How do new fusions solidify when they are always moving?

**Katie** · 08-06-2010, 11:24 PM

When we break a bone, it is usually put in a cast to immobilize it. But with some fusions like mine, there is nothing to control the movement of the vertebrae. I only have the PEEK cage between them, with no rods or screws to minimize movement.

It's one question I forgot to ask the surgeon. How does solid bone form between the levels when everything is moving?

My new x-rays show that everything is in place and it looks like bone is growing properly. I just don't understand how.

**ajj1001** · 08-07-2010, 04:29 AM

"Cage devices are filled with materials that are osteoinductive or osteoconductive and provide scaffolding for bony fusion to occur from endplate to endplate."

http://ukpmc.ac.uk/articles/PMC26973...A4FBD3D5B.jvm1

**Katie** · 08-07-2010, 09:06 AM

Thanks Alison! That makes more sense now. It does say that there is more success when extra hardware is used though. Guess I just cross my fingers.

**Cindylou** · 08-07-2010, 10:41 AM

Great article Alison. Katie, I offer as some hopeful comfort, that I too have no other hardware in my L6-S1 other than a pedicle screw and I fused just fine. :thumpup:

**ajj1001** · 08-07-2010, 11:28 AM

Originally Posted by Katie

Thanks Alison! That makes more sense now. It does say that there is more success when extra hardware is used though. Guess I just cross my fingers.

.... it doesn't always work even if there is hardware there

! good to hear that bone is showing on the x rays

.

**Susanna** · 08-20-2010, 04:30 AM

Cindylou

Where did you get your ALIF L6-S1 fusion. Sorry didn't mean to

I am just trying to figure out how to get this when my insurance won't cover it!

Susanna

**Cindylou** · 08-20-2010, 11:58 PM

Susanna, I had my ALIF fusion done at Abbott Northwestern Hospital in Minneapolis. My surgeon is with ILBNC (Institute for Low Back and Neck Care). I am sorry you are having to fight so hard for your fusion. Don't give up.

**Susanna** · 08-21-2010, 12:31 AM

CL,

Hmmm, that might now be a bad place for me to go if my insurance covers it. It would be close to my husband. How do you feel about the doc. that did your surgery. What is the part about bone cement leaking into your joint? Was that from your L6/S1 fusion?

So maybe you can tell me if you had leg pain going into this fusion or back pain or both? And how do those areas feel today? I realize you have other problem area's but if you only had that problem area, did the fusion fix it?

**MDE** · 08-24-2010, 02:17 PM

This is difficult to describe with words, but stick with me...

A motion segment consists of 2 vertebrae and 1 disk. The motion of this segment is controlled by the two facet joints and the disc (so called three joint complex). There are also a variety of ligaments and muscles that limit the extent of movement, or activate movement in the motion segment. (simplified to reduce confusion) All together these structures still allow all 6 degrees of motion. if you think of a XYZ axis system sitting at the center of the disc, each vertebrae can translate and rotate on each axis. (3 axes, two movements on each axis, 6 degrees of freedom)

Now as most of you know, your spine does not move specifically on those 3 axes, but instead typically moves in combined movements. When there is a healthy disc, there are 4 general movements. Flexion/Extension, Lateral bending, Rotation, and axial compression.

When you remove the disc and replace it with an interbody device, you're typically using a "press fit" size of implant to restore the original, healthy disc height. This device then doesn't allow for the flexion/extension, lateral bending, or axial compression to occur. (these can occur if the device has insufficient surface area and subsides into the endplate, but let's not go there for now)

The only movement that isn't fully constrained by the interbody device is rotation. Most of the devices have ridges on them to prevent rotation when loaded however this can't completely constrain this potential motion. This is obvious by the fact that the device was placed through "sliding" along the endplate in the first place.

Pedicle screw systems from the posterior, or anterior plating systems can provide this additional support and resistance to insure a higher level of stability, and typically a lower complication rate.

So to summarize, interbodies do limit almost all motion between the vertebrae by themselves. You are correct in assuming that if the to vertebrae are moving in relation to each other, there is a much lower chance of a fusion occurring across the joint.

**sportsnut3007** · 08-24-2010, 02:36 PM

Katie be glad you didnt have more hardware. Alot of times they say th.e hardware can cause major problems. They are working on hardware that after like a year or 2 it dissolves somehow in the body, thus enough time to hold it in place for fusion but eventually going away.