An implantable orthopedic assembly comprises a bone fixator and head assembly for securing a stabilizing rod to the spine. The head assembly allows multi-axial repositioning of the bone fixator relative to the head assembly. A primary drive interface located on the bone fixator may be used to adjust the depth of bone penetration when the bone fixator and head assembly are substantially coaxial. A secondary drive interface located on the head assembly may be used to adjust the depth of bone penetration while independently adjusting the stabilizing rod position when the bone fixator and the head assembly are not coaxial, transferring torsional loads to the bone fixator.
