Patent ID: 7628814

Claim:
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.