The present application is directed to devices with expandable lengths for treating bony members. The device may include an elongated member with two sections that are movable relative to each other. An expansion chamber may be positioned between the first and second sections. A pump may move fluid from a reservoir and through a conduit into the expansion chamber. The expansion chamber expands upon receiving the fluid to cause the first and second sections to move apart and increase the length of the elongated member. The device may include multiple expansion chambers along the length, and the elongated member may include multiple sections.