An intervertebral spacer having opposing plates seatable against opposing vertebral bones, separated by at least one spring mechanism, preferably a spirally slotted belleville washer having a wide end rigidly fixed to an upper plate and a narrow end rotatably mounted to a lower plate. The lower plate...http://www.google.de/patents/US6764515?utm_source=gb-gplus-sharePatent US6764515 - Intervertebral spacer device utilizing a spirally slotted belleville washer and a rotational mounting
