Abstract:
An orthopedic device for ball and socket joint reconstruction. The anchor stem is adapted to be anchored in a medullary canal. A proximal portion of the anchor stem includes a threaded hole oriented along a longitudinal axis thereof. Metaphyseal portion includes a proximal end with recess and a longitudinal bore in fluid communication with the recess, and a distal end adapted to interface with the proximal portion of the anchor stem. An anti-rotation structure is preferably located at an interface of the anchoring stem to the metaphyseal portion to prevent rotation of the anchor stem relative to the metaphyseal portion around the longitudinal axis. A fastener is provided to extend through the longitudinal bore and to engage with the threaded hole on the anchor stem to fix the metaphyseal portion to the anchoring stem. The locking assembly is located in the recess and mechanically couples the head of the fastener to the metaphyseal portion to limit rotation of the fastener relative to the metaphyseal portion. An insert with an articular surface is provided that engages with the proximal end of the metaphysical portion and extends over the recess in the metaphyseal portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to French application No. 0757675 filed on Sep. 19, 2007. 
     FIELD OF THE INVENTION 
     The present invention relates to an orthopedic device for reconstruction of an articulating joint. The invention also relates to a method for positioning such an orthopedic device. 
     BACKGROUND OF THE INVENTION 
     In so far as a prosthesis is installed for a long period of time, it is important to ensure the rigidity and mechanical stability of a prosthesis component. If the screw is not tightened sufficiently during the positioning of the prosthesis, the risk of disassembly of the prosthetic component is aggravated. 
     EP-A-1 769 050 mentions the principle of locking a screw for controlling the displacement of a wedge-like ring which dilates a widened portion of an anchor stem of a prosthesis. This arrangement is specific to locking by means of a wedge-like ring. The means allowing such locking to be obtained are not described. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is intended more particularly to overcome such disadvantages by providing a new component of an articular prosthesis wherein undesirable unscrewing of the fixing screw may be avoided. Owing to the invention, the locking assembly prevents the screw from becoming loose in an inadvertent manner which ensures the mechanical stability of the orthopedic device. The locking assembly is effective even if the fixing screw is not screwed completely into the corresponding threaded hole. 
     In one embodiment, the orthopedic device for ball and socket joint reconstruction includes an anchor stem with a distal portion adapted to be anchored in a medullary canal and a proximal portion with a threaded hole oriented along a longitudinal axis of the anchor stem. Metaphyseal portion includes a proximal end with recess and a longitudinal bore in fluid communication with the recess, and a distal end adapted to interface with the proximal portion of the anchor stem. An anti-rotation structure is preferably located at an interface of the anchoring stem to the metaphyseal portion to prevent rotation of the anchor stem relative to the metaphyseal portion around the longitudinal axis. A fastener is provided to extend through the longitudinal bore and to engage with the threaded hole on the anchor stem to fix the metaphyseal portion to the anchoring stem. The locking assembly is located in the recess and mechanically couples the head of the fastener to the metaphyseal portion to limit rotation of the fastener relative to the metaphyseal portion. An insert with an articular surface is provided that engages with the proximal end of the metaphysical portion and extends over the recess in the metaphyseal portion. 
     According to advantageous but non-compulsory embodiments of the invention, such a orthopedic device may incorporate one or more of the following features. 
     The locking assembly is provided with at least one projecting member which is capable of being introduced between a head of the screw and the metaphyseal portion adjacent to a housing for receiving the head in an assembled configuration of the orthopedic device. 
     The locking assembly comprises at least two projecting members which are capable of being introduced simultaneously between the head of the screw and the metaphyseal portion, at one side and the other of the head. 
     The external radial surface of the head of the screw is provided with reliefs that are capable of co-operating with the projecting member in order to fix the head of the screw and the locking assembly in terms of rotation. Those reliefs are advantageously concave channels which have a shape which complements the shape of the projecting member(s). 
     In another embodiment, the metaphyseal portion comprises a notch or a number of notches equal to the number of projecting members, and the or each notch opens in the housing for receiving the screw head. Each notch is capable of partially receiving the projecting member or one of the projecting members in an assembled configuration of the orthopedic device. 
