About a year ago, I had the disc at L5-S1 replaced because of degenerative disc disease. I was hoping this operation would help me keep all of my natural motion. The latest tests show that I only got about half the normal motion back. Is there any explanation for this?

Total disc replacement (TDR), also known as artificial disc replacement (ADR) is a fairly new procedure in the United States. They are used most often with patients who have painful symptoms from degenerative disc disease. Usually at least six months of conservative care is tried first before doing this surgery.

The advantages of TDR over spinal fusion include preserving motion and disc height. This means the spinal joints remain in better alignment, too. The affect of TDR on motion at other levels in the spine has been under investigation for a while.

In a recent study from Korea, scientists tried to find factors that might predict the final results. One of the things they looked at closely was the issue of range of motion. Just as you experienced, they noticed less motion at the L5-S1 level in their patients, too.

They suggested this might be caused by the way the spine is put together at that junction. Because it's the place where the lumbar spine meets the sacrum, there are slight differences in the bones and soft tissues. In particular, there are many more ligaments in this region giving the area a natural increased stiffness.

They checked to see if motion before the surgery made any difference. It didn't. They analyzed age, gender, and body mass index to see if any of these factors made a difference. They didn't.

Overall, it looked like it was just the location at that particular segment. And it may be the design of the implant has to be changed to get better motion. This is a matter for further investigation in other studies.