An orthopedic fastener is designed to attach an implant to bone in such a manner that, until the fastener is tightened, the implant may be rotationally adjusted against the bone. The implant may have a semispherical bone apposition surface that permits polyaxial rotation of the implant against the bone. The orthopedic fastener has an interpositional member and a compression member. The interpositional member may be a split ring with a conical exterior surface that mates with a conical surface of the implant. The compressing member has a threaded bore that engages a proximal end of a fixation member implanted in the bone such that, in response to rotation of the compression member, the interpositional member is sandwiched securely between the implant and the compression member. The conical surface of the implant compresses the interpositional member about a semispherical surface of the compression member, thereby restricting rotation of the implant.