An expandable intervertebral cage device (10, 100) adapted to be implanted into an intervertebral disc space in a patient's body, characterized in that the device (10, 100) comprises: a first base plate having a first outer bearing surface configured to interface with a first vertebra of the intervertebral disc space; a second base plate having a second outer bearing surface configured to interface with a second vertebra of the intervertebral disc space; a proximal block (24, 122a) mechanically coupled to the first base plate and the second base plate, wherein the proximal block (24, 122a) comprises internal threading; a distal block (22, 122c) comprising an internal passage; only two arm assemblies (110a, 110b), wherein a first one of the two arm assemblies (110a, 110b) is arranged on a first side of the device (10, 100) and a second one of the two arm assemblies (110a, 110b) is arranged on a second side of the device (10, 100), wherein each of the only two arm assemblies (110a, 110b) comprises: only a first arm and a second arm that pivot with respect to one or more of the first base plate and the second base plate; the first arm mechanically coupled to the first base plate and the distal block (22, 122c); and the second arm is mechanically coupled to the second base plate and the distal block (22, 122c); and a screw arranged partially within the internal threading of the proximal block (24, 122a) and passing through the internal passage of the distal block (22, 122c), such that rotation of the screw relative to the proximal block (24, 122a) causes a change in distance between the proximal block (24, 122a) and the distal block (22, 122c), and a corresponding change in the spacing and lordosis of the device (10, 100) due to an expansion or contraction of the arm assemblies (110a, 110b). a first base plate having a first outer bearing surface configured to interface with a first vertebra of the intervertebral disc space; a second base plate having a second outer bearing surface configured to interface with a second vertebra of the intervertebral disc space; a proximal block (24, 122a) mechanically coupled to the first base plate and the second base plate, wherein the proximal block (24, 122a) comprises internal threading; a distal block (22, 122c) comprising an internal passage; only two arm assemblies (110a, 110b), wherein a first one of the two arm assemblies (110a, 110b) is arranged on a first side of the device (10, 100) and a second one of the two arm assemblies (110a, 110b) is arranged on a second side of the device (10, 100), wherein each of the only two arm assemblies (110a, 110b) comprises: only a first arm and a second arm that pivot with respect to one or more of the first base plate and the second base plate; the first arm mechanically coupled to the first base plate and the distal block (22, 122c); and the second arm is mechanically coupled to the second base plate and the distal block (22, 122c); and a screw arranged partially within the internal threading of the proximal block (24, 122a) and passing through the internal passage of the distal block (22, 122c), such that rotation of the screw relative to the proximal block (24, 122a) causes a change in distance between the proximal block (24, 122a) and the distal block (22, 122c), and a corresponding change in the spacing and lordosis of the device (10, 100) due to an expansion or contraction of the arm assemblies (110a, 110b). only a first arm and a second arm that pivot with respect to one or more of the first base plate and the second base plate; the first arm mechanically coupled to the first base plate and the distal block (22, 122c); and the second arm is mechanically coupled to the second base plate and the distal block (22, 122c); and a screw arranged partially within the internal threading of the proximal block (24, 122a) and passing through the internal passage of the distal block (22, 122c), such that rotation of the screw relative to the proximal block (24, 122a) causes a change in distance between the proximal block (24, 122a) and the distal block (22, 122c), and a corresponding change in the spacing and lordosis of the device (10, 100) due to an expansion or contraction of the arm assemblies (110a, 110b).