The present invention provides plate systems for distracting and fixating vertebral bodies of animal (preferably human) spines. In some embodiments, the system includes: a biocompatible plate with at least two holes, at least two biocompatible distraction screws for insertion through the holes, each screw having an expandable head, a bore and a threaded shank, and at least two biocompatible fixating screws with threaded shanks. Insertion of the fixating screws into the distraction screws causes the expandable heads to expand and lock to the biocompatible plate. Optionally, the plate and the expandable heads comprises mating teeth configured to lock the expandable heads to the plate upon expansion of the expandable heads. The present invention also relates to use of the plate system to distract and fixate vertebral bodies.
