An orthopaedic cage device having a rectangular cross-section and an intervertebral space shape conforming structure is formed of two opposing shell elements being hinged at one end to form an interior volume therebetween. The surface of the interior volume is tapered in the axial direction. A threaded shaft is axially disposed in the interior volume and is held in place by a retaining ring slideably mounted at the non-hinged axial end of the device. A nut, being of substantially the same dimension as the maximum cross-section of the interior volume in its initial disposition, is disposed on the threaded shaft such that rotation of the shaft causes the nut to translate axially within the interior volume. This translation causes the nut to engage the tapered surface of the interior volume, which in turn causes the non-hinged end of the device to spread such that the device conforms to the natural space between the vertebral bones and provides for the proper curvature of the spine.