A spinal implant apparatus that is an expandable spacer including features to minimize or eliminate spacer cant or offset during and after completing the expansion process. The spacer includes a top component, a base component in engagement with the top component, and an expansion mechanism arranged to change the top component's position with respect to the base component. The mechanism for causing expansion may be a screw, a cam, a wedge or other form of distracting device. In one embodiment, the expandable spacer includes a base component with a set of towers and a top component with a set of corresponding silos, where the towers and silos are configured to minimize or eliminate tilt of the top component as it extends upwardly from the base component. In another embodiment, the spacer may include a stepped arrangement around the perimeter of the top component and the base component for engagement during height expansion with minimal canting or slippage. In another embodiment, the spacer may include texturing modification at the opposite ends of the longitudinal axis of the spacer to prevent tilting, slipping, or canting. Additionally, a portion of one or more exterior surfaces of the spacer may be textured, sawtoothed, dovetailed or the like to increase frictional intervertebral contact. The spacer may contain one or more passageways of selectable shape/dimension for bone growth through the spacer.
