A bone graft or spinal interbody device includes a frame member having two end segments for forming a chamber in the frame member, and two arms each include an outer end portion hinged to the outer end portion of the end segments of the frame member, and the inner end portions of the arms are hinged together for allowing the arms to be pivoted toward the frame member at an innermost folding position or away from the frame member to an outermost working position, and the arms are sprung away from the frame member to the outermost working position when the arms are pushed away from the frame member for a selected distance to an inner dead center (D).
