Abstract:
The application relates to a method of orienting a bone-milling cutter and an impact instrument for a hip-prosthesis cup in an acetabulum. The method includes initially positioning a manipulation cup by a manipulation joint head and representing this position by at least one guide rod or fixation rod that is fixed in a bone. The method also includes removing the manipulation cup and adjusting a position of both the bone-milling cutter and the impact instrument with respect to either the guide rod itself or a guide rod that is attached to a holding device disposed on at least one fixation rod.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 10/501,004 filed on Dec. 13, 2004, which issued as U.S. Pat. No. 7,828,806 on Nov. 9, 2010, which is a U.S. National Phase Application of PCT/EP03/00035 filed Jan. 3, 2003 designating the U.S. and published in German on Jul. 17, 2003 as WO 03/057087, which claims priority to German Application No. 102 00 690.3 filed Jan. 10, 2002. The disclosures of these applications are incorporated by reference herein in their entirety. 
    
    
     FIELD OF INVENTION 
     The invention relates to an accessory for implantation of a hip joint endoprosthesis, as well as to a method for manipulating it, in particular for orienting a bone-milling cutter and an impact instrument to implant a prosthesis cup in the acetabulum. 
     BACKGROUND 
     When hip endoprostheses are being inserted, the surgeon must proceed through various stages of the operation in which tools are employed; in particular, it is necessary to use a bone cutter in order to mill out the natural acetabulum and thus form a bearing socket within which an artificial cup can be anchored. An impact instrument is also used to drive the cup into place. When using either tool the surgeon must take care that the tools are oriented as precisely as possible, so that the prosthesis cup will ultimately be positioned as intended, with the greatest possible precision. 
     Important accessories that assist correct positioning and orientation of the tools include so-called navigation systems that function with computer assistance. Obviously, such systems are quite elaborate, and the costs of employing them are correspondingly high. In view of the fact that in medicine, as elsewhere, it is important to reduce costs without any deterioration in the quality of medical care, the present invention is directed toward the objective of providing an accessory for the implantation of a hip joint endoprosthesis that allows exact positioning of the prosthesis cup in relation to the femur, specifically to the joint head anchored in the femur, with simple mechanical means. During this operation care must be taken to implant the cup in such a way that during every conceivable movement of the femur, a collision between the edge of the cup and the neck of the femur is avoided. 
     SUMMARY OF THE INVENTION 
     This objective is achieved in accordance with the invention by an accessory that comprises the following basic elements: Manipulation cup Manipulation joint head with means for orienting the manipulation cup in the acetabulum, and Device to represent the correctly oriented position of the manipulation cup, so that by means of this device it is then possible to orient appropriately a bone-milling cutter and an impact instrument, which are used for placement of the prosthesis cup. 
     The central point of the accessory in accordance with the invention is thus that by means of a manipulation joint head the manipulation cup is put into a position within the acetabulum such that for all conceivable movements of the femur, a collision between the cup edge and the femoral neck is ruled out. For this purpose, the manipulation joint head is provided with appropriate mechanical or optical orientation means. In a first preferred exemplary embodiment the orientation means is constructed in the form of a shoulder that extends radially outward beyond the spherical part of the manipulation joint head. This shoulder corresponds to the rim of the manipulation cup when the latter is correctly oriented in the acetabulum. When the femur is in its “zero position”, the shoulder on the manipulation joint head is spaced apart from the rim of the manipulation-cup opening by an approximately uniform amount over the entire circumference of the latter. The manipulation joint head is fixed to the neck of a manipulation rasp, in particular is set onto it, to assist orientation of the manipulation cup. The manipulation rasp itself is fixed within the femur. Subsequently the operator causes the femur to make all conceivable movements, as follows: Flexion/extension about the “mediolateral” axis Abduction/adduction about the “anterior/posterior” axis Inward/outward rotation about the “craniocaudal” axis. 
