Abstract:
Embodiments of the invention include an orthopedic milling machine for preparing a glenoid bone. The milling machine uses a hub and a sleeve. The hub includes reliefs arranged to cut or mill the bone and the sleeve couples to the hub to transfer rotational motion to the hub. The hub has an axial bore sized to receive an orthopedic guide pin. The hub also has a lateral passage slot that allows the hub to move laterally towards the guide pin in order to place the guide pin within the axial bore.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/411,429, filed Nov. 8, 2010, and claims foreign priority to French Patent Application No. FR 1059302, filed Nov. 10, 2010. These applications are herein incorporated by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    During the implantation of a glenoid component of a shoulder prosthesis, the surgeon must prepare the glenoid of the patient in order to bear and immobilize the glenoid component of the shoulder prosthesis. To that end, the surgeon generally uses a motorized or manual milling machine. The milling machine comprises a burr whose proximal side is secured to a driving grip. The distal surface of the burr has reliefs, such as teeth, blades, and/or tips. The burr rotates or oscillates around its central axis in order to shave the bone material making up the glenoid and hollow, cut into, and/or grate the bone material until the glenoid is given a shape adapted to the prosthetic glenoid component to be implanted. For example, the burr hollows a bowl-shaped cavity in the glenoid in which a dedicated portion of the prosthetic glenoid component is housed in a substantially complementary manner. The bowl-shaped cavity may be a hemisphere or another concave cavity. 
         [0003]    Furthermore, one potentially significant parameter for lasting stability of a prosthetic glenoid component relates to the proper positioning of that component on the glenoid. Thus, during surgical operations aiming to implant a glenoid component, an orthopedic guide pin, which may be a rod, is pushed partially into the glenoid at a predetermined point and in a predetermined direction. In that manner, the longitudinal part of said rod protrudes from the glenoid and may be used by the surgeon to guide and manipulate different ancillaries. For example, particular bone preparation ancillaries for the glenoid are axially engaged around the guide pin and then slid along said pin. 
         [0004]    In particular, the surgeon has milling machines, like those mentioned above, in which the burr includes a hub with a central through bore that is dimensioned to axially receive the guide pin. During a surgical operation, after having placed the guide pin, the surgeon axially slips the proximal end of the pin into the central bore of the burr and then slides said burr and its proximal sleeve along the guide pin towards the glenoid until the distal surface of the burr is pressed against the glenoid. Burrs with a central hub may also be referred to as “cannulated burrs.” By rotating or oscillating the burr around the guide pin, the glenoid is milled precisely, in that the milling is well positioned relative to the glenoid due to the cooperation between the central hub of the burr and the guide pin. 
         [0005]    However, the use of cannulated burrs poses implementation difficulties related to the presence of soft tissues around the glenoid as well as the proximity of the humeral head of the operated patient. It is therefore often necessary to place spacers to widely expose the glenoid in order to bring the glenoid longitudinally closer to the pin and avoid interference between the soft tissues and the burrs slid along the guide pin towards the glenoid. It is also often necessary to greatly displace the humeral head, or even resect the humeral head. In some cases, this procedure has the possibility of resulting in trauma and scars that may be significant for the patient. 
       SUMMARY 
       [0006]    Embodiments of the present invention relate to an orthopedic milling machine for bone preparation, in particular glenoid preparation, and to a surgical method for preparing a bone, in particular a glenoid, by milling the bone using a milling machine. 
         [0007]    Some embodiments of the present invention include an orthopedic burr that is easier for the surgeon to use and that is less traumatic for the patient. Specifically, those embodiments relate to an orthopedic milling machine for bone preparation, in particular glenoid preparation, having a burr that includes a hub. The hub includes an axial bore for receiving an orthopedic guide pin and the hub delimits a lateral passage slot for the guide pin. The slot emerges substantially radially from the bore through the hub. 
