An expandable intervertebral cage device adapted to be implanted into an intervertebral disc space in a patient's body, characterized in that the device 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 mechanically coupled to the first base plate and the second base plate , wherein the proximal block comprises internal threading; a distal block comprising an internal passage ; only two arm assemblies , wherein a first one of the two arm assemblies is arranged on a first side of the device and a second one of the two arm assemblies is arranged on a second side of the device , wherein each of the only two arm assemblies 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 ; and the second arm is mechanically coupled to the second base plate and the distal block ; and a screw arranged partially within the internal threading of the proximal block and passing through the internal passage of the distal block , such that rotation of the screw relative to the proximal block causes a change in distance between the proximal block and the distal block , and a corresponding change in the spacing and lordosis of the device due to an expansion or contraction of the arm assemblies . 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 mechanically coupled to the first base plate and the second base plate , wherein the proximal block comprises internal threading; a distal block comprising an internal passage ; only two arm assemblies , wherein a first one of the two arm assemblies is arranged on a first side of the device and a second one of the two arm assemblies is arranged on a second side of the device , wherein each of the only two arm assemblies 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 ; and the second arm is mechanically coupled to the second base plate and the distal block ; and a screw arranged partially within the internal threading of the proximal block and passing through the internal passage of the distal block , such that rotation of the screw relative to the proximal block causes a change in distance between the proximal block and the distal block , and a corresponding change in the spacing and lordosis of the device due to an expansion or contraction of the arm assemblies . 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 ; and the second arm is mechanically coupled to the second base plate and the distal block ; and a screw arranged partially within the internal threading of the proximal block and passing through the internal passage of the distal block , such that rotation of the screw relative to the proximal block causes a change in distance between the proximal block and the distal block , and a corresponding change in the spacing and lordosis of the device due to an expansion or contraction of the arm assemblies . <EOS>