A linearly expanding spine cage has a minimized diameter in its unexpanded state that is equal to the diameter of an insertion groove cut into adjacent vertebral bodies. The cage conformably engages between the endplates of adjacent vertebrae to effectively distract the disc space, widen neuroforamina, stabilize the motion segments and eliminate pathologic spine motion. Angular deformities can be corrected, and natural curvatures maintained. The cage enhances spinal arthrodesis by creating a rigid spine segment. Expanding linearly (vertically, along the vertical axis of the adjacent spine) rather than uniformly, the cage height increases and holds the vertebrae with fixation forces greater than adjacent bone and soft tissue failure forces. Stability is thus achieved immediately, enabling patient function by eliminating painful motion. The cage width remains stable, so as to decrease impingement upon a second cage, or upon soft tissue structures in the immediate vicinity, including neural or vascular elements.