Patent Publication Number: US-2023132876-A1

Title: Guided milling device for prosthetic surgery

Description:
FIELD OF THE INVENTION 
     The present invention concerns a guided milling device for prosthetic surgery suitable for the preparation of seatings for bone fillers or for the preparation of housing seatings in the bone for a prosthesis. 
     In particular, the milling device is particularly suitable for making seatings for bone fillers for a knee prosthesis or for the preparation of a bone seating for a shoulder joint prosthesis, also called humeral prosthesis, or for a hip prosthesis. 
     BACKGROUND OF THE INVENTION 
     It is known that, in orthopedic surgery for the implantation of a prosthesis, when it is required to prepare a seating for a bone filler or prepare a housing seating for a prosthesis, it is necessary to make a hole in the bone and/or a milling operation to make the seating with the desired profile. 
     Often, in fact, congenital or traumatic degenerative diseases, for example primary arthrosis or secondary arthrosis, due to trauma or caused by infections, rheumatoid arthritis, inflammatory arthritis, osteonecrosis, or bone tumors, or other similar problems, require implantation of a prosthesis able to reproduce, overall, a movement similar to that of the healthy joint. 
     It is also known that when, due to the pathologies as above, the spongy part of the bone is unable to support the prosthesis, it is necessary to create appropriate bone seatings for the implantation of a bone or metal filler that acts as a support for the prosthesis. This problem can become critical especially for knee prostheses and hip and shoulder prostheses. 
     The knee prosthesis typically comprises a femoral component, which is attached to the distal end of the femur, and a tibial component, which is attached to the proximal end of the tibia. 
     Especially in the case where it is necessary to recondition a previously implanted knee prosthesis, the creation of a bone seating, for the application of suitable support cones, first requires that a hole is made, with one or more boring devices of increasing diameter, and subsequently that the hole is shaped with a suitable milling device. 
     For this purpose, milling devices are known, which can be used during prosthetic surgery for the preparation of said seatings. 
     These milling devices typically comprise a handling body provided with a rotating rod which develops along a longitudinal axis, substantially coinciding with the axis of the intra-medullary canal, depending on the case, of the tibia or femur, and provided with a proximal end which has a connector to a drive member and a distal end connected to a milling tool, made to rotate by the drive member. 
     Given that both tibia and femur have an asymmetrical elongated conformation, one of the main problems encountered during the preparation of a bone seating is to avoid perforation of the cortical zone of the tibial and femoral bone. 
     One of the disadvantages of known milling devices is that they are configured to shape the bone seating in the direction of a milling axis which substantially coincides with the axis of the intra-medullary canal, and consequently with the longitudinal axis around which the rotating rod is driven, depending on the case, of the tibia or femur; such devices are therefore not able to follow the specific anatomy of the tibial and femoral bone. 
     To help the surgeon in the milling operation, the milling device often comprises, or is combined with, a guide rod which is previously inserted into the intra-medullary canal. The guide rod is slidably positioned inside the milling device along the longitudinal axis, and therefore is also coaxial to the milling axis. Although this solution allows the surgeon to follow a desired milling direction in a guided way, it does not allow to incline the milling axis with respect to the longitudinal axis and therefore to the axis of the intra-medullary canal, with the consequent risk of damaging, in particular perforating, the cortical zone. This risk occurs in particular when the milling diameter is increased to make the implant seating. 
     Sometimes, to avoid perforation of the cortical zone, the surgeon is therefore obliged to make bone seatings of a limited size which may, however, not be sufficient to guarantee adequate joint stability of the prosthesis, especially in the case where previous prostheses implants have damaged or otherwise rendered unusable an extended zone of the spongy part of the bone, or the removal of the previous implant has created significant bone loss or there is degeneration or lack of bone. 
     There is therefore a need to perfect a guided milling device for prosthetic surgery which can overcome at least one of the disadvantages of the state of the art. 
     In particular, one purpose of the present invention is to provide a guided milling device for prosthetic surgery which is able to perform milling operations while avoiding damage to the cortical zone of the bone. 
     Another purpose of the present invention is to provide a guided milling device for prosthetic surgery which is able to obtain a stable milling with respect to a milling axis different from the axis of the intra-medullary canal or different from the axis of the guide rod that is inserted into it. 
     Another purpose of the present invention is to provide a guided milling device for prosthetic surgery which is simple to use and which consists of a limited number of components. 
     Another purpose of the present invention is to provide a guided milling device for prosthetic surgery which is simple to assemble, in order to carry out the surgical operation, and to disassemble, in order to carry out cleaning and sterilization thereof. 
     The Applicant has studied, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages. 
     SUMMARY OF THE INVENTION 
     The present invention is set forth and characterized in the independent claim. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea. 
     In accordance with the above purposes, the guided milling device for prosthetic surgery comprises a milling tool rotating about a milling axis, and a handling body having a drive rotating rod which develops along a longitudinal axis of linear rotation. The rotating rod is connected to the milling tool in order to make the milling tool rotate about the milling axis. 
     The rotating rod is internally hollow and has a guide channel parallel to the longitudinal axis and in which a guide rod is positioned coaxially in a slidable manner, able to be positioned so as to extend beyond the milling tool along the longitudinal axis. 
