A constrained spinal implant is inserted between adjacent vertebrae to function as an disk prosthesis. The prosthesis has two plates fastened to adjacent vertebrae facing each other. The facing sides of the plates each have a depending skirt formed as concentric arcs of about 90 degrees. The skirts are...http://www.google.de/patents/US20070162133?utm_source=gb-gplus-sharePatent US20070162133 - CONCENTRIC INTERIOR INSERT BALL AND DUAL SOCKET JOINT
