A spine stabilization prosthesis which supports the spine while providing for the preservation of spinal motion. The spine stabilization prosthesis incorporates a bone anchor having a deflectable post and a compound spinal rod which provide for load sharing while preserving range of motion and reducing stress exerted upon the bone anchors and spinal anatomy. The bone anchor includes a deflectable post connected by a ball-joint to a bone screw. The compound spinal rod includes a coupling mounted to the deflectable post and connected by a pivoting joint to a rod. The combined motions of the ball-joint and the pivoting joint support a range of motion of adjacent vertebrae which closely approximates the natural range of motion of the spine.