An expandable spinal prosthesis is disclosed, including a first surface having a first plurality of tissue anchors; a second surface opposite the first surface, the second surface having a second plurality of tissue anchors; a first wall between the first and second surfaces, and a second wall between the first and second surfaces, the second wall located opposite the first wall and being movable with respect to the first wall. A surgical instrument is also provided, including an elongated shaft defining a proximal end and a distal end; a first prosthesis engagement element accessible from the proximal end and extending from the distal end; and a second prosthesis engagement element accessible from the proximal end and extending from the distal end, the second prosthesis engagement element including a plurality of gear teeth.