An expandable vertebral interbody/intravertebral (spinal) body device for insertion into a spinal (intervertebral or intravertebral) space is provided. The interbody/intravertebral body device is expandable from a first circumference to a second circumference through axial compression of segments of the vertebral interbody/intravertebral body device, particularly once the interbody/intravertebral body device has been properly situated within a vertebral space. The interbody/intravertebral body device is characterized by a plurality of axially stacked, individual segments that are provided on a central insertion and deployment rod. Each segment includes a central plate or body to which are pivotally attached plate or leaf structures. Pivoting of the structures provides a collapsed or unexpanded position of the first circumference and an open or expanded position of the second circumference. The vertebral interbody/intravertebral body device may be formed of a bio-compatible radiolucent material. The radial profile of an interbody/intravertebral body device is easily defined by plate or leaf structures of the segments.