A fixation system may comprise at least one carriage element being capable of receiving one or more bone fasteners. The carriage element is mountable on a plate, and the plate has an engaging portion for adjustably securing the carriage element to the main plate. The engaging portion of the carriage...http://www.google.de/patents/US7479143?utm_source=gb-gplus-sharePatent US7479143 - Unidirectional fixation device
