An expandable inter-vertebral prosthesis. The prosthesis takes over the supporting function of the inter-vertebra disc between two adjacent vertebra bodies, and includes one or more cages and a reinforcing element. Upon cage expansion, a hollow central portion of the cage can accommodate the reinforcing element. The reinforcing element, upon expansion, assumes a spiral shape, and substantially fills up the hollow central portion of the cage to provide enhanced load-bearing capability in a substantially longitudinal spinal direction. Hinges in the cage permit expansion and, once the cage has expanded, prevent it from collapsing. Delivery of the cage in an unexpanded condition into an inter-vertebral space is ensured with a restraining tool that engages the hinge members. The cage, reinforcing element and restraining tool are inserted with the aid of a conventional delivery tube.