     A fastener is provided for fixing the locking assembly and the screw in a configuration in which the locking assembly prevents rotation of the screw about its longitudinal axis. For example, a threaded hole is provided in the head of the screw and an auxiliary screw is screwed into the threaded hole, pressing the locking assembly against the head of the screw, in a configuration in which the projecting member(s) is/are arranged between the head of the screw and the metaphyseal portion. 
     In one embodiment, the locking assembly is provided with at least a first relief which is capable of co-operating with at least a corresponding relief of the head of the screw in order to fix the locking assembly and the screw in terms of rotation and with at least a second relief which is capable of co-operating with at least a relief which is fixed relative to the metaphyseal portion in order to lock rotation of the locking assembly. 
     According to some embodiments, the locking assembly is a ring, and its first relief is internal and the corresponding relief is an external radial relief of the head of the screw. In this case, the first relief of the ring may be a tooth and the corresponding relief of the head of the screw is a notch. In a variant, the ring is provided with an internal peripheral tooth arrangement which forms a plurality of first reliefs, and the head of the screw is provided with an external peripheral tooth arrangement which forms a plurality of reliefs corresponding to the first reliefs of the ring. 
     According to other embodiments, the locking assembly is a stopper which covers the head of the screw and the first relief is provided at a side of the stopper directed towards the head of the screw, and the corresponding relief is provided at the face of the head of the screw opposite the shank thereof. The head of the screw may carry at least one projection which projects relative to its face opposite the shank, and the stopper is provided with at least one housing for receiving the projection. In a variant, the stopper is provided with a tooth arrangement which forms a plurality of first reliefs and the face of the head of the screw opposite its shank is provided with a tooth arrangement which forms a plurality of reliefs corresponding to the first relief of the stopper. 
     The second relief of the locking assembly extends over or from the external peripheral edge of the orthopedic device. 
     A spacer may be arranged between the anchor stem and the metaphyseal portion, the spacer being provided, at its opposing faces directed towards the anchor stem and the metaphyseal portion, respectively, with reliefs which are intended to come into engagement with corresponding reliefs which are provided on the anchor stem and the metaphyseal portion, respectively, preventing rotation of the metaphyseal portion relative to the anchor stem about a longitudinal axis of the spacer. 
     The invention also relates to an articular prosthesis, particularly a shoulder prosthesis, which comprises an orthopedic device as set out above. Such a prosthesis is more reliable and easier for a surgeon to install than those in the prior art. 
     The present invention also relates to a method of implanting an orthopedic device for ball and socket joint reconstruction. The method includes the steps of: 
     inserting a distal portion of an anchor stem in a medullary canal; 
     engaging a distal end of a metaphyseal portion with a proximal end of the anchor stem; 
     limiting rotation of the metaphyseal portion relative to the anchor stem; 
     inserting a distal end of a fastener through a longitudinal bore in the metaphyseal portion; 
     engaging threads on the distal end of the fastener with corresponding threads on the anchor stem so a head of the fastener is located in a recess on the metaphyseal portion; 
     mechanically coupling a locking assembly to the head of the fastener and to the metaphyseal portion to limit rotation of the fastener relative to the metaphyseal portion; and 
     engaging an insert to a proximal end of the metaphysical portion so that an articular surface on the insert extends over the recess in the metaphyseal portion. 
     The invention also relates to a method for positioning an orthopedic device as set out above and, more specifically, a method which comprises steps involving: 
     a) anchoring the anchor stem in a bone; 
     b) securing the metaphyseal portion to the anchor stem, with a spacer optionally being interposed; 
     c) introducing the screw into a longitudinal bore of the metaphyseal portion; 
     d) screwing the screw into a threaded hole of the anchor stem until the metaphyseal portion is firmly pressed against the stem, with the spacer optionally being interposed; 
     e) moving a locking assembly into engagement with at least one corresponding relief of a head of the screw and at least one corresponding relief of the metaphyseal portion. 
     Advantageously, during step e), at least one projecting member of a locking assembly is introduced between a head of the screw and the metaphyseal portion adjacent to a housing for receiving the head. 