     During this movement sequence the collisions that occur between the shoulder of the manipulation joint head and the rim of the manipulation cup cause the manipulation cup to move into a position such that, after the final implantation of the hip-joint endoprosthesis, collision between the rim of the prosthesis cup and the femoral neck will be reliably avoided. 
     Another device will of course be needed to represent the position in which the manipulation cup is correctly oriented, after the latter has been removed. With this device it is then possible to orient a bone-milling cutter and an impact instrument for positioning the prosthesis cup within the socket that has been milled out in the acetabulum. 
     The above-mentioned shoulder on the manipulation joint head can also be defined by shoulder sections distributed approximately uniformly over the circumference of the head. In the extreme case these sections can also be replaced by peg-like projections. Naturally, there must then be a sufficient number of these projections to achieve the orientation of the manipulation cup described above. 
     As a device to represent the correctly oriented position of the manipulation cup, it is preferable to use a guide rod that can be fixed in the bone and corresponds to a guide device disposed on the manipulation cup. The guide rod can be constructed either as a nail or also as a threaded rod. In the latter case the guide rod comprises a screw thread on the end section to be anchored in the bone, so that it can be screwed into the bone (namely the pelvic bone). 
     The guide device on the manipulation cup that is associated with the guide rod preferably comprises a component connected to the manipulation cup by way of an arm; this component is in particular a guide block or a guide sleeve with a bore within which the guide rod is guided. Accordingly, after the manipulation cup has been oriented, the guide rod is passed through the guide bore in the guide device disposed on the manipulation cup and is anchored in the bone. Then the manipulation cup is detached from the guide rod. This leaves the guide rod free so that a template can be attached thereto, in particular pushed onto it, for orienting a cutting head or its drive axis in such a way that the orientation of the cutting head corresponds to that of the manipulation cup. When only a single guide rod is available, the orienting template is preferably also rotatable about said rod. 
     In a preferred implementation of the first exemplary embodiment the orienting template comprises an arm, in particular an angled strap, that can be pushed onto the guide rod and at its free end (i.e., the end opposite the guide rod) bears a direction plate, in particular a plate provided with directional marks with which to orient the milling-cutter drive axle; for such orientation said axle is pivoted while in complete, i.e. gap-free contact with the direction plate and where appropriate also parallel thereto. The marks preferably also provided on the direction plate allow the milling-cutter drive axle to be pivoted parallel to the direction plate into a position aligned with a predetermined directional mark, in particular a predetermined zero position. Accompanying this zero position can be marks for two maximal-tolerance positions, namely±5°. 
     So that the direction plate can be held against the drive axle in a gap-free manner even when the milling cutter is in operation, the cutter drive axle is provided with a bush within which it is rotatably seated, and to which the direction plate can be apposed without a gap even during the milling process. 
     As already mentioned above, an impact instrument is also provided with which to hammer the prosthesis cup into its final position, in a prespecified orientation. The cup impact instrument can likewise be oriented with respect to the above-mentioned direction plate of the orienting template, in the same way as is the cutting head or its drive axle. Because the cup impact instrument is known per se, there is no need to describe it further here. 
     The manipulation cup can also be provided with a guide device by means of which two or more guide rods can be fixed in the bone parallel to one another. In this case the orienting template, which positions the cutting head or its drive axle as well as the cup impact instrument, likewise comprises two or three corresponding through-bores so that it can be pushed onto the guide rods fixed in the bone. 
     Another implementation of the first exemplary embodiment is characterized by a U-shaped curvature of the direction plate on the orienting template, in which case the space between the two limbs of the plate serves as a receptacle for the milling-cutter drive axle. The axle is preferably seated therein substantially without play, i.e. is parallel to the direction plate, so that the operator need only be concerned with adjusting the drive axle to the zero position. In order to better identify this zero position, the limb of the plate toward the operator, in particular the upper limb, can be provided at its end face with recesses that serve as markings for positioning the milling-cutter drive axle parallel to the direction plate. 
