US Patent 7909876 Intervertebral disc prosthesis with shear-limiting core

An intervertebral disc prosthesis comprises a superior endplate, an inferior endplate, and an intermediate core positioned between the endplates. The core comprises a central disc portion and a radial flange. The central disc portion of the core is defined by a superior bearing surface and inferior bearing surface. The radial flange of the core includes a first portion that extends radially outward from the central disc portion of the core. The radial flange also includes a second portion that extends axially from the first portion of the flange. The second portion of the flange extends a substantially greater distance toward the inferior endplate than toward the superior endplate. In one embodiment, the second portion of the flange extends completely to the inferior endplate and engages the inferior endplate when the inferior endplate is in a neutral position relative to the core.