Patent ID: 8221472

Claim:
A bone anchor for attaching a fixation element to a bone, the bone anchor comprising: an anchor member having a head portion and a bone engaging portion for attachment to the bone; an anchor head having a top portion, a bottom portion and a hollow interior bore extending from the top portion to the bottom portion, the head portion of the anchor member being receivable within the hollow interior bore of the anchor head such that the anchor member is polyaxially rotatable with respect to the anchor head, the anchor head including a generally U-shaped opening for receiving the fixation element; and a locking cap comprising a main body and a set screw, the main body being releasably engageable with the top portion of the anchor head, the set screw being friction fit and rotatably mounted to the main body in a preload condition, a predetermined torque being applied in a first direction to the set screw relative to the main body to rotate the set screw relative to the main body from the preload condition to a free condition, wherein the set screw further comprises a flared portion at a bottom end that engages a bottom end of the internal threads of the main body in the preload condition thus preventing rotation of the set screw relative to the main body in a second direction, opposite the first direction, in the preload condition.