Spinal prosthetic devices having various engagement structures are disclosed. In one aspect a spinal prosthesis system comprises a first component with a first engagement structure extending from a surface of the first component at an oblique angle and a second component with a second engagement structure extending from a surface of the component at an oblique angle. In another aspect, a pair of flange members extend from the first engagement surface at an oblique angle such that the flange members are substantially perpendicular to one another. In another aspect, a first flange member extends transversely from the first engagement surface at a first oblique angle to the longitudinal axis of the surface and a second flange member extends transversely from the first engagement surface at a second oblique angle to the longitudinal axis such that the flange members are non-parallel.