     An additional step may be provided, wherein the locking assembly is immobilised in the configuration in which its projecting member(s) lock(s) the head of the screw in terms of rotation relative to the metaphyseal portion. 
     In a variant, during step e), at least a first relief of the locking assembly is engaged with a corresponding relief of the screw head in order to fix the locking assembly and the screw in terms of rotation, and at least a second relief of the locking assembly is engaged with a relief which is fixed relative to the metaphyseal portion in order to lock rotation of the locking assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The invention will be better understood and other advantages and features thereof will be appreciated more clearly from the following description which is given purely by way of example and with reference to the appended drawings, in which: 
         FIG. 1  is a schematic perspective illustration, partially exploded, of a humeral component of a shoulder prosthesis according to an embodiment of the present invention. 
         FIG. 2  is a front view of the humeral component of  FIG. 1  in an assembled configuration. 
         FIG. 3  is a section view of the humeral component of  FIG. 2  along line III-III in  FIG. 2 . 
         FIG. 4  is a view, drawn to an enlarged scale, of detail IV in  FIG. 3 . 
         FIG. 5  is a section along line V-V in  FIG. 3 . 
         FIG. 6  is a view, drawn to an enlarged scale, of detail VI in  FIG. 5 . 
         FIG. 7  is a partial section, drawn to an enlarged scale, along line VII-VII in  FIG. 6 . 
         FIG. 8  is a perspective view of the locking assembly for the orthopedic device of  FIGS. 1 to 7  during assembly. 
         FIG. 9  is a partial perspective view of an alternate locking assembly in according with an embodiment of the present invention. 
         FIG. 10  is a top view of the locking assembly illustrated in  FIG. 9  in an assembled configuration of the orthopedic device. 
         FIG. 11  is a perspective view of an alternate locking assembly in according with an embodiment of the present invention. 
         FIG. 12  is a perspective view of an alternate locking assembly in according with an embodiment of the present invention. 
         FIG. 13  is a perspective view of an alternate locking assembly in according with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The humeral orthopedic device  1  of a shoulder prosthesis illustrated in  FIGS. 1 to 6  comprises an anchor stem  2  which is intended to be introduced and anchored in the medullary canal of a humerus, after resection of its upper end. The stem  2  is provided with external channels  21  which are intended to facilitate its immobilisation in terms of rotation inside the medullary canal. The stem  2  is provided with an axial threaded hole  22  which extends along the longitudinal axis X 2  thereof. 
     The orthopedic device  1  also comprises a spacer  3  which is intended to allow longitudinal adjustment of the orthopedic device  1  taking into consideration the morphology of the patient and the fitting depth of the stem  2  in the humeral medullary canal. The spacer  3  may be selected from a set of spacers having different lengths and different diameters. 
     The spacer  3  has a cylindrical external radial wall  31  having a circular base. The spacer  3  also has a central bore  32  whose longitudinal axis X 3  is intended to be aligned with the axis X 2  in an assembled configuration of the orthopedic device  1 . The axis X 3  is also the axis of symmetry of the surface  31 . The bore  32  comprises a median portion  321  which has a first diameter D 1  and two portions  322  and  323  which form the opening of the bore  32  at the upper face  33  and the lower face  34  of the spacer  3 , respectively. The portions  322  and  323  have the same diameter D 2  which is greater than the diameter D 1 . In this manner, the median portion  321  of the bore  32  forms two shoulders at the bottom of the opening portions  322  and  323 . 
     The face  33  of the spacer  3  is provided with grooves  331  which extend radially around the axis X 3 . The face  34  is provided with grooves  341  of the same type, only the outline of which is visible in  FIGS. 1 and 2 . 
     The upper face  23  of the stem  2 , at which the threaded hole  22  opens, is provided with radial grooves  231  which co-operate with the grooves  341  in order to immobilise the spacer  3  relative to the stem  2  in terms of rotation, about the aligned axes X 2  and X 3 , when the surfaces  34  and  23  are in abutment against each other. 
     The orthopedic device  1  also comprises a metaphyseal portion  4  which forms a support for an insert  5  which defines a concave articular surface  51  which is intended to interact with a convex articular surface which belongs to a glenoid component of the shoulder prosthesis or an intermediate component when use is made of such an intermediate component. 