         [0008]    Embodiments of the present invention also relate to a surgical method for preparing a bone, in particular a glenoid, by milling, wherein: 
         [0009]    a bone to be milled is exposed, 
         [0010]    an orthopedic guide pin is placed in the bone, 
         [0011]    a burr is positioned near the guide pin, the burr including a hub provided with a bore that can receive the guide pin and that delimits a lateral passage slot for the guide pin, the slot emerging substantially radially from the bore, 
         [0012]    the burr is brought laterally closer to the guide pin so that the guide pin is engaged radially through the slot until it reaches the inside of the bore, and 
         [0013]    the burr is driven around the pin to mill the bone. 
         [0014]    In those embodiments, the burr is brought laterally closer to the orthopedic guide pin, so as to bring the burr opposite a bone to be milled. Specifically, the burr is not brought frontally relative to said bone, but instead approaches laterally thereto. In this way, in the case of a glenoid milling machine, the burr can be slid or inserted between the patient&#39;s humeral head and shoulder blade until the burr is centered with the guide pin, without having to distract the patient&#39;s shoulder too greatly, or without having to move the soft tissues surrounding the glenoid away over the entire periphery thereof. To achieve such centering, the guide pin passes radially through the wall of the hub, which is made possible according to some embodiments by engaging the guide pin through a slot of the hub, dimensioned to that end. Thus, the burr may be placed on the bone, in particular on the glenoid, in a simplified and minimally invasive manner while still being able to mill the bone precisely using the burr and the guide pin. In practice, the actuation of the burr, for example rotating or oscillating the burr around the axis of its hub, can either be motorized or manual; in both cases, the hub of the burr can be coupled to an ad hoc driving mechanism that is slid axially around the guide pin. 
         [0015]    Releasing the burr according to embodiments of the invention may be done just as easily, by moving it laterally to the glenoid so as to disengage its hub from the guide pin, via the slot of the hub. 
         [0016]    Some embodiments include additional features that may be used individually or in combination, such as: 
         [0017]    the burr includes a milling body, which is provided with bone etching reliefs and which extends transversely to the hub and outwardly surrounds the periphery of the hub at least in part, while leaving the opening of the slot open, radially opposite the bore; 
         [0018]    the milling body extends all around the hub and includes both a crown, radially distant from the hub, and lugs that connect the hub and the crown in a substantially radial direction and that are distributed around the hub; 
         [0019]    the slot extends, radially opposite the bore, in a free volume delimited between two consecutive lugs around the hub; 
         [0020]    the crown delimits a lateral passage for the guide pin, said passage connecting said free volume and the outer peripheral surface of the crown; 
         [0021]    the passage and the slot are situated substantially aligned in a direction radial to the axis of the hub; 
         [0022]    the edges of the passage are inclined by at least 30° relative to a direction radial to axis X-X of the hub; 
         [0023]    the crown is uninterrupted around the entire periphery thereof; 
         [0024]    one of the lugs delimits an opening for laterally receiving the guide pin, said opening connecting the outer peripheral surface of the crown and the slot; 
         [0025]    the milling body extends over only a peripheral portion of the hub, outside of which the slot is situated; and/or 
         [0026]    the milling machine also includes mechanisms for driving the burr, which are adapted to be simultaneously engaged around the guide pin and coupled to the hub in order to drive the burr around the axis of its hub. 
         [0027]    While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a perspective view of a first embodiment of a burr of a milling machine. 
           [0029]      FIG. 2  is an elevation view along arrow II of  FIG. 1 . 
           [0030]      FIG. 3  is a perspective view of the burr of  FIGS. 1 and 2 , along with a glenoid to be milled and a guide pin placed in the glenoid. 
           [0031]      FIG. 4  is a perspective view of the burr of  FIGS. 1 and 2 , along with a glenoid to be milled and a guide pin placed in the glenoid, in which the guide pin passes through a passage in the burr. 
