Abstract:
An elbow prosthesis which includes a humeral component having a rod extending along a longitudinal axis and this component further includes a generally cylindrical body having a first articulating surface about which an ulnar component is pivotally mounted so as to pivot about a longitudinal axis of the body. A spacing between a plane extending through the longitudinal axis of the body and the longitudinal of the rod of the humeral component is selected to define a desirable spacing therebetween depending upon a patient&#39;s morphology.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit of and is a divisional application of Ser. No. 09/568,421 filed May 10, 2000, now U.S. Pat. No. 6,379,387. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an elbow prosthesis comprising at least one humeral component and one ulnar component. 
     2. Background of the Invention 
     As a function of the articular clearance and of the mode of coupling the humeral and ulnar prosthetic elements together, two principal types of prostheses are distinguished: 
     prostheses with hinge arrangements, in which a common hinge pin is introduced in aligned orifices provided on the humeral component and on the femoral component. Taking into account the mode of assembling these prostheses, the hinge pin which defines the articulating surface necessarily presents a rectilinear generatrix, which is substantially different from the natural articulating surface of the trochlea. These hinge arrangements present good stability and allow a rotation in the sagittal plane of the joint. However, they prevent transverse movements such as the varus-valgus movement or a movement of ulnar axial rotation. To allow such a movement, the hinge must be provided with a considerable radial clearance, which leads to premature wear of the articulating surfaces. 
     sliding prostheses, as known in particular from U.S. Pat. No. 4,242,758, in which the ulnar component comes into abutment on a substantially cylindrical humeral articulating surface. Such prostheses allow transverse movements, but are unstable perpendicularly and/or parallel to the sagittal plane, hence there is a considerable risk of dislocation or transverse instability inducing parasitic movements when the elbow is flexed. 
     It is a particular object of the present invention to overcome these drawbacks by proposing an elbow prosthesis which allows certain transverse movements, such as the varus-valgus movement, while presenting a largely increased stability over known sliding prostheses. 
     SUMMARY OF THE INVENTION 
     To that end, the invention relates to an elbow prosthesis comprising a humeral component forming a first, substantially cylindrical articulating surface and an ulnar component forming a second articulating surface adapted to be arranged around a part of this first articulating surface and to pivot about a longitudinal axis of this first articulating surface, characterized in that the ulnar component is provided with means for mounting a locking element forming a third articulating surface, extending the second articulating surface and adapted to be disposed around the first articulating surface, these second and third articulating surfaces extending together, in transverse section of the first articulating surface, over more than 180° about the first articulating surface. 
     Thanks to the invention, the second and third surfaces of the ulnar component and of the locking element make it possible to surround or to enclose the first articulating surface, this eliminating the risks of dislocation of the joint. The geometry of the articulating surfaces may be chosen to be close to the natural articulating surfaces and, in particular, is not limited to the cylindrical surfaces with rectilinear generatrix used up to the present time in hinge-type prostheses. In effect, the cylindrical nature of the first articulating surface means that it is generated by rotation of a generatrix about an axis, its generatrix not necessarily being rectilinear but may be concave, which makes it possible to approach the natural morphology of the trochlea best. 
     According to advantageous aspects of the invention, the prosthesis incorporates one or more of the following features: 
     The second and third articulating surfaces extend together over an angle included between 190° and 360°, preferably between 225° and 315°, preferably still of the order of 270°, about the first articulating surface. 
