A multi-piece disc replacement implant device for replacing a disc removed
by a discectomy including an upper plate member, a lower plate member,
and an intermediate resilient member providing movement between the two
plate members replicating the natural movement of the spine including
flexion/extension, lateral bending, and, in some embodiments, rotation.
The plate members are rigid and have orthogonal sidewalls forming an
enclosure. The resilient member is an elastic solid or a multi-chamber
balloon structure of fluid-filled sacks that collectively define a
non-uniform shape such as an oblate spheroid, or a helically coiled
string of beads. Such an implant is capable of supporting the compressive
and cyclic loads required of a natural disc. The upper and lower plate
members are cooperatively formed to selectively limit the allowable range
of motion in any given direction. Alternate embodiments of the invention
may be employed in conjunction with removal of the nucleus pulposus when
removal of the annulus fibrosus (annulotomy) is not required or
desirable.