           [0032]      FIG. 5  is a perspective view of the burr of  FIGS. 1 and 2 , along with a glenoid to be milled, a guide pin, and a sleeve, in which the guide pin resides in a bore in the burr and the sleeve is placed over the guide pin. 
           [0033]      FIG. 6  is a perspective view of the burr of  FIGS. 1 and 2 , along with a glenoid to be milled and a sleeve, in which the sleeve is coupled to the burr. 
           [0034]      FIG. 7  is an elevation view of a burr according to embodiments of the present invention. 
           [0035]      FIG. 8  is an elevation view of a burr according to embodiments of the present invention. 
           [0036]      FIG. 9  illustrates a perspective view of a burr according to embodiments of the present invention. 
           [0037]      FIG. 10  illustrates an elevation view of the burr of  FIG. 9  along arrow X of  FIG. 9 . 
           [0038]      FIG. 11  illustrates a perspective view of a burr according to embodiments of the present invention. 
           [0039]      FIG. 12  is an elevation view of the burr of  FIG. 11  along arrow XII of  FIG. 11 . 
       
    
    
       [0040]    While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0041]      FIGS. 1 to 6  show embodiments of a milling machine  1  that include a burr  10 , shown alone in  FIGS. 1 and 2 , and mechanism  20  for driving the burr  10 , shown in  FIGS. 5 and 6 . The mechanism  20  for driving the burr may include a sleeve  21 , which is described in more detail below, in light of  FIGS. 5 and 6 . 
         [0042]    According to the embodiments shown in  FIGS. 1 to 3 , the burr  10  has a discoid shape with a circular base, centered on an axis X-X. More specifically, the burr  10  includes two concentric annular portions, e.g. an inner hub  11  and an outer crown  12 , both centered on axis X-X. The hub  11  and the crown  12  are rigidly connected to one another by six individually identical lugs  13 , which each extend lengthwise from the hub  11  in a direction substantially radial to axis X-X and which are distributed substantially uniformly around the hub. These lugs  13  need not be strictly rectilinear, but may have a slight, lengthwise curve. The lugs  13  may have longitudinal profiles of various shapes and sizes, and the embodiments described below are non-limiting examples. 
         [0043]    On their distal surface, e.g., the surface facing the reader looking at  FIGS. 1 and 2 , the lugs  13  are each provided with a blade  14  that runs over the entire length of the lug  13 . The blades  14  are designed to etch the bone matter and thus to mill the bone matter when the burr  10  is rotated around its axis X-X. To that end, each blade  14  is, for example, provided with a cutting edge extending over the distal end rim of the corresponding lug  13 . In some embodiments, each of the blades  14  do not extend strictly in a plane perpendicular to axis X-X but are curved to match a spherical enclosure that is curved towards the distal side of the burr  10  and the axis X-X. In other words, each lug  13  will arch up and away from the crown  12  towards the axis X-X with a specific curvature that may substantially correspond to the curvature of a sphere. In this way, when the burr  10  is rotated around axis X-X, the blades  14  are able to hollow out a bowl-shaped cavity in the bone matter when revolving around the axis X-X. In some embodiments, the bowl-shaped cavity is a hemisphere or another concave cavity. 
         [0044]    Bone etching reliefs may include components other than the blades  14 , such as spurs, teeth, tips, and the like. Furthermore, by way of one alternative not illustrated, such bone etching reliefs can be provided on all or part of the distal surface of the crown  12 , as well as on all or part of the distal surface of the hub  11 . In other words, more generally, the crown  12  and the lugs  13  form, at least in part, a milling body that is arranged coaxially and transversely to the hub  11  and that can assume various forms. 
         [0045]    Given its angular shape, the hub  11  inwardly delimits a bore  15  that is centered on the axis X-X and passes axially all the way through the hub  11 , thereby emerging on the distal surface of the hub  11 , as shown in  FIGS. 1 and 2 , and on the proximal surface of the hub  11 , as shown in  FIG. 3 . As described below, the bore  15  may be inwardly tapped so as to accept a threadable connection with a driver. 
