Elbow prosthesis

[0002] 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.

[0003] 1. Field of the Invention

[0004] The present invention relates to an elbow prosthesis comprising at least one humeral component and one ulnar component.

[0005] 2. Background of the Invention

[0006] 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:

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] According to advantageous aspects of the invention, the prosthesis incorporates one or more of the following features:

[0013] 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.

[0014] The prosthesis comprises means for adjusting, as a function of the patient'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'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's morphology.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] A functional clearance between the above-mentioned surfaces is formed by the difference of their diameters or radii of curvature of their respective generatrices.

[0020] 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.

[0021] An orifice for passage of at least one suture thread is made near the longitudinal axis of the first articulating surface and parallel thereto.

[0022] 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:

[0023] FIG. 1 is an exploded view in perspective of an elbow prosthesis according to the invention.

[0024] FIG. 2 is a view in perspective of the ulnar component of the prosthesis of FIG. 1 in the course of assembly.

[0025] FIG. 3 is a front view of the prosthesis of FIG. 1 mounted in an elbow in extension, in a first configuration.

[0026] FIG. 4 is a section along plane IV—IV in FIG. 3.

[0027] FIG. 5 is a view similar to FIG. 3 while the prosthesis is in a second configuration.

[0028] FIG. 6 is a section along plane VI—VI in FIG. 5.

[0029] 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.

[0030] 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 12aor 13afor passage of a screw 14 forming shaft. Orifice 12ais tapped, which enables it to cooperate with the outer threading of screw 14.

[0031] 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.

[0032] An elongated piece 16 is provided with a central bore 16awhose dimensions allow it to receive the screw 14. Two end surfaces 16band 16cof the piece 16 are provided to come respectively into contact with the opposite surfaces 12band 13bof the tabs 12 and 13, while screw 14 traverses the orifices and bores 13a, 16aand 12a.

[0033] In this position shown in FIGS. 3 to 6, an end surface 13cof the tab 13 is in abutment against an end shoulder 16dof the piece 16. Similarly, an end surface 12cof the tab 12 comes into contact with a surface 16eof complementary shape provided on the piece 16, beyond the surface 16b. In this way, the piece 16 is immobilized in rotation about the screw 14 by cooperation of shapes of the surfaces 13cand 16d, on the one hand, 12cand 16e, on the other hand.

[0034] Between the surfaces 16band 16c, the piece 16 is substantially cylindrical and forms an articulating surface S₁likewise substantially cylindrical, of which the generatrix G₁is curved and concave, in that the diameter of the surface S₁is minimum in the central part of that portion of the piece 16 included between the surfaces 16band 16c. X₁denotes the axis of symmetry of the surface S₁, D₁its diameter, which is variable along axis X₁, and R₁the radius of curvature of the generatrix G₁in the plan of FIG. 7.

[0035] The piece 16 extends by an extension 16fof which the outer surface S₄is convex. The extension 16fcovers tab 12 when the piece 16 is mounted on tabs 12 and 13.

[0036] The whole of the humeral component 10 is made of metal.

[0037] 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 23awhich cover lateral fins 22aof the tab 22. A headless screw 24 makes it possible to immobilize elements 22 and 23 with respect to each other.

[0038] 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 23acover the fins 22aand undergoes a movement of slide represented by arrows F until they come into abutment against a stop surface 22bformed on the interior of a boss 26 on the tab 22. When the lining 23 is in abutment against the surface 22b, 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.

[0039] 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:

[0040] 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.

[0041] a particularly efficient hold of the lining 23 on the tab 22.

[0042] 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.

[0043] 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.

[0044] The lining 23 is provided with a lateral notch 23bin order not to interfere with the tissues passing near the component 20 when the prosthesis is in mounted position.

[0045] The inner surface of the lining 23 forms an articulating surface S₂of shape complementary of that of surface S₁. X₂denotes the central axis of the elements 22 and 23, D₂the diameter of the surface S₂, this diameter being variable along axis X₂. In section in a plane parallel to axis X₂, the surface S₂is convex, in that its generatrix G₂is curved and convex, with a centre of curvature disposed towards the tab 22, i.e. the opposite of axis X₂. R₂denotes the radius of curvature of the generatrix G₂.

