Patent ID: 7641693

Claim:
An intervertebral implant comprising: a lower implant part having a hollow cylindrical cavity with an outer casing and an axis of rotation, and an apposition part intended for contacting a covering surface of an adjoining lower vertebra, the cavity in communication with a depression extending through the outer casing; an upper implant part having an essentially circularly, cylindrical shaft having an external thread and an axis of rotation, and an apposition part intended for contacting a covering surface of an adjoining upper vertebra, wherein the shaft extends into the cavity of the lower implant part; and a circular ring with an internal thread which is disposed between the upper implant part and the lower implant part and interacts with the external thread of the upper implant part, wherein the upper implant part and the lower implant part are secured to prevent rotation about the axis of rotation, wherein the upper implant part, the lower implant part and the ring are disposed coaxially along the axis of rotation, so that by rotating the ring on the external thread of the shaft, a distance between the two apposition parts can be variably changed, wherein the ring includes a toroidal undercut and the outer casing of the lower implant part includes an annular bead, the toroidal undercut mates with the annular bead so that the ring is axially fixed but rotatively movably with the lower implant part, the toroidal undercut and the annular bead forming a continuous cylinder about the intervertebral implant; and wherein the ring has an outer surface, an inner surface, a lower annular surface facing the lower implant part and an upper annular surface facing the upper implant part, the ring including a straight-cut ring gear suitable for accommodating a corresponding pinion, the straight-cut ring gear extending from the outer surface to the inner surface, and from the lower annular surface thereof.