     Another exemplary embodiment of an accessory in accordance with the invention is characterized in that as a means for orienting the manipulation cup in the acetabulum optical identifiers are provided, e.g. in the form of an indentation or groove that extends over the circumference of the spherical part of the manipulation joint head. Instead of an indentation or groove, a marking line can be provided. All such markings extend within a plane that is either perpendicular to the central axis of the joint head or set at a predetermined angle thereto. In the first case the manipulation cup is correctly oriented when the marking becomes visible above the edge of the manipulation cup. In the second case the orientation of the manipulation cup is anatomically correct when the marking is undetectable on all sides, i.e. over the entire circumference of the manipulation cup. 
     In each case the manipulation joint head is fixed to the neck of a manipulation rasp in such a way that the central axis of the joint head coincides with the neck axis. 
     In a third exemplary embodiment the means for orienting the manipulation cup in the acetabulum is a circumferential shoulder extending outward from the joint head in a plane perpendicular to the central axis of the head, combined with a receptacle for the neck of a manipulation rasp, which is positioned at an angle to the central axis of the joint head such that its long axis is parallel to the axis of the femoral neck. 
     In the case of this exemplary embodiment, the manipulation cup is correctly oriented when the circumferential shoulder on the manipulation joint head is flush with the outer annular surface around the circumference of the manipulation cup. 
     As a device to represent the correct orientation of the manipulation cup, it is also possible to use separate fixation rods that extend through a device for holding the manipulation cup. These fixation rods are provided with helically threaded end sections, which can be screwed into the bone so as to anchor the rod therein. In this case it is preferable for a guide rod to be connectable to the aforementioned holding device, in such a way that the guide rod extends approximately parallel to the central axis of the manipulation cup. Then it is possible to attach to this guide rod a guide element that serves to guide a milling-cutter drive axle or a cup impact instrument. The guide element ensures that the orientation of the cutter drive axle and the impact instrument corresponds to that of the manipulation cup. 
     Regarding further details of this embodiment, reference is made to the relevant subordinate claims. 
     In the following, exemplary embodiments of the accessory in accordance with the invention, i.e. an instrument for the orientation of manipulation cups, is explained in greater detail with reference to the attached drawings, which illustrate the following objects and actions: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  manipulation joint head fixed to the neck of a manipulation rasp that is placed within the femur, shown in position with respect to the natural acetabulum; 
         FIG. 2  orienting a manipulation cup placed in the acetabulum by means of the manipulation joint head according to  FIG. 1 ; 
         FIG. 3  placement of a guide rod within a guide device associated with the manipulation cup, for future representation of the correct orientation of the manipulation cup, for which purpose the guide rod is anchored in the pelvic bone; 
         FIGS. 4 and 5  removal of the manipulation cup from the acetabulum and from the guide rod anchored in the bone; 
         FIG. 6  placement of a bone-milling cutter in the acetabulum, and pushing an orienting template onto the guide rod that is anchored in the bone, to assist orientation of the cutter and/or its drive axle. 
         FIGS. 7 and 8  placement of the orienting template and cutter drive axle with respect to one another, and keeping them in this relative position by hand (of the surgeon or an assistant); 
         FIG. 9  placement of the orienting template and cup impact instrument with respect to one another, in accordance with the relative positions of orienting template and cutter drive axle as shown in  FIGS. 7 and 8 ; 
         FIG. 10  the complete set of instruments for implantation of a hip joint endoprosthesis, viewed in perspective; 
         FIG. 11  the manipulation cup together with the guide device for a guide rod that can be anchored in the bone, viewed in perspective; 
         FIG. 12  a modified embodiment of an orienting template, viewed in perspective; 
         FIG. 13  another embodiment of a device for representing the correct orientation of the manipulation cup, viewed in perspective; 
         FIG. 14  a second exemplary embodiment of a manipulation joint head in association with a manipulation cup, in schematic section; 
         FIG. 15  a third exemplary embodiment of a manipulation joint head in association with a manipulation cup, in schematic section; and 
         FIG. 16  the arrangement of a guide rod on a manipulation-cup holder, as well as the placement of a guide element on said guide rod for guiding a cup impact instrument, in a position that corresponds to the correctly oriented position of the manipulation cup, in perspective. 
