A modular polyaxial pedicle screw and orthopaedic rod implant device including same includes a shaft portion, a cuff, a stem portion, and a rod coupling sub-assembly. The shaft portion is designed to be inserted into the pedicle, has a recess formed in its top, and includes a threading formed on the exterior surface around the recess. The stem portion is a threaded post having an enlarged ball formed at the base thereof, the ball being ideally suited to polyaxially rotate within the recess of the shaft. The cuff is a cylindrical element designed to seat around the interface of the ball portion of the stem and the recess of the shaft, initially so that the stem and shaft may polyaxially rotate relative to one another, and subsequently to hold the stem and shaft in final securement. The rod coupling sub-assembly consists of a rod coupling element which is mountable on the post portion of the stem, and a top locking nut which secures the rod coupling element to the post between the nut and the cuff. Spacer elements may be utilized which are positioned on the post between the cuff and the rod coupling element to permit axial variability on the stem in addition to the angular variability inherent in the shaft and stem interface.