An implant for insertion between vertebral members in which an inner member, intermediate member, and outer member are concentrically disposed. The inner and outer members may comprise end plates to contact the vertebral members. The outer member may include a tapered interior wall. A locking element is movably contained within an opening that extends through a sidewall of the intermediate member. The intermediate member is displaceable longitudinally in first and second directions relative to the outer member. Displacement of the intermediate member in the first direction tends to force the locking element laterally into contact with the inner and outer members. A biasing member may urge the intermediate member in the first direction. Displacement of the intermediate member in the second direction allows the locking element to be laterally displaced out of contact with the inner member.