This topic may be getting confusing (even to me), so I just want to clarify something of importance: the surgeon determines the size of end-plate sizes of the artificial disc. These disc endplate designs -- and sizes -- vary by mfr. That said, I've posted many times of my personal preference against keeled designs in that they are too destructive; in that they cause vertebral instability, make revisions almost impossible and increase the risk of HO (heterotopic ossification). I've been singin' that tune for years now.
See this specs here for Synthes et al:
http://www.adrsupport.org/forums/f55/synthes-9503/
Due to earlier design limitations, and surgeons' errors in selecting plate sizes (too small causes subsidence of devices into softer bone), many corrections in endplate designs were made in the last decade (yes, decade!).
Msrudy, let's email or talk soon, so I can help you add a signature.