     The milling axis is inclined with respect to the longitudinal axis, so that the milling tool is disposed inclined with respect to the rotating rod and also with respect to the guide rod. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein: 
         FIG.  1    shows an exploded perspective view of a milling device for prosthetic surgery, in particular for application to the tibial bane, in accordance with some embodiments described here; 
         FIG.  2    shows a lateral elevation section view of  FIG.  1   ; 
         FIG.  3    shows another lateral elevation section view of  FIG.  1   ; 
         FIG.  4    shows a schematic top plan view of a component of  FIG.  1   ; 
         FIG.  5    shows a schematic view of a possible application of the milling device for prosthetic surgery in accordance with some embodiments described here; 
         FIG.  6    shows a lateral view of a milling device for prosthetic surgery, in particular for application to the tibial bone, in accordance with some embodiments described here; 
         FIG.  7    is another lateral view of  FIG.  6   ; 
         FIG.  8    is a section along line VIII-VIII of  FIG.  6   ; 
         FIG.  9    is a section along line IX-IX of  FIG.  7   ; 
         FIG.  10    shows an exploded perspective view of a milling device for prosthetic surgery, in particular for application to the femoral bone, in accordance with some embodiments described here; 
         FIG.  11    shows a lateral elevation section view of  FIG.  10   ; 
         FIG.  12    shows a lateral view of a milling device for prosthetic surgery, in particular for application to the femoral bone, in accordance with some embodiments described here; 
         FIG.  13    is a longitudinal section of  FIG.  12   ; 
         FIG.  14    shows an exploded perspective view of a milling device for prosthetic surgery, in particular for application to the shoulder joint, in particular for the glenoid, in accordance with some embodiments described here; 
         FIG.  15    shows a lateral elevation section view of  FIG.  14   ; 
         FIG.  16    shows a lateral view of a milling device for prosthetic surgery, in particular for application to the shoulder joint, in particular for the glenoid, in accordance with some embodiments described here; 
         FIG.  17    is a longitudinal section of  FIG.  16   ; 
         FIG.  18    shows a section view of a milling device for prosthetic surgery, in particular for application to the tibial bone, in which the guide rod is shown; 
         FIG.  19    shows a section view of a milling device for prosthetic surgery, in particular for application to the femoral bone, in which the guide rod is shown; 
         FIG.  20    shows a section view of a milling device for prosthetic surgery, in particular for application to the shoulder joint, in particular for the glenoid, in which the guide rod is shown; 
         FIG.  21    shows a lateral view of a milling device for prosthetic surgery, in particular for application to the shoulder joint, in particular for the glenoid, in accordance with some embodiments described here; 
         FIG.  22    shows an enlarged detail of  FIG.  21   ; 
         FIG.  23    is a section view of  FIG.  22   ; 
         FIG.  24    shows an enlarged detail of the rotating rod present in  FIGS.  21 - 23   ; 
         FIGS.  25 - 29    show a possible operating sequence of use of a milling tool for surgical application to the tibial bone; 
         FIGS.  30 - 33    show a possible operating sequence of use of a milling tool for surgical application to the femoral bone; 
         FIGS.  34 - 36    show a possible operating sequence of use of a milling tool for application to the shoulder joint, in particular for the glenoid cavity; 
         FIG.  37    shows a top view of a milling device for prosthetic surgery, in particular for application to the tibial bone, in accordance with other embodiments described here; 
         FIG.  38    is a section along line XXXVIII-XXXVIII of  FIG.  37   ; 
         FIG.  39    is a representation of  FIG.  38    in which the milling tool is shown separate; 
         FIG.  40    shows a top view of a milling device for prosthetic surgery, in particular for application to the tibial bone, in accordance with other embodiments described here; 
         FIG.  41    is a section along line XLI-XLI of  FIG.  40   ; 
         FIG.  42    is a representation of  FIG.  41    in which the milling tool is shown separate; 
         FIG.  43    shows a top view of a milling device for prosthetic surgery, in particular for application to the femoral bone, in accordance with other embodiments described here, in which the guide rod is shown; 
         FIG.  44    is a cross-section view of  FIG.  43   ; 
         FIG.  45    shows a top view of a milling device for prosthetic surgery, in particular for application to the femoral bone, in accordance with other embodiments described here; 
         FIG.  46    is a section view of  FIG.  45   ; 
         FIGS.  47 - 49    respectively show a lateral view, a section and section with separated components of a milling device for prosthetic surgery, in particular for application to the femoral bone, in accordance with other embodiments described here; 
         FIG.  50    is an enlarged detail of  FIG.  48   . 
     
    
    
     To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications. 
     DETAILED DESCRIPTION OF SOME EMBODIMENTS 
     We will now refer in detail to the various embodiments of the invention, of which one or more examples are shown in the attached drawings. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, the characteristics shown or described insomuch as they are part of one embodiment can be adopted on, or in association with, other embodiments to produce another embodiment. It is understood that the present invention shall include all such modifications and variants. 
     Before describing these embodiments, we must also clarify that the present description is not limited in its application to details of the construction and disposition of the components as described in the following description using the attached drawings. The present description can provide other embodiments and can be obtained or executed in various other ways. We must also clarify that the phraseology and terminology used here is for the purposes of description only, and cannot be considered as limitative. 
     Embodiments described using the attached drawings concern a guided milling device for prosthetic surgery, indicated as a whole with reference number  10  in the attached drawings. 