     The prosthesis comprises means for adjusting, as a function of the patient&#39;s morphology, the position of the longitudinal axis of the first surface with respect to the longitudinal axis of an anchoring rod of the humeral component. In effect, the trochlea may be more or less forward in the sagittal plane with respect to the longitudinal axis of the humerus, independently of the size of the bone, this morphological variation not, up to the present time, being taken into account by elbow prostheses. The prosthesis of the present invention therefore makes it possible to take this variable into account when placing a prosthesis. In particular, the first surface may be provided to be formed by an elongated piece while tabs fast with the anchoring rod are provided with bores for receiving an assembly pin, the relative position of the bores of the piece and of the tabs being adapted as a function of the patient&#39;s morphology. For example, the prosthesis may comprise a plurality of elongated pieces and/or a plurality of rods, these pieces and rods being adapted to be assembled together and allowing different positions of the longitudinal axis of the substantially cylindrical parts with respect to the axes of the rods, to be obtained. According to another variant embodiment, the rod and the elongated piece forming the first surface may be provided to be fixed with respect to each other, in particular in one piece, the prosthesis comprising a plurality of such piece/rod assemblies of different geometries for a given size of humerus. It is then possible for the surgeon, when placing a prosthesis, to choose a rod/piece assembly as a function of the patient&#39;s morphology. 
     The ulnar element and the locking element are each provided with a free edge, the distance between these free edges being smaller than the minimum diameter of the first articulating surface when the locking element is mounted on the ulnar component. In this way, the assembly formed by the ulnar component and the locking element cannot be dislocated with respect to the first articulating surface. 
     The assembly means comprise at least one tapping for receiving a screw engaged in a housing provided in the locking element or a housing for receiving a screw adapted to be screwed in a corresponding tapping in the locking element. 
     The first articulating surface has a concave generatrix, while the second and third articulating surfaces present, in a plane of section parallel to the axis of the first articulating surface, a convex generatrix. Thanks to this arrangement, the axis of the varus-valgus movement is permanently located in the ulnar component, which gives a better transverse stability to the prosthesis thus produced, in particular with respect to the one known by U.S. Pat. No. 4,242,758, in which the axis of the varus-valgus movement is, in the extreme configurations, located in the bobbin forming the humeral element. 
     The first articulating surface extends in a fourth, substantially convex, articulating surface for bearing a radial component. This allows a total elbow prosthesis to be produced. 
     A functional clearance between the above-mentioned surfaces is formed by the difference of their diameters or radii of curvature of their respective generatrices. 
     The ulnar component and/or the locking element comprise a reinforcement and a lining mounted on the reinforcement by cooperation of shapes thanks to returns adapted to cover lateral fins of the reinforcement. 
     An orifice for passage of at least one suture thread is made near the longitudinal axis of the first articulating surface and parallel thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more readily understood on reading the following description of two embodiments of an elbow 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 view in perspective of the ulnar component of the prosthesis of FIG. 1 in the course of assembly. 
     FIG. 3 is a front view of the prosthesis of FIG. 1 mounted in an elbow in extension, in a first configuration. 
     FIG. 4 is a section along plane IV—IV in FIG.  3 . 
     FIG. 5 is a view similar to FIG. 3 while the prosthesis is in a second configuration. 
     FIG. 6 is a section along plane VI—VI in FIG.  5 . 
     FIG. 7 schematically shows, on a larger scale and in longitudinal section, certain contact surfaces of the prosthesis of FIGS. 1 to  6 , and FIG. 8 is a partial section similar to FIG. 4 for a prosthesis in accordance with a second embodiment of the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, the prosthesis visible in FIGS. 1 to  6  comprises a humeral component  10  presenting a rod  11  intended to be driven in the medular channel of a humerus H and extending in two tabs  12  and  13  each pierced with an orifice  12   a  or  13   a  for passage of a screw  14  forming shaft. Orifice  12   a  is tapped, which enables it to cooperate with the outer threading of screw  14 . 
     The rod  11  also extends in a third tab  15  intended to abut against the cortex of the humerus H and to prevent a possible forward tipping of the humeral rod. 
     An elongated piece  16  is provided with a central bore  16   a  whose dimensions allow it to receive the screw  14 . Two end surfaces  16   b  and  16   c  of the piece  16  are provided to come respectively into contact with the opposite surfaces  12   b  and  13   b  of the tabs  12  and  13 , while screw  14  traverses the orifices and bores  13   a ,  16   a  and  12   a.    
