Neck fusion or disc replacement? These are my two options right now for my degenerative disc disease. I'm slowly learning the pros and cons of each one. I'll be doing a complete study before making the final decision. Just one question for you: does a disc replacement guarantee me normal neck motion once again?
There are many variables to consider when making a decision between these two surgical procedures. As you point out, there are advantages and disadvantages to both. The goal is to weigh the risks against the benefits in light of your own situation and make the best choice you can for yourself.
It is agreed that if you have a disc replacement, it's better than a fusion (in terms of motion). Movement of the spine is maintained with the implant (called a disc arthroplasty. But your question: does a disc arthroplasty provide the same kind of spinal movement (called kinematics) as the normal, natural spine is a good one? And one that a recent study was done to find out.
The authors conducted a systematic review (collecting all the published materials on this topic) and a meta-analysis (combined all the data together). They compared the results of a disc arthroplasty with anterior cervical disc removal and fusion (called an anterior discectomy and fusion or ACDF). The cervical spine refers to the neck.
The main measure of results or outcomes was change in movement at the spinal level next to (adjacent) the implant. Kinematic (movement) measurements were made by looking at overall (global) neck range of motion. Special flexion-extension X-rays were used to measure changes in cervical spine motion.
They looked at the motion at the spinal segments above and below the arthroplasty and the fusion site. There was interest in knowing if either of these adjacent areas would end up with increased stress, force, and motion.
They also looked at movement of the vertebra (spinal bone) forward over the vertebra below it. This motion is called anterior translation. And they studied changes in the center of rotation of the discs and vertebra above and below the sites of fusion or arthroplasty.
There really wasn't any significant difference in motion at the adjacent levels between the two groups (arthroplasty versus fusion). The studies followed patients for up to two years after the surgery. Longer-term results might show a difference but this wasn't evident in the short-term.
Likewise, there were no measurable differences in center-of-rotation or anterior translation motion between the two groups in the first two years. Observing center-of-rotation motion gives us an idea of the quality (not just quantity) of motion. And that's important because early joint degeneration leading to arthritic changes can occur when the center-of-rotation is off. Uneven load on the spinal joints and increased pressure through the disc can occur when there is a shift in the vertebral center-of-rotation.
As this study showed, there was no major difference in kinematics at the adjacent levels after disc replacement compared with spinal fusion. There were some significant changes in alignment after disc replacement but they thought this was because decreased pain allowed for increased neck function.
There is still plenty of room for more research in this area. Most of the studies included only followed patients for two-years. So we don't have long-term results to say what might happen 10 or even 20 years down the road. And implant design keeps changing as new technology arises and results of studies done so far are used to keep improving surgical techniques. But for the moment, there is probably enough information available to help you sort out what is the best choice for you.