Karger, I have some activ-L models... if you live near me (southern california) come see them. All of the discs are held in place by the tension on the ligaments that hold your spine together. Hence the need for good ligaments and facets in order to be OK for ADR.
The amount of force required to distract the disc space is pretty dramatic. You'd be shocked how hard they have to hit the insertion tool in order to literally pound it into place. Once the disctraction tools are released, the prosthesis is in and not going anywhere. It's as if you jacked up the wheel of a truck... removed the wheel and put a bunch of flat rocks under the axel. Lower the jack and you can't pull the rocks out.
Mark
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