MENISCAL BEARING PLATFORM AND BEARINGS FOR JOINT ENDOPROSTHESIS

Abstract: A prosthetic joint is provided including a meniscal bearing platform (10), bearing components (26, 28), and a femoral component (50). The tibial platform (10) is formed to allow for sliding movement of the bearing components (26, 28) thereabout. The movement of the bearing components (26, 28) is constrained to a predetermined path of movement by the combination of a raised portion (16) extending from the tibial platform (10), as well as lateral constraint provided by the femoral component (50).

Description: MENISCAL BEARING PLATFORM AND BEARINGS FOR JOINT ENDOPROSTHESIS This application claims priority on U.S. Provisional Appl. No. 60/050,291, filed June 20, 1997. BACKGROUND OF THE INVENTION A well-known bearing platform and meniscal bearing combination is disclosed in U.S. Patent Nos. 4,309,778, and 4,340,978, to the same inventors of this application. U.S. Patent Nos. 4,309,778 and 4,340,978, are incorporated by reference herein for a complete and thorough disclosure of the prior art design. Briefly, referring to FIGS. 1-4 herein, a tibial platform 116 is formed to define two curved tracks 148, 153. Each of the tracks 148, 153 is formed by raised portions 169 and 171, and 169 and 170, respectively, and cross- sectionally defines a dovetail configuration. Projections 149, 172 extend from the inferior surface of the platform 116 and are provided to help distribute joint loads, supply additional load transfer to the cancellous bone, and provide resistance against possible tensile loading. Additionally, two tibial bearing components 117 are also provided to be disposed in the tracks 148, 153. As shown in FIGS. 3-4, each of the bearing elements 117 is formed with a primary load bearing surface 141 on its superior side and a second bearing surface 142 on its inferior side. Each of the second bearing surfaces 142 includes a flat surface 143 and a projecting dovetail surface 144. The dovetail surface 144 is cross-sectionally formed to substantially the same dimensions as the dovetail configuration defined by each of the tracks 140, 153. As can be seen in FIG. 4, the dovetail surface 144 extends longitudinally over a substantial portion of the length of the bearing component 117 and is curved with the same radius of curvature as each of the respective tracks 148, 153. It is to be understood, that the tracks 140, 153 curve symmetrically about the platform 116, and, each of the bearings is formed to curve in a similar fashion. With the dovetail surfaces 142 of the bearing components 117 being interengaged with the dovetail configurations of the tracks 148, 153, anterior-posterior shift of the bearing elements 117 relative to the platform 116 is attainable. Although the above-described prior art design has many positive features, there is a constant need in the field of endoprosthetics to enhance the load- bearing capabilities of an endoprosthesis . SUMMARY OF THE INVENTION To meet the above-identified need, a combination of a new and improved meniscal bearing platform and bearing components is provided for use in a prosthetic joint. The combination is used in conjunction with a femoral component. The prior art bearing platform, as shown in FIGS. 1-2, is formed for mounting onto a resected tibia. The platform of the subject application does not include the lateral track walls that had been included in the prior art bearing platform and that are designated by reference numerals 170, 171 in FIG. 2. Rather the platform of the subject invention includes a central raised portion having curved longitudinal edges which are each formed with a dovetail type configuration . Two bearing components are provided, each formed with a bearing surface on its superior side, and a bearing surface on its inferior side. For each of the bearing components, only a partial dovetail configuration is formed along a single edge thereof. Specifically, each of the bearing elements is formed with an inner edge having a dovetail configuration formed therein which mates with one of the edges of the raised portion formed on the platform. The mating dovetail configurations provide dislocation resistance for the platform and bearing elements combination. The outer edges, however, of the bearing elements are formed smoothly, with no such dovetail configuration. Consequently, the inferior bearing surface of each of the bearing elements, which is in contact with the platform, is larger in area