Expandable bone device

An expandable bone device comprising:

• first and second bone support elements;
• a manipulator positioned between said first and second bone support elements and connected to them by link members, said manipulator adapted to move said first and second bone support elements between a collapsed orientation and an expanded orientation, wherein in the collapsed orientation said first and second bone support elements are drawn towards said manipulator and in the expanded orientation said first and second bone support elements are moved outwards away from a longitudinal axis of said manipulator;
• and
• deformable support struts connected between said manipulator and said first and second bone support elements that deform when moved by said manipulator from the collapsed orientation to the expanded orientation and vice versa, wherein in the expanded orientation said deformable support struts oppose forces directed normal to bone support faces of said first and second bone support elements so as to maintain said first and second bone support elements in the expanded orientation, and wherein said deformable support struts pass through a phase of elastic instability when moved by said manipulator from the collapsed orientation to the expanded orientation and vice versa, and wherein said link members maintain parallelism between said first and second bone support elements throughout movement between the collapsed and expanded orientations.