     With particular reference to the attached drawings,  FIGS.  1 - 9 ,  37 - 42    concern a guided milling device  10  suitable for making seatings for bone fillers for the tibial bone,  FIGS.  10 - 13 ,  43 - 46    concern a milling device  10  suitable for making seatings for bone fillers for the femoral bone and  FIGS.  14 - 17    concern a milling device  10  suitable for making seatings for a shoulder joint prosthesis, also called humeral prosthesis.  FIGS.  18 - 20    show embodiments of the milling device  10  respectively configured for the preparation of a seating in the tibial bone, in the femoral bone and in the shoulder joint, in which a guide rod  50  is slidingly associated.  FIGS.  21 - 24    concern another embodiment of the milling device  10  suitable for making seatings for a shoulder joint prosthesis, in particular for the glenoid,  FIGS.  25 - 29  and  30 - 33    concern the use for milling of the tibial and femoral bone respectively. Other embodiments shown in  FIGS.  47 - 50    concern a milling device  10  suitable for making seatings for the hip joint. In this case, the guide rod  50  which is coupled, during use, with the device  10  is the coupling cone of a hip prosthesis rod already previously implanted in the femoral canal. 
     The guided milling device for prosthetic surgery  10 , hereafter device  10 , comprises a milling tool  11 , rotating about a milling axis R, and a handling body  14  having a drive rotating rod  22  which develops along a longitudinal axis Z of linear rotation. The rotating rod  22  is connected to the milling tool  11  to make the milling tool  11  rotate about the milling axis R. This longitudinal axis Z is favorably a linear axis. 
     In accordance with some embodiments described here, the rotating rod  22  is cannulated, that is, it is internally hollow and has a guide channel  42  parallel to the longitudinal axis Z and suitable to house a guide or reference rod  50  necessary to axially position the device  10  in the desired milling position during the surgical operation. 
     The guide rod  50  is coaxially housed in the guide channel  42  and is slidably positioned therein to extend beyond the milling tool  11  along the longitudinal axis Z. The amount by which the guide rod  50  extends beyond the milling tool  11  is coordinated and aimed at the insertion of the guide rod  50  into the intra-medullary canal, in order to guide the milling operation (see for example  FIGS.  21 - 23 ,  25 - 27 ,  30 - 32 ,  34 - 36   ). As will be described in more detail below, the guide rod  50  can also be the coupling cone of a hip prosthesis rod previously implanted in the femoral canal ( FIGS.  47 - 50   ). 
     In accordance with the present invention, the milling axis R is inclined with respect to the longitudinal axis Z, so that the milling tool  11  is disposed inclined with respect to the rotating rod  22  and also with respect to the guide rod  50 . 
     Consequently, according to the present invention, since the guide rod  50  is inserted into the guide channel  42  along the longitudinal axis Z, it follows that the milling axis R is actually also inclined with respect to such guide channel  42  and therefore to the guide rod  50 , when in use. 
     In accordance with some embodiments, the guide rod  50  has, at least in the proximal part, a transverse size, in particular a diameter, which is smaller than the transverse size of the guide channel  42 , so that it can be inserted in the latter, but with limited transverse play. In the distal part, on the other hand, the guide rod  50  can have a diameter which is also larger, which is a function of the anatomical canal. 
     The guide rod  50 , or at least a guide portion  50   a  thereof, can have a shorter length than the length of the guide channel  42  measured along the longitudinal axis Z. 
     The milling tool  11 , although it is guided along the guide rod  50  and therefore along the longitudinal axis Z, allows to define a bone seating having a development along an axis that is different to that of the guide rod  50 , that is, along the milling axis R inclined with respect to the longitudinal axis Z. 
     In accordance with possible embodiments, the guide rod  50  can be a reference pin, a more or less thin rigid shaft, a so-called Kirschner wire or “lead wire”, for example in the case of a shoulder joint, or similar guide element. Depending on the applications, the guide rod  50  can have a shaped tip, with teeth, coils or other elements, to act as a reamer mean, for example in the event it is used for the tibial or femoral intra-medullary canal. 
     In particular, in accordance with some embodiments, shown in  FIGS.  18 - 19   , at least in the case of a milling device  10  for the femoral and/or tibial bone, the guide rod  50  can generally be a reaming device which, suitably driven by a motorized or manual drive mean, is used before the device  10  in order to create a first hole, or first holes of increasing diameters in the intra-medullary canal. Once the suitable diameter of the hole has been reached, the guide rod  50  is left in the intra-medullary canal where the hole was created and is released from the drive mean. After that, the device  10  is prepared so that the guide rod  50  is inserted into the guide channel  42  and acts as an axial guide during the milling operation. In the example described here, the guide rod  50  comprises a guide portion  50   a  able to cooperate with the guide channel  42 , and a reaming portion  50   b  which always remains outside the milling tool  11 . 
     According to the embodiment shown in  FIG.  20   , the guide rod  50  is configured as a guide wire, also called Kirschner wire or k-wire, or it can also be a so-called “lead wire”. In fact, in the case of the shoulder joint, the intra-medullary canal has a reduced cross-section compared to the tibial or femoral bone and it is not possible to use a reaming tool as in the applications to the femoral and tibial bones. As shown in  FIGS.  34 - 36   , the milling tool  11  is guided and advances along the wire, which in this case acts as a guide rod  50 , previously inserted and aligned along the final axis of the prosthetic implant. At the same time, the milling tool  11  is able to rotate and prepare a seating, for example of a spherical shape, oriented along an axis—the milling axis R—that is inclined with respect to that of the wire which acts as a guide rod  50 —coinciding with the longitudinal axis Z. In this specific case, the inclined axis along which the seating being prepared is oriented, defined by the milling axis R, is an axis essentially orthogonal to the eroded surface of the glenoid. In accordance with some embodiments, the handling body  14  comprises an angular positioning assembly  51  configured to define the inclined disposition of the milling tool  11  with respect to the guide rod  50  and to the rotating rod  22 , as described above. 
