A spinal plate assembly includes a screw (400), spinal plate (100) and cap (500). A head of the screw includes a portion of a first sphere that has a first center and a portion of a second sphere that has a second center approximately concentric with the first center. A body of the screw extends from the first sphere. 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. In the first rotational configuration, the body threads into a vertebra in a selected trajectory through the alignment opening and the opening in the spinal plate and the head engages at least a portion of the opening in the selected trajectory. In the second rotational configuration, the cap compresses the second sphere into the first sphere approximately through its center such that the head is compressed into the engaged portion of the opening.