     The metaphyseal portion  4  is provided with a longitudinal bore  41  which is centred about an axis X 4  which is intended to be aligned with the axes X 2  and X 3  in an assembled configuration of the orthopedic device  1 . The bore  41  comprises a median portion  411  whose diameter is designated D 3 . The bore  41  also comprises a portion  412  which opens at a face  42  which is intended to be in abutment with the face  33  of the spacer  3  in an assembled configuration of the orthopedic device  1 . The diameter of the portion  412  is designated D 4 . This diameter D 4  is substantially equal to the diameter D 2 . The bore  41  comprises a third portion  413  which adjoins the portion  411  and extends counter to the portion  412  in relation to the portion  411 . The diameter of the portion  413  is designated D 5 . The bore  41  finally comprises a fourth portion  414  which opens at a face  43  of the portion  4  which is inclined relative to the axis X 4  and which defines the bottom of the housing for receiving the insert  5  in the portion  4 . The diameter of the recess  414  is designated D 6 . The diameter D 5  is greater than the diameter D 4  and less than the diameter D 6 . 
     The threaded hole  22  does not extend as far as the level of the face  23  of the stem  2 , since a countersinking  221  is brought about in the connection zone between the threaded hole  22  and the face  23 . The countersinking  221  has a diameter D 7  which is substantially equal to the diameter D 2 . In fact, the portions  322 ,  323 ,  412 ,  413  and  414  of the bores  32  and  41  are also countersinkings which are brought about around the median portions  321  and  411 , respectively. 
     Grooves  421  extend radially over the face  42  of the portion  4  around the axis X 4 . Those grooves have a shape similar to that of the grooves  331 , with which they can be engaged. 
     When the orthopedic device  1  is assembled, two rings  81  and  82  are secured in the countersinkings  221  and  322 , respectively. The rings  81  and  82  allow relative transverse immobilisation of the portions  2 ,  3  and  4  of the orthopedic device  1  to be brought about during assembly. In practice, the rings  81  and  82  are identical. 
     When those portions  2 ,  3  and  4  are in abutment with each other, it is possible to rotate the portion  4  about the axis X 4 , with the surfaces  23  and  34  or  33  and  42  being moved away from each other in order to adjust the angular orientation of the insert  5  relative to the axes X 1 , X 2  and X 3  which define the longitudinal axis X 1  of the orthopedic device  1 . 
     When this temporary assembly is brought about, a screw  9  is introduced successively into the bore  41  then the bore  31  and the threaded hole  22 . The shank of the screw  9  is designated  91  and its head is designated  92 . The longitudinal axis of the shank  91  is designated X 9  and is aligned with the axes X 1 , X 2 , X 3  and X 4  in an assembled configuration of the orthopedic device  1 . 
     The head  92  is provided with engagement features  921  which are arranged at its external radial face  922 . In the illustrated embodiment the engagement features  921  comprise a plurality of peripheral channels. The head  92  is also provided with four grooves  923  which allow it to co-operate with a flat or cross-head screwdriver in order to move it in rotation about the axis X 9  when it is screwed into the threaded hole  22 . When the orthopedic device  1  is assembled, the screw  9  is screwed into the threaded hole  22  until its head  92  moves firmly into abutment against the bottom  4131  of the portion  413  of the bore  41 . The elements which constitute the orthopedic device  1  are then firmly retained in position relative to each other, the grooves  231  and  341 , on the one hand, and  331  and  341 , on the other hand, being engaged with each other, which contributes to the immobilisation in terms of relative rotation of the portions  2 ,  3  and  4  about the aligned axes X 1 , X 2 , X 3  and X 4 . 
