An expandable intervertebral implant (10) includes a first member (20), a second member (40), and a collar operatively associated with the first and second members, wherein the collar includes a threaded mechanism so that rotation of the collar causes the second member to axially move with respect to the first member. The implant includes a ratchet mechanism (50, 80) so that when at least a predetermined amount of force is applied, the second member moves with respect to the first member in an axial, ratchet-type manner. The collar preferably includes a drive ring (50) rotatably attached to the first member and a ratchet ring (50) operatively associated with the drive ring. The ratchet ring includes an inner bore having at least one corresponding ratchet thread tooth form formed thereon for engaging a ratchet thread tooth form formed on the second member.