An intervertebral spacer device having a pair of opposing plates for seating against opposing vertebral bone surfaces, separated by at least one spring mechanism. The preferred spring mechanism is a belleville washer. In a first embodiment there are two belleville washers which are oriented in opposite directions such that the narrow ends thereof are in contact with each other and the wider ends are in contact with the respective end plates. In a second embodiment there is a single belleville washer which is modified to mount onto a ball-shaped head. The lower plate of this embodiment includes a post extending upwardly from the inner surface of the plate, the post including a ball-shaped head. The modified belleville washer is lockably mounted to the head such that the wider portion of the washer seats against the upper plate.