         [0046]    As shown in  FIGS. 1 to 3 , the annular wall  50  of the hub  11 , which delimits the bore  15 , is slotted over its entire axial dimension in only a portion of its periphery, according to embodiments of the present invention. In other words, the annular wall  50  of the hub  11  delimits a transverse slot  16  that connects the distal and proximal surfaces of the hub  11  in the direction of axis X-X and that connects the bore  15  and the outer peripheral surface of the hub  11 , for example in a direction radial to axis X-X. In a plane perpendicular to axis X-X, the edges  52 ,  54  of the slot  16  are remote from one another with a spacing denoted e in  FIG. 2 . In the embodiments illustrated in  FIGS. 1 to 3 , the edges  52 ,  54  of the slot  16  form parallel planes that are also substantially parallel to a diametric plane of the burr  10  passing through axis X-X. By way of one alternative embodiment not illustrated, the aforementioned edges  52 ,  54  of the slot  16  can have a certain curve, in particular with a profile curved in a plane perpendicular to axis X-X, as long as said edges  52 ,  54  maintain the spacing e between them in a plane perpendicular to axis X-X. 
         [0047]    As illustrated in  FIGS. 1 to 3 , the slot  16  may be formed in a portion of the hub  11  that is situated along the periphery of the hub  11  between two consecutive lugs  13 , more specifically between the ends  56 ,  58  of said consecutive lugs  13 , facing axis X-X. In this way, the slot  16  opens radially opposite its opening to the bore  15  into a free volume V of the milling body of the burr  10 . The free volume V is delimited by the two aforementioned consecutive lugs  13  and by the peripheral portion of the crown  12  that connects the ends of the aforementioned consecutive lugs  13 , opposite axis X-X. Moreover, within in the aforementioned portion of the crown  12  is a transverse passage  17  that passes radially through the crown  12 , thereby connecting the free volume V and the outer peripheral surface of the crown  12 . This passage  17  is therefore similar to a through slot made radially through the crown  12 . For reasons specified below, this passage  17  may be arranged to be substantially aligned with the slot  16  in a direction radial to axis X-X, as shown in  FIG. 2 . 
         [0048]    The opposite edges  60 ,  62  of the passage  17  are separated from one another in a plane perpendicular to axis X-X, with a relative spacing substantially equal to the spacing e between the edges of the slot  16 . 
         [0049]    One example of the use of the burr  10  will now be presented in light of  FIGS. 3 to 6 , in the context of a surgical operation aiming to prepare the glenoid G of a shoulder blade S in order to implant a glenoid component of a shoulder prosthesis. 
         [0050]    As shown in  FIG. 3 , before using the burr  10  an orthopedic guide pin  30  is placed in the glenoid G. That guide pin  30  consists of a rigid rod with a small transverse section that is, on a distal end portion, pushed into the bone material of the glenoid G. In practice, the tip for pushing the pin  30  into the glenoid G, as well as the direction of that pushing relative to the glenoid, are imposed by the surgeon, who places the pin  30  in accordance with a preferred implantation axis of the aforementioned prosthetic glenoid component. In some embodiments, the surgeon will use the guide pin  30  during surgical operation with several surgical ancillaries. The placement of the guide pin  30  is a well-known operation in orthopedic shoulder surgery, and it will not be described here in further detail. 
         [0051]    As shown in  FIG. 3 , the surgeon brings the burr  10  close the glenoid G to be milled, not by sliding the bore  15  axially around the guide pin  30  but by moving the burr  10  laterally to the guide pin  30  following a plane perpendicular and/or askew to said pin. This lateral approach of the guide pin  30  by the burr  10  is indicated by an arrow F 1  in  FIG. 3 . This lateral approach makes it possible to slide the burr  10  between the shoulder blade S and the humeral head associated with said shoulder blade (not shown), while the distal surface of the burr faces the shoulder blade. In this way, it is not necessary for the surgeon to distract the shoulder joint too much, thereby limiting the trauma to that joint. 