     The angular positioning assembly  51  comprises articulation means  54 , to connect the milling tool  11  to the rotating rod  22  in an articulated manner, and a positioning member  20 , disposed on a tubular handle  23  of the handling body  14 . 
     In accordance with some embodiments, the articulation means  54  can comprise an angular joint  18  (see for example  FIGS.  1 ,  10  and  14   ), disposed on one end of the rotating rod  22 , or, or in addition, a pair of articulated surfaces  52 ,  53  (see for example  FIGS.  23 - 24   ) respectively defined on the rotating rod  22  and on an internal part of the milling tool  11 , so as to configure a spherical joint. Favorably, the angular joint  18  lies on the longitudinal axis Z. In particular, the angular joint  18  essentially lies on the intersection of the longitudinal axis Z and the milling axis R. 
     For example, the angular joint  18  can be completely contained inside the milling tool  11 , see for example  FIGS.  8 - 9   , or be partly outside and partly inside the milling tool  11 , see for example  FIG.  23    and  FIG.  50   . 
     The articulation means  54  allow to selectively define a plurality of inclined positions of the milling tool  11  with respect to the longitudinal axis Z. 
     The positioning member  20  comprises a stabilizing body  21  disposed eccentric with respect to the longitudinal axis Z and configured to cooperate with the milling tool  11  so as to selectively define, from among the plurality of inclined positions as above, a single specific stable inclined position of the milling tool  11  with respect to the longitudinal axis Z. 
     On the basis of the conformation of the stabilizing body  21  and the reciprocal cooperation with the milling tool  11 , it is therefore possible to determine the desired angular position, which, once selected, is used to carry out the milling with the chosen angle of inclination of the milling axis R. 
     The specific stable inclined position allows the milling tool  11  to rotate with respect to the milling axis R. 
     The milling axis R is inclined with respect to the longitudinal axis Z of rotation of the rotating rod  22  by an angle of inclination α which varies according to the surgical application (application to the tibial bone, to the femoral bone or to the shoulder joint). Therefore it can be said that the milling tool  11  is inclined with respect to the rotating rod  22  and with respect to the guide rod  50 . 
     In particular, the positioning member  20  defines the angle of inclination a so that when the rotating rod  22  rotates with respect to the longitudinal axis Z, the milling tool  11  rotates with respect to the milling axis R. 
     As shown schematically in  FIG.  5   , with this configuration of the device  10  it is possible to create a bone seating without damaging the cortical zone  110  of the bone. In fact, while overall the device  10  is used so that the longitudinal axis Z is substantially orthogonal to the tibial resection, that is, substantially parallel to the intra-medullary canal, this device  10  shapes the bone seating as above with respect to the angle of inclination α that corresponds to the specific stable inclined position. Optionally, the milling tool  11  can have the profile of a solid of revolution, obtained rotating a desired curve, which for example approximates the internal geometry of the tibia or femur. In particular, a known milling device is schematically shown in a dashed line, the device  10  in accordance with the embodiments described here is shown in a continuous line. Evidently, the known milling device comes much closer to the cortical zone  110 , with the risk of damaging it by perforating it. 
     In addition, this allows the user to create a deeper bone seating, being able to ensure, especially in the case of severe degeneration of the spongy part of the bone, a suitable joint stability of the prosthesis. 
     The milling tool  11  has a concave coupling seating  12  having a polar coupling aperture  13 , through which the guide rod  50  is made through. The guide rod  50 , therefore, has a smaller transverse size than the transverse size of the polar coupling aperture  13 . The rotating rod  22  is provided with a distal end  16  connected to the milling tool  11  inside the concave coupling seating  12  in correspondence with the polar coupling aperture  13 , and a proximal end  15  which has a tang  17  for attachment to a drive member to make the milling tool  11  rotate about the milling axis R. The distal end  16  is open to allow the guide rod  50  access to the guide channel  42 . 
     Here and hereafter, the relative terms “proximal” and “distal” when they describe the rotating rod  22  of the milling device  10  are defined with reference to the perspective of the milling device  10 . Thus, “proximal” refers to the direction of coupling with the attachment tang  17  and “distal” refers to the direction of coupling with the milling tool  11 . Consequently, the relative terms “proximal” and “distal” when applied to other components refer to the reference described above. 
     With particular reference to  FIGS.  21 - 24   , in the case of surgical application of the device  10  to the shoulder joint, the rotating rod  22  can be provided, in the head or distal position, with a front milling tip  55  which is outside the milling tool  11  and cooperating with the latter to create a seating for the prosthetic implant. 