     
    
    
     DETAILED DESCRIPTION 
     Prior to consideration of the individual steps, for a first exemplary embodiment the complete set of instruments for anatomically correct implantation of a hip joint endoprosthesis will be described with reference to  FIG. 10 , which shows the following parts (from left to right):  11  Pelvic bone  12  Acetabulum  13  Proximal section of a femur, within which a manipulation rasp (not shown in detail) is fixed  14  Proximal end of the manipulation rasp placed within the femur  15  Prosthesis neck  16  Manipulation joint head set onto the prosthesis neck in the conventional way, in particular by means of a “stick-on cone” connection  17  Guide rod anchored in the pelvic bone  18  Guide block, which can be attached to a manipulation cup to accommodate the guide rod  17   19  Manipulation cup with holder strap  19  for the guide block  18   24  Orienting template  25  Drive axle for milling cutter  26  Axle bush  27  Cup impact instrument  28  Cutting head 
     As shown in  FIG. 1 , the first step is to tilt the femoral neck back and insert into it, beginning at the plane of resection, a manipulation rasp onto the neck of which a manipulation joint head  16  will be set. The manipulation joint head  16  comprises a spherical part  21 , around the circumference of which is a shoulder  22  that extends radially outward. This shoulder  22  is used to establish correspondence with the rim  23  around the opening of the manipulation cup  20 , as shown in  FIG. 2 . In a “zero position” the distance separating the shoulder  22  from the rim  23  of the cup opening is approximately equal around the circumference of the rim  23 . Starting from this zero position, the femur  13  together with the manipulation joint head  16  is moved in all anatomically conceivable directions, as described above. As a result of this movement, collisions between the shoulder  22  and the rim  23  of the manipulation cup  20  are very likely to occur at several places, with the consequence that the manipulation cup  20  becomes appropriately oriented within the acetabulum. 
     The oriented position of the manipulation cup  20  must be preserved so that both the bone-milling cutter and the impact instrument for the prosthesis cup can be appropriately oriented. For this purpose the manipulation cup  20  is connected by way of a holder strap  19  to a guide device in the form of a guide block  18  comprising a guide bore, the axis of the block being directed toward the pelvic bone  11  and outside the region in which collision with the manipulation cup is possible. Through said guide bore is passed a guide rod  17 , as shown in  FIGS. 3 and 4 . The guide rod  17  has a threaded section  29  at its end that points toward the bone  11 , by means of which the guide rod  17  can be screwed into the bone  11  and thus fixed there. The guide rod  17  is, of course, not screwed into the bone  11  until the manipulation cup  20  has been correctly oriented, so that the rod can represent the position of the manipulation cup within the acetabulum. After the guide rod  17  has been fixed within the pelvic bone  11  as just described, the manipulation cup is detached from the guide block  18  as shown in  FIG. 5  and removed from the acetabulum. 
     Subsequently, as shown in  FIGS. 6 and 7 , an orienting template  24  is pushed onto the guide rod  17 . The orienting template  24  accordingly comprises a guide sleeve fastened to an arm, in this case the angled strap  31 . At the free end of the strap  31  a direction plate  32  is formed. This direction plate  32  is provided with marks  33 , namely a central zero mark and two tolerance marks at +5°. These marks are identified in  FIGS. 6 and 7  by “0°” and “5°”. 
     This orienting template is first used to assist the orientation of a bone-milling cutter with hemispherical cutting head  28  and cutter drive axle  25 . To orient the cutting head and its drive axle  25 , the template is rotated about the guide rod  17  so as to bring the direction plate  32  into complete, i.e. gap-free contact with the drive axle  25 , and then the axle is swivelled parallel to the plate until it is in a position corresponding to a predetermined one of the marks, preferably the zero position “0”, as can clearly be seen in  FIG. 7 . 
