The invention relates to a spinal disc endoprosthesis. The endoprosthesis has a resilient body formed of one or more materials which may vary in stiffness from a relatively stiff exterior annular gasket portion to a relatively supple central nucleus portion. Concaval-convex elements at least partly surround...http://www.google.es/patents/US6001130?utm_source=gb-gplus-sharePatente US6001130 - Human spinal disc prosthesis with hinges