     The front milling tip  55  can be made in a single piece with the rotating rod  22 , in correspondence with its distal end  16 , and is therefore integral in rotation with the rotating rod  22 . The front milling tip  55  has an axial aperture to allow the passage of the guide rod  50  in the guide channel  42 . When the milling tool  11  is driven in rotation and advances removing the bone, at the same time the front milling tip  55  also rotates, thus also making an axial hole in the bone (along the longitudinal axis Z) which houses the part of the rotating rod  22  axially protruding from the milling tool  11 . The front milling tip  55 , therefore, rotates about an axis coaxial to the longitudinal axis Z, and not about the milling axis R of the milling tool  11 . In particular, in this variant described with reference to  FIGS.  21 - 24   , the point of intersection of the milling axis R and the longitudinal axis Z falls outside the milling tool  11  (see in particular  FIG.  23   ). 
     The embodiment shown in  FIGS.  47 - 50    also shows a device  10  provided with a front milling head  155 . In this specific case, the device  10  is suitable for surgical applications of the hip joint. 
     The device  10  therefore comprises both lateral cutting edges—see the external surface of the milling tool  11 —and also front cutting edges—see the front part of the front milling head  155 . 
     The front milling head  155  is coupled with the milling tool  11  and disposed outside, beyond the polar coupling aperture  13 . 
     The front milling head  155  has a front aperture  59  substantially aligned with the polar aperture  13  of the milling tool  11  and through which the guide rod  50  is configured to pass. 
     In this solution, the guide channel  42  has a more limited extension/depth than the embodiments previously described. In fact, in this case the guide channel  42  has to contain a guide rod  50  which has a rather limited extension. The guide rod  50  in this case is the coupling cone of a hip prosthesis rod already previously implanted in the femoral canal. 
     The front milling head  155  also has, laterally, discharge apertures for the passage of the material removed and to facilitate the cleaning of the component. 
     The front milling head  155  has a curved lateral surface defining the angular joint  18 . The curved lateral surface, as a whole, defines a single convex curved portion  24 . 
     In particular, the coupling of the angular joint  18  and the polar aperture  13  of the milling tool  11  allows to position the latter according to any possible inclination whatsoever with respect to the longitudinal axis Z, while the final angle always remains determined by the positioning member  20 , see the enlarged detail in  FIG.  50   . 
     In accordance with some embodiments, the angular joint  18  is positioned in correspondence with the distal end  16  of the rotating rod  22  or in the proximity thereof, and is rotatably coupled with the polar coupling aperture  13  with degrees of freedom able to allow the milling tool  11  to selectively assume a plurality of positions that are inclined with respect to the longitudinal axis Z. 
     In accordance with some embodiments, the handling body  14  comprises the tubular handle  23  which is coaxially coupled, in a removable manner, with the rotating rod  22  and is provided with the positioning member  20 . 
     The tubular handle  23  is provided with a distal aperture  25  and with a proximal aperture  26 , respectively associated with the distal end  16  and the proximal end  15  of the rotating rod  22 . 
     The tubular handle  23  has a longitudinal channel  27  made through from the distal aperture  25  to the proximal aperture  26  for the rotational coupling with the rotating rod  22 . Advantageously, the longitudinal channel  27  has a size in a direction orthogonal to the longitudinal axis Z which is greater than that of the rotating rod  22 , thus allowing to prevent unwanted sliding. 
     In accordance with possible solutions, the tubular handle  23  can be made in a single piece or it can be made in two separate parts which can be selectively joined in order to form a shell to house the rotating rod  22 . Advantageously, the tubular handle  23  can be made of plastic material in order to reduce possible friction with the rotating rod  22  and with the milling tool  11  to a minimum. 
     In accordance with the embodiments described here, with particular reference to  FIGS.  8 - 9    and  FIG.  13    and  FIG.  17   , and which can be combined with all the other embodiments described, the size of the proximal aperture  26  is slightly smaller than the size of the longitudinal channel  27  in order to cooperate with a retaining edge, or tooth  30 , for example circumferential, of the rotating rod  22  and guarantee a desired positioning of the rotating rod  22  in the direction of the longitudinal axis Z. The retaining edge  30  allows the snap-in attachment of the tubular handle  23  onto the rotating rod  22 . 
     Advantageously, the tubular handle  23  can have, externally, an ergonomic and non-slip grip  28  so that it is easier for the user to grip and handle it. For this purpose, the tubular handle  23  has longitudinal grooves  29  which extend at least in a central zone thereof, possibly having knurled surfaces. In addition, the grip  28  can have a camber in order to further improve the grip. 
     Advantageously, in some embodiments, see for example  FIGS.  26 ,  27 ,  31 ,  32 ,  34 ,  37 - 46   , and which can be combined with all the embodiments described here, the tubular handle  23  can have, or be associated with, a safety clamping nut  58 . The safety clamping nut  58  secures the tubular handle  23  along the longitudinal axis Z in order to prevent the tubular handle  23  from being accidentally released, during the surgical act, due to pressure on it. 
     The positioning member  20  and in particular the stabilizing body  21  is configured to cooperate with the concave coupling seating  12 . 
     In accordance with some embodiments, the stabilizing body  21  is configured to make a same-shape coupling with the concave coupling seating  12  of the milling tool  11  so as to define the above described specific stable inclined position of the milling tool  11  with respect to the longitudinal axis Z based on the eccentricity with respect to the longitudinal axis Z. 
     The positioning member  20  comprises the distal aperture  25  and a sliding coupling seating  31  configured to house a shaped portion  40  of the rotating rod  22  in order to guarantee a desired positioning of the rotating rod  22  in the direction of the longitudinal axis Z. In particular, the seating  31  is concentric with respect to the longitudinal axis Z. 
