A selectively expanding spine cage has a minimized cross section in its unexpanded state that is smaller than the 
diameter of the neuroforamen through which it passes in the distracted spine. The cage conformably engages between the endplates of the adjacent vertebrae to effectively distract the anterior 
disc space, stabilize the motion segments and eliminate 
pathologic spine motion. Expanding selectively (anteriorly, along the 
vertical axis of the spine) rather than uniformly, the cage height increases and holds the vertebrae with fixation forces greater than adjacent bone and 
soft tissue failure forces in natural 
lordosis. Stability is thus achieved immediately, enabling patient function by eliminating painful motion. The cage shape intends to rest 
proximate to the anterior column cortices securing the desired spread and fixation, allowing for bone graft in, around, and through the 
implant for arthrodesis whereas for 
arthroplasty it fixes to endpoints but cushions the spine naturally.