US Patent 7686835 Pedicle screw system with provisional locking aspects

A tulip assembly configured to be coupled to a head of a bone fixation device includes at least one inner member configured to fix the tulip assembly to the head of a bone fixation device, and an outer member including at least one engagement surface configured to selectively fix a rod in the tulip assembly via rotation of the outer member, wherein the fixation of the tulip assembly to the head of the bone fixation device is independent of the fixation of a rod in the tulip assembly.