Methods and devices are provided for replacing a nucleus of a spinal disc,
and in particular for preventing nucleus disc replacement expulsion. The
nucleus of a spinal disc can be removed from the annulus by forming a
small opening in the annulus. Once the nucleus is removed, one or more
insert devices can be implanted within the annulus of a spinal disc and
they can be mated to one or both endplates of the adjacent vertebrae. The
insert(s) is configured to interact with a nucleus disc replacement
implant to prevent expulsion of the implant from the annulus.