Abstract:
This invention relates to a prosthetic element comprising two principal components intended to be assembled together and immobilized with respect to each other by means of a screw, which may be screwed by means of at least one thread in two tappings which are respectively fast or intended to be rendered fast with one and the other principal components. The screw comprises at least one radial element in relief adapted to come into abutment against a stop surface fast with a first component, and a non-threaded end forming guide finger and adapted to slide in a housing, of cross-section correspondiong to that of this finger and made in the second component.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a prosthetic element comprising two principal components, to the use of such an element, and to processes for assembly of such an element.  
         BACKGROUND OF THE INVENTION  
         [0002]    A prosthetic element most often comprises a part intended to constitute an articular surface and a part for anchorage in the patient&#39;s bone. Taking into account their respective mechanical functions, these parts are sometimes composed of distinct components, such components each being optimalized as far as the choice of their constituent materials and their mode of manufacture are concerned. These components should then be able to be assembled precisely and easily. For example, an anchoring component may be fixed in the bone and a component forming an articular surface added thereon.  
           [0003]    In certain prior art devices, such as disclosed in FR-A-2 605 514 for example, it is known to use a screw for locking one part of a prosthesis on another part provided with a corresponding tapping. It is also known from FR-A-2 689 756 to use a screw for locking a shank fast with an articular head inside a bore made in a prosthesis anchoring part. It is also possible, as in FR-A-2 737 107, to provide using a screw captive in a housing made on one of the parts and intended to cooperate with a tapping made in the other part.  
           [0004]    The known devices require precise positioning and alignment of the components constituting a prosthetic element, which is not always possible as the operative field is difficult to access and as it is delicate to visualize due to the traumatic depression of the glenoid cavity. In addition, the screws used in the known system may be displaced or poorly aligned with respect to the parts with which they are to cooperate, hence a risk of distorting their threads or the tapping with which they are to cooperate.  
           [0005]    It is a more particular object of the present invention to overcome these drawbacks by proposing a prosthetic element that may be assembled in particularly easy and precise manner, while remaining very practical to use.  
         SUMMARY OF THE INVENTION  
         [0006]    To that end, the present invention relates to a prosthetic element which comprises two principal components intended to be assembled together and immobilized with respect to each other by means of a screw, this prosthetic element being characterized in that the screw is adapted to be screwed by means of at least one thread in two tappings which are respectively fast or intended to be rendered fast with one and the other principal components and in that the screw comprises at least one radial element in relief adapted to come into abutment against a stop surface fast with a first component, and a non-threaded end forming guide finger and adapted to slide in a housing made in the second component.  
           [0007]    Thanks to the invention, the locking screw may be immobilized with respect to one of the principal components, this guaranteeing its positioning and orientation with respect thereto. Then, when its guide finger is inserted in the housing of the second component which has a transverse section corresponding to that of the finger, the components are guided with respect to one another in a movement of mutual approach. The radial element in relief provided on the screw allows it to exert on the stop surface an effort directed towards the second component, in order to firmly apply these components against one another and thus to contribute to their relative immobilization, after screwing of the screw in the second tapping.  
           [0008]    According to advantageous but non-obligatory aspects of the invention, this prosthetic element incorporates one or more of the following characteristics:  
           [0009]    the element of the screw in relief is formed by a radial flange made on the screw between the two threads thereof.  
           [0010]    the stop surface is annular and surrounds this screw. In that case, this stop surface may be provided to be formed by the face of a ring surrounding the screw, this ring being rigidly connected to a bush screwed in the first component. This ring and this bush allow an efficient transmission of effort between the screw and the first component.  
           [0011]    the first and second components are respectively provided with truncated bearing surfaces, the screw being adapted to apply, by its screwing, these surfaces against each other. This aspect of the invention takes advantage of the fact that the screw of the invention guarantees satisfactory positioning and movement of approach of the truncated bearing surfaces provided respectively on the first and second components, this limiting the risks of misalignment of these surfaces. These bearing surfaces are advantageously respectively centred on the central axis of the screw, when the latter is screwed in the first component, and on the central axis of the housing for slide of the centering finger.  