as compared to the prior art design. Also the bearing elements of the subject invention are each formed thicker in a superior to inferior direction in the region of highest loading as compared to the prior art design. This greater thickness is attributable to the absence of a dovetail at the lateral and medial extremes of the prosthesis. Thus, this design is more robust than the prior art. The movement of the bearing components relative to the central raised portion of the tibial platform is constrained by the femoral component. The femoral component, prevents radially outward movement of the bearing components whereas, the central raised portion prevents radially inward movement of the bearing components . These and other features of the invention will be better understood through a study of the following detailed description and accompanying drawings . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional view of a prior art tibial platform. FIG. 1 is taken from FIG. 15 of U.S. Patent No. 4,309,778. FIG. 2 is a plan view of the prior art tibial platform. FIG. 2 is taken exactly from FIG. 16 of U.S. Patent No. 4,309,778. FIG. 3 is a cross-sectional view of a prior art bearing element. FIG. 3 is taken from FIG. 19 of U.S. Patent No. 4,309,778. FIG. 4 is a bottom plan view of the prior art bearing element. FIG. 4 is taken from FIG. 21 of U.S. Patent No. 4,309,778. FIG. 5 is a top plan view of the new and improved tibial platform of the subject application. FIG. 6 is a bottom plan view of the new and improved tibial platform of the subject application. FIG. 7(A) and 7(B) are top and bottom views of the new and improved bearings of the subject application. FIG. 8 is a plan view of the bearings disposed on the tibial platform of the subject application. FIG. 9 is a side view of a prosthesis including the tibial platform and bearing elements of the subject application. FIG. 10 is a front plan view of a prosthesis including the tibial platform and bearing elements of the subject application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring generally to FIGS. 5, 6 and 9, a tibial platform 10 is provided having a superior surface 12, an inferior surface 14 and an edge surface 15. As can be seen from FIG. 10, a raised portion 16 extends centrally from the superior side 12 of the platform 10 in an anterior-posterior direction. The side edges 18, 20 of the raised portion 16, as shown in FIG. 10, each are formed to define an arcuate dovetail- type surface. Referring to FIG. 5, the side edges 18, 20 are curved in opposite directions along the longitudinal length of the platform 10. The tibial platform 10, the raised portion 16, and the side edges 18, 20 are formed in accordance with the teachings of U.S. Patent Nos. 4,309,778 and 4,340,978. Surface portions 21, 23, respectively, extend laterally from the raised portion 16 to the portions of the edge surface 15 located at lateral-most portions of the tibial platform 10. Surface portions 21, 23 are preferably planar, but can also be formed to define other shapes. As can be seen from FIGS. 9-10, projections 22,24 extend from the inferior surface 14 of the platform 10. The projections 22, 24 are also formed in accordance with U.S. Patent Nos. 4,309,778 and 4,340,978. Two bearing elements 26, 28 are also provided, which are preferably formed from a thermoplastic material. Each of the bearing elements 26, 28 has a superior bearing surface 30 and an inferior bearing surface 32. Although reference is only to the bearing element 26 in FIGS. 7(A) and 7(B), it is to be understood the bearing element 28 is formed identically. As best can be seen in FIG. 10, the bearing elements 26, 28 each are formed with an inner edge 34 having substantially the same dovetail-type configuration as the side edges 18, 20 of the raised portion 16 of the platform 10, but are oriented as a mirror image, to allow face-to-face engagement of the side edges 18 and 34, and inner edges 20 and 34, respectively. As shown in FIGS. 7(A) and 7(B), the inner edges 34 of the bearing elements 26, 28 are curved in a similar fashion to the side edges 18, 20 of the raised portion 16 of the platform 10. Consequently, as shown in FIGS. 8-10, the bearing elements 26, 28 are disposed on the platform 10 with the respective inner edges 34 in mating contact with the side edges 18, 20, respectively, of the raised portion 16, with the inferior bearing surfaces 32 of the bearing elements 26, 28 being in face-to-face engagement with