[jss]

Steve,

I don't have the qualifications to state that the M6 is "better", but I can tell you how it is different. The M6 is designed to emulate every aspect of the movement provided by your natural discs. The ProDisc and Prestige preserve most motion, but preserve it in only unnatural ways.

When you walk, run, stand, sit, hit a bump in your car, etc... your head is forced downward while the rest of your body doesn't move. Your intervertebral discs act just like a shock absorber in that they cushion this motion. The Spinal Kinetcs M6 and Nuvasive NeoDisc both cushion this up and down motion. The ProDisc and Prestige and ACDF don't cushion this motion and instead force the discs above and below to absorb the extra motion.

When you turn your head left and right, the joint between C2 and C3 does most of the turning. But your other intervertebral discs all the way down to C7/T1 also twist to let your head turn. The M6 and NeoDisc both provide resistance to turning that gets stronger the more your head turns; just like your natural discs. This lets all of the intervertebral discs do about the same amount of work when the head is turned. With ACDF the fused joint doesn't turn any, requiring that all of the other discs do more work when the head is turned. The ProDisc and Prestige have so little resistance to turning, that they will allow that joint to turn all the way to "full dead stop" before the other intervertebral joints begin to turn, causing the other discs to do less work. However, the facet joints, the joints that come to "full dead stop", now have to do a lot more work at the ADR level than they were designed to do. This is why the ProDisc and Prestige are suspected in accelerating facet joint degeneration.

The benefits of the ProDisc and Prestige over the M6 are that they contain only three or four pieces each, where the M6 contains many more. I don't know that there's been any study done on this, but that suggests that the ProDisc and Prestige may be less prone to failure than the M6. The ProDisc and Prestige have also been in use longer and so much more is known about how they will perform over time.

I'm an engineer and liked the M6 enough that I was willing to travel to Spain and pay almost $30k to have two of them implanted rather than have my insurance cover ProDisc/Prestige here in DFW. My thinking is that even though the M6 may be more prone to failure (that's unknown) that it is also more prone to preserve my remaining anatomy (that's also unknown) making it less likely that I'll loose more discs in the future (yet another unknown).

As you're considering ADR, I would encourage you to learn about all of the different ADR devices out there and then weigh the advantages and disadvantages of each. Though the M6 is my favorite, I don't know that any one device has been "proven" to be the best.

Good luck!

Jeff