The invention is a pedicle screw assembly (10) for use with a rod (11) for the immobilization of bone segments. The assembly is composed of a screw (12), a poly-axial housing (20), a washer (34), a set screw (48), and a cup shaped washer (40). When the screw is placed inside the poly-axial housing (21), the head of the screw (12) comes into contact with a middle section of the poly-axial housing (18), and is secured into the bone so that the poly-axial housing is pivotable. The housing includes a pair of upstanding posts (38) with interior threads. A washer (24) is inserted between the head of the screw (12) and the rod. A cap (40), having a bottom with a pair of openings (43) and a lateral cross connector (44), is placed over the posts (38) so that the cross connector (44) engages the rod. The cross connector and washer have semi-cylindrical rod engaging surfaces. A set screw (42) is threaded into the housing posts to secure the rod.