An intervertebral spacer device having a pair of opposing plates for seating against opposing vertebral bone surfaces, separated by a spring mechanism. The preferred spring mechanism is a slotted domed arch strip spring which is coupled to the upper plate by set screws. The spring includes a socket formed in the peak thereof and mounts onto a ball-shaped head extending outwardly from the lower plate. The spring and post members are thereby flexibly coupled such that the upper and lower plates may rotate relative to one another.