Abstract: An anti-rotation mechanism for a sacroiliac screw that is designed to prevent screw backout. The sacroiliac screw includes a screw head cap coupled to a screw implant. The anti-rotation mechanism includes geometric features on the screw head cap and/or screw implant that allows rotation in a first direction and prevents rotation in a second or opposite direction. The geometric anti-rotation mechanism for the sacroiliac screw is unique due to the self-contained mechanism within the screw assembly. There are no extra components or process steps required to achieve rotational fixation between the screw body and the screw head cap.