Abstract:
A humeral component, forming a first articulating surface, and an ulnar component forming a second articulating surface adapted to be disposed around a part of the first articulating surface and to pivot about its longitudinal axis. This ulnar component is provided with structure for mounting a locking element which forms a third articulating surface extending the second and adapted likewise to be disposed around a part of the first surface. These mounting structure comprise guiding structures adapted to cooperate with complementary structure provided on the locking element in order to guide this element in translation with respect to the ulnar component, up to a position where blocking structure provided respectively on the locking element and on the ulnar component may be employed to immobilize this element on this component, these blocking structure being able to be employed only in this position.

Description:
This application claims the benefit of U.S. provisional application No. 60/473,446 filed May 28, 2003. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an elbow prosthesis comprising at least one humeral component and one ulnar component. 
     It concerns more particularly an elbow prosthesis of which the ulnar component is adapted to receive a locking element which forms an articulating surface extending that of the ulnar component, the articulating surfaces of the locking element and of the ulnar component being adapted to be arranged together around at least a part of another articulating surface belonging to a humeral component. A prosthesis of this type is known from EP-A-1 051 954. 
     BACKGROUND OF THE INVENTION 
     In such a prosthesis, the locking element is maintained in position on the ulnar component thanks to a screw introduced in a through housing in this element and tightened in a tapping provided on the ulnar component. It has proved in practice that the positioning of the locking element on the ulnar component is not always optimum when such a screw is tightened, which may lead to a skewed positioning of the screw with respect to the tapping, to such a point that the thread of the screw or the tapping may be distorted, thus preventing the locking element from being mounted. In addition, the afore-mentioned screw serves both to bring the locking element into correct position with respect to the ulnar component and to ensure blocking of these two elements with respect to each other. As a result, such an ulnar component must most often be fitted while the articulation of the elbow is in maximum flexion, which renders the surgeon&#39;s work more complex. It even happens that such fitting in maximum flexion is not possible, particularly in the case of marked obesity of the patient. 
     It is a more particular object of the invention to overcome these drawbacks by proposing an elbow prosthesis whose fit is facilitated, when it comprises a locking element as mentioned hereinabove. 
     SUMMARY OF THE INVENTION 
     To that end, the present invention relates to an elbow prosthesis comprising a humeral component, forming a first articulating surface, and an ulnar component forming a second articulating face adapted to be disposed around a part of the first articulating surface and to pivot about a longitudinal axis of this surface, the ulnar component being provided with means for mounting a locking element which forms a third articulating surface extending the second articulating surface and adapted likewise to be disposed around a part of the first articulating surface. This prosthesis is characterized in that the afore-mentioned mounting means comprise guiding means adapted to cooperate with complementary means provided on the locking element in order to guide this element in translation with respect to the ulnar component, up to a position where blocking means provided respectively on the locking element and on the ulnar component may be employed to immobilize the locking element on the ulnar component, these blocking means being able to be employed only in this position. 
     Thanks to the invention, the guiding means ensure an adequate positioning of the locking element with respect to the ulnar component before the blocking means are employed to effect an efficient immobilization of the locking element with respect to the ulnar component. In other words, the blocking means do not serve to bring the locking element in a configuration allowing its blocking, this function being performed by the guiding means which may be positioned and configured to ensure this function best. 
     In addition, an elbow prosthesis may incorporate one or more of the following characteristics, taken in any technically admissible combination: 
     The blocking means comprise a screw and a complementary tapping provided respectively on the locking element and on the ulnar component, or vice versa, the direction of relative translation between the locking element and the ulnar component as imposed by the guiding means being non-parallel to the longitudinal axis of the tapping and/or of the afore-mentioned screw. 
     The guiding means comprise at least one element in relief projecting with respect to a principal part of the ulnar component, while the complementary means provided on the locking element are adapted to interact with this element in relief by cooperation of shapes. In that case, the afore-mentioned element in relief may be a nose, while the complementary means comprise a fork of which two branches define therebetween a volume for receiving and for slide of this nose. 
     The guiding means and the blocking means are arranged in the vicinity of two opposite edges of the second articulating surface of the ulnar component, while the complementary means and the blocking means provided on the locking element are arranged on two opposite edges of that element. 
     The blocking means comprise a screw and a tapping, which are complementary and respectively provided on the locking element and on the ulnar component, or vice versa, while means are provided for blocking this screw in rotation. The head of the screw may thus be of non-circular section, while the piece against which this head bears forms a space for receiving this head, with contact between the surface of this piece and the outer surface of the head. More particularly, the head of the screw may be provided with catch elements adapted to penetrate superficially in the surface of the afore-mentioned piece. In a variant, the piece against which the head of the screw bears may be provided with a tab foldable into configuration of blockage of this head. In that case, the head of the screw may be of polygonal profile, with faces whose width is greater than the width of the foldable tab. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood and other advantages thereof will appear more clearly in the light of the following description of a form of embodiment of a prosthesis in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings, in which: 
         FIG. 1  is an exploded view in perspective of an elbow prosthesis according to the invention. 
