Method of expanding an intradiscal space and providing an osteoconductive path during expansion

A method of expanding an intradiscal space between two opposing vertebral bodies of the spine and establishing a stress loaded osteoconductive path therebetween during expansion, comprising the steps of;

• introducing into said intradiscal space an expandable interbody fusion device comprising an upper element and a lower element, each of said upper element and said lower element comprising a body and a region of different porosities, each region comprising a porous biocompatible material and a material for promoting bony through growth, said region of each of said upper element and said lower element extending through the respective bodies of said upper element and said lower element and being in substantial alignment with each other, said device being placed such that the region of said upper element faces and communicates with the endplate of one vertebral body and the region of said lower element faces and communicates with the endplate of the opposing vertebral body;
• and
• introducing at least one intermediate element into said interbody fusion device between said upper element and said lower element to achieve ligamentotaxis, said at least one intermediate element including an outer border surrounding a generally central region consisting essentially of porous biocompatible material having pores throughout for bony through growth, said outer border being structurally stronger and formed of material different than said generally central region and consisting essentially of a solid, relatively non-porous biocompatible material, said generally central region being defined by an insert being attached to said body outer border, said insert and said outer border forming said at least one intermediate element prior to introduction into said device, said intermediate element being placed such that said generally central region of said intermediate element is in compressive contact with the regions of both said upper element and said lower element, said region of said upper element is in compressive contact with the endplate of one vertebral body and the region of said lower element is in compressive contact with the endplate of said opposing vertebral body.