A spinal plate assembly includes a spinal plate and a cap. The spinal plate includes an opening through the spinal plate and an associated recess in the spinal plate that is eccentric with the opening. The cap includes an alignment opening and is configured to be rotationally engaged in the recess between a first rotational configuration and a second rotational configuration. The first rotational configuration enables a threaded body of a screw to be thread into a vertebra in a selected trajectory through the alignment opening and the opening in the spinal plate, and further enables a portion of the opening to engage a head of the screw in the selected trajectory. The second rotational configuration enables the cap to compress the head of the screw approximately through its center into the engaged portion of the opening.
