Intervertebral disc replacement

An apparatus for replacing at least a portion of an intervertebral disc in a spinal column between endplates of a first vertebral body and a second vertebral body of a spinal column, the apparatus comprising:

• (a) a first member having a first vertebral contact surface for engagement with the first vertebral body endplate, and having a first articulation surface;
• and
• (b) a second member having a second vertebral contact surface for engagement with the second vertebral body endplate, and having a second articulation surface,
• wherein an intervertebral spacing is defined as the axial component of a line extending between a centroid of said first vertebral contact surface and a centroid of said second vertebral contact surface,
• and wherein said first articulation surface and said second articulation surface form at least part of an articulation arrangement configured such that, when loaded with compressive axial force:
• (i) said first and second vertebral contact surfaces are supported against the compressive force to ensure a predefined minimum intervertebral spacing;
• (ii) said second member is displaceable relative to said first member in motion corresponding to axial rotation, anterior-flexion and posterior extension, and lateral bending, each of said motions having a corresponding range of motion;
• and
• (iii) said intervertebral spacing increases as a smooth function of angular displacement from a neutral position over at least part of said range of motion in each direction for each of said axial rotation, anterior-flexion and posterior extension, and lateral flexion, thereby providing non-impact motion attenuation.