     To prevent a collision between direction plate  32  and milling-cutter drive axle  25  while the cutter is in operation, the axle  25  is enclosed in a bush, within which the axle  25  is rotatably seated and onto the surface of which the direction plate  32  can be set and held in gap-free contact during the milling process, as can be seen in  FIG. 8 . 
     When the apparatus is positioned according to  FIG. 8 , the acetabulum can be milled out in the conventional manner. Thanks to the guide rod and the orienting template  24 , the hemispherical cutting head  28  is in a position that matches the previously adjusted, anatomically correct position of the manipulation cup  20 . 
     In order to better adjust the cutter drive axle  25  to the zero position, the bush  26  likewise bears a mark  33 , a line extending in the long direction. This mark is preferably brought into alignment with the zero mark “0” on the direction plate  32 . Thereafter the milling process can be carried out, to produce a suitable bearing socket into which the prosthesis cup can be inserted. Finally, the prosthesis cup is either screwed into this bearing socket or anchored there by so-called “press-fitting”. 
     After milling of the bearing socket in the acetabulum has been completed, the impact instrument  35  (already shown in  FIG. 10 ) is used to hammer in the prosthesis cup  34  that is to be permanently implanted. In this process, of course, care must also be taken that the impact against the prosthesis cup is such that the cup&#39;s final position corresponds to that of the manipulation cup  20 . Hence the cup impact instrument  27  must be oriented similarly to the bone-milling cutter, i.e. to the cutter&#39;s drive axle. The corresponding orientation of the impact instrument  27  is illustrated in  FIG. 9 . Here, again, the axial structure connecting the impact head to the struck end of the instrument is brought into gap-free contact with the direction plate  32 , preferably in alignment with the same marking as was the cutter drive axle. Then it is ensured that when the prosthesis cup  34  is hammered into the previously milled-out bearing socket in the acetabulum, it will be in the anatomically correct orientation. 
     In  FIG. 11  the manipulation cup with guide block for the guide rod  17  is shown again, now in perspective side view. The guide bore in the guide element  30  is indicated by dashed lines and identified by the numeral  36 . The guide element  30 , as can be seen in  FIG. 10  as well as  FIG. 5 , can be detached from the holder strap  19 . The connection between holder strap  19  and guide block is preferably implemented by a catch connector. 
     With reference to  FIG. 12  a modified embodiment of an orienting template  24  is described, which is distinguished firstly by the fact that the guide element  30  comprises two through-bores  42  to receive two guide rods  17  that extend parallel to one another. Another distinguishing feature of the orienting template  24  shown in  FIG. 12  is that the direction plate  32  is bent into a U shape, the space between the two plate limbs  37 ,  38  serving as a receptacle for the milling-cutter drive axle  25  and/or the cup impact instrument  27 . Hence these instruments can be pivoted only in a single plane, parallel to the two plate limbs  37 ,  38  between which they are held, as indicated by the double-headed arrow  39  in  FIG. 12 . The arrangement of the two guide rods unambiguously determines the position of the orienting template  24  relative to the acetabulum. Then all that is required of the surgeon is to position the cutter drive axle  25  and/or the cup impact instrument  27  between the two plate limbs  37 ,  38  in a plane parallel thereto. To facilitate this positioning, recesses  40  are provided in the end faces of the upper plate limb  37 . These correspond to the previously mentioned “0” and “±5°” marks. 
     The guide element  30  additionally comprises a fixing screw  41  to fix the orienting template  24  to the guide rods  17 . Because two guide rods  17  are used here, it is of course also necessary for the guide block  18  associated with the manipulation cup  20  to be constructed with two through-bores  42  for the guide rods  17 , as is likewise illustrated in  FIG. 12 . 
