Abstract: An intervertebral fusion cage implant is generally elongate and defines superior and inferior bearing surfaces. The inferior bearing surface has vertebral body engaging interferences and the superior bearing surface has a substantially smooth surface profile, sagittal plane convexity and sagittal plane curvature asymmetry. The sagittal plane convexity defines a saggital plane axis rising anteriorly with respect to a horizontal saggital plane axis. The superior bearing surface defines a central section having coronal plane convexity and lateral sections adjacent the central section.

Abstract: This invention concerns an artificial intervertebral disc for installation in an intervertebral space between adjacent vertebral bodies. The artificial intervertebral disc prosthesis comprises an upper plate, a lower plate and a mobile core element, which is, in use, located between the upper and lower plates. The mobile core element includes a first contoured surface that has a flexion/extension radius that is larger by a determined amount than the radius of its second contoured surface that results in an instantaneous centre of rotation below the midline of the intervertebral disc space, thereby approximating the typical instantaneous centre of rotation of a natural disc. The first contoured surface of the mobile core element has a lateral bending radius that is unequal to the value of the flexion/extension radius, thereby allowing the mobile core element to self-centre on the second surface of the upper plate when under preload.