trkdoc714 asked me to post the July Orthoknow article that has an overview of the current and coming crop of motion preservation devices.
While I am not the Internet Police, I can't post an article that may violate the copyright. John Englehardt, the founder of Orthoknow is a friend, so I emailed him for permission. Instead of the July Orthoknow, he sent a more complete article from a sister publication, Orthopaedic Product News. This data is a superset of what was published in Orthoknow (minus the pictures).
With the author's permission...
Orthopaedic Product News, September/October 2008
Mark