           [0012]    the tapping which is fast or intended to be rendered fast with the second component is formed in the housing for slide of the centering finger, towards an inlet zone of the screw.  
           [0013]    the first component forms a convex articular surface and defines a volume in which the screw may be mounted and the second component engaged, at least partially. The first component may for example be in the form of a portion of sphere.  
           [0014]    the housing for slide of the guide finger is made in a shank for anchoring the second component in a bone.  
           [0015]    According to a first advantageous form of embodiment of the invention, the screw is provided with two threads adapted to cooperate successively with two tappings respectively fast with one and the other principal components.  
           [0016]    According to a second advantageous form of embodiment of the invention, the screw is provided with a single thread adapted to cooperate successively with two tappings which are respectively fast or intended to be rendered fast with one and the other of the principal components.  
           [0017]    A prosthetic element as described hereinabove can be used in particular in the production of the glenoid part of a total shoulder prosthesis.  
           [0018]    The invention also relates to a first process for assembling a prosthetic element as described hereinabove and, more precisely, to a process which comprises steps consisting in:  
           [0019]    immobilizing the screw with respect to a first principal component of the prosthetic element by screwing this screw in a first tapping fast or intended to be rendered fast with the first principal component, a surface forming stop, at a distance from the screw with respect to the first component, being arranged around this screw after or before this immobilization;  
           [0020]    covering with a housing made on a second component, a free end of the screw projecting with respect to the first component;  
           [0021]    pushing the first and second components towards each other, causing the end of the screw to slide in the afore-mentioned housing;  
           [0022]    unscrewing the screw with respect to the first tapping, and  
           [0023]    screwing the screw in a second tapping made in the second component, exerting on the afore-mentioned stop surface an effort of approach of the first and second components.  
           [0024]    According to a second process of assembly in accordance with the invention, the screw is immobilized and its free end is covered as indicated hereinabove, following which:  
           [0025]    one of the principal components is impacted in the direction of the other so as to bring them closer, causing the free end of the screw to slide in the housing, until the components are brought into contact with each other;  
           [0026]    the screw is unscrewed with respect to the first tapping, and  
           [0027]    the screw is screwed in a second tapping made in the second component until an effort of relative immobilization of the components is obtained in their position in contact, this effort being exerted on the afore-mentioned stop surface.  
           [0028]    Thanks to the processes of the invention, the screw is permanently correctly positioned with respect to the components constituting the prosthetic element, this ensuring for the surgeon precision of assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    The invention will be more readily understood on reading the following description of two forms of embodiment of a prosthetic element and of its process of assembly in accordance with its principle, given solely by way of example and with reference to the accompanying drawings, in which:  
         [0030]    [0030]FIG. 1 is an exploded side view of a prosthetic element in accordance with a first form of embodiment of the invention.  
         [0031]    [0031]FIG. 2 is an axial section of the prosthetic element of FIG. 1, during a first step of its assembly.  
         [0032]    [0032]FIG. 3 is a section similar to FIG. 2, during a second step of assembly.  
         [0033]    [0033]FIG. 4 is a section similar to FIG. 2, during a third step of assembly.  
         [0034]    [0034]FIG. 5 is a section similar to FIG. 2, when assembly is terminated.  
         [0035]    [0035]FIG. 6 is a view similar to FIG. 3 for a prosthetic element in accordance with a second form of embodiment of the invention, and  
         [0036]    [0036]FIG. 7 is a view similar to FIG. 5 for the element of FIG. 6. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0037]    Referring now to the drawings, the prosthetic element E shown in the Figures is intended to be mounted on a shoulder in order to constitute an articular surface S intended to cooperate with a cupule (not shown) belonging to a complementary prosthetic element anchored in the patient&#39;s humerus.  
