JOINT PROSTHESIS

Abstract

A joint prosthesis comprises a first component and a second component being connected via a ball-and-socket-joint, wherein the first component comprises two outward spherical sections, at least one of the spherical sections having a projection; the ball-and-socket-joint comprises two gliding blocks each having an inward spherical section and at least one of the gliding blocks comprising a hole, the gliding blocks being attached to the second component, the outward spherical sections are in gliding engagement with the inward spherical sections of the gliding blocks so that the first component is movably attached to the second component; and the projection is inserted into one of the holes of the gliding blocks, so as to limit the mobility of the ball-and-socket-joint.

Claims

1. A Joint prosthesis, comprising a first component and a second component being connected via a ball-and-socket-joint, wherein the first component comprises two outward spherical sections, at least one of the outward spherical sections having a projection; the ball-and-socket-joint comprises two gliding blocks each having an inward spherical section and at least one of the gliding blocks comprising a hole, the gliding blocks being attached to the second component, the outward spherical sections are in gliding engagement with the inward spherical sections of the gliding blocks so that the first component is movably attached to the second component; and the projection is inserted into the hole of one of the gliding blocks, so as to limit the mobility of the ball-and-socket-joint.

2. The joint prosthesis of claim 1, wherein the projection has a conical shape with the end of the conical projection away from the spherical section being smaller in circumference than the end of the conical projection at the spherical section.

3. The joint prosthesis of claim 1, wherein the second one of the two outward spherical sections has a second projection and the second one of the two gliding blocks also comprises a hole into which hole the second projection is inserted, preferably the second projections is in a conical shape with the end of the conical projection away from the spherical section being smaller in circumference than the end of the conical projections at the spherical section.

4. The joint prosthesis of claim 1, wherein the second component comprises two mounting recesses in which the gliding blocks are inserted and attached.

5. The joint prosthesis of claim 4, wherein the gliding blocks are secured with a screw in the mounting recesses.

6. The joint prosthesis of claim 4, wherein the mounting recesses comprise a projection to hinder rotational movement of the gliding blocks.

7. The joint prosthesis of claim 4, wherein the mounting recess comprises a step or a pin.

8. The joint prosthesis of claim 1, wherein the first component comprises a bone member and a joint member comprising the outward spherical sections and the at least one projection.

9. The joint prosthesis of claim 1, wherein the two outward spherical sections are arranged so that they form a spherical convex joint surface.

10. The joint prosthesis of claim 1, wherein the second component comprises at least one or two cut out portions through which the at least one projection of the first component can be inserted.

11. The joint prosthesis of claim 1, wherein the diameter of curvature of the outward spherical sections and the diameter of curvature of the inward spherical sections are substantially equal.

12. The joint prosthesis of claim 8, wherein the joint member, the outward spherical sections and the at least one projection are integrally formed as one member.

13. The joint prosthesis of claim 1, wherein the joint prosthesis is an elbow joint prosthesis, wherein the first component is an ulnar component and the second component is a humeral component.

14. A method of assembly of a joint prosthesis, comprising introducing the first component into the second component and subsequently movably fixing the first component by inserting the gliding blocks.

15. The method of assembly of a joint prosthesis of claim 14, wherein after insertion of the gliding blocks, the gliding blocks are secured to the second component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The following figures illustrate preferred embodiments of the present invention. These embodiments are not to be construed as limiting but merely for enhancing the understanding of the invention in context with the following description.

[0043] FIG. 1 shows a top view of an elbow joint prosthesis as an exemplary embodiment of a joint prosthesis according to the present disclosure;

[0044] FIG. 2 is a perspective drawing of a humeral component acting as a second component of the joint prosthesis according to the present disclosure;

[0045] FIG. 3A is a perspective drawing of a ulnar component acting as a first component of the joint prosthesis according to the present disclosure;

[0046] FIG. 3B depicts the joint member of the ulnar component;

[0047] FIGS. 4A and 4B are perspective views showing the gliding blocks;

[0048] FIG. 5 is a perspective drawing showing the gliding blocks in engagement with the joint member of the ulnar component;

[0049] FIG. 6 shows the configuration of FIG. 5 with the humeral component holding the gliding blocks;

[0050] FIG. 7A schematically shows how the range of motion of the ulnar component is limited by projections;

[0051] FIG. 7B shows the varus-valgus movement of the ulnar component; and

[0052] FIGS. 8A, 8B and 8C show the assembly steps necessary for the joint prosthesis.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0053] In the appended drawings, the same reference numerals will be used for similar or the same elements. A repetitive description of these elements will be omitted. Therefore, description of an element may refer not only to a particular figure but several or all figures.

