running and laterally open grooves with an approximately semicircular cross section and the central longitudinal axes of which are again at the distance A from the central longitudinal axis of the first guiding channel  80 . 
     As described above, with the second exemplary embodiment three aiming wires running parallel to one another and aligned in a row can be set. 
     In addition, however, it is also possible now to achieve other geometries on resultant drilled holes. 
       FIG. 17  corresponds to a structural state such as that described in  FIG. 9 , that is the state after the first two aiming wires  32  and  68  have been set. 
     As is evident from the transition from  FIG. 17  to  FIG. 18 , after pulling off of the guiding sleeve  78  from the second aiming wire  68 , the latter is turned only by 90°, as indicated by an arrow  83 . Subsequently, the guiding sleeve  78  is pushed in again axially. 
     As a result, the second aiming wire  68  then enters the fourth cannulation  88 , angularly offset anticlockwise by 90°. A third aiming wire  70  can then be pushed in through the second guiding channel  82 , so that the alignment of the three aiming wires  32 ,  68 ,  70  at the corners of a triangle resulting from  FIG. 19  is obtained. 
     Renewed detachment and pulling off of the guiding sleeve  78  from the third aiming wire  70  allows the guiding sleeve  78  to be turned once again by 90°, as represented in  FIG. 20  by an arrow  85 . 
     The third aiming wire  70  has then entered the third cannulation  88 ; the second aiming wire  68  lies in the first cannulation  84 . A fourth aiming wire  89  can then be set in the second guiding channel  82 , which has become free again. 
     After removal of the device and overdrilling of the four aiming wires  32 ,  68 ,  70  and  89 , a drilled hole  90  with an approximately “T”-shaped profile, as represented in  FIG. 21 , then results in the bone  64 .

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