         FIG. 2  is a longitudinal section of the ulnar component and of the locking element in the course of assembly. 
         FIG. 3  is a section similar to  FIG. 2  while the locking element is mounted on the ulnar component. 
         FIG. 4  is a view in perspective of the metal part of the ulnar component. 
         FIG. 5  is a section along line V—V of FIG.  3  and 
         FIG. 6  is a view in perspective of the ulnar component and of the locking element of the prosthesis, on a larger scale. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the drawings, the prosthesis visible in  FIGS. 1  to  3  comprises a humeral component  10  comprising a stem  11  intended to be driven in the medullary canal of a humerus H and extending in two branches  12  and  13 , each pierced with an orifice  12   a ,  13   a  for passage of a hollow screw  14  forming pin. The hollow nature of the screw  14  allows the passage of suture yarns. The orifice  12   a  is tapped, allowing the screw  14  to be screwed. The stem  11  also extends in a third branch  15  intended to come into abutment against the cortex of the humerus. 
     An elongated piece  16  is provided with a central bore  16   a  whose dimensions are such as to receive the screw  14 , this making it possible to mount the piece  16  between the branches  12  and  13 . The piece  16  is provided with two end surfaces  16   b  and  16   c  provided to come respectively into contact with the opposite surfaces of the branches  12  and  13 . 
     Between the surfaces  16   b  and  16   c , the piece  16  is substantially cylindrical, with circular base, and forms a surface of articulation S 1  which is also substantially cylindrical, whose generatrix G 1  is curved and concave, in that the diameter of the surface S 1  is minimum in the central part of the piece  16  included between the surfaces  16   b  and  16   c . X 1  denotes the axis of symmetry of the surface S 1 . 
     The piece  16  extends in an extension  16   d  whose outer surface S 4  is convex and which covers the branch  12  when the piece  16  is mounted between the branches  12  and  13 . 
     The whole of the humeral component  10  is made of metal. 
     The ulnar component  20  comprises a metal stem  21  intended to be inserted in the medullary canal of the ulna C and which is in one piece with a branch  22  likewise made of metal, of concave shape and whose inner surface is covered with a lining  23  made of a material adapted to the friction with the metal piece  16 , for example polyethylene. The lining  23  is mounted on the branch  22  by cooperation of shapes. A pin  27  makes it possible to immobilize elements  22  and  23  with respect to each other. 
     The inner surface of the lining  23  forms a surface of articulation S 2  whose shape is complementary to that of surface S 1 . X 2  denotes the central axis of elements  22  and  23 . 
     The respective diameters of surfaces S 1  and S 2 , which diameters are variable along axes X 1  and X 2 , are chosen so that the surface S 2  may be disposed around the surface S 1 , with a slight clearance, this allowing a rotation of the components  10  and  20  with respect to each other about axes X 1  and X 2  which, in that case, merge. 
     Moreover, the profiles of the generatrices of surfaces S 1  and S 2  are chosen so as to allow a degree of mobility of the surface S 1  in surface S 2 , in the sense of varus-valgus, i.e. about an axis perpendicular to X 1  and X 2 . 
     A locking element  30  is intended to be mounted on the component  20  and comprises a metal casing  32  and a lining  33  immobilized with respect to each other by clipping. The lining  33  is advantageously made of the same material as the lining  23  and forms a concave articulating surface S 3  intended to extend the surface S 2  and, with it, surround the surface S 1 . 
     In order to facilitate assembly of the element  30  on the component  20 , this component is provided, in extension of the outer surface  24  of the branch  22 , with an element in relief  25  in the form of a nose or beak which projects beyond the part  22   a  of the branch  22  covered by the lining  23 . 
     Furthermore, the casing  32  of the element  30  extends beyond its part  32   a  covered by the lining  33 , in an extension in the form of a fork  35  of which the two branches  35   a  and  35   b  together define a volume  35   c  for slide and reception of the nose  25  when the element  30  is mounted on the component  20 . 
     The nose  25  is disposed in a space  23   c  defined by the lining  23  which extends beyond the part  22   a  of the branch  22  that it covers. In its part  23   d  which extends in overhang with respect to the part  22   a , the lining has a substantially U-shaped cross-section. The space  23   c  is defined at the centre of this U. 
     The nose  25  has a width decreasing in the direction of the bottom of the U formed by the part  23   d . In this way, the sides  25   a  and  25   b  of the nose  25  diverge, moving away from this bottom and approaching the branches of the U formed by the part  23   d . The nose  25  has a section substantially in the form of a dove-tail. 
     In addition, grooves  25   c  and  25   d  are formed on either side of the nose  25 . These grooves have profiles allowing them to receive convex parts  35   d  and  35   e  of the branches  35   a  and  35   b.    
