A spinal implant system comprises at least two fixation elements, each including a threaded bone-engaging portion, and at least two corresponding receiver members, each including two branches defining a U-shaped channel configured to receive an elongated member. The receiver members are positionable...http://www.google.es/patents/US20080154308?utm_source=gb-gplus-sharePatente US20080154308 - Spinal fixation system