     The seating  31  is configured to exert an action of positioning the rotating rod  22  in cooperation with the positioning action exerted by the retaining edge  30 . In this way, once the rotating rod  22  is operatively inserted in the longitudinal channel  27 , its positioning in the direction of the longitudinal axis Z is substantially determined. In particular, the shaped portion  40  is in rotational coupling with the seating  31 . This coupling presupposes that there is a minimum space between the surfaces of the seating  31  and the surfaces of the shaped portion  40 , so as to allow the functional movement. 
     In accordance with some embodiments, for example shown in  FIGS.  1 - 3    and in  FIGS.  10 - 11   , the shaped portion  40  has a substantially cylindrical shape. 
     In some embodiments, see for example  FIGS.  1 - 3 ,  6 - 9 ,  10 - 13 ,  14 - 20 ,  37 - 39 ,  43 - 46    it can be provided that the stabilizing body  21  is coupled with the inside of the milling tool  11 , that is that the stabilizing body  21  acts as a male element for coupling with a respective female seating of the milling tool  11 . In other embodiments, as explained in detail below, a mechanical inversion can be provided in the coupling between the stabilizing body  21  and the milling tool  11  (for example  FIGS.  40 - 42   ). 
     In some embodiments, see for example  FIGS.  1 - 3 ,  8 - 9 ,  10 - 13 ,  18 - 19 ,  38 - 39 ,  48 - 50   , the stabilizing body  21  has an external surface  32  coupled slidingly with an internal surface  33  of the concave coupling seating  12  of the milling tool  11 . The external surface  32  is defined by a cylindrical portion and is inclined with respect to the longitudinal axis Z by an angle of inclination a that substantially defines the angle of the milling axis R with respect to the longitudinal axis Z. The internal surface  33  of the concave coupling seating  12  has an advantageously cylindrical profile having a diameter slightly larger than the diameter of the cylindrical portion that defines the external surface  32 , in order to guarantee the sliding coupling as above. This sliding coupling guarantees the single specific stable inclined position of the milling tool  11  with respect to the longitudinal axis Z. 
     The external surface  32  and the internal surface  33  are, for example, defined by two cylindrical and concentric portions, which can have an arc with an amplitude even smaller than 180°. 
     The stabilizing body  21 , also, has a base surface  34  provided with the distal aperture  25 , which allows access to the seating  31 . The surface of the seating  31  and the external surface  32  are connected to the base surface  34 , the first externally, the second internally with respect to the distal aperture  25 . In particular, since the stabilizing body is disposed eccentric with respect to the longitudinal axis Z, the distal aperture  25  is not centered with respect to the base surface  34 , but is concentric with the longitudinal axis Z. 
     As shown schematically in  FIG.  4   , and also valid for the corresponding embodiments in which it is provided, the base surface  34  is altogether eccentric with respect to the longitudinal axis Z and is defined by a first portion  34   a , delimited for illustrative purposes only with a dashed line, which is concentric with respect to the longitudinal axis Z, and by a second portion  34   b  which is eccentric with respect to the longitudinal axis Z, these portions  34   a ,  34   b  essentially being one a continuation of the other. The greater the second portion  34   b , and therefore the greater the eccentricity of the base surface  34 , the greater the angle of inclination of the milling tool  11  with respect to the longitudinal axis Z in the stable inclined position as above. 
     The base surface  34  is inclined with respect to the longitudinal axis Z by an angle of inclination α which corresponds to the angle of inclination a of the single specific stable inclined position of the milling tool  11  with respect to the longitudinal axis Z. In the case of a milling device  10  for the preparation of a bone seating for a knee joint prosthesis, the angle of inclination α is between about 7° and 15° (in this case, for example, in the operative variant with bilobed milling, see  FIGS.  25 - 29   ) for the milling device  10  for the tibial bone, and is about 4° for the milling device  10  for the femoral bone. 
     In accordance with some embodiments, shown in  FIGS.  14 - 15   , the shaped portion  40  can have a substantially conical shape. 
     Also, in some embodiments described using  FIGS.  14 - 20 ,  21 - 24  and  40 - 42   , the milling tool  11  is provided with a central body  44  coupled slidingly with a seating  45  of the positioning member  20 . This seating  45  can for example be inclined by an angle of inclination a which corresponds to the angle of inclination α of the single specific stable inclined position of the milling tool  11  with respect to the longitudinal axis Z. The concave coupling seating  12  is defined inside the central body  44 . Both the seating  45 , and also the central body  44  are eccentric with respect to the longitudinal axis Z. This sliding coupling guarantees the single specific stable inclined position of the milling tool  11  with respect to the longitudinal axis Z. In the case of a milling device  10  for the preparation of a bone seating for a shoulder joint prosthesis, in particular for the glenoid, the angle of inclination a can be selected, as needed, so that it is greater than 0° and up to about 25°. 
     In the embodiments described using  FIGS.  14 - 20 ,  21 - 24    in which the seating  45  is provided, the latter has an internal surface  56  coupled slidingly with an external surface  57  of the central body  44  of the concave coupling seating  12  of the milling tool  11 . This internal surface  56  is defined by a cylindrical portion and is inclined with respect to the longitudinal axis Z by an angle of inclination α which substantially defines the angle of the milling axis R with respect to the longitudinal axis Z. The external surface  57  of the central body  44  of the concave coupling seating  12  has a cylindrical profile having a diameter slightly smaller than the diameter of the cylindrical portion that defines the internal surface  56 . The internal surface  56  and the external surface  57  are, for example, defined by two cylindrical and concentric portions, which can have an arc with an amplitude even smaller than 180°. 
