Prosthesis for restoring motion in an appendage or spinal joint and an intervertebral spacer
View Patent ↗A motion restoring prosthesis to be interposed between the ends of two bones adjoining a mammalian appendage or spinal joint is formed of two components with the components having inner cooperating articulating surfaces and outer bone engaging surfaces. At least one of the components has an inner section made of relatively hard, stiff material defining one or the articulating surfaces and an outer section made of a softer material defining the bone engaging surface. The softer material having a hardness/stiffness characteristic compatible with the bone to reduce stress shielding and more evenly distribute the forces from the articulating surfaces to the associate bone interface.
1. A motion restoring prosthesis to be interposed between the ends of mammalian bones adjoining a natural appendage or spinal joint to provide articulation therebetween comprising:
two components, each component defining an outer surface for attachment to a respect bone end and an articulating surface for engaging the articulating surface of the other component;
at least one of the components having an inner and outer section, the inner section defining the articulating surface and being formed of a primary, relatively hard, stiff material having a first flexural modulus, the outer section defining a bone facing surface to be attached to one of the bone ends and formed of a secondary softer material having a second flexural modulus, the first flexural modulus being greater than the second flexural modulus, the outer section functioning as a stress softening material to more evenly distribute the forces from the articulating surfaces to the associated bone end, wherein the bone facing surface of said at least one component has been roughened and/or made uneven to enhance an attachment of adjacent bone and covered with a thin coating of Ti within a range of 0.5 to 15 microns in thickness to enable bone-on growth while maintaining an appropriate distribution of forces through the thin coating of Ti to permit the stress shielding characteristic of the coated secondary softer material to be operative.
2. The motion restoring prosthesis of claim 1 wherein the first flexural modulus is about 70 or greater on the GPa scale and the second flexural modulus is about 60 or less on the GPa scale.
3. The motion restoring prosthesis of claim 1 wherein the secondary material is PEEK with or without the presence of carbon fiber reinforcement.
4. The motion restoring prosthesis of claim 1 wherein the other component also includes an inner section which corresponds in structure to the inner and outer sections of said at least one component.
5. The motion restoring prosthesis of claim 4 wherein the primary and secondary materials have a flexural modulus on the GPa scale of about 80 or more and 60 or less, respectively.
6. The motion restoring prosthesis of claim 5 wherein the prosthesis is an artificial spinal disc with the bone facing surfaces being generally planar to buttress respective vertebral bodies.
7. The motion restoring prosthesis of claim 1 wherein the secondary material has a flexural modulus on the GPa scale within the range of about 4-25.
8. The motion restoring prosthesis of claim 1 wherein the secondary material partially encapsulates the primary material to substantially prevent macromotion between the inner and outer sections of the components.
9. The motion restoring prosthesis of claim 8 wherein the secondary material is partially encapsulated around the primary material by an injection molding process.
10. The motion restoring prosthesis of claim 1 wherein the coating of Ti is within a range of 0.5 to 3.0 microns.
11. The motion restoring prosthesis of claim 10 wherein the bone facing surface has a micro surface roughening.
12. A motion restoring prosthesis or intervertebral spacer including a bone buttressing material having a GPa flexural modulus of about 60 or less and defining a bone buttressing surface, the bone buttressing surface functioning as a stress softening material, said surface being roughened or made uneven when abutted against the bone, to enhance an attachment of adjacent bone and covered with a thin coating of Ti within a range of 0.5 to 15 microns in thickness to enable bone-on growth while maintaining an appropriate distribution of force through the thin coating of Ti to permit the stress shielding characteristics of the bone buttressing surface to be operative.
13. The invention of claim 12 wherein the bone buttressing material is made of PEEK or CRFPEEK with a GPa flexural modulus within the range of about 4-30.
14. The invention of claim 13 wherein the GPa flexural modulus of the bone buttressing material is about 17±5−8.
15. The invention of claim 12 wherein the bone facing surface has a micro surface roughening.
16. The invention of claim 15 wherein the bone facing surface has a micro surface roughening.
17. An intervertebral spacer for replacing a natural disc, the spacer being formed of a material which has a GPa flexural modulus within the range of about 4-40 and defining opposing bone buttressing surfaces which are roughened or made uneven to enhance an attachment of adjacent bone and coated with a thin micron coating of a titanium bone-on growth enhancing material within a range of 0.5 to 15 microns in thickness which does not adversely affect bone stress transfer characteristics of the bone buttressing material.
18. The invention of claim 17 wherein the spacer material comprises PEEK or CRFPEEK with a GPa flexural modulus of about 17±5−8.
19. The invention of claim 17 wherein the bone facing surface has a micro surface roughening.
20. The invention of claim 19 wherein the bone facing surface has a micro surface roughening.