the superior surface 12 of the platform 10. Each of the bearing elements 26, 28 is also formed with an outer edge 36 which is not formed with a dovetail configuration and is preferably flat. As shown in FIG. 10, since the outer edge 36 is not formed with a dovetail configuration, the thickness of solid material forming the bearing elements 26, 28, as measured between the respective superior bearing surfaces 30 and the inferior bearing surfaces 32, is greater in proximity to the outer edge 36 than to the inner edge 34. The superior bearing surfaces 30 of the bearing elements 26, 28 are formed to engage in articulation with at least portions of a bearing surface 52 of a femoral component 50. The femoral component 50 constrains movement of the bearing elements 26, 28 about the raised portion 16. The bearing surface 52 of the femoral component 50 and the respective superior bearing surfaces 30 of the bearing elements 26, 28 are formed as in U.S. Patent Nos. 4,309,778 and 4,340,978 and as such the interengagement therebetween provides lateral constraint for the bearing elements 26, 28. With reference to FIG. 8, the bearing elements 26, 28 may move along a path defined adjacent the raised portion 16, as designated by the arrow 54, but not in radially inward directions (as represented by arrow 56) due to constraint by the raised portion 16, or in radially outward directions (as represented by arrow 58) due to constraint by the femoral component 50.

Claims: WHAT IS CLAIMED IS; 1. A prosthetic joint comprising: a tibial platform having a first superior bearing surface, a first inferior bearing surface, and an edge surface extending therebetween, said first inferior bearing surface being formed for attachment to a bone, said first superior bearing surface being formed with a raised portion extending therefrom, said raised portion extending in an anterior-posterior direction, and said first superior bearing surface being formed with surface portions extending laterally from said raised portion to portions of said edge surface located at lateral-most portions of said tibial platform; and two bearing elements, each having a second superior bearing surface and a second inferior bearing surface, said second inferior bearing surface being formed to slidably engage said first superior bearing surface of said tibial platform for sliding movement relative thereto. 2. A prosthetic joint as in claim 1, further comprising a femoral component having a third superior bearing surface formed for sliding articulation with said second superior bearing surfaces of said bearing elements, said femoral component being formed to constrain sliding movement of said bearing elements to a predetermined path relative to said raised portion. 3. A prosthetic joint as in claim 1, wherein said raised portion is elongated, and wherein said raised portion is formed to define curved side edges. 4. A prosthetic joint as in claim 3, wherein said bearing elements are each formed with an inner edge and an outer edge, said inner edge being curved and defining the same radius of curvature as said side edges . 5. A prosthetic joint as in claim 4, wherein said inner edges of said bearing elements are in dovetail engagement with said side edges of said raised portion. 6. A prosthetic joint as in claim 1, wherein said bearing elements are each formed with an inner edge and an outer edge, said inner edge being disposed to face said raised portion, and wherein each said bearing element is formed with a greater thickness of solid material adjacent to said outer edge than said inner edge, said thickness being measured in a direction extending between said second superior bearing surface and said second inferior bearing surface. 7. A prosthetic joint as in claim 2, wherein said predetermined path of sliding movement of said bearing elements is curvilinear, wherein said raised portion constrains movement of said bearing elements in radially inward directions relative to said predetermined path, and wherein said femoral component constrains movement of said bearing elements in radially outward directions relative to said predetermined path. 8. A prosthetic joint as in claim 1, wherein said surface portions are substantially planar.

Inventors: BUECHEL FREDERICK F, PAPPAS MICHAEL J, BUECHEL, FREDERICK, F., PAPPAS, MICHAEL, J.
Applicants: BUECHEL FREDERICK F, PAPPAS MICHAEL J, BUECHEL, FREDERICK, F., PAPPAS, MICHAEL, J.
Application year: 1998
Main classification: A61F2
IPC codes: A61F2