         [0052]    As visible by comparing  FIGS. 3 and 4 , the lateral approach to the guide pin  30  by the burr  10  is continued until the crown  12  of the burr  10  comes into the immediate vicinity of the guide pin  30 , more specifically the intermediate portion  64  of said guide pin  30 , emerging from the glenoid G. The movement of the burr  10  is then continued, as indicated by arrow F 2  in  FIG. 4 , so as to transversely engage the guide pin  30  through the passage  17  in a direction radial to axis X-X. 
         [0053]    For the guide pin  30  to be able to pass through the crown  12  via the passage  17 , the spacing between the edges  60 ,  62  of said passage  17  are at least equal to, or slightly larger than the diameter of the guide pin  30 , according to embodiments of the present invention. After crossing the passage  17 , the guide pin  30  is positioned inside the crown  12 , extending axially through the free volume V. 
         [0054]    Still while continuing the lateral approach to the guide pin  30  with the burr  10 , the surgeon brings the hub  11  closer to the intermediate portion  64  of said guide pin  30 , until said intermediate portion  64  of the guide pin  30  is engaged through the slot  16 , as indicated by arrow F 3  in  FIG. 5 . According to the same considerations as before regarding the passage  17 , it is understood that the spacing e between the edges  52 ,  54  of the slot  16  is sufficient, compared to the diameter of the pin  30 , to allow said guide pin  30  to pass through the wall of the hub  11 , via the slot  16 , until the guide pin  30  is located inside the bore  15 , in particular in a configuration coaxial to said bore  15 , as shown in  FIG. 5 . In other words, in that configuration, the axis X-X of the burr  10  is combined with the central axis of the guide pin  30 . Thus, it will be noted that, in return for the lateral approach described above in reference to  FIGS. 3 to 5 , the burr  10  has been moved until it is coaxial with the guide pin  30  without needing to axially engage said burr  10  from the proximal end of the guide pin  30 . This lateral approach allows the surgeon to limit the extent of the surgical incisions in the soft tissue surrounding the glenoid G, in that those soft tissues only need to be incised and spaced apart over about half of the periphery of the glenoid G. 
         [0055]    As shown in  FIGS. 5 and 6 , a tubular sleeve  21  is configured to slide around the guide pin  30  while being axially engaged around said guide pin  30  from the proximal end thereof. The tubular sleeve  21  slides around the guide pin  30 , toward the burr  10 , as indicated by arrow F 4  in  FIG. 5 . That sliding movement continues until the distal end  22  of the sleeve  21  reaches the burr  10 . The distal end  22  of the sleeve  21  is then mechanically coupled to the hub  11 . In some embodiments, that coupling is done by screwing the end  21 , threaded for that purpose, into the tapping of the bore  15 . Other forms of mechanical coupling between the sleeve  21  and the hub  11  can be used in the context of the present invention. 
         [0056]    During coupling operations, the surgeon may manipulate the burr  10  by gripping it by the proximal end of the hub  11 . For example, as shown in  FIG. 5 , the proximal end of the hub  11  delimits two diametrically opposite flats  18 , shown in  FIG. 5 , which allow the surgeon to firmly immobilize the burr  10  in rotation around axis X-X, in order to facilitate screwing of the end  22  of the sleeve  21  in the bore  15 . Furthermore, these flats  18  can be used by the surgeon, by themselves if necessary, in order to manipulate the burr  10  during all or each of the steps of its placement. 
         [0057]    Once the sleeve  21  is secured to the burr  10 , as shown in  FIG. 6 , said sleeve  21  is rotated around its central longitudinal axis, for example by connecting its proximal end to an ad hoc driving motor. The rotational movement imposed on the sleeve  21  is transmitted to the burr  10  such that the blades  14  shave the bone material making up the glenoid G and mill the bone material as mentioned above. Of course, rather than being motorized, the sleeve  21  can be driven manually. 