     The branches  35   a  and  35   b  thus have a geometry compatible with their introduction in the space  23   c , on either side of the nose  25 . Their surfaces intended to face towards the nose  25  deviate from each other towards the outside of the element  30 , with the result that these surfaces are substantially parallel to sides  25   a  and  25   b.    
     In this way, the direction of assembly of the element  30  on the component  20  is necessarily that indicated by arrow F 1  in  FIG. 2 , this direction being imposed by the cooperation of shapes between the nose  25  and the fork  35 . In effect, as indicated hereinabove, the transverse sections of the nose  25  on the one hand and of the inner parts of the branches  35  are chosen to impose this direction of slide. 
     Furthermore, the component  20  is provided with a tapping  26  for receiving a screw  36  which traverses a through housing  37  provided to that end in the element  30 . 
     The tapping  26  and the housing  37  are configured so that they are aligned, in a direction Y 1  perpendicular to axis X 2 , at the end of the slide of the element  30  with respect to the component  20 . Such slide takes place until the linings  23  and  33  come into abutment against each other in the vicinity of the members  25  and  35 , as shown in FIG.  3 . It is then possible to screw the screw  36  in the tapping  26 , in the direction of arrow F 2  in  FIGS. 2 and 3 . In the configuration of  FIG. 3 , the central axes of the screw  36  and of the tapping  26  merge and are parallel to direction Y 1 . 
     The direction Y 1  is not parallel to the direction of displacement of the element  30  with respect to the component  20  during its assembly, i.e. to arrow F 1 , with the result that the screw  36  can be introduced in the tapping  26  only at the end of slide of the element  30  on the component  20  in the direction of arrow F 1 . 
     In this way, the screw  36  serves solely for blocking the element  30  in position on the component  20  and can be tightened only once a correct position of the element  30  on the component  20  has been attained. The risks of the screw  36  being tightened askew in the tapping  26  are thus avoided. 
     In addition, the mechanical strength of the assembly formed by the elements  20  and  30  in the configuration of  FIG. 3  is much greater than that able to be obtained with the prosthesis known from EP-A-1 051 954 as, once the screw  36  is tightened, the element  30  is immobilized with respect to the component  20  on its two sides. 
     In effect, the nose  25  is provided in the vicinity of a first edge  20   a  of the component  20  and of the surface S 2 , while the tapping  26  is provided near the opposite edge  20   b  of this component. In the same way, elements  35  and  37  are respectively provided in the vicinity of the two opposite edges  30   a  and  30   b  of the element  30  and of the surface S 3 . 
     In other words, the function of guiding of the element  30  with respect to the component  20  is obtained in the vicinity of the edges  20   a  and  30   a  of these members, while the function of blocking is obtained in the vicinity of the edges  20   b  and  30   b.    
     The housing  37  is formed by a circular orifice  37   a  made in the metal casing  32  for the passage of the shank of the screw  36 , as well as by a concave zone  37   b  made in an end part of the lining  33 , in the vicinity of the edge  30   b.    
     The head  36   a  of the screw  36  presents a non-circular external section as it is equipped with peripheral catching elements or teeth  36   b  provided to engage superficially in the inner radial surface  37   c  of the concave zone  37   b , this contributing to the immobilization of the screw  36  in rotation and thus ensures an efficient blocking of the element  30  on the component  20 . 
     In addition, a tab  38  extends the casing  32  in the vicinity of the housing  37 , this tab being able to be folded into abutment against the head  36   a  of the screw  36  when the latter is tightened, in the direction of arrow F 3  in  FIG. 3 , so that it performs a function of non-return for this screw, this also contributing to the efficient blocking of the element  30  on the component  20 . 
     According to a variant embodiment of the invention (not shown), the head  36   a  may present a polygonal profile, for example hexagonal or octagonal, with planar faces. In that case, the width of the tab  38  is chosen to be less than the width of the lateral faces of this head, this allowing the screw  36  to be blocked in rotation by surface abutment of one of these faces against this tab. 
     When the element  30  is mounted on the component  20 , the assembly thus produced may pivot about axis X 1  and the joining of surfaces S 2  and S 3  surrounds the surface S 1  over 360°. 
     A radial component adapted to be mounted on the radius R is advantageously provided in the prosthesis according to the invention, this component  40  defining a surface intended to cooperate with the surface S 4 . However, this is not compulsory. 
     The invention is not limited to the sole form of embodiment represented. In particular, it may concern a prosthesis in which the projecting element, such as the nose  25 , is provided on the element  30 , while a structure of fork type is provided on the ulnar component. Similarly, the tapping for receiving the blocking screw may be provided on the locking element, the ulnar component in that case defining a housing for receiving the locking screw. 
     Any mechanical means for blocking the locking element on the ulnar component may be envisaged within the framework of the present invention.