A method of securing a fixation rod to a screw assembly that includes a screw, a bushing, and a receiver includes the steps of inserting the fixation rod within a receiver portion of the bushing and the receiver, advancing a locking member into contact with an engagement surface on a proximal portion of the bushing, applying a force with the locking member to increase an amount of friction between a distal engagement surface of the bushing and a head portion of the screw, and increasing the force to deform a deformable portion of the bushing and increase an amount of friction between the fixation rod and the bushing.