An expandable interbody spacer comprising: - a first jointed arm comprising a plurality of links (110, 120) pivotally coupled end to end; - and a second jointed arm comprising a plurality of links (200, 210) pivotally coupled end to end; - wherein the first jointed arm and the second jointed arm are interconnected at a proximal end of the expandable interbody spacer, - wherein the first jointed arm and the second jointed arm are interconnected at a distal end of the expandable interbody spacer, and - wherein the first jointed arm and the second jointed arm are each configured to fold inward in opposite directions to place the expandable interbody spacer in an expanded position, characterized in that - the first arm and the second arm when folded inward in opposite directions define a completely hollow interior cavity configured to receive bone-growth inducing material to fill the completely hollow interior cavity - the expandable interbody spacer further comprises a screw having a head and an elongated body extending parallel to longitudinal axis of the spacer through the expandable interbody spacer from a proximal end to a distal end, and - wherein the expandable interbody spacer further comprises washers disposed between the first jointed arm and a proximal connection member and the distal connection member at their respective connections and washers disposed between the second arm and the proximal connection member and the distal connection member at their respective connections, the washers have an interference fit to cause friction such that the spacer may hold its shape in the entire range of the expanded implant - a first jointed arm comprising a plurality of links (110, 120) pivotally coupled end to end; - and a second jointed arm comprising a plurality of links (200, 210) pivotally coupled end to end; - wherein the first jointed arm and the second jointed arm are interconnected at a proximal end of the expandable interbody spacer, - wherein the first jointed arm and the second jointed arm are interconnected at a distal end of the expandable interbody spacer, and - wherein the first jointed arm and the second jointed arm are each configured to fold inward in opposite directions to place the expandable interbody spacer in an expanded position, characterized in that - the first arm and the second arm when folded inward in opposite directions define a completely hollow interior cavity configured to receive bone-growth inducing material to fill the completely hollow interior cavity - the expandable interbody spacer further comprises a screw having a head and an elongated body extending parallel to longitudinal axis of the spacer through the expandable interbody spacer from a proximal end to a distal end, and - wherein the expandable interbody spacer further comprises washers disposed between the first jointed arm and a proximal connection member and the distal connection member at their respective connections and washers disposed between the second arm and the proximal connection member and the distal connection member at their respective connections, the washers have an interference fit to cause friction such that the spacer may hold its shape in the entire range of the expanded implant