A bone screw extension assembly for use in placing a connecting rod percutaneously into tissue of a patient comprises a multi-axial bone screw and a screw extension releasably coupled to yoke of the bone screw. The screw extension includes coaxially disposed outer sleeve and inner sleeves that are movable axially relative to each other. A screw engaging member projects radially from the distal end of the inner sleeve and is configured to releasably engage an extension coupling surface on the inner surface of opposed upstanding arms of the yoke. A securement member including cooperative surfaces is defined adjacent the distal end of the inner and outer sleeves that is operable upon relative axial movement of the inner and outer sleeves to radially secure the sleeves together for minimization of splaying and to thereby maintain the engagement of the screw engaging member and the bone screw.