Metallic bearings for joint replacement
View Patent ↗An orthopedic prosthesis comprising a first component having a soft metal bearing surface and a second component having a hard metal bearing surface, in particular a hip prosthesis comprising a spherical bearing member, a femoral stem, and a modular neck configured for interposition between the spherical bearing member and the stem, together with an acetabular implant having a concave bearing surface configured for articulation with the spherical bearing member. One of the spherical bearing member and the concave bearing surface comprises a soft metal bearing surface, the soft metal bearing surface having a hardness of at least about 20 Rc, while the other one of the spherical bearing member and the concave bearing surface comprises a hard metal bearing surface, the hard metal bearing surface having a hardness greater than the soft metal bearing surface by at least about 15 Rc.
1. A hip prosthesis comprising:
a spherical bearing member, said spherical bearing member having a neck recess therein,
a femoral stem, said femoral stem having a recess adjacent a proximal end thereof,
a modular neck member, a proximal end of said modular neck member configured to fixedly engage said neck recess of said spherical bearing member, a distal end of said modular neck member configured to fixedly engage said recess of said stem,
an acetabular implant having a concave bearing surface configured for articulation with said spherical bearing member,
wherein one of said spherical bearing member and said concave bearing surface comprises a soft metal bearing surface of cobalt chrome alloy, said soft metal bearing surface having a hardness of at least about 20 Rc, and
wherein said other one of said spherical bearing member and said concave bearing surface comprises a hard metal bearing surface of cobalt chrome alloy, said hard metal bearing surface having a hardness greater than said soft metal bearing surface by at least about 15 Rc, such that there is a hardness differential between said spherical member and said concave bearing surface to thereby reduce wear of said hip prosthesis.
2. The prosthesis of claim 1 , wherein the differential hardness of said hard metal bearing surface to said soft metal bearing surface is at least about 1.5.
3. The prosthesis of claim 1 , wherein the differential hardness of said hard metal bearing surface to said soft metal bearing surface is between about 1.5 and about 3.
4. The prosthesis of claim 1 , wherein said hard metal bearing surface is not more than about 40 Rc harder than said soft metal bearing surface.
5. The prosthesis of claim 1 , wherein said hard metal bearing surface has a hardness of between about 40 Rc and about 60 Rc.
6. The prosthesis of claim 1 , wherein said spherical bearing member comprises said hard metal bearing surface and said concave bearing member comprises said soft metal bearing surface.
7. The prosthesis of claim 1 , wherein said cobalt chrome alloy of said soft metal bearing surface conforms to ASTM F75 and said cobalt chrome alloy of said hard metal bearing surface conforms to ASTM 1537.
8. The prosthesis of claim 1 , wherein said hard metal bearing surface is heat treated to increase hardness of said hard metal bearing surface.
9. The prosthesis of claim 1 , wherein said spherical bearing member has a diameter of between about 40 mm to about 60 mm.
10. The prosthesis of claim 1 , wherein said spherical bearing member has a diameter of about 54 mm.
11. The prosthesis of claim 4 , wherein said hard metal bearing surface has a hardness of between about 40 Rc and about 60 Rc.
12. The prosthesis of claim 11 , wherein said spherical bearing member comprises said hard metal bearing surface and said concave bearing member comprises said soft metal bearing surface.
13. The prosthesis of claim 12 , wherein said cobalt chrome alloy of said soft metal bearing surface conforms to ASTM F75 and said cobalt chrome alloy of said hard metal bearing surface conforms to ASTM 1537.
14. The prosthesis of claim 1 , wherein said soft metal bearing surface has a hardness of between about 25 Rc to about 35 Rc.
15. The prosthesis of claim 1 , wherein said recess of said femoral stem is tapered.
16. The prosthesis of claim 15 , wherein said recess of said femoral stem has an oval cross-section.
17. The prosthesis of claim 15 , wherein said recess of said femoral stem has a race track configuration in cross-section, said race track configuration having opposing flat sides and opposing curved portions.
18. The prosthesis of claim 15 , wherein an axis of said distal end of said modular neck is coincident with an axis of said recess of said femoral stem.
19. The prosthesis of claim 18 , wherein an axis of said proximal end of said modular neck is axially aligned with an axis of said distal end of said modular neck.
20. The prosthesis of claim 18 , wherein an axis of said proximal end of said modular neck is axially offset from an axis of said distal end of said modular neck.