[0054] FIG. 1 shows a joint prosthesis 1 comprising a first component 12, a second component 10 and a ball-and-socket-joint 14. The exemplary joint prosthesis illustrated in the figures and described in the following is configured as an elbow joint prosthesis. The first component 12 and the second component 10 of the joint prosthesis are configured for anchorage to the adjacent bones.

[0055] More specifically, the first component 12 of the exemplary embodiment is configured as an ulnar component that preferably comprises a bone member 12A and a joint member 12B. The bone member 12A is to be anchored to the ulna of a patient upon implantation of the prosthesis. Accordingly, the second component 10 is configured as a humeral component and comprises a joint member and a bone member (not shown), wherein the bone member is configured for being anchored to the humerus. The skilled person will appreciate that the first component 12 and second component 10 may also be configured vice versa, i. e. the first component 12 may be configured as a humeral component and the second component 10 may be configured as an ulnar component.

[0056] Nonetheless, the configuration as an elbow joint prosthesis is an exemplary embodiment. The configuration of the joint prosthesis of this disclosure is more generally directed joints that have a combination of a large range of motion in one rotational direction and a much smaller range of motion in another rotational direction. For example, the joint prosthesis 1 may alternatively be configured as a knee joint prosthesis, an ankle joint prosthesis, or a wrist joint prosthesis.

[0057] Like the elbow joint prosthesis, the first component 12 and the second component 10 in these alternative embodiments are also adapted to be anchored to the bone tissue adjacent to the joint prosthesis 1. The bone members of any of these joint prosthesis configurations may be anchored indirectly via bone cement or directly via bone ingrowth.

[0058] As illustrated in FIG. 1, the joint member 12B is connected to the second component 10 via the gliding blocks 16. The gliding blocks 16 are preferably secured/fixed to the second component 10 by means of screws 18.

[0059] In the following paragraphs the second component 10, the first component 12 and the gliding blocks 16 will be individually described with reference to FIGS. 2 to 4B.

[0060] The second component 10 is y- or yoke-shaped and comprises two mounting recesses 30 facing each other. More specifically, one mounting recess 30 is formed through each of the two branches of the yoke-shaped second component 10. Each mounting recess 30 may comprise an insertion stop such as a step 34 or any of the other features described further below for limiting insertion of a gliding block 16.

[0061] Transverse to the mounting recess 30, the second component 10 may include a through hole 36 in which a screw can be inserted upon assembly for securing the gliding block 16 within the mounting recess 30.

[0062] Further, an indexing structure for preventing a rotation of the guiding blocks 16 arranged in the mounting recesses 30. For example, a projection 32 for engaging a corresponding recess (not shown) of the gliding block 16 may be provided for hindering the rotation of the gliding block 16.

[0063] In the illustrated embodiment, each mounting recess 30 comprises a step 34. The step acts as an abutment surface for the gliding blocks 16, once they are inserted into the mounting recess 30 of each branch from the outside towards the inside of the joint prosthesis 1. In other words, the gliding blocks 16 can be pushed into the mounting recess 30 until the gliding blocks 16 abut against said step 34.

[0064] While the illustrated embodiment shows a step 34 in the mounting recesses 30 of the second component 10, alternative means to limit insertion of the gliding blocks 16 are conceivable. For example, instead of a step 34 a protrusion or a pin limiting insertion of the gliding block 16 may be used.

[0065] As yet another alternative, the gliding blocks may comprise a protrusion or the like and the second component 10 may comprise a kerf, groove or cut-out portion so that insertion of the gliding blocks 16 is limited when the projection of the gliding block 16 reaches the end of the groove, cut-out portion or kerf.

[0066] As mentioned above, each mounting recess 30 may further comprise a projection 32 for preventing a rotation of the gliding blocks 16. Accordingly, the gliding blocks 16 comprise a recess 58 or groove, which engages the projection 32 upon insertion of the gliding block 16 into the mounting recess 30 of the second component 10. However, the present invention is not limited to said configuration and alternatively the gliding block 16 may comprise a projection while the second component 10 comprises a corresponding recess.

[0067] To facilitate the insertion of the first component 12 and specifically the joint member 12B thereof into the second component 10, cut-out portions 38 are preferably formed in each of the mounting recesses 30. This facilitates insertion of the joint member 12B of the first component 12 and in particular projections 44 of this component described in more detail below into the second component 10 since the cut-out portions 38 at least reduce the necessity of having to rotate or twist the first component 12 during assembly.

[0068] The first component 12 comprises a bone member 12A and a joint member 12B. The joint member 12B comprises outward spherical sections 42. FIGS. 3A and 3B show spherical sections 42A and 42B both of which spherical sections 42 also comprise a projection 44A and 44B, respectively. The projections 44 define a first pivotal axis of the first component 12 for the dominant degree of freedom in terms of range of motion.

