An intervertebral stabilization device and method is disclosed. The device preferably includes a planar spring enclosed within a housing. The housing is joined to an articulation component at either end, and the articulation components have couplings connectable to anchoring components which are securable to adjacent vertebrae. The planar spring can flex and retract providing relative motion between the adjacent vertebrae. The articulation components are ball and socket joints which allow the entire assembly to flexibly follow the curvature of the spine. A fusion rod with articulation components and couplings at either end may be substituted for the spring device. The couplings enable interchangeability between a fusion rod assembly and spring assembly, so that dynamic stabilization can occur at one vertebral level and fusion at the adjacent vertebral level. An overhung spring assembly with a sideways displaced housing which allows for a shorter pedicle to pedicle displacement is also disclosed.