Disc Replacement Content
19-10-2009

Varsha Arun Kumar

Introduction Artificial or Total disc replacement (ADR or TDR) is relatively new. In June 2004, the first TDR for the lumbar spine (low back) was approved by the FDA for use in the US.

The Cervical disc replacement uses the same principle and techniques. The disc is part of a complex joint in the spine. Making a replacement disc that works and that will last is not an easy task.

The artificial disc is inserted in the space between two vertebrae. The goal is to replace the diseased or damaged disc while keeping your normal neck motion. The hope is that your spine will be protected from similar problems above and below the affected spinal level.

This chapter will help you What your surgeon hopes to •What parts of the spine are involved •understand: How do I prepare for surgery •Who can benefit from this procedure •achieve What to expect as you recover Anatomy: •What happens during the procedure • What parts of the spine are invovled? Disc replacement typically occurs at cervical spine levels C4-5, C5-6, or C6-7.

However, any disc may be replaced. Rationale: What does the surgeon hope to achieve? Disc replacement surgery is done to stop the symptoms of degenerative disc disease. Discs wear out or degenerate as a natural part of aging and from stress and strain on the neck. Eventually, the problem disc collapses.

This causes the vertebra above to sink toward the one below. This loss of disc height affects the nearby structures especially the facet joints. When the disc collapses, it no longer supports its share of the load in the cervical spine. The facet joints of the spine begin to support more of the force that is transmitted between each vertebra.

This increases the wear and tear on the articular cartilage that covers the surface of the joints. The articular cartilage is the smooth, slippery surface that covers the surface of the bone in any joint in the body.

Articular cartilage is tough, but it does not tolerate abnormal pressure well for long. When damaged, articular cartilage does not have the ability to heal. This wear and tear is what is commonly referred to as arthritis.

Shrinking disc height also reduces the size of the neural foramina, the openings between each vertebral pair where the nerve roots leave the spinal column. The arthritis also results in the development of bone spurs that may protrude into these openings, further narrowing the space that the nerves have to exit the spinal canal.

The nerve roots can end up getting squeezed where they pass through the neural foramina. The traditional way of treating severe neck pain caused by disc degeneration is a procedure called an anterior cervical discectomy and fusion.

In this procedure, the surgeon makes an incision in the anterior (front) of the neck, performs a discectomy (removes the disc) and fuses the two vertebrae together. A fusion simply means that two bones grow together. Usually, when two vertebrae are fused together, a small piece of bone called a bone graft is inserted between the two vertebrae where the disc has been removed.

This bone graft serves to both separate the vertebrae and to stimulate the two bones to grow together - or fuse. The fusion procedure usually involves the use of hardware, such as screws, plates, or cages to keep the bones from

Fusion restricts movement in the problem area, but it creates greater strain on the healthy spinal segments above and below by forcing them to bend more to achieve the same amount of movement. The added strain may eventually cause these segments to wear out.

This is called Adjacent-Segment Degeneration. Replacing the damaged disc with an artificial disc, or implant, called prosthesis can restore the normal distance between the two vertebrae. The artificial disc sits between the two vertebrae and ‘jacks up’ the upper vertebra.

Enlarging the disc space relieves pressure on the facet joints. It also opens up the space around the spinal nerve roots where they pass through the neural foramina. Another benefit of the artificial disc replacement is that it mimics a healthy disc.

Natural motion is preserved in the spine where the new disc is implanted. And it helps maintain stability in the spinal joints above and below it. Who can benefit from this procedure? The indications for a cervical disc replacement are generally the same as for a cervical discectomy and fusion.

A person must have symptoms from a cervical disc problem. Symptoms include neck and/or arm pain, arm weakness, or arm and hand numbness. These symptoms may be due to a herniated disc and/or bone spurs called osteophytes pressing on adjacent nerves or the spinal cord. This condition typically occurs at cervical spine levels C4-5, C5-6, or C6-7. Cervical artificial disc replacement is indicated for the treatment of radiculopathy (pressure on the spinal nerve) and myelopathy (pressure on the spinal cord) at one or two levels.

In the selected cases, it may be used for the treatment of three or more symptomatic levels or levels adjacent to a cervical spine fusion. Cervical artificial disc replacement is not advised when there is cervical spine instability, significant
Preparation: How should you prepare for surgery? Your Neuro-Spine surgeon will gather a variety of information before recommending disc replacement surgery. In addition to taking a history and doing a physical exam, your surgeon may order various diagnostic studies, such as x-rays, magnetic resonance imaging (MRI) scans, and CT scans.
Once you and your surgeon have agreed that disc replacement surgery is indicated, certain preparations for the surgery are important. Your doctor may tell you to be NPO for a certain amount of time before the procedure. This means that you should not eat or drink anything for a certain amount of time before your procedure. This means no water, no coffee, no tea - not anything.
You may receive special instructions to take your usual medications with a small amount of water. Check with your doctor if you are unsure what to do. You should tell your doctor if you are taking any medications that thin your blood or interfere with blood clotting. Aspirin, ibuprofen, and nearly all of the anti inflammatory medications affect blood clotting. So do medications used to prevent strokes such as Clopidogrel.
These medications usually need to be stopped a few days prior to the procedure. Be sure to let your doctor know if you are on any of these medications. You should stop smoking or using tobacco in any form as soon as possible before surgery. This is very important to reduce complications from heart and lung problems.

