Tibial knee component with a mobile bearing

Abstract: An orthopaedic knee component for implanting within a proximal tibia includes a tibial tray with a distally extending stem, a proximal tibial plateau and a post extending from the tibial plateau. The post defines an axis of rotation. An intermediate carrier has an opening in which the post is disposed. The carrier is pivotal about the axis of rotation. A bearing carried by the tibial tray has an articular bearing surface for engagement with a femoral component. The bearing has a recess in which the intermediate carrier is disposed. The projection, carrier and recess allow pivotal movement of the bearing relative to the tibial plateau about the axis of rotation.

Description: 1. Field of the invention. The present invention relates to an orthopaedic implant, and, more particularly, to a tibial knee component. 2. Description of the related art. A tibial knee component is implanted within a proximal tibia and engages with a femoral component implanted within a distal femur. The tibial knee component typically includes a bearing which is immovably affixed to a tibial tray. The tibial tray includes a stem which is implanted within the intramedullary (IM) canal in the proximal tibia. The bearing may be in the form of a wear resistant and low friction material such as ultra high molecular weight polyethylene (UHMWPE) which is immovably attached to the tibial tray. Pivotal movement between the femoral component and the bearing surface of the bearing occurs with relatively low friction and low wear characteristics. It is also known to provide a mobile bearing which moves relative to the tibial tray. During deep flexion between the femur and tibia, the bearing rotates about a longitudinal axis associated with a pivot point at the attachment location between the bearing and tibial tray. While some designs allow for 360 degrees of rotation between the mobile bearing and the tibial tray, most designs have a rotational limit provided. Although known designs are adequate to allow limited rotation between the bearing and tibial tray, they may be relatively complex and thus expensive to manufacture. What is needed in the art is a tibial knee component with a mobile bearing which is easier to manufacture and still allows adequate movement between the bearing and tibial tray during deep flexion of the knee joint. A tibial knee component according to the preamble of Claim 1 is disclosed in EP-A-0 568 756. SUMMARY OF THE INVENTION The present invention provides a tibial knee component with a tibial tray, intermediate carrier and bearing which interconnect together and allow pivotal movement between the bearing and tibial tray. The invention comprises, in one form thereof, an orthopaedic knee component for implanting within a proximal tibia. A tibial tray includes a distally extending stem, a proximal tibial plateau and a post extending from the tibial plateau. The post defines an axis of rotation. An intermediate carrier has an opening in which the post is disposed. The carrier is pivotal about the axis of rotation. A bearing carried by the tibial tray has an articular bearing surface for engagement with a femoral component. The bearing has a recess in which the intermediate carrier is disposed. The projection, carrier and recess allow pivotal movement of the bearing relative to the tibial plateau about the axis of rotation. An advantage of the present invention is that the bearing is free to pivot relative to the tibial tray about an axis of rotation. Another advantage is that the bearing is inhibited from moving in an axial direction relative to the axis of rotation. Yet another advantage is that the keeper block inhibits radial movement of the carrier relative to the post. A further advantage is that the carrier includes a deflectable ramp which inhibits radial movement of the bearing relative to the post. BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: Fig. 1 is an exploded, perspective view of an embodiment of an orthopaedic knee component of the present invention; Fig. 2 is a bottom view of the bearing of Fig. 1 as viewed along line 2-2; Fig. 3 is a top view of the orthopaedic knee component of Fig. 1, with the bearing in a neutral position; Fig. 4 is a top view of the orthopaedic knee component of Fig. 1, with the bearing in a rotated position; Fig. 5 is a fragmentary, side, partially sectioned view taken along line 5-5 in Fig. 3; Fig. 6 is a fragmentary, front, partially sectioned view taken along line 6-6 in Fig. 3; and Fig. 7 is a side view of the orthopaedic knee component of Figs. 1 and 3-6, implanted within a tibia and engaged with a femoral component. Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, there is shown an embodiment of an orthopaedic knee component in the form of a tibial knee component 10 (Fig. 1) which is implanted within a proximal tibia 12 (Fig. 7). Tibial knee component 10 engages with a femoral component 14 which is implanted within a distal femur 16. Tibial knee component 10 includes a tibial tray 18, bearing 20 and intermediate carrier 22. Tibial tray 18 has a proximal tibial plateau 24 and a distally extending stem 26. Tibial plateau 24 has a generally planar proximal surface which extends transverse (e.g., generally orthogonal) to a longitudinal axis 28 of stem 26. A generally cylindrically shaped post 30 with a retainer 32 has an axis of rotation 34 which extends generally orthogonal to tibial plateau 24, and thus also extends generally parallel to axis 28 of stem 26. Tibial tray 18 also includes a keeper block 36 positioned adjacent to an anterior ledge 38. Keeper block 36 extends from tibial plateau 24 and inhibits movement of carrier 22 in a radial direction relative to post 30, as will be described in more detail hereinafter. Retainer 32 includes a radially extending flange which inhibits movement of intermediate carrier 22 in a direction generally parallel to axis of rotation 34. Intermediate carrier 22 has a longitudinal extension which extends between two longitudinally opposite ends 40, 42. An opening 44 is disposed adjacent to and in communication with end 40. Opening 44 has a diameter which corresponds to and is just slightly larger than the diameter of post 30. Post 30 is received within opening 44 such that intermediate carrier 22 is pivotable about axis of rotation 34, as indicated by assembly lines 46. Intermediate carrier 22 also includes a recess 48 positioned axially adjacent to opening 44. Recess 48 is sized and configured to receive retainer 32 therein when post 30 is positioned within opening 44 (Figs. 5 and 6). Intermediate carrier 22 also includes two side walls 50 which extend between first end 40 and second end 42. Each side wall 50 has an outwardly extending flange 52 which engages with bearing 20 and inhibits relative movement between bearing 20 and intermediate carrier 22 in a direction generally parallel to axis of rotation 34, as will be described in more detail hereinafter. Intermediate carrier 22 further includes a deflectable ramp 54. Ramp 54 is of cantilever construction (Fig. 5) and thus may be deflected in a direction away from bearing 20 when intermediate carrier 22 is coupled with bearing 20. Ramp 54 retains intermediate carrier 22 with bearing 20 and inhibits relative movement therebetween in a radial direction relative to axis of rotation 34. Bearing 20 has an articular bearing surface 56 for engagement with femoral component 14. Articular bearing surface 56 is disposed on either side of a center projection 58. Each discrete portion of articular bearing surface 56 on either side of center projection 58 engages a corresponding condyle of femoral knee component 14, with center projection 58 being disposed between the condyles. Bearing 20 also includes a generally slot shaped recess 60 in which intermediate carrier 22 is slidably disposed. Slot shaped recess 60 includes a first wall 62 and a second wall 64 which are positioned generally parallel to each other. First wall 62 and second wall 64 each include an undercut 66 which extends generally away from slot shaped recess 60. Each undercut 66 is sized and shaped to receive a corresponding flange 52 of intermediate carrier 22 therein. When coupled together, flanges 52 and undercuts 66 inhibit movement of bearing 20 relative to intermediate carrier 22 in a generally axial direction relative to axis of rotation 34. Bearing 20 also includes a hole 68 positioned in communication with slot shaped recess 60 Hole 68 is located within bearing 20 such that deflectable ramp 54 is received therein when intermediate carrier 22 is slid to a fully seated position within bearing 20 Since hole 68 extends through bearing 20 and is not a blind hole within bearing 20, any fluid which may accumulate within hole 68 is free to exit therefrom without building up pressure. To assemble tibial knee component 10, intermediate carrier 22 is positioned against tibial plateau 24 in the orientation shown in Fig. 1. Intermediate carrier 22 is then slid in a direction toward post 30 such that post 30 is received within opening 44. Intermediate carrier 22 is then rotated about axis of rotation 34 until second end 42 is positioned adjacent keeper block 36. Retainer 32 inhibits movement of intermediate carrier 22 in an axial direction relative to axis of rotation 34, while post 30 and keeper block 36 inhibit movement of intermediate carrier 22 in a radial direction relative to axis of rotation 34. Bearing 20 is then positioned against tibial plateau 24 adjacent first end 40 of intermediate carrier 22. Intermediate carrier 22 is slid into slot shaped recess 60 of bearing 20, such that flanges 52 are retained within undercuts 66. At a fully seated position, deflectable ramp 54 projects into hole 68 and thus inhibits sliding movement between bearing 20 and intermediate carrier 22 (i.e., in a direction radial to axis of rotation 34). Tibial knee component 10 may then be implanted within a prepared proximal tibia Of course, it will be appreciated that tibial tray 18 may be implanted within the proximal tibia when disassembled from intermediate carrier 22 and bearing 20. That is, intermediate carrier 22 and bearing 20 may be assembled with tibial tray 18 after tibial tray 18 is implanted within proximal tibia 12. While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.

