An intervertebral spacer having opposing plates seatable against opposing
vertebral bones, separated by at least one spring mechanism, preferably a
spirally slotted belleville washer having a wide end rigidly fixed to an
upper plate and a narrow end rotatably mounted to a lower plate. The lower
plate includes an inwardly deflecting central post extending upwardly from
the inner surface of the lower plate, the post including a head that is
received through a central opening in the narrow end of the washer so that
the washer is restricted from angulation with respect to the lower plate,
but allowed to rotate with respect to the lower plate so that the plates
can rotate relative to one another. The plates can angulate relative to
one another because the washer deflects under lateral deflection forces
and return to its undeflected shape when the forces are relieved.
