Artificial disc devices are disclosed that restore correct anatomical
intervertebral spacing for damaged discs while maintaining a substantially normal
range of biomechanical movement for the vertebrae between which they are implanted.
The disc devices include center bearing and outer or annular bearing portions with
the center bearing portion including generally axially extending locating surfaces
which cooperate with the facing vertebral surfaces to resist migration. The outer
bearing portion is for load bearing or load sharing with the center bearing portion
and includes surfaces that extend radially toward the periphery of the vertebrae
so that subsidence about the center bearing portion is minimized. Alternate forms
of the disc devices include one with an axially enlarged center ball bearing having
an annular ring bearing extending thereabout and another having upper and lower
plate members with a central bumper member and a surrounding resilient annular
member therebetween.