     In order to prevent accidental unscrewing of the screw  9 , under the effect of repeated forces on the orthopedic device  1 , and particularly vibrations to which it may be subject, a locking stopper  10  is installed on the head  92 . That stopper comprises an annular portion  101  at the centre of which an opening  102  is defined and from which two pins  103  and  104  extend and are diametrically opposed in relation to the opening  102 . The pins  103  and  104  extend from the same face of the portion  101 . Those pins are separated by a distance d 10  which is substantially equal to or slightly greater than the diameter D 92  of the head  92  taken at the level of the bottom of the channels  921 . In this manner, the pins  103  and  104  may be arranged at one side and the other of the head  92 , being partially engaged in the channels  921 , the shape of the channels  921  being selected so as to substantially complement the shape of the internal portions of the pins  103  and  104  directed towards the opening  102 . In practice, the channels  921  are cylindrical and have generating lines in the form of an arc of a circle, and the pins  103  and  104  are cylindrical having a generating line which is circular, with a diameter substantially equal to that of the channels. The stopper  10  and the head  92  are fixed in terms of rotation when the pins  103  and  104  are engaged in the channels  921 . 
     The portion  413  of the bore  41  is further bounded by two engagement features  45  and  46 , in which the pins  103  and  104  are engaged when they are arranged around the head  92  in position in that portion  413  which forms a housing for receiving the head  92 . In the illustrated embodiment, the engagement features  45 ,  46  comprise notches. The notches  45  and  46  open in the portion  413 . In this manner, when the head  92  is received in the housing formed by the portion  413 , it may be covered by the stopper  10  with the pins  103  and  104  being partially engaged in two of the channels  921  and the remainder being received in the notches  45  and  46 . 
     If the screw  9  begins to become unscrewed, indicated by the arrow F 1  in  FIG. 7 , the pins  103  and  104  are moved in rotation by the channels about the axis X 9  and move into abutment with sides  451  and  461  of the notches  45  and  46 , which has the effect of locking the screw  9  in terms of rotation, which cannot be unscrewed any further. 
     Therefore, the stopper  10  constitutes a first embodiment for locking the screw  9  in terms of rotation relative to the metaphyseal portion  4  and, on that basis, other elements of the orthopedic device  1 , that is to say, the stem  2  and the spacer  3 . 
     An auxiliary screw  11  is provided in order to immobilise the stopper  10  on the head  92 . To that end, the head  92  is provided with a threaded hole  924  which is aligned with respect to the axis X 9  and in which the shank  111  of the screw  11  can be engaged, extending through the opening  102  of the stopper  10 . Once the stopper  10  is in position on the head  92 , with its pins engaged both in two of the channels  21  and in the notches  45  and  46 , it can thereby be immobilised on the head  92  by tightening the auxiliary screw  11  in the threaded hole  924  using a male key which is inserted into a polygonal recess  112  of the screw  11 . 
     In this manner, once the stopper  10  and the auxiliary screw  11  are in position, the screw  9  is not at risk of becoming unscrewed with an angular clearance greater than that corresponding to the displacement of the pins  103  and  104  in order to move into contact with the sides  451  and  461  of the notches  45  and  46 . That angular clearance may be relatively small owing to judicious selection of the respective dimensions of the pins  103  and  104  and the notches  45  and  46 . 
     Furthermore, the locking of the screw  9  in terms of rotation is brought about owing to co-operation of the pins  103  and  104 , on the one hand, and the notches  45  and  46 , on the other hand, even if the screw  9  is not completely tightened in the threaded hole  22 . In this manner, the assembly of the orthopedic device  1  is permanent even if the surgeon has not completely tightened the screw in the threaded hole  22 . 
     According to a variant of the invention which is not illustrated, the stopper  10  may be maintained in position on and around the head  92  by other mechanisms than the auxiliary screw  11 , in particular by a flange which is provided on the rear surface of the insert  5 , which flange then moves into abutment with the stopper  10  when the insert  5  is assembled on the portion  4 . 
     The invention has been illustrated with an orthopedic device  1  provided with a spacer  3 . However, it is applicable without such a spacer, the metaphyseal portion  4  being directly in contact with the stem  2 . For example, the grooves  231 ,  341 ,  331 ,  421  preferably have the same size, shape and pitch. Consequently, the grooves  231  on the upper face  23  of the stem  2  can engage directly with the grooves  421  on the metaphyseal portion  4 . 
