Maintaining motion: the cervical disc replacement

Jack was a 40-year-old man who had severe neck and arm pain for about 10 months. To get treated, he went through all the right steps. He saw his primary doctor, who ordered an x-ray. There was a small amount of arthritis, but no significant problems otherwise. He went to physical therapy and worked on stretching and strengthening. Next, he got an MRI which showed severe compression of his C6 and C7 nerves. But still, he wanted to try to get by without surgery. He even tried steroid injections in his neck to see if he could avoid it. Eventually, the pain was too great, and it wasn’t going away. He decided to try surgery.

He underwent a C5 to C7 fusion and decompression surgery through the front of his neck. The incision was small, he spent only one night in a hospital, and he had no complications. Within about two months, his arm pain completely went away. Over the next four months, his neck pain also eased up considerably, although he did have a bit more stiffness and lack of range of motion than before surgery. He did well for about six years. However, after about seven years, he began to have arm pain again - this time in a slightly different spot on his arm. He also had bad radiating pain near his shoulder blade. An MRI showed a disc herniation below his fusion, at the levels C7-T1. He had to go in for another surgery. This time his recovery was not quite as fast and not quite as complete.

Is there anything that could have helped prevent the second surgery?

What is arthroplasty?

The idea of arthroplasty is not a new technology. Patients with arthritis and other conditions have had it as an option for hips, knees, and shoulders for decades. However, it is a relatively new - and underutilized - technology in the cervical spine. The idea of arthroplasty is simple: replace the diseased joint with a prosthetic, or mechanical, joint that mimics natural motion. Once patient heals from surgery, and the prosthesis heals into place, the joint will function normally.

An anterior cervical fusion. At the level of surgery, the disc has been removed and replaced with bone. A plate and screws are preventing movement. Over time, the two bones will heal together into one fused bone structure.

Arthroplasty is designed as an alternative to fusion. During a fusion procedure, a combination of hardware and surgical techniques is used to make two bones grow together into one. A lot of people don’t realize it, but fusions used to be common options all throughout the body. Before the advent of our advanced technologies for joint replacement, many conditions including severe arthritis had to be treated with fusion, even in very large and mobile joints such as the hip and knee. Today, of course, we wouldn’t even consider a fusion procedure for a hip or knee for arthritis because the arthroplasty devices are so good. Still, fusion in the spine continues to be a common tool.

Cervical fusion for the treatment of arm pain (radiculopathy) and neck pain is an excellent procedure. Neurosurgeons and orthopedic spine surgeons have been doing this procedure for nearly 70 years. There is good relief of pain, good healing, and low complication rates. However, there is one major issue: fusion of two, three, or four vertebrae together radically changes the way the neck moves.

After the bones are fused together, there is no motion at those levels after surgery. However, people still want to move their necks. Therefore, the other levels - especially the levels closest, or adjacent, to the fusion - have to work overtime to attempt to give patients as much mobility as they desire.

A postoperative X-ray showing an arthroplasty device in place.

It’s easy to imagine: move your next front and back, or side to side. Now imagine that out of the seven joints that make up your neck, one, two, or three of them are no longer moving. How much additional stress will the remaining joints feel? Once patients have healed from surgery, they are back to feeling normal. They want to move their necks, look around, and don’t want to be stiff. But every time they move, the adjacent levels experience higher stresses, leading to the development of worsening arthritis.

So, the idea of arthroplasty is simple: don’t fuse the neck. Accomplish a procedure that relieves pressure on the nerves while maintaining normal motion. And over the past two decades there has been an explosion in arthroplasty technology. We have many devices with differing characteristics. We have excellent long-term follow up that shows that patients do as well as fusion and sometimes better. And we have data showing that there is more natural motion after an arthroplasty, less degeneration in the remaining levels, and less surgery farther down the line. All that’s left is to make sure patients know about this option, and use it when we can.

When is an arthroplasty the best option?

One of the hardest parts of my job as a neurosurgeon is making sure patients understand why I’m recommending spine surgery. When it comes to brain conditions, it’s usually a little bit easier. We found a brain tumor. It looks benign. Here, you can see it on the scan. We need to remove it. Obviously, it’s not so simple, but most patients can understand that they have a brain problem that needs to be removed.

It comes to spine, it’s a different story. There can be neck pain, arm pain, both, neither. Patients can have trouble walking or have falls. The imaging can look severe, or moderate, or not bad at all, and patients can still have severe symptoms. Or no symptoms at all. Understanding why we recommend fusion or arthroplasty can be difficulty but is very important for patients.

