Bone plate system

A method of securing a bone plate to a bone using a preassembled bone anchor assembly, the method comprising:

• connecting the preassembled bone anchor assembly to a driver, the preassembled bone anchor assembly including a bone anchor having an uppermost end and a lowermost end and a longitudinal axis extending therebetween, the preassembled bone anchor assembly further including a locking cap distinct from the bone anchor that is assembled with the bone anchor and a locking member distinct from the bone anchor that is assembled with the bone anchor, the locking cap extending around the uppermost end of the bone anchor and the locking member, the locking cap including a radially outer portion of the locking cap and a plurality of projections extending radially inward from the radially outer portion, wherein the locking cap of the preassembled bone anchor assembly is retained on the bone anchor to inhibit relative axial movement of the locking cap along the bone anchor in either an upward axial direction or a downward axial direction;
• advancing, using the driver, a shank of the bone anchor of the preassembled bone anchor assembly through a throughbore of the bone plate and into the bone;
• locating a rigid head portion of the bone anchor and the locking cap assembled with the bone anchor in the throughbore of the bone plate so that the locking cap contacts a throughbore surface of the bone plate;
• shifting the radially outer portion of the locking cap radially outward against the throughbore surface of the bone plate to secure the preassembled bone anchor assembly relative to the bone plate and secure the bone plate relative to the bone by shifting the locking member, using a second driver, along the bone anchor rigid head portion which causes the locking member to urge the plurality of projections of the locking cap radially outward;
• and
• urging a radially inner portion of the locking cap radially inward against the bone anchor rigid head portion by shifting of the locking member along the bone anchor rigid head portion which causes the locking member to urge the projections radially outward.