Intervertebral disc prosthesis
View Patent ↗Intervertebral disc prosthesis including an upper apposition plate appropriate to rest against the base plate of an upper vertebra, a lower apposition plate spaced apart from the upper apposition plate and suitable to rest against the base plate of a lower vertebra, a plurality of elastic devices mounted between the two apposition plates and in their peripheral zones in a manner that the two apposition plates shall be displaceable in mutually resilient manner, and a central axis which runs essentially perpendicularly to the two apposition plates, the elastic devices being designed/configured in a manner that the intervertebral disc prosthesis as a whole exhibits asymmetrical stiffness.
1. An intervertebral disc prosthesis having a longitudinal axis, the prosthesis comprising:
a first plate having a first plate longitudinal axis, the first plate configured to engage a first vertebrae;
a second plate having a second plate longitudinal axis, the second plate configured to engage a second vertebrae; and
first and second helical spring elements disposed at least partially between the first and second plates, the first and second helical spring elements being coaxially aligned in a series along the longitudinal axis of the prosthesis, each of the first and second helical spring elements including a lumen defining a longitudinal axis such that the longitudinal axis of the first and second helical spring elements, the first plate longitudinal axis and the second plate longitudinal axis are all parallel to the longitudinal axis of the prosthesis;
wherein the first helical spring element has a first stiffness, and the second helical spring element has a second stiffness; and wherein the first stiffness is greater than the second stiffness.
2. The prosthesis of claim 1 , wherein the first helical spring element is comprised of a different material than the second helical spring element.
3. The prosthesis of claim 1 , wherein the first and second helical spring elements are substantially equally sized.
4. The prosthesis of claim 1 , wherein the first and second helical spring elements have substantially different cross-sections.
5. The prosthesis of claim 1 , wherein the first helical spring element is more tightly coiled than the second helical spring element.
6. The prosthesis of claim 1 , wherein the first and second plates are rectangular.
7. The prosthesis of claim 1 , wherein the first and second helical spring elements have mutually opposite turn pitches.
8. The prosthesis of claim 1 , wherein the first and second helical spring elements each include a plurality of turns and the first and second plates each include an elevation extending from an inner surface thereof, the elevation being parallel to the longitudinal axis of the prosthesis, each elevation including a plurality of boreholes running transversely to the longitudinal axis of the prosthesis, each borehole receiving one of the turns of the first and second helical spring elements.