         [0038]    The surface S is approximately in the form of a portion of sphere and constitutes the outer surface of a first principal component  1  made of a material compatible with the movements of articulation on the cupule associated therewith.  
         [0039]    X 1  denotes a central axis of the component  1  which constitutes a diameter of the surface S. The component  1  is provided with a central recess  11  centred on axis X 1  and of which  12  denotes the peripheral surface, this surface being of truncated shape.  
         [0040]    A tapping  13  is provided at the bottom of the recess  11 , centred on axis X 1    
         [0041]    A second tapping  14  is centred on axis X 1  and opens to the outside, at the level of surface S.  
         [0042]    A circular bore  15  is made between the tappings  13  and  14 , the radius R 15  of this bore being included between the radii of the tappings  13  and  14 .  
         [0043]    A second principal component  2  is provided to be anchored in the glenoid cavity of the shoulder and, to that end, comprises a shank  21  provided with grooves  22 . X 2  denotes the axis of the shank  21  which is substantially cylindrical and of circular cross-section.  
         [0044]    The component  2  also comprises a plate  23  which is solid and in one piece with the shank  21 , this plate being provided with a truncated outer surface  24  centred on axis X 2 .  
         [0045]    The maximum radii of the surfaces  12  and  24  are substantially identical and their respective taper angles α and β are identical, this making it possible to provide a surface bearing of these surfaces against each other.  
         [0046]    The shank  21  is provided with a central bore  25 , of cylindrical shape and which extends in the plate  23  via a tapping  26 .  
         [0047]    The element E also comprises a screw  3  of which X 3  denotes the longitudinal axis. This screw is provided with a first thread  31  intended to cooperate with the tapping  14  in order to immobilize the screw  3  on the component  1 , axes X 1  and X 3  in that case merging.  
         [0048]    [0048] 32  denotes the end of the screw  3  towards the thread  31 . This end is provided with a polygonal hollow housing  33  for receiving a manoeuvring wrench (not shown) allowing the screw  3  to be rotated about axis X 3 .  
         [0049]    The screw  3  is also provided with an outer radial flange  34  of which R 34  denotes the radius.  
         [0050]    A second thread  35  is also provided on the screw  3 , opposite thread  31  with respect to the flange  34 . In other words, the flange  34  is disposed axially, along the screw  3 , between the threads  31  and  35 .  
         [0051]    R 31  and R 35  respectively denote the radii of the threads  31  and  35 . Radius R 34  is greater than radii R 31  and R 35 , with the result that the flange  34  constitutes a radial element of the screw  3  in relief, particularly with respect to the threads  31  and  35 .  
         [0052]    The screw  3  comprises, towards its rounded end  36  opposite end  32 , a cylindrical part  37  of circular cross-section of which R 37  denotes the radius.  
         [0053]    Parts  36  and  37  of the screw  3  form a guiding and centering finger intended to slide in the bore  25  which is of circular cross-section and of which R 25  denotes the radius, this radius itself being slightly greater than radius R 37 . The respective transverse sections of the housing  25  and of the part  37  correspond to each other, this making it possible to guide part  37 , and consequently the centering finger, in translation when it slides in the housing  25 .  
         [0054]    The tapping  26  and the thread  35  are provided to cooperate so as to allow the screw  3  to be screwed in the component  2  after introduction of the centering finger in the bore  25 .  
         [0055]    The tapping  26  is formed in the plate  23 , i.e. on the side of introduction of the screw  3  in the housing  25 . The inlet zone  25   a  of the housing  25  is of rounded and concave shape, which makes it possible to pre-center the end  36  when it is introduced in the housing  25 .  
         [0056]    In a variant embodiment, the zone  25   a  may be replaced by a truncated chamfer.  
