An artificial disc replacement (ADR) includes a pair of opposing endplate
components, each attached to one of the upper and lower vertebrae, a
cushioning component disposed between the endplate components; and a
filler material contained within the cushioning component. The filler
material may be a gas, liquid, foam, or gel, including a hydrogel. In a
preferred embodiment, the ADR may further include one or more opposing,
spaced-apart projections configured to impinge if the endplate components
are subjected to an excessive force. Such projections may allow for
unrestricted motion between the endplates until impingement, or may
restrict translation between the endplates until a greater excessive
force is reached. One or both of the endplate components may include a
modified surface to increase adherence to the respective vertebral
endplates.