IMHO, multi-level constructs are not good candidates for mobile core devices. (Spinal Kinetics M6, mobi-c, mobi-l, Charite, .... ) If you search ispine for the words "tiddley winks", you should find my description of how if something pushes one core in one direction, it can cause the adjacent level cores to be pushed in the opposite direction. This sets up a configuration that is not secure and the problems at each level multiplies the problems at the next level. I've seen too many of these configurations require revision.
Please note that I have a 2-level Charite' with no problems. Properly implanted in a stable spine, they are fine. Unfortunately, it's too easy to have a problem with this configuration and a problem with multi-level mobile-core ADR's are much worse than the corresponding multi-level stationary core configurations. If you have this (as I do) and are doing well, don't look a gift horse in the mouth... you are fine. However, if you are considering multi-level ADR, consider the mobile core issue very carefully.
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