     In this position shown in FIGS. 3 to  6 , an end surface  13   c  of the tab  13  is in abutment against an end shoulder  16   d  of the piece  16 . Similarly, an end surface  12   c  of the tab  12  comes into contact with a surface  16   e  of complementary shape provided on the piece  16 , beyond the surface  16   b . In this way, the piece  16  is immobilized in rotation about the screw  14  by cooperation of shapes of the surfaces  13   c  and  16   d , on the one hand,  12   c  and  16   e , on the other hand. 
     Between the surfaces  16   b  and  16   c , the piece  16  is substantially cylindrical and forms an articulating surface S 1  likewise substantially cylindrical, of which the generatrix G 1  is curved and concave, in that the diameter of the surface S 1  is minimum in the central part of that portion 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 , D 1  its diameter, which is variable along axis X 1 , and R 1  the radius of curvature of the generatrix G 1  in the plan of FIG.  7 . 
     The piece  16  extends by an extension  16   f  of which the outer surface S 4  is convex. The extension  16   f  covers tab  12  when the piece  16  is mounted on tabs  12  and  13 . 
     The whole of the humeral component  10  is made of metal. 
     An ulnar component  20  comprises a metal rod  21  intended to be inserted in the medullar channel of the ulna C and which extends in a likewise metallic tab  22  of concave shape of which the inner surface is coated with a lining  23  made of a material adapted for friction with the metallic piece  16 , for example polyethylene. The lining  23  is mounted on the tab  22  by cooperation of shapes thanks to returns  23   a  which cover lateral fins  22   a  of the tab  22 . A headless screw  24  makes it possible to immobilize elements  22  and  23  with respect to each other. 
     The assembly of the lining  23  on the tab  22  is represented in FIG.  2 . The lining  23  is engaged on the tab  22  so that its returns  23   a  cover the fins  22   a  and undergoes a movement of slide represented by arrows F until they come into abutment against a stop surface  22   b  formed on the interior of a boss  26  on the tab  22 . When the lining  23  is in abutment against the surface  22   b , the screw  24  is introduced and screwed in the lining  23  and in the tab  22 , as represented by arrow F′. The tab  22  then constitutes an enveloping reinforcement for the lining  23 . 
     The process of assembly used between the lining  23 , which may in particular be made of plastics material, and the tab  22 , which is made of metal, presents the following advantages: 
     a considerable facility of machining of the lining  23 , as its constituent material may be machined solely by turning, without resorting to numerical control machines. 
     a particularly efficient hold of the lining  23  on the tab  22 . 
     the presence of a large quantity of matter, for example polyethylene, forming the lining  23  on either side of the metal forming the tab  22 , which makes it possible to avoid any contact between the metal parts  16  and  22  during the articular movement. 
     Although the mode of assembly described hereinabove is particularly advantageous, the relative immobilization of the elements  22  and  23  may be effected by other means, in particular by blocking, crimping or clipping. 
     The lining  23  is provided with a lateral notch  23   b  in order not to interfere with the tissues passing near the component  20  when the prosthesis is in mounted position. 
     The inner surface of the lining  23  forms an articulating surface S 2  of shape complementary of that of surface S 1 . X 2  denotes the central axis of the elements  22  and  23 , D 2  the diameter of the surface S 2 , this diameter being variable along axis X 2 . In section in a plane parallel to axis X 2 , the surface S 2  is convex, in that its generatrix G 2  is curved and convex, with a centre of curvature disposed towards the tab  22 , i.e. the opposite of axis X 2 . R 2  denotes the radius of curvature of the generatrix G 2 . 
     The respective diameters D 1  and D 2  and the respective radii of curvature R 1  and R 2  of the surfaces S 1  and S 2  are substantially equal. The slight differences in values of D 1  and D 2 , on the one hand, and of R 1  and R 2 , on the other hand, make it possible to create a diametral functional clearance J and a longitudinal functional clearance J′ which are exaggerated in FIG. 7 in order to render the drawing clearer. These functional clearances J and J′ which have low values, allow the relative movement of varus-valgus and of axial rotation of the ulnar component  20  with respect to the humeral component  10 . 