     The embodiment according to FIG.  12 —as explained above—permits correction of the angle of the cutter drive axle and/or the cup impact instrument to be carried out only in one plane. The guide rods  17  can be have different lengths. They preferably, as in previous embodiments, have a screw thread  29  at the end toward the bone. 
     It is obvious that after the prosthesis cup  34  has been put into place, the guide rods  17  must be removed from the bone. Preferably the guide rods  17  consist of so-called “Kirschner wires”. 
     As mentioned above, the guide block  18  associated with the manipulation cup must also obviously be adapted so that it can be used with two guide rods  17  (two through-bores  36  in the guide block  18  to receive the rods  17 , as also shown in  FIG. 12 ). 
     The manipulation joint head with manipulation rasp must be removed from the femur and replaced by the permanent hip shaft with its joint head. Then the hip joint can be re-assembled in the conventional manner. Because of the manipulation and orientation procedures described above, it is then ensured that there will be no collision between the neck of the prosthesis and the rim around the opening of the prosthesis cup  34 . 
       FIG. 13  shows a modified embodiment for a device to represent the oriented position of the manipulation cup  20 ; this device comprises three fixation rods  110 ,  111 ,  112 , which extend through a retaining device  118  such that each is at an angle with respect to the others. The fixation rods  110 ,  111 ,  112  comprise screw threads  129  on the end sections that are to be anchored in the bone, so that they can be screwed into the bone  11 . The retaining device  118  in the present case comprises two rows  113 ,  114  of holes for the fixation rods  110 , so that a sufficient number of holes are available for optimal placement of the fixation rods  110  in the bone  11 . The manipulation cup  20  is attached to the retaining device  118  by way of the holder strap  19 . Furthermore, it is also possible to connect to the retaining device  118  a guide rod  117 , in such a way that the guide rod extends approximately parallel to the central axis  115  of the manipulation cup, indicated in  FIG. 13  by the reference numeral  115 . 
     To the guide rod  117  there can be attached a guide element  118   a  in the form of a half-sleeve  119 . The half-sleeve  119  serves to guide a cutter drive axle  25  (not shown in detail in  FIG. 16 ) or a bush  26  enclosing said axle. It additionally serves to guide or orient a cup impact instrument  35 , whereby the guide element  118   a  in the form of a half-sleeve  119  ensures that the orientation of the cutter drive axle and of the cup impact instrument corresponds to that of the manipulation cup  20 . In this case the central axis  115  of the manipulation cup coincides with the long axis of the cutter drive axle as well as with the long axis of the cup impact instrument. 
     The half-sleeve  119  serving as a guide element is connected by way of a flat connector strap  131  to the guide rod  117 . The length of the connector strap  131  in the illustrated embodiment can be adjusted. At the end of the connector strap  131  that is associated with the guide rod  117  there is likewise disposed a half-sleeve  120  to serve as an attachment means and sliding shoe. Thus the guide element  118   a  can be put into position on the guide rod  117  in a simple way, and displaced longitudinally thereon. 
       FIGS. 14 and 15  show two further, alternative exemplary embodiments of a manipulation joint head  116  and  216 , respectively. In both cases the joint heads are mounted on the neck  121  of a manipulation rasp  126 . The manipulation rasp  126  has been inserted into the proximal end of a femur  13  (not shown in detail). The long axis of the peg-shaped neck  121  corresponds to the axis of the femoral neck and is identified by the reference numeral  123 . The manipulation cup  20  comprises a metallic outer shell  124 , onto which has been molded the holder strap  19 , as well as an inner shell made of plastic, i.e. an inlay  125 . To this extent the structure of the manipulation cup  20  corresponds to that of a prosthesis cup intended for permanent implantation. 
     In the exemplary embodiment shown in  FIG. 14 , the means provided for orientation of the manipulation cup  20  in the acetabulum are optical detection means  122 . Specifically, the optical detection means  122  is constructed as an indentation or groove extending along the circumference of the spherical part of the manipulation joint head  116 . In the present case the path of this groove is perpendicular to the central axis  127  of the joint head, which in the exemplary embodiment according to  FIG. 14  coincides with the femoral-neck axis  123 . 