     The grooves  231 ,  341 ,  331 ,  421  comprise an anti-rotation structure at the interface of the components  2 ,  3 ,  4 , which still permitting the components  2 ,  3 ,  4  to be positioned relative to each other in a discrete number of orientations around the longitudinal axes X 1 , X 2 , X 3 , X 4  (collectively “X”) of the orthopedic device  1 . The grooves  231 ,  341 ,  331 ,  421  retain the components  2 ,  3 ,  4  in the desired orientation around the longitudinal axis X both before and after the screw  9  is engaged with the stem  2 . A variety of other structures are possible to perform the anti-rotation feature of the grooves  231 ,  341 ,  331 ,  421 . 
     The stopper  10  may have only a single locking pin of the same type as the pins  103  and  104  or, conversely, more than two pins, for example, three or four pins which are advantageously distributed regularly around the centre axis of the opening  102 . The geometry of the portion  413 , in particular the number and the distribution of the notches  45 ,  46  and the like, is/are adapted to the number and distribution of the pins. 
     In the embodiments illustrated in  FIGS. 9 to 13 , elements similar to those of the first embodiment have identical reference numerals. 
     The orthopedic device  1  partially illustrated in  FIGS. 9 and 10  comprise a screw  9  whose shank  91  is supposed to be screwed into an anchor stem which is not illustrated. The head  92  of the screw  9  is provided with an external peripheral tooth arrangement  921 , whose teeth generally have a triangular cross-section. In an assembled configuration of the orthopedic device  1 , the head  92  is received in a housing  413  which is provided in the metaphyseal portion  4  of the orthopedic device  1 . The housing  413  has a circular cross-section with a diameter which is strictly greater than that of the head  92 , and a notch  45  is provided in the portion  4  and opens in the housing  413 . 
     Furthermore, a locking ring  10  is provided in order to be introduced into the housing  413  around the head  92 , as illustrated by the arrow F 10  in  FIG. 9 . The ring  10  is provided with an internal tooth arrangement  105  whose teeth have a triangular cross-section and a shape which complements the teeth of the tooth arrangement  921 . The radius of the tooth arrangement  105  is adapted to the radius of the head  92  in such a manner that, when the ring is arranged around the head  92 , the tooth arrangements  921  and  105  are engaged, which brings about fixing of the head  92  and the ring  10  in terms of rotation about the axis X 9  of the screw  9 . 
     The external radial surface  106  of the ring  10  has a circular cross-section with a diameter which is slightly less than that of the housing  413 , with the exception of a portion in which a rib  107  projects radially relative to the surface  106  which forms the external edge of the ring  10 . When the ring  10  is positioned around the head  92  in the housing  413 , the rib  107  is engaged in the notch  45 . The rib  107  extends radially outwards relative to the surface  106  sufficiently in order to lock the ring  10  relative to the portion  4  in terms of rotation about the longitudinal axis X 1  of the orthopedic device  1  with which the axis X 9  of the screw  9  is in alignment. 
     In this manner, once the screw  9  is tightened relative to the anchor stem and the portion  4 , its rotation about the axis X 9  is prevented by the ring  10  whose rib  107  can have only a small angular clearance in the notch  45 . 
     In  FIGS. 9 and 10 , the reference numeral  925  designates a hexagonal recess for maneuvering the screw  9  using an Allen key. 
     In the embodiment of  FIG. 11 , the screw  9  is provided with a shank  91  and a head  92  whose external peripheral edge is circular, with the exception of a notch  921 . The head  92  is also provided with a hexagonal maneuvering recess  925 . 
     The screw  9  is intended to be inserted into a bore  41  whose upper portion  413  forms a housing for receiving the head  92 . A pin  46  which extends parallel with a centre axis X 1  of the orthopedic device  1  and a longitudinal axis X 9  of the screw  9 , which are therefore in alignment, is arranged in the housing. 