     The respective dimensions and orientations of the surfaces S 1  and S 2  are such that the ulnar component may be disposed around a part of the surface S 1 , as shown in FIGS. 3 and 4. In this position, the lining  23  surrounds the piece  16  over a part of its circumference represented in FIG. 4 by an angle α defining the range of the congruence between the surfaces S 1  and S 2  visible in FIG.  4  and smaller than about 180°. The angle α is smaller than 180° in order to allow the positioning of the ulnar component on the piece  16 . The operational clearances J and J′ provided between the surfaces S 1  and S 2  can make it possible for the angle α to be greater than 180°, without compromising the free assembly of the component  20  on the piece  16 . 
     In this configuration, the prosthesis behaves like a sliding prosthesis. 
     When the surgeon realizes that the tendons and ligaments of the joint are in good condition and that there is little risk of the joint being dislocated, the prosthesis can be used in the configuration of FIGS. 3 and 4. 
     According to the invention, the prosthetic joint can be rendered safer by using a locking element  30  intended to be mounted on the ulnar component  20  and formed by a reinforcement  32  and a lining  33  immobilized with respect to each other thanks to fins and returns similar to those of the tab  22  and the lining  23  and to a headless screw  34  visible in FIG.  6 . The lining  33  is made of a material adapted for friction with the piece  16 , for example polyethylene, this material advantageously being identical to that of the lining  23 . The lining  33  is mounted on the reinforcement  32  in similar fashion to the assembly described with reference to FIG.  2 . 
     A lateral notch  33   b  is provided on the lining  33 , this notch being diametrally opposite the notch  23   b  when the element  30  is in mounted position and having the same function as the notch  23   b.    
     The inner surface of the lining  33  forms a third articulating surface S 3  whose geometry is comparable to that of the surface S 2 . More precisely, the generatrices of surfaces S 2  and S 3  are substantially identical, with the result that, when the element  30  is mounted on the component  20 , the surface S 3  extends the surface S 2 . The configuration is in that case that of FIGS. 5 and 6 in which the surfaces S 2  and S 3  of the assembly formed by the elements  20  and  30  surround the surface S 1 , the axes X 1  and X 2  being able to be displaced with respect to each other, both in translation and in rotation, by distances or angles given by the value of the diametral and longitudinal functional clearances J and J′ made between the surface S 1  and the combination of the surfaces S 2  and S 3 . In effect, the combination of the surfaces S 1  and S 2  and S 3  make it possible to obtain: 
     a sufficient contact surface between pieces  16  and  20  or  16 ,  20  and  30 , whatever the relative position of the humeral and ulnar components. 
     the possibility of a movement of varus-valgus and of an axial rotation whatever the efforts undergone by these components. 
     the possibility of a medio-lateral translation of the ulna on the humerus. 
     the possibility of an antero-posterior translation of the ulna on the humerus. 
     In the plane of FIG. 6, the surfaces S 2  and S 3  together surround the surface S 1  over an angle β of the order of 270°. In fact, the locking obtained thanks to the element  30  is efficient as long as angle β is greater than 180°. Satisfactory results have been obtained with an angle β included between 225 and 315°, this angle reasonably being able to extend over a range from 190 to 360°. 
     As long as the angle β is greater than 180°, the cooperation of surfaces S 1  on the one hand, S 2  and S 3  on the other hand, avoids a dislocation of the joint, while movements of varus-valgus remain possible by transverse slide and/or pivoting of the surfaces S 2  and S 3  with respect to the surface S 1 . 
     Assembly of the element  30  on the component  20  is obtained thanks to a tapping  25  made in the boss  26  provided on the tab  22 , while a housing  35  is provided in the reinforcement  32  for receiving a screw  36  intended to be tightened in the tapping  25 . In an alternative solution, a tapping may be provided in the reinforcmeent  32  while a housing for receiving a screw head is provided in the tab  22 . Other fixing means may be envisaged, in particular possibly truncated studs or a tenon-and-mortise assembly. 