     The indentation  122  extending around the circumference of the spherical part of the manipulation joint head  116  lies within the complementary bearing surface of the manipulation cup  20  when the central axis  127  of the manipulation joint head  116  coincides with the central axis of the manipulation cup. The circumferential indentation  122  does not become visible unless a relative rotation of the manipulation joint head within the manipulation cup  20  occurs. Its invisibility serves as a sign that the manipulation cup  20  is correctly oriented. Preferably the manipulation joint head, i.e. its spherical part, and the manipulation cup comprise markings that correspond to one another, both extending in the circumferential direction, so that the orientation of the manipulation cup about the femoral-neck axis  123  can also be undertaken correctly. The possible movements of the manipulation cup  20 , which are those characteristic of a universal joint, are indicated in  FIG. 14  by the double-headed arrows  128 ,  129 . 
     A third exemplary embodiment of means to orient the manipulation cup  20  within the acetabulum  12  is diagrammed in  FIG. 15 . There the manipulation cup  20  is oriented by the interplay of a circumferential shoulder  222 , which extends in a plane perpendicular to the central axis  127  of the joint head, with a receptacle for the neck  121  of the manipulation rasp  126  that extends at an angle to the joint-head central axis  127  (as previously mentioned, the long axis of the neck  121  is parallel to the femoral-neck axis  123 ). 
     In this case the manipulation cup  20  has been correctly oriented when said circumferential shoulder  222  is flush with the circumferential ring  223  of the manipulation cup  20 , i.e. of the inlay  125 . 
     The two last-mentioned exemplary embodiments thus both comprise optical detection means for orientation of the manipulation cup. They can be handled in a simple manner and function reliably. 
     In the exemplary embodiment according to  FIG. 15 , of course, care must be taken that the manipulation joint head is oriented in the prespecified manner with respect to the manipulation rasp  126 , i.e. that the joint-head central axis  127  is aimed in a prespecified direction. Only then will it be certain that the objective stated initially is achieved by the final implant. 
     All the characteristics disclosed in the application documents are claimed as essential to the invention insofar as they are new to the state of the art individually or in combination. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               11  Pelvic bone 
               12  Acetabulum 
               13  Femur 
               14  Proximal end of a manipulation rasp 
               15  Prosthesis neck 
               16  Manipulation joint head 
               17  Guide rod 
               18  Guide block 
               19  Holder strap 
               20  Manipulation cup 
               21  Spherical part of the manipulation joint head 
               22  Shoulder 
               23  Opening rim 
               24  Orienting template 
               25  Drive axle or shaft for milling cutter 
               26  Axle bush 
               27  Cup impact instrument 
               28  Cutting head 
               29  Threading 
               30  Guide sleeve or guide element 
               31  Angled strap 
               32  Direction plate 
               33  Marking 
               34  Prosthesis cup 
               36  Guide bore 
               37  Limb of plate 
               38  Limb of plate 
               39  Double-headed arrow 
               40  Recess 
               41  Fixing screw 
               42  Guide bore 
               110  Fixing rod 
               111  Fixing rod 
               112  Fixing rod 
               113  Row of holes 
               114  Row of holes 
               115  Central axis of manipulation cup 
               116  Manipulation joint head 
               117  Guide rod 
               118  Retaining device 
               118   a  Guide element 
               119  Half-sleeve 
               120  Half-sleeve 
               121  Neck of a manipulation rasp 
               122  Circumferential indentation 
               123  Neck/femoral-neck axis 
               124  Outer shell 
               125  Inlay 
               126  Manipulation rasp 
               127  Central axis of joint head 
               128  Double-headed arrow 
               129  Double-headed arrow 
               131  Connector strap 
               216  Manipulation joint head 
               222  Circumferential shoulder 
               223  Circumferential annular surface