Kate, it has been years since I studied the Mobi design. But I recall its comparative advantages over other designs -- namely less bone removed during surgery. That means far less of a chance of HO -- which is a huge design advantage IMHO.
See:
http://us.ldr.com/Portals/1/2LPRODUCTBROCHURE.pdf
And:
Mobi-C
Zeegers always liked this design for this and many other reasons, like a greater number of configurations for different, individualized fits. And he's no slouch in the world of spinal arthroplasty.
Less keel is better. My non-keeled Charite and spine are great after 11 years.
