US Patent 9198695 Polyaxial pedicle screw

A polyaxial bone anchor including a housing, a bone screw, and a retainer for pivotably coupling the head of the bone screw to the housing. The retainer is positioned into the bore of the housing and includes a plurality of alternating tabs and slots circumferentially arranged to define a cavity for receiving the head portion of the bone screw therein. The retainer is axially moveable in the housing from a first position in which the head portion is not passable through the lower opening of the retainer to a second position in which the head portion is passable through the lower opening of the retainer.