[0046] The respective diameters D₁and D₂and the respective radii of curvature R₁and R₂of the surfaces S₁and S₂are substantially equal. The slight differences in values of D₁and D₂, on the one hand, and of R₁and R₂, 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.

[0047] The respective dimensions and orientations of the surfaces S₁and S₂are such that the ulnar component may be disposed around a part of the surface S₁, 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 S₁and S₂visible 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 S₁and S₂can 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.

[0048] In this configuration, the prosthesis behaves like a sliding prosthesis.

[0049] 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.

[0050] 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.

[0051] A lateral notch 33bis provided on the lining 33, this notch being diametrally opposite the notch 23bwhen the element 30 is in mounted position and having the same function as the notch 23b.

[0052] The inner surface of the lining 33 forms a third articulating surface S₃whose geometry is comparable to that of the surface S₂. More precisely, the generatrices of surfaces S₂and S₃are substantially identical, with the result that, when the element 30 is mounted on the component 20, the surface S₃extends the surface S₂. The configuration is in that case that of FIGS. 5 and 6 in which the surfaces S₂and S₃of the assembly formed by the elements 20 and 30 surround the surface S₁, the axes X₁and X₂being 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 S₁and the combination of the surfaces S₂and S₃. In effect, the combination of the surfaces S₁and S₂and S₃make it possible to obtain:

[0053] a sufficient contact surface between pieces 16 and 20 or 16, 20 and 30, whatever the relative position of the humeral and ulnar components.

[0054] the possibility of a movement of varus-valgus and of an axial rotation whatever the efforts undergone by these components.

[0055] the possibility of a medio-lateral translation of the ulna on the humerus.

[0056] the possibility of an antero-posterior translation of the ulna on the humerus.

[0057] In the plane of FIG. 6, the surfaces S₂and S₃together surround the surface S₁over 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°.

[0058] As long as the angle β is greater than 180°, the cooperation of surfaces S₁on the one hand, S₂and S₃on 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 S₂and S₃with respect to the surface S₁.

[0059] 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.

[0060] In the configuration of FIGS. 5 and 6, the distance d, between the respective free edges 20aand 30aof the component 20 and of the element 30, is less than the minimum diameter D of the surface S₁, which corresponds to the desired locking thanks to the element 30.

[0061] X₃denotes the longitudinal axis of the rod 11 and d′ the shift of axes X₁and X₃in the plane of FIGS. 4 and 6. The value of d′ is a parameter which depends on the patient's morphology.

[0062] 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 16ais more or less offset with respect to axis X₁, as shown in dashed and dotted lines in FIG. 1 with references 16a′ and 16a″. 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 X₁, the one which best corresponds to the anatomical position of the trochlea.

[0063] In any case, the surfaces 12cand 13cof the tabs 12 come respectively into abutment against the surfaces 16dand 16eof the piece 16.

[0064] 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 12aand 13abeing more or less offset with respect to axis X₃. In that case, a single elongated piece 16 may be used.

[0065] 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.

[0066] 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.

[0067] 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 S₅provided to come into abutment against the surface S₄of the piece 16. In this configuration, the prosthesis of the invention is a total prosthesis.

[0068] 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 S₄.

[0069] In the second embodiment of the invention shown in FIG. 8, elements similar to those of the first embodiment bear identical references. A shoe 23dextends the lining 23 opposite its edge provided to come into contact with the element 30. The inner surface S₆of the shoe 23dextends the surface S₂tangentially, 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.

[0070] According to an advantageous but non-compulsory aspect of the invention, an axial orifice 14ais 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 X₁and parallel thereto, in particular in the one-piece variant mentioned hereinabove.

[0071] According to a variant of the invention applicable whatever the form of embodiment in question, the clearance between the surfaces S₁and S₂or between the surface S₁and the combination of the surfaces S₂and S₃may 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 S₁, S₂and S₃can be expected.