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 polyaxial housing 20, a washer 34, a set screw 48, and a cup-shaped cap 40. When the screw is placed inside the polyaxial housing 20, the head of the screw 18 comes into contact with a middle section of the polyaxial housing 20 and is secured into the bone so that the polyaxial housing is pivotable with three degrees of freedom. The housing includes a pair of upstanding posts 30 with interior threads. A washer 34 is inserted between the head of the screw 12 and the rod. A cap 40, having a bottom, with a pair of posts accommodating openings 43 and a lateral cross connector 44, is placed over the posts 30 so that the cross connection 44 engages the rod. A set screw 48 is threaded into the housing posts to secure the rod within the housing.