     In accordance with some embodiments, described using  FIGS.  21 - 24   , the shaped portion  40  has a substantially cylindrical shape and has a convex upper articulation surface  52  which develops around the body of the rotating rod  22 . The central body  44  has a concave lower articulation surface  53  coupled slidingly, alternatively during the rotation, with the seating  45  and with the upper articulation surface  52 . The upper  52  and lower articulation surfaces  53  define the articulation means  54 . In the embodiments of  FIGS.  21 - 24   , this coupling therefore configures a ball joint having the function of a joint, which is disposed outside the milling tool  11 , differently for example from the variant of  FIGS.  14 - 17    in which the joint, see the convex portions  24  of the angular joint  18  described in detail below, is actually disposed inside the milling tool  11 . Advantageously, this joint, disposed outside the milling tool  11 , reduces the risk of wear and deterioration of the components during milling operations. In particular, the radii of curvature of the upper  52  and lower articulation surfaces  53  are the same. Furthermore, during use, the centers of these radii of curvature have to be coinciding with each other and coinciding with the center of rotation positioned on the longitudinal axis Z in a central position between anti-rotation constraint elements  19  that transmit the rotation. In this case, the center of rotation is outside the milling tool  11 . In particular, in this variant described with reference to  FIGS.  21 - 24   , the point of intersection of the milling axis R and the longitudinal axis Z falls outside the milling tool  11  (see in particular  FIG.  23   ). 
     In other embodiments, see for example  FIGS.  40 - 42   , it can be provided that the stabilizing body  21  is coupled with the outside of the milling tool  11 , that is, that the milling tool  11  acts as a male element for coupling with a respective female seating of the stabilizing body  21 . 
     In particular, this can be described with reference to the embodiments of  FIGS.  40 - 42   , in which the positioning member  20  has a seating  45  as described above, which, however, does not couple with a central body  44  inside the concave coupling seating  12  of the milling tool  11 , but rather couples outside the milling tool  11 . 
     In these embodiments, described by way of example with reference to the variant for interventions to the tibial bone, the stabilizing body  21  has an internal surface  63 , in particular with an annular conformation and delimiting the seating  45 , and in a mating manner the milling tool  11  has an external surface  62  able to produce a sliding coupling with the internal surface  63 . 
     The internal surface  63  is advantageously defined by a cylindrical portion and is inclined with respect to said longitudinal axis Z by an angle of inclination a which substantially defines the angle of the milling axis R with respect to the longitudinal axis Z. 
     The external surface  62  has a cylindrical profile having a slightly smaller diameter than the diameter of the cylindrical portion which defines the internal surface  63 . 
     The external surface  62  and the internal surface  63  are, for example, defined by two cylindrical and concentric portions, for example with an arc with an amplitude even smaller than 180°. 
     In accordance with some embodiments, the anti-rotation constraint elements  19  are present on the distal end  16  of the rotating rod  22  and are operatively coupled with coupling seatings  35  provided in the concave seating  12  of the milling tool  11 . The anti-rotation constraint elements  19  are configured to angularly constrain the milling tool  11  with respect to the handling body  14  so that they are able to rotate integrally about the longitudinal axis Z. The anti-rotation constraint elements  19  are configured as means for transmitting torque, from the rotating rod  22  to the milling tool  11 . 
     The anti-rotation constraint elements  19  comprise rigid transmission tongues  41  with a shape mating with corresponding coupling seatings  35  present on the milling tool  11 , for the transmission of the rotational motion to the milling tool  11 . 
     The anti-rotation constraint elements  19  protrude radially from the profile of the rotating rod  22 , advantageously in a diametrically opposite position to each other if they are present in a number greater than one. Advantageously, in fact, the anti-rotation constraint elements  19  are two, in order to guarantee a better transmission of the rotation torque from the rotating rod  22  to the milling tool  11 . This diametrically opposite disposition of the two anti-rotation constraint elements  19  allows the milling tool  11  to oscillate or rotate on a plane orthogonal to the one passing through the anti-rotation constraint elements  19 , in such a way as to selectively assume a plurality of positions that are inclined with respect to the longitudinal axis Z, and in particular to assume a single specific stable inclined position defined by the same-shape coupling of the stabilizing body  21  with the concave coupling seating  12  of the milling tool  11 . 
     The anti-rotation constraint elements  19  are removably keyed into the coupling seatings  35 , made in correspondence with the polar coupling aperture  13  of the milling tool  11 . 
     The coupling seatings  35  are substantially radial with respect to the longitudinal axis Z and are configured to guarantee the constraint necessary for the transmission of the rotation torque from the rotating rod  22  to the milling tool  11 . 
     Advantageously, the coupling seatings  35  are in a number coherent with the number of anti-rotation constraint elements  19 . This guarantees a unique and determinate connection of the milling tool  11  onto the rotating rod  22 , preventing possible assembly errors. 