         [0058]    The milling of the glenoid G by the burr  10  is thus guided by the guide pin  30 , inasmuch as said guide pin constitutes the application axis of the burr  10  on the glenoid G. Once the milling of the glenoid G is finished, the sleeve  21  is, after separating the sleeve  21  and the hub  11 , released by sliding the sleeve  21  along the guide pin  30  toward the proximal end of said pin. The surgeon then releases the burr  10  laterally from the guide pin  30 , making the intermediate portion of said guide pin successively pass through the slot  16  and the passage  17 , following a lateral movement opposite to that described in reference to  FIGS. 3 to 5 . 
         [0059]      FIG. 7  shows an alternative embodiment of the burr  10 , where elements similar to elements in the embodiments shown in  FIGS. 1 to 6  bear the same references. This alternative embodiment differs from the embodiment of  FIGS. 1 to 6 , for example, by the transverse passage provided through the crown  12 , said passage being referenced  17 ′ in  FIG. 7 . More specifically, the passage  17 ′ differs from the passage  17  in that, unlike the passage  17 , its edges  60 ′,  62 ′ do not extend in planes parallel to a diametric plane of the burr  10  passing through axis X-X. Instead, those edges  60 ′,  62 ′ of passage  17 ′ are, in a plane perpendicular to said axis X-X, substantially inclined relative to a direction radial to said axis X-X. Thus, in a plane perpendicular to axis X-X, the line connecting the inner and outer ends of each of the edges  60 ′,  62 ′ of the passage  17 ′ form, with a direction radial to axis X-X, a non-zero angle α that is greater than or equal to 30°, or even 45°. In this way, the passage  17 ′ does not extend, between its openings on the outside of the crown  12  and on the free volume V, strictly in a direction radial to axis X-X but along a path inclined relative to said radial direction in comparison to the passage  17 . Having a passage  17 ′ oriented as shown in  FIG. 7  results in less interference or gripping between the opening on the outside of the passage  17 ′ and elements outwardly surrounding the crown  12  when the burr  10  is rotated in the direction indicated by arrow R in  FIG. 7 , i.e., in the direction opposite the incline α of the passage  17 ′ relative to the direction radial to axis X-X. In fact, the rear edge  62 ′ of the passage  17 ′ forms, with the outer peripheral surface of the crown  12 , an obtuse angle β, greater than or equal to 135°, which pushes elements that would enter the passage  17 ′ during the rotation of the burr  10  toward the outside of passage  17 ′. Such elements are, for example, the soft tissue surrounding the glenoid G. In other words, with the embodiment of  FIG. 7 , the risks of the passage  17 ′ gripping or catching the soft tissue surrounding the glenoid during setting in rotation of the burr  10  in direction R are lower, compared to the embodiment of the burr  10  of  FIGS. 1 to 6 . Advantageously, rather than being strictly planar, the edges  60 ′,  62 ′ of the passage  17 ′ have, in a cutting plane perpendicular to axis X-X, a curved profile that is curved in the direction opposite axis X-X. This reinforces the non-catching effect of the soft tissue that may be present around the crown  12  when the burr  10  is rotated in direction of rotation R. 
         [0060]    It will be noted that the incline α of the passage  17 ′ relative to the direction radial to axis X-X means that its opening on the outside is offset, in a peripheral direction of the crown  12 , relative to its opening on the free volume V. Consequently, to place the burr  10  on the glenoid G, the burr must be moved in a different manner than the burr described in  FIGS. 1 to 6 , in which the engagement of the guide pin  30  through the passage  17  and then the slot  16  more simply consists of a substantially rectilinear movement of the burr  10  relative to the guide pin. 
