Patent ID: 8257442

Claim:
An intervertebral spacer comprising: first and second members each with an outer side and an inner side, the members positioned in a stacked orientation with the inner sides facing together; a threaded extension that extends outward from the inner side of the first member; a cavity formed on the inner side of the second member, the cavity including a floor opposite from an open side; a ring gear positioned in the cavity and against the floor, the ring gear including a threaded bore that receives the threaded extension and teeth that extend around an outer circumference; a worm gear positioned in the cavity and including helical teeth that engage with the teeth on the ring gear, the worm gear being rotatably positioned in the cavity with rotation in a first direction causing the first and second members to move apart and rotation in a second direction causing the first and second members to move together; and a longitudinal axis of the ring gear being offset from a longitudinal axis of the threaded extension such that the axes do not intersect.