Tobacco use, especially smoking, also decreases the success rate of spine surgery. Stopping smoking will increase your chances of a successful result. A doctor who will be performing your anesthesia (an anesthesiologist) will evaluate and counsel you regarding anesthesia. Surgical Procedure: What happens during the operation? Before we describe the procedure, let's look first at the artificial disc itself.

The cervical artificial disc has several different designs. Some look like a sandwich with two endplates separated by a plastic spacer. The two endplates are made of cobalt chromium alloy, a safe material that has been used for many years in replacement joints for the hip and knee. A plastic (polyethylene) core fits in between the two metal endplates. The core acts as a spacer and is shaped so that the endplates pivot in a way that imitates normal motion of the two vertebrae.

There are small prongs on one side of each endplate. The prongs help anchor the endplate to the surface of the vertebral body. Another artificial disc replacement design is a ball and socket articulation to allow for normal translation of motion at that segment.

The implant may be made of titanium and polyurethane in a metal-on-plastic design. Some are made of stainless steel and are all metal-on-metal. Inserted between two vertebrae, the prosthesis reestablishes the height between two vertebrae. As a result of enlarging the disc space, the nearby spinal ligaments are pulled tight, which helps hold the prosthesis in place.

The prosthesis is further held in place by the normal pressure through the spine. The Operation The operation is done from the anterior (front) of the neck. This surgical approach is the same as that presently used for a discectomy and fusion operation. To do this, the patient is placed on his or her back.

An incision is made through the skin and the thin muscles of the front of the neck. The blood vessels, the trachea (windpipe), and the esophagus are moved to the side so that the surgeon can see the front of the cervical spine. The disc that is to be replaced is identified using the fluoroscope.

The fluoroscope is an x-ray machine that allows the doctor to actually see an x-ray image while doing the procedure. Working from the front of the spine, the spine surgeon removes a large section from the middle of the damaged disc. Next, the bones of the spine are spread apart to make more room to see and work inside the disc space. Using a surgical microscope, any remaining disc material toward the back of the disc is removed.

The surgeon will also remove any disc fragments pressing against the nerve and shave off any osteophytes (bone spurs). The disc space is distracted (jacked up) to its normal disc height. This step helps decompress or take pressure off the nerves.

At this point, x-rays or a fluoroscope, is used to insert the artificial disc device into the prepared disc space. This allows the doctor to watch where the implant goes as it is inserted. This makes the procedure much safer and much more accurate.

Finally, moving the spine in various positions tests the prosthesis. An X-ray may be taken to double check the location and fit of the new disc. Complications: What might go wrong? All types of spine surgery, including artificial disc replacement, have certain risks and benefits. Weigh these as you gather advice and information. Be sure to discuss the possible risks of disc replacement with your spine surgeon.

Anesthesia Complications Most surgical procedures require that some type of anesthesia be done before surgery. A very small number of patients have problems with anesthesia. These problems can be reactions to the drugs used, problems related to other medical complications such as heart disease. Be sure to discuss the risks and your concerns with your anesthesiologist.

Infection following spine surgery is rare but can be a very serious complication. Some infections may show up early, even before you leave the hospital. Infections on the skin’s surface usually go away with antibiotics. Deeper infections that spread into the bones and soft tissues of the spine are harder to treat and may require additional surgery to treat the infected portion of the spine.

Hoarseness The nerve to the voice box is sometimes affected during surgery on the front of the For Patient Education Purposes Only. neck. During surgery, the nerve may get stretched too far when retractors are used to hold the muscles and soft tissues apart.

When this happens, patients may be hoarse for a few days or weeks after surgery. Spontaneous Ankylosis (fusion) Sometimes the spine fuses itself, a process called spontaneous ankylosis. This is particularly common in patients with some kind of on-going artfritic or inflammatory process.

Such patients will often have calcium deposits in their ligaments and soft tissues with bridges of bone extending between spinal bones. Despite the disc replacement, this process continues on its own. Loss of neck motion is the main side effect of this problem. Bone may also form in the soft tissues around the vertebrae. For example, cartilage turns to bone or bone-like tissue.

This process is called ossification. Ossification may encase the disc like a capsule and prevent movement of that segment. Subsidence (sinking) Subsidence is another possible problem. The implant actually sinks into the vertebral body above or below it.

It is articularly seen in patients with bones left brittle or softened by loss of calcium, a condition called Osteoporosis. This results in a loss of the normal disc height. Implant Failure (rare) Over time, wear and tear just from the physical process of motion across a bearing surface can cause tiny bits of debris to flake off the implant.

The body may react to these particles with an inflammatory response that can cause pain, implant loosening, and implant failure. So far, significant inflammatory reactions have not been reported for spinal artificial disc replacements. In rare cases, the artificial disc replacement can dislocate.

After Surgery: What happens after surgery? Patients generally recover quickly after the artificial disc procedure. Most people spend three or four days in the hospital. You may require an extra day or two if for some reason you’re having extra pain or unexpected difficulty.

You should be able to get out of bed and walk within a few hours. Move carefully and comfortably, and avoid extending your neck (bending backward) too far. You may need to wear a brace or soft collar for a few days after the operation to help relieve pain. When you leave the hospital, there are very few activity restrictions.

You should be safe to sit, walk, and drive. However, you should avoid lifting items for at least four weeks. Your surgeon will probably release you to return to work in two to four weeks. If your job requires moving and lifting heavy items, you may require a longer period of recovery. Your surgeon may give you the okay to do all your activities by the fourth week after surgery.

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