In one aspect, a bone anchor assembly is provided. The bone anchor assembly includes a bone anchor, a crown member, a saddle, and a sleeve. The bone anchor assembly is configured such that the bone anchor is moveable with respect to the saddle when the sleeve is positioned around the saddle and the bone anchor is locked relative to the saddle by compression of the head portion of the bone anchor between the crown member and a seat of the saddle. In another aspect, a system for orthopedic implantation is provided. The system includes an elongated member, a compression member, and a bone anchor assembly. In another aspect, a method of assembling a bone anchor assembly is provided.