     In the configuration of FIGS. 5 and 6, the distance d, between the respective free edges  20   a  and  30   a  of the component  20  and of the element  30 , is less than the minimum diameter D of the surface S 1 , which corresponds to the desired locking thanks to the element  30 . 
     X 3  denotes the longitudinal axis of the rod  11  and d′ the shift of axes X 1  and X 3  in the plane of FIGS. 4 and 6. The value of d′ is a parameter which depends on the patient&#39;s morphology. 
     According to an advantageous but non-compulsory aspect of the invention, it is possible to adjust the value of d′ by using different pieces  16  whose central bore  16   a  is more or less offset with respect to axis X 1 , as shown in dashed and dotted lines in FIG. 1 with references  16   a ′ and  16   a ″. In this way, after testing the rod  11  in the humerus, the surgeon can choose, from a plurality of pieces  16  of which the central bore is more or less offset with respect to the axis X 1 , the one which best corresponds to the anatomical position of the trochlea. 
     In any case, the surfaces  12   c  and  13   c  of the tabs  12  come respectively into abutment against the surfaces  16   d  and  16   e  of the piece  16 . 
     Other variants enable the same result to be obtained, in particular the use of pieces forming parts  11  to  15  of variable geometry, the orifices  12   a  and  13   a  being more or less offset with respect to axis X 3 . In that case, a single elongated piece  16  may be used. 
     According to another alternative, elements  11  to  16  may be formed in one piece, an assembly forming a prosthesis comprising different one-piece assemblies of which the shift d′ is variable. The surgeon may thus choose the most suitable piece from these one-piece assemblies, after having positioned and tested a temporary phantom prosthesis. 
     In practice, whatever the mode of adjustment of the shift envisaged, it appears that an amplitude of more or less 5 mm around the median position represented in solid lines in FIG. 1, covers the majority of the operational cases. 
     A radial component  40  is provided, comprising a rod  41  intended to be inserted in the medullar channel of the radius R and a head  43  made of plastics material, for example polyethylene encircled by a metallic hoop  42 . The head  43  forms a concave articulating surface S 5  provided to come into abutment against the surface S 4  of the piece  16 . In this configuration, the prosthesis of the invention is a total prosthesis. 
     According to a variant of the invention (not shown), the prosthesis may be partial, in that it does not comprise a radial component, the anatomical head of the radius in that case being directly articulated on the metallic surface S 4 . 
     In the second embodiment of the invention shown in FIG. 8, elements similar to those of the first embodiment bear identical references. A shoe  23   d  extends the lining  23  opposite its edge provided to come into contact with the element  30 . The inner surface S 6  of the shoe  23   d  extends the surface S 2  tangentially, with the result that it constitutes an additional protection against a dislocation of the prosthesis, usable with or without the element  30  which may be mounted on the component  20  in the position shown in dashed and dotted lines. The locking obtained is further improved with respect to the first embodiment. 
     According to an advantageous but non-compulsory aspect of the invention, an axial orifice  14   a  is made longitudinally in the screw  14  so as to allow passage of suture threads intended to attach the ligamentary structures in contact with the prosthesis or the bone, near their anatomical point of anchoring located on the axis of bending of the elbow. An equivalent orifice may also be made in the piece  16 , near the axis X 1  and parallel thereto, in particular in the one-piece variant mentioned hereinabove. 
     According to a variant of the invention applicable whatever the form of embodiment in question, the clearance between the surfaces S 1  and S 2  or between the surface S 1  and the combination of the surfaces S 2  and S 3  may be solely diametral or, on the contrary, not present any diametral clearance or present a very small diametral clearance, the operational clearance in that case being essentially longitudinal. In the first case, a good resistance to the movements of varus-valgus and of rotation is obtained, to the detriment of the transverse mobility. In the second case, operation is correct, but a certain wear of surfaces S 1 , S 2  and S 3  can be expected.