Data presented for all the discs looks remarkably similar.
Dr. Bertagnoli still likes ProDisc, although many people I know have requested that he do Activ-L. He does Activ-L with keel, where Zeegers does without keel.
You mentioned bone-density and reservation about keel in same sentence. Keel will provide additional resistance against subsidence as it provides more surface area for support.... kind of like the way pilings support a building... surface tension on vertical surface is what provides the support... not the small footprint at the bottom of the piling.
Mark
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