Claims: An orthopaedic knee component for implanting within a proximal tibia, which comprises: a tibial tray (18) including a distally extending stem (26), and a proximal tibial plateau (24) an intermediate carrier (22); and a bearing (20) carried by said tibial tray and having an articular bearing surface 36 for engagement with a femoral component, said bearing having a recess 60 in which said intermediate carrier is disposed, characterised in that the tibial tray further comprises a post (30) extending from the tibial plateau and defining an axis of rotation (34) and in that the intermediate carrier (22) has an opening (44), said post received within said opening and said carrier pivotal about said axis or rotation, and in that said post, intermediate carrier and recess allow pivotal movement of said bearing relative to said tibial plateau about said axis of rotation. The orthopaedic knee component of claim 1, wherein said recess is generally slot shaped and said carrier is slidably disposed within said recess. The orthopaedic knee component of claim 1 or 2, wherein said bearing includes a hole and said carrier includes a deflectable ramp positioned within said hole. The orthopaedic knee component of claim 3, wherein said ramp is of cantilever construction. The orthopaedic knee component of any one of the preceding claims, wherein said carrier has a longitudinal extension with two longitudinally opposite ends, and said opening is disposed adjacent and in communication with one of said ends. The orthopaedic knee component of any one of the preceding claims, wherein said post includes a radially extending flange inhibiting movement of said carrier in a direction generally parallel to said axis of rotation. The orthopaedic knee component of any one of the preceding claims, wherein said recess includes a first wall and a second wall generally parallel to each other, at least one of said first wall and said second wall including an undercut, said carrier including at least one outwardly extending flange extending into a corresponding said undercut. The orthopaedic knee component of claim 7, wherein each said flange and said corresponding undercut define a means for inhibiting movement of said bearing relative to said carrier in a direction generally axial to said axis of rotation. The orthopaedic knee component of claim 7, wherein each of said first wall and said second wall include an undercut, and said projection includes two flanges which respectively extend into a corresponding said undercut. The orthopaedic knee component of any one of the preceding claims, wherein said tibial plateau includes an anterior ledge and a keeper block extending from said tibial plateau adjacent said anterior ledge, said carrier disposed between said post and said keeper block. The orthopaedic knee component of claim 10, wherein said keeper block defines a means for preventing movement of said carrier in a radial direction relative to said post. The orthopaedic knee component of any one of the preceding claims, wherein said carrier is substantially immovable relative to said bearing in a direction generally parallel to said axis of rotation. The orthopaedic knee component of claim 12, wherein said carrier is substantially immovable relative to said bearing in a rotative direction relative to said axis of rotation.

Inventors: HILEMAN DALE E, HILEMAN, DALE E.
Applicants: ZIMMER TECH INC, ZIMMER TECHNOLOGY, INC.
Application year: 2000
Main classification: A61F2
IPC codes: A61F2