[0069] In the illustrated embodiment, the two projections 44A and 44B have a conical shape with the circumference of the projections 44 being reduced the further the projection is away from the spherical sections 42. The present invention is, however, not limited to conically shaped projections and any shape of projection is conceivable, as long as the projection can limit the range of motion of the joint, as will be further explained with reference to FIG. 7A.

[0070] The joint member 12B of the first component 12 preferably comprises an interface part for engaging the bone member 12A. In the illustrated embodiment, this interface is configured as hole 40 for inserting a corresponding interface part of the bone member 12A, the interface part of the bone member 12A being preferably formed as a protrusion. The interface between the bond member 12A and the joint member 12B is preferable configured as a conical connection. As already described above, the configuration of the bone members of the joint prosthesis 1 depends on the bone tissue the bone member is to be anchored to. For example, for an adjacent long bone, a bone member is preferably anchored using an implant stem such as the implant stem of the bone member 12A illustrated in the figures. For smaller bones other structures may be used such as fins, pins, or screws.

[0071] As depicted in FIG. 3B, the outward (i. e. convex) spherical sections 42A and 42B are extending in opposite directions and are symmetrical in relation to a plane C so as to form a convex spherical joint surface. This joint surface is configured to interact with a concave spherical joint surface formed by the inward spherical sections 52 of the gliding block via a surface contact. They are preferably formed as an integral part of the joint member 12B. The spherical joint surface of the outward spherical sections 42 enhances the stability and reduces wear of the joint prosthesis 1 as it provides for a varus-valgus movement about a second pivotal axis of the joint while substantially keeping a surface contact area. In other words, this configuration allows for a rotation about the first and second pivotal axes without a substantial change of the size of the surface contact area. Rotation about the first pivotal axis of the first component 12 allows for a range of motion of the joint in flexion-extension (e. g. for an elbow joint in a range of 0° to 160°). Rotation about the second pivotal axis of the first component 12 allows for a smaller range of motion in varus-valgus (e. g. approximately ±5°).

[0072] FIGS. 4A and 4B show a three-dimensional view of a gliding block 16. The gliding block 16 comprises an inward (i. e. concave) spherical section 52 and a hole 50 formed in the center of the inward spherical section 52. Upon assembly, a projection 44 is inserted into hole 50. While the present embodiment comprises two projections 44 that are inserted into holes 50 of the gliding blocks, respectively, the invention is not limited thereto, and the presence of only one projection to limit the range of motion may suffice. When being mounted to the joint member 12B, the inward spherical sections 52 of the gliding blocks form a concave spherical joint surface.

[0073] The gliding block 16 further comprises a step 55, which engages step 34 of mounting recess 30 upon insertion into the second component 10. Gliding block 16 further comprises a threaded hole 5, in which a screw 18 can be inserted to secure the gliding block 16 in the mounting recess 30 of the second component 10. Gliding block 16 also comprises a recess 58, which cooperates with projection 32 of the mounting recess 30 for preventing rotation of the gliding block 16 within the mounting recess 30 of the second component 10 and providing guidance during assembly. Insertion of the gliding block 16 is preferably facilitated by the opening of recess 58 being chamfered. Preventing rotation of the gliding block 16 also facilitates the insertion of screw 18 through hole 36 of the joint member of the second component 10 and into the threaded hole 56. More specifically, the illustrated configuration assists in aligning holes 36 and 56 upon insertion of gliding block 16 into mounting recess 30 due to the cooperation of recess 58 and projection 32.

[0074] FIG. 5 is a perspective view showing the concave joint surface of the inward spherical sections 52 of the two gliding blocks 16 in contact with the convex joint surface of the outward spherical sections 42A and 42B of the joint member 12B. A similar configuration is shown in FIG. 7A, where the gliding blocks 16 are depicted in a transparent configuration for the detailed description of FIG. 7A further down below.

[0075] FIG. 6 is also a perspective view of two gliding blocks 16 being in engagement with the joint member 12B of the first component 12. In addition to FIG. 5, the second component 10 is shown and the gliding blocks 16 are located in the mounting recesses 30 of this component. One of the gliding blocks 16 is already secured via a screw 18 to the second component 10.

[0076] In the following, the varus-valgus movement of the first component 12 will be explained in more detail with reference to FIGS. 5, 7A and 7B. As described above, the outward spherical sections 42 of the first component 12 are configured to be in engagement (i. e. in contact) with the inward spherical sections 52 of the gliding blocks 16. Two projections 44 are inserted into two holes 50 of the gliding blocks 16, respectively. As shown in FIG. 7A, the hole 50 is preferably cylindrical.

