Abstract: An artificial disc includes an intermediate section which is disposed between upper and lower retainers. The intermediate section includes a first portion which resists rotation of one of the retainers, for example, the upper retainer, from a first position to a second position. A second portion of the intermediate section of the artificial disc resists rotation of the upper retainer from the second position to a third position. The second portion of the intermediate section of the artificial disc is ineffective to provide significant resistance to relative rotation between the retainers during rotation of the upper retainer relative to the lower retainer from the first position to the second position. The artificial disc may be provided with projections which engage protrusions on the intermediate section to resist rotation of the upper retainer relative to the lower retainer from the second position to the third position.