A locking pedicle screw assembly has been designed which avoids misalignment and locks into place once the cap is fully threaded into the tulip, avoiding over tightening or stripping of the threads. The locking cap includes a retaining or locking ring, positioned either at the bottom of the cap so that it locks into a groove at the bottom of the threads in the tulip or at the top of the threads in the cap, locking into a groove at the top of the tulip when the cap is fully seated. In one embodiment, an audible signal is generated when the cap locks. In another embodiment, the cap is secured to a swiveling saddle that locks the rod into place as the screw cap is tightening, but does not interfere with the locking mechanism.