         [0057]    A threaded bush  4  is also provided. X 4  denotes its central axis and  41  its outer thread which is provided to cooperate with the tapping  13 , in order to immobilize the bush  4  on the component  1 , axes X 1  and X 4  in that case merging.  
         [0058]    This bush comprises a ring  42  of which  421  denotes the inner radial surface and  422  the lateral surface facing the flange  34  when the pieces  3  and  4  are in the configuration of FIG. 1. The ring  42  is in one piece with the rest of the bush  4  and connected thereto by tabs  43  which may take any shape adapted to their function.  
         [0059]    The bush  4  is provided with a central bore  44  of which R 44  denotes the radius, this radius being greater than radius R 34 .  
         [0060]    The prosthetic element E is assembled in the following manner:  
         [0061]    The screw  3  is firstly introduced in the recess  11 , in the direction of arrow F 1 , until its thread  31  is taken in the tapping  14 . It is then possible to manoeuvre the screw  3 , causing it to undergo a movement of rotation represented by arrow R 1 , by means of a male wrench (not shown) introduced in the housing  33 , from outside the component  1 .  
         [0062]    This operation makes it possible to immobilize the screw  3  on the component  1  by aligning axes X 1  and X 3 .  
         [0063]    The flange  34  is then received in the bore  15  and bears against the bottom  15   a  thereof. To that end, the radius R 15  is slightly greater than radius R 34 .  
         [0064]    It is then possible to screw the bush  4  in the tapping  13 , as represented by arrow R′ 1 , the ring  42  in that case being disposed around the screw  3 .  
         [0065]    The components  1  and  2  may then be brought closer to each other as represented by arrows F 2  in FIG. 2, which means causing the guiding and centering finger  36 - 37  to penetrate and slide in the bore  25 , as represented by the arrow of slide C. This induces an alignment of axis X 2  on axes X 1  and X 3 .  
         [0066]    Components  1  and  2  may then be respectively advanced in the directions of arrows F 2  until surfaces  12  and  24  are brought into contact, as shown in FIG. 3.  
         [0067]    It is then possible to unscrew the screw  3  with respect to the tapping  14 , as represented by arrow R 2  in FIG. 3, then to push the screw  3  in the direction of the component  2  as represented by arrow F 3 , which has the effect of bringing the thread  35  into contact with the tapping  26 , the flange  34  in that case being in abutment against the surface  422  of the ring  42 , as shown in FIG. 4.  
         [0068]    It is then possible to screw the screw  3  in the component  2  thanks to the thread  35  and to the tapping  26 , as represented by arrow R 3  in FIG. 4, which has the effect of further approaching components  1  and  2  towards each other, as represented by arrows F 2 . This makes it possible to pass from the configuration of FIG. 4 to that of FIG. 5, where the surfaces  12  and  24  are in firm abutment against each other, this guaranteeing the relative immobilization of components  1  and  2 .  
         [0069]    The threads  35  and  41  are of opposite directions, which avoids an untimely unscrewing of the bush  4  during screwing of the screw  3  in the tapping  26 .  
         [0070]    During screwing of the screw  3  on the component  2 , the flange  34  exerts on the surface  422  of the ring  42  an effort E 1  parallel to axes X 1 , X 2  and X 3  and directed towards the component  2 , this effort being transmitted by the bush  4  to the component  1  which thus advances in the direction of the plate  23 .  
         [0071]    In a variant embodiment, in the position of contact between the thread  35  and the tapping  26 , the flange  34  may be in the vicinity of the surface  422 . In that case, the beginning of screwing of screw  3  on the component  2  causes the flange  34  and the ring  42  to approach each other, before the effort E 1  is applied.  
         [0072]    In the course of the phases of assembly of the element E shown respectively in FIGS.  2  to  5 , and as represented by arrow C, the guide finger constituted in essence by the cylindrical part  37  of the screw  3 , slides in the bore  25 , efficiently guiding the screw  3  with respect to the component  2 , this avoiding misalignment of the axes X 1 , X 2  and X 3  and thus guaranteeing a correct relative positioning of the truncated bearing surfaces  12  and  24 .  