         [0061]      FIG. 8  shows another alternative of the burr  10  of  FIGS. 1 to 6 , in which the components of the burr that are similar to components in the embodiment of  FIGS. 1 to 6  bear the same numerical references. The alternative of  FIG. 8  differs from the burr of  FIGS. 1 to 6 , for example, by the absence of the passage  17 . In other words, unlike the crown  12 , the crown  12 ″ of the burr  10  of  FIG. 8  is uninterrupted over the entire periphery thereof. The absence of passage  17  facilitates the manufacture of the burr  10  but causes a slightly different use from that of the embodiment of  FIGS. 1 to 6 . For example, inasmuch as the crown  12 ″ is not slotted, it is not possible to bring the guide pin  30  through the free volume V via a lateral approach of said guide pin  30 . Also, unlike what was described above in light of  FIGS. 3 and 4 , the surgeon engages the guide pin  30  axially in the free volume V, e.g., axially engaging the proximal end of said guide pin between the successive lugs  13  delimiting said free volume V. Then, the surgeon slides the burr  10  along the guide pin  10  while the guide pin  30  extends through the free volume V, preferably while the guide pin is pressed laterally against the inner peripheral surface  66  of the crown  12 ″; in this way, the surgeon brings the burr  10  close to the glenoid G while keeping the burr  10  centric relative to the guide pin  30 , preferably as centrically as possible. In so doing, the surgeon can play on the incline of the burr  10  to get around the humeral head, as well as other organs of the patient, while limiting the extent of the incisions and spacing of the soft tissues surrounding the glenoid. Once the burr  10  is slid to the level of the intermediate portion of the guide pin  30  emerging from the glenoid  10 , the surgeon brings the hub  11  closer to the guide pin  30  laterally relative thereto, in a similar manner as previously described in light of  FIG. 5 , so as to engage said intermediate portion of the guide pin  30  through the slot  16  until the bore  15  is made coaxial with the guide pin. 
         [0062]      FIGS. 9 and 10  show a burr  110  representing an alternative embodiment of the burr  10 . Said burr  110  is in particular designed to be used with the sleeve  21  described above, within a milling machine similar to the milling machine  1 . 
         [0063]    Similar to the burr  10 , the burr  110  includes an inner annular hub  111 , which is centered on axis X-X and inwardly delimits a through bore  115 , and a milling body that extends transversely around the hub  111 . This milling body includes an outer crown  112  and five lugs  113 . The lugs  113  connect the hub  111  and the crown  112  in a direction substantially radial to axis X-X and are distributed around that axis along the periphery of the hub  111 . Similarly to the lugs  13  of the burr  10 , the lugs  113  of the burr  110  include cutting blades  114  on their distal surfaces. 
         [0064]    The lugs  113  differ from the lugs  13  in that, in a cutting plane perpendicular to axis X-X, they have a substantially rectilinear profile. Furthermore, unlike the lugs  13  that are all individually identical, the lugs  113  are broken down into a group of four identical lugs  113 . The remaining lug  113 ′ differs from the other lugs  113  by the presence of an opening  119  that passes all the way through the lug  113 ′ in the direction of axis X-X, thereby connecting the distal and proximal surfaces of said lug, and running over the entire radial dimension of the lug  113 ′, thereby connecting the inner and outer ends of said lug. More specifically, at the outer end of the aforementioned lug  113 ′, an opening  119  emerges on the outer peripheral surface of the crown  112 , while, at the inner end of said lug  113 ′, the opening  119  is extended by a slot  116 , functionally similar to the slot  16 , delimited through the annular wall of the hub  111 . As visible in  FIG. 10 , in a plane perpendicular to axis X-X, the opening  119  fits into the rectilinear extension of the slot  116 , its opposite edges being separated from one another by a space substantially equal to the spacing e between the edges of the slot  116 . 
         [0065]    The burr  110  is used in substantially the same way as the burr  10 : before coupling the hub  111  to the sleeve  21  that slides along the guide pin  30 , the burr  110  is brought closer to said guide pin  30  laterally to the intermediate portion thereof, so as to radially engage said intermediate portion of the guide pin  30  through the opening  119  and the slot  116  successively, until reaching the inside the bore  115 . 