The most important and most common reason for arthroplasty is degenerative disc disease. Most people of heard of a slipped disc, but what does that really mean? You can think of the disks as shock absorbers between the two bones. They are firmly attached, and prevent abnormal movement between the two vertebrae. But, they still allow some gentle motion. The spinal cord and spinal nerves are found behind the discs, and the nerve roots course next to the discs, in some cases touching them. In very young, healthy spine, the disc is plump and well-hydrated, and the spinal cord and nerves are floating safely behind them with no compression whatsoever.

However, as we age, our spines start to degenerate. These are the wear and tear changes of life. The disc dries out a little bit and there’s a little bit less motion between the vertebrae. The disc can bulge and even herniate. When a disc herniates, it means a part of the disc is squished out of its normal spot and moves backward towards the spinal cord or nerves. Sometimes this causes no problems at all, but sometimes it just causes severe nerve pain. There can also be other signs of arthritis - growth of bony spurs, or the growth of inflammatory tissue. Any of these things can cause neck pain or compressed nerves causing arm and shoulder blade pain.

The number one goal of every spine surgery for degenerative disc disease is to decompress the nerves. Whether it’s an anterior fusion, arthroplasty, poster fusion, foraminotomy, laminoplasty, or any other choice from the seemingly endless list of medical jargon, the number one reason we were we perform surgery is to remove the compression of the nerves and ease the pain.

Cervical disc replacement. This model shows one of the available devices in place. Two silver “end-plates” connect to the vertebrae. In between these two end-plates a “mobile core” made of strong polyethylene provides mobility for the joint.

Now, when we do an anterior decompression surgery, and remove the disease disc, what do we do with the empty space? Originally, surgeons many years ago would leave it empty. As you can imagine, when there’s an empty space, the bones that were previously being held apart tended to move together, causing abnormal curvature of the spine. Surgeons quickly moved away from leaving an empty space. The next option was fusion. We have known that when you place a piece of bone into this empty space it will grow into place, very similar to a fractured bone healing naturally. So, surgeons started placing pieces of bone and inserting it into the spaces. This led to the development of the anterior discectomy and cervical fusion - ACDF - the common procedure neurosurgeons perform today. And as I discussed above, this is an excellent procedure. But still, could we make it better?

The push for improvement is what led to the arthroplasty in the cervical spine. Now, surgeons could remove the disease disc and decompress the nerves, and then instead of replacing the empty space with a piece of bone, we could use an artificial disc. Early on, many surgeons were not convinced this would be a good option. The ACDF is too good, it is unknown if the device will be safe for many years, it’s going to be too risky. And so, when the early clinical trials began, not many surgeons were using arthroplasty. However, surgeons continued studying these conditions, and over the past 20 years they have produced a huge amount of data. And now we know: these devices are safe. They don’t wear out. They offer excellent relief of arm and neck pain. And they result in lower rates of secondary surgery later in life.

Is it for everyone?

So, what’s the downside? Is arthroplasty an option for every patient?

There are a few reasons why patients wouldn’t be candidates for arthoplasty. Some are more or less obvious - if the spine is very unstable from a trauma or infection, it wouldn’t make sense to use a device that preserves motion. Those patients need stability and fusion. Some people are allergic to the materials, so we can’t use the device. Neither of these two reasons is very common. The most common reason to not use arthroplasty is spondylosis.

Spondylosis is the medical term for the development of severe arthritis in the spine. Although wear and tear changes are found in almost everyone, some patients, due to a combination of genetics, lifestyle, and bad luck, have it worse than others. In a neck with severe spondylosis, they can be large bone spurs and severe arthritis of the facet joints, small joints in the back of the spine. In patients with such severe arthritis all throughout their spine, especially in a facet joints, it doesn’t make sense to try and replace only one portion of the spine with an arthroplasty. Those patients are better suited for fusion procedures, or decompression surgery without fusion.

Is it right for you?

Early on after the advent of arthroplasty, not many patients met criteria. However, with time, we have come to learn it is a good option for many patients.

The only way to know if an arthroplasty is the right option for you is to see a spine surgeon. Neurosurgeon or orthopedic surgeon, it doesn’t matter, as long as the individual routinely performs both and can guide you through the process of understanding the pros and cons of all options.

Degenerative disc disease in the neck is common, and many patients would benefit from arthroplasty. If you have any questions, message me today!