The invention relates to a nucleus or inter-vertebral disc prosthesis that
comprises at least two plates capable of movement relative to each other
through at least one articulation interface defined by a female surface
and a male surface each having an essentially spherical shape and
essentially equal diameters. The two articulation surfaces are
respectively intersected by surfaces that define between them a relative
mobility space for the plates when the articulation surfaces are coapted;
the surface intersecting the female surface being contained in the volume
defined by an equatorial plane of said sphere except for said equatorial
plane itself, the surface intersecting the male surface being planar or
convex.