In one aspect, a bone anchor assembly is provided having a bone anchor with a head, a resilient locking cap extending about a portion of the bone anchor head, and a cap drive member having a depending annular wall. The annular wall and locking cap have engagement surfaces configured to engage and expand the locking cap as the cap drive member is shifted from an unlocked to a locked position. In another form, a bone plate system is provided including a bone plate having an elongated throughbore and a resilient support member received therein. The support member has an opening sized to receive a bone anchor head and an actuator device carried thereon. The bone plate and support member have interfering portions configured to be shifted to a locked orientation to lock the support member and the bone anchor head at an axial position in the throughbore.
