US Patent 8167949 Hydrostatic interbody

An intervertebral implant includes an upper surface configured for engagement with a first vertebral body, and a lower surface configured for engagement with a second vertebral body. A wall extends between the upper surface and the lower surface, and forms a chamber for containing osteogenic material. At least a portion of the wall is collapsible from a first position associated with a first volume of the chamber to a second position associated with a second volume of the chamber. The second volume is less than the first volume.