     In the embodiments described using  FIGS.  21 - 24   , in which the front milling tip  55  is provided and the point of intersection of the milling axis R and the longitudinal axis Z falls outside the milling tool  11 , the risk of wear and deterioration of the transmission tongues  41  is reduced, since the torque necessary for the milling and the torque necessary to create the seating of the spherical cap during the forward movement does not have to come exclusively from the transmission tongues  41 , but part of the milling action is performed by the cutting edges of the front milling tip  55  which is integral with, and made in a single piece on, the rotating rod  22  of the handling body  14  and, therefore, act independently of the milling tool  11 . 
     In accordance with some embodiments, the angular joint  18  has one or more convex curved portions  24  disposed around the longitudinal axis Z. 
     Advantageously, the angular joint  18  has at least two convex curved portions  24  disposed diametrically opposite each other with respect to the longitudinal axis Z. 
     In accordance with the embodiments described here, the anti-rotation constraint elements  19  are disposed around the longitudinal axis Z alternating with the convex curved portions  24 . 
     The convex curved portions  24  protrude radially from the profile of the rotating rod  22  in a diametrically opposite position with respect to that of the anti-rotation constraint elements  19  and are configured to couple with respective shaped concavities  36 , having a shape mating with that of the convex curved portions  24 . 
     Advantageously, the shaped concavities  36  allow an elastic snap-in coupling that univocally determines the axial position of the milling tool  11 . In fact, when the milling tool  11  is coupled with the rotating rod  22 , the convex curved portions  24  are removably forced to associate with the shaped concavities  36 . 
     Advantageously, the one or more convex curved portions  24  are sphere portions. 
     In accordance with some embodiments, the angular joint  18  comprises elastic keying tongues  37  each provided with one of the convex curved portions  24 , for example conformed as a hemispherical portion (see for example  FIGS.  1 ,  3 ,  10 ,  11 ,  14 ,  24   ). 
     Each keying tongue  37  has an extension in the direction of the longitudinal axis Z and has a tip  39  provided with the convex curved portion  24 , and a base  38 , opposite the tip  39 , stably attached to the rotating rod  22 . Advantageously, only the base  38  is stably attached to the rotating rod  22  so that the keying tongue  37  can flex with respect to the base  38  when a pressure is exerted on the tip  39 . 
     The keying tongue  37  can flex in a direction orthogonal to the longitudinal axis Z. For this purpose, the angular joint  18  has a chamber  43 ,  FIG.  3    and  FIG.  11   , made through orthogonally in the rotating rod  22  and configured to allow the inward flexion of the keying tongues  37 , at least during the coupling with the milling tool  11 . 
     In accordance with some embodiments, shown in  FIGS.  25 - 29   , a possible operating sequence of use of the milling tool  10  for surgical application to the tibial bone is shown. In the example described here, there is shown an operating sequence to obtain a “bilobed” type milling, useful in the event that the degeneration of the spongy part of the bone is rather extensive. In fact, in this case it is more appropriate to mill with a smaller milling tool  11 , performing a double milling as described below. However, the same procedure can be applied to produce a single milling, for example using a milling tool  11  of larger sizes. 
     After having performed the proximal resection of the tibial bone, perpendicular to the intra-medullary axis, a reaming tool is used that allows to define, possibly with several passes with increasing diameter, a lead-in channel  111  for the milling tool  11 ,  FIG.  25   . Advantageously, the part of the reaming tool that does not have the cutting edges remains protruding from the resection plane and acts as a guide rod  50  for the milling tool  11 . 
     Once the lead-in channel  111  has been made, the milling tool  11  is positioned vertically so that the longitudinal axis Z is aligned with the axis of development of the guide rod  50 , and moved closer to it so that the guide rod  50  couples slidingly in the guide channel  42  of the rotating rod  22 . 
     At this point, since the milling is asymmetrical, it is possible to define a right milling, in which the angle of inclination α with respect to the longitudinal axis Z has a positive value ( FIG.  26   ), and a left milling, in which the angle of inclination α with respect to the longitudinal axis Z has a negative value ( FIG.  27   ). 
     What is obtained is a seating that is substantially symmetrical with respect to a central (sagittal) plane transverse to the previously prepared lead-in channel  111 , and equidistant from the cortical zone  110  of the bone,  FIGS.  28 - 29   . This solution allows to simplify and speed up the milling operation for the preparation of such a seating  112  for a bone filler, and to avoid breaking the cortical zone of the bone in the event of extensive bone gaps following the failure of previous implants. 
       FIGS.  30 - 33    are used to describe a possible operating sequence of use of a milling device  10  provided with a milling tool  11  for surgical application to the femoral bone.  FIG.  30    shows the use of the reaming tool to create the guide channel  111  in the femoral bone. Also in this case, the guide rod  50  corresponding to the part of the reaming tool that remains protruding from the resection plane is indicated. After that,  FIG.  31   , the milling tool  11  is coupled with the guide rod  50 . The latter, therefore, is aligned with the longitudinal axis Z, while the milling tool  11  is inclined along the respective milling axis R.  FIG.  32    shows the milling operation, where it can be clearly seen that the milling has an angle of inclination cc with respect to the longitudinal axis Z.  FIG.  33    shows the seating  112  thus obtained, once the milling device  10  has been removed. 
     It is clear that modifications and/or additions of parts may be made to the guided milling device for prosthetic surgery as described heretofore, without departing from the field and scope of the present invention as defined by the claims. 
     It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of guided milling device for prosthetic surgery, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby. 
     In the following claims, the sole purpose of the references in brackets is to facilitate reading and they must not be considered as restrictive factors with regard to the field of protection claimed in the specific claims.