         [0073]    According to another approach, the element E may be assembled, from the configuration of FIG. 2, by impacting the principal component  1  in the direction of the principal component  2  so that the cylindrical part  37  of the screw  3  is in essence driven in the housing  25 . Impaction takes place until the components  1  and  2  come into contact. It is then possible to unscrew the screw  3  with respect to the component  1  and to screw it in the tapping  26 , which enables an effort of relative immobilization of components  1  and  2  to be exerted on the surface  422 , and thanks to the flange  34 .  
         [0074]    In the second form of embodiment of the invention, shown in FIGS. 6 and 7, elements similar to those of the first embodiment bear identical references increased by  100 . The prosthetic element E of this embodiment comprises two principal components  101  and  102  as well as a screw  103  and a bush  104 . The component  102  is provided to be engaged in a central recess  111  of the component  101 . X 101 , X 102 , X 103  and X 104  respectively denote the central axes of the elements  101  to  104 . These axes merge in the positions of FIGS. 6 and 7. The bush  104  is provided with a thread  141  allowing it to be screwed in a tapping  113  provided in the component  101 . The bush  104  is also provided with a central tapping  145  provided to cooperate with a thread  131  made on the screw  103 .  
         [0075]    As previously, the screw  103  is provided, at the level of its upper end  132 , with a housing  133  for a manoeuvring wrench. A flange  134  of relatively great radius R 134  is also provided on the screw  103 , this flange being able to come into abutment against a lateral surface  522  of a ring  142  formed by the bush  104 .  
         [0076]    A bore  125  is made in the anchoring shank  121  of the component  102  and passes through a plate  123  intended to be engaged in a central recess  111  of the component  101 .  
         [0077]    The bore  125  is provided, in the vicinity of its inlet zone  125   a , with a tapping  126  oriented and configured in order to be able to cooperate with the thread  131  of the screw  103 .  
         [0078]    A cylindrical part  137  and an end  136  of the screw  103  constitute a finger for guiding and centering this screw in the housing  125 .  
         [0079]    Functioning is as follows:  
         [0080]    In order to assemble the element E, the screw  103  is introduced in the bush  104 , causing end  136  to traverse a central recess of the bush  104 , this recess being bordered by the tapping  145 . The screw  103  is then screwed in the tapping  145  and the sub-assembly  103 - 104  thus produced is screwed on the component  101  thanks to the thread  141  and the tapping  113 . It is then possible to pre-centre the component  101  with respect to the component  102 , possibly already in place on a patient, by the cooperation of the finger  136 - 137  and the housing  125 , then to approach these elements towards each other as represented by arrows F 2  in FIG. 6.  
         [0081]    It is then possible to unscrew the screw  103  with respect to the bush  104  while pushing it in the direction of the plate  123 , the translation of the screw  103  with respect to the component  102  being guided by the finger  136 - 137 . The components  101  and  102  may then be approached towards each other, as shown in FIG. 6, and the screw  103  screwed in the tapping  126  thanks to the thread  131 , which makes it possible to obtain a firm immobilization of the elements  102  and  103  with respect to each other, thanks to an effort E 1  exerted by the flange  134  on the surface  522 .  
         [0082]    As mentioned with reference to the first form of embodiment, another process of assembly may consist, from the position of FIG. 6, in impacting the component  101  in the direction of the component  102  so as to bring these components into contact. The screw  103  is then unscrewed with respect to the bush  4  then screwed in the tapping  126  in order to maintain these components in contact with each other, thanks to the effort E 1 .  
         [0083]    The thread  131  of the second form of embodiment performs the functions of the threads  31  and  35  of the first embodiment.  
         [0084]    The invention has been represented with a prosthetic component intended to equip the glenoid cavity of a shoulder. However, it is applicable to any type of prosthetic element comprising two principal components.