         [0066]      FIGS. 11 and 12  show an alternative burr  210 , according to embodiments of the present invention. In practice, similar to the burrs  10  and  110 , the burr  210  is coupled to the sleeve  21  within a milling machine similar to the milling machine  1 . 
         [0067]    The burr  210  includes an annular hub  211 , centered on an axis X-X and functionally similar to the hub  11  or  111  of the burrs  10  or  110 . 
         [0068]    The bur  210  differs from the burrs  10  and  110 , for example, by the overall shape of its milling body; in fact, this body extends over a peripheral portion of the hub  211  and consists of a crown portion  212  connected to the hub  211  by one or more radial lugs  213 . On its distal surface, the crown portion  212  is provided with an etching or toothing  214  for milling the glenoid bone matter. In some embodiments, the milling body of the burr  210  has a bulk that is globally much smaller than that of the milling body of the burrs  10  and  110 . It is thus understood that the burr  210  may be used to produce bone preparations on a smaller scale. 
         [0069]    For balancing reasons, the burr  210  advantageously includes a counterweight  212 ′, which extends transversely from the hub  211  and which is arranged diametrically opposite the crown portion  212 . 
         [0070]    Similarly to the hub  11  or  111  of the burrs  10  and  110 , the hub  211  of the burr  210  simultaneously delimits an inner bore  215 , centered on axis X-X, and a lateral slot  216 , which connects the inside of the bore  215  and the outside of the hub  211  in a direction radial to axis X-X. As visible in  FIG. 12 , this slot  216  is situated along the periphery of the hub  211  outside the milling body, i.e., outside the portion delimited by the two lugs  213  in which the crown portion  212  extends. More specifically, in the embodiment shown in  FIGS. 11 and 12 , the slot  216  extends in a direction radial to axis X-X that is arranged substantially at 90° to the diametric direction in which the crown portion  212  and the counterweight  212 ′ are opposite. As a non-illustrated alternative, the slot  216  can be situated in the same portion as the crown portion  212  and to connect to the free volume V between the two lugs  213 . 
         [0071]    The use of the burr  210  is similar to that described above for the burrs  10  and  110 , in that the placement of the burr  210  on a glenoid to be milled, provided beforehand with the guide pin  30 , consists of bringing the burr  210  closer to said guide pin  30  laterally to the intermediate portion of said guide pin  30  so as to radially engage said intermediate portion of the guide pin through the slot  216  until it reaches the inside of the bore  215 . 
         [0072]    Various arrangements and alternatives to the milling machine described above, in particular the burrs  10 ,  110  and  210 , can also be included alone or in combination, including but not limited to one or more of the following characteristics and/or features: 
         [0073]    by way of non-illustrated alternatives for the burrs  10  and  110 , their crown  12 ,  12 ″, or  112  can be eliminated at one or more portions along their periphery, or over the entire periphery thereof, in particular for small burrs; 
         [0074]    by way of non-illustrated alternatives for the burr  210 , the counterweight  212 ′ can be replaced by a toothed crown portion, symmetrical to the crown portion  212  relative to axis X-X; 
         [0075]    rather than having a circular base, the milling body of the burrs  10 ,  110  and  210  can be centered on axis X-X while having an oval or ovoid or multi-lobed base; 
         [0076]    as mentioned above, the geometry of the cavity hollowed out by the burrs  10 ,  110  and  210  in the bone material is not a necessary limitation of those embodiments; thus, in return for ad hoc arrangements of the distal surface of their milling body, these burrs can perform both a concave spherical activity as described above, or a convex spherical relief, a planar resection, a cavity with a spherical central region and a flat peripheral edge, and the like; and/or 
         [0077]    embodiments of the invention can be applied to orthopedic milling machines intended to be used on bones other than the glenoid of a shoulder blade; thus, embodiments of the invention are for example applicable to milling the humerus or the bones of the hand or foot. 
         [0078]    Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.