     A locking ring  10  is provided so as to be arranged around the head  92  in the housing  413 . That ring carries, at its internal edge  108 , a tooth  105  whose dimensions allow it to be engaged in the notch  921  with minimal or zero angular clearance. The external peripheral edge  106  of the ring  10  is circular, with the exception of a sector in which a cut-out  107  is provided, which is intended to receive the pin  46  in an assembled configuration of the orthopedic device  1 . The edges of the cut-out  107  are designated  1071  and  1072 , respectively. When the screw  9  is positioned in the bore  41 , with its head  92  being received in the housing  413 , it is possible to engage the ring  10  around the head  92  and in the housing  413 , with the tooth  105  being arranged in the notch  921 , and the cut-out  107  is positioned around the pin  46 . Any rotational movement of the screw  9  about the axis X 9  is limited owing to the abutment of one of the surfaces  1071  or  1072  against the pin  46 . 
     In the embodiment of  FIG. 12 , the screw  9  of the orthopedic device  1  comprises a shank  91  and a head  92  which is provided with a maneuvering recess  925 . The head  92  is provided, at its upper face  926  opposite the shank  91 , with an annular tooth arrangement  921  which is provided around the centre axis X 9  of the screw and the recess  925 . 
     The housing  413  for receiving the head  92  which is provided in the metaphyseal portion  4  generally has a circular cross-section with an extension  45  which communicates with the main portion of the housing  413 . 
     A stopper  10  is further provided so as to be arranged above the head  92  in an assembled configuration of the orthopedic device  1 . That stopper comprises a centring portion  108  which is intended to be engaged in a correspondingly shaped recessed housing  928  formed at the face  926 . The stopper  10  is further provided with a tooth arrangement  105  whose geometry is adapted to that of the tooth arrangement  921 . In this manner, when the portion  108  is engaged in the housing  928 , the tooth arrangements  921  and  105  are in engagement and the components  9  and  10  are fixed in terms of rotation about the axis X 9 . 
     The peripheral edge of the stopper  10  is provided with a catch  107  which is engaged in the notch  45  in an assembled configuration of the orthopedic device  1 . The possibility of angular rotation of the screw  9  about the axis X 9  is thereby limited owing to the abutment of the catch  107  against one or other of the edges  451  and  452  of the notch  45 . 
     In the embodiment of  FIG. 13 , the screw  9  of the orthopedic device  1  comprises a shank  91  and a head  92  which is provided with two projections  921  and  921 ′ which extend from the face  926  of the head  92  opposite the shank  91 . 
     A stopper  10  is further provided so as to be mounted on the head  92  in an assembled configuration of the orthopedic device  1 . That stopper comprises two housings  105  and  105 ′ whose geometry is adapted in order to receive the projections  921  and  921 ′ when the stopper  10  is assembled on the head  92 . In this manner, the components  9  and  10  are fixed in terms of rotation. 
     The stopper  10  is further provided with two fins  107  and  107 ′ which are intended to be engaged in two notches  45  and  46  which are provided in the metaphyseal portion  4  adjacent to a housing  413  for receiving the head  92 . 
     As above, when the stopper  10  is assembled on the head  92 , its rotation about the axis X 9  is prevented by co-operation of the fins  107  and  107 ′, on the one hand, and the notches  45  and  46 , on the other. This allows rotation of the screw  9  to be locked. 
     In the embodiments illustrated in  FIGS. 9 to 13 , it is possible to use a member for immobilising the ring or the stopper  10  which is similar to the auxiliary screw  11  of the first embodiment in terms of its function. 
     The invention has been illustrated in the case of a humeral component of a shoulder prosthesis whose articular surface is concave. However, it may be applied to components whose articular surface is convex. Generally, the invention may be applied to any prosthesis component comprising an anchor stem, irrespective of the geometry of that stem, and a metaphyseal portion which are fixed by a screw, whatever the prosthesis to which it belongs. In particular, the invention also applies to elbow, hip and knee prostheses. 
     According to a variant of the invention which is not illustrated and which may be applied to all the embodiments, the metaphyseal portion  4  may itself form the articular surface  51 . 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the inventions. The upper and lower limits of these smaller ranges which may independently be included in the smaller ranges is also encompassed within the inventions, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either both of those included limits are also included in the inventions. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and described the methods and/or materials in connection with which the publications are cited. 
     The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. 
     Other embodiments of the invention are possible. Although the description above contains many specific examples, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above. 
     Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.