US Patent 8628558 Uni-planer bone fixation assembly

A bone fixation assembly includes a plurality of bone fixation elements that each include a bone anchor configured to be implanted into underlying bone, such as a vertebra. Each bone anchor is received in an anchor seat, and the anchor seats are joined by a fixation rod so as to operatively couple and fix the position and orientation of the vertebrae relative to each other. The bone anchor is free to rotate relative to the anchor seat, and is also free to pivot in a desired direction relative to the anchor seat.