A modular head bone screw assembly has a bone screw, a tulip and a saddle. The saddle is positioned in a recess inside of the tulip. The saddle has a proximal end for engaging a rod and a distal end for receiving a hemispherical or at least partial hemispherical head of the bone screw. The saddle is sized to move axially inside the tulip. The saddle has a plurality of fingers separated by slots extending from near the proximal end through the distal end in an initial un-loaded position and upon insertion of the tulip over the head of the bone screw, the saddle moves proximally over the head simultaneously causing the fingers to move past a maximum diameter of the hemispherical head and upon tightening the rod by a set screw, the fingers locking the bone screw into the tulip.