[0077] The hole 50 of a gliding block 16 and the projection 44 extending centrally from the outward spherical section 42 of the first component 12 are formed so that they are not in contact between a neutral position (i. e. the longitudinal axis of the projection 44 is aligned with the longitudinal axis of the hole 50) and up to but excluding a maximum deflection of a varus-valgus movement. As FIG. 7A illustrates, at maximum deflection the outer surface of the projection 44 is in contact with (abuts) the inner surface of the hole 50. In other words, the interaction between the projection 44 and the hole 50 acts as a stop for limiting the varus-valgus movement of the joint prosthesis 1.

[0078] FIG. 7B shows the varus-valgus movement of the first component 12 about the second pivotal axis, wherein the center configuration of FIG. 7B shows the first component 12 in a neutral position. Preferably, the projections 44 are substantially centered within holes 50 of the gliding blocks in said neutral position. The left and right configurations of FIG. 7B show the limits of the varus-valgus movement of the joint.

[0079] As explained above, the projections 44 serve to limit the varus-valgus movement of the first component 12. This limitation of the range of motion of the joint can be adjusted by adjusting the ratio of the diameter of the hole 50 of the gliding block 16 to the diameter of projections 44. The smaller the projections are in diameter in comparison to the diameter of hole 50, the more movement, i.e. range of motion in varus-valgus direction and rotation of the first component 12 is possible. In contrast, when the diameter of holes 50 of gliding blocks 16 and projections 44 are almost the same (i. e. they still allow a rotation about the first pivotal axis), hardly any movement is possible.

[0080] More specifically, the base of the conical projection 44 is preferably circular and has a smaller diameter than the diameter of the cylindrical hole 50. This allows for a rotation about the center of the outward spherical sections 42, i. e. the varus-valgus movement.

[0081] Limiting the range of motion via a projection 44 and a hole 50 is advantageous since it defines a limitation for the varus-valgus movement and distributes the abutment force more evenly. Further, allowing a defined amount of varus-valgus movement allows for a better adaptation to the kinematics of a patient's body, which in turn reduces wear of the joint, and at the same time provides predictable behavior of the joint (i. e. it prevents slackness of the joint).

[0082] It is beneficial to form the gliding blocks 16 out of UHMWPE and in particular X-Linked PE and/or Vitamin-E X-Linked PE. These materials have excellent properties for absorbing peak forces (e. g. when reaching the limits of the varus-valgus movement) and have advantageous wear characteristics. These materials have also proven to have the gliding performance needed for artificial joints.

[0083] It is particularly preferred to form the projections 44 with a conical shape so that the contact surface between the inner surface of hole 50 and the outer surface of projections 44 is basically established by a line contact.

[0084] Although it is particularly preferred that a conical projection 44 interacts with a cylindrical hole 50, other configurations may be implemented for establishing a line contact at maximum deflection of the varus-valgus movement. For example, the hole 50 may be conical and the projection 44 may be cylindrical. It is also possible that both the hole 50 and the projection 44 have a conical shape.

[0085] The projection 44 and the hole 50 are configured to allow for a rotation about the center of the outward spherical sections 42 enabling a varus-valgus movement of the joint prosthesis 1. This is possible due to an increasing gap between the inner circumference of the hole 50 and the outer circumference of the projection 44 (for example in the neutral position in relation to each other), wherein the gap increases in a direction away from the center of the outward spherical sections 42 (see FIG. 7A).

[0086] Now with reference to FIGS. 8A to 8C, the assembly of the joint prosthesis 1 will be explained. The first component 12 comprising the bone member 12A and the joint member 12B is inserted into the second component 10, i. e. into the yoke of the second component 10. In the illustrated embodiment, the projections 44 of the joint member 12B comprising the outward spherical sections 42 are inserted through cut-out portions for arranging the first component 12 between the two branches of the second component 10.

[0087] After insertion of the first component 12 into the second component 10, gliding blocks 16 are inserted into mounting recesses 30 of the second component 10 so as to engage with the outward spherical sections 42A and 42B as described above. Once the gliding blocks 16 are fully inserted into the mounting recesses 30, the gliding blocks are secured with screws 18 to the second component 10.

REFERENCE SIGNS

[0088] 1 Joint prosthesis [0089] 10 Second component [0090] 12 First component [0091] 12A Bone member [0092] 12B Joint member [0093] 14 Ball-and-socket-joint [0094] 16 Gliding block [0095] 18 Screw [0096] 30 Mounting recess [0097] 32 Projection hindering rotation [0098] 34 Step [0099] 36 Hole for screw [0100] 38 Cut out portion [0101] 40 Hole for bone member [0102] 42 Outward spherical section [0103] 44 Projection [0104] 50 Hole [0105] 52 Inward spherical section [0106] 54 Step [0107] 56 Threaded hole [0108] 58 Recess