What is Disc Replacement?

The vertebral disc is the “shock absorber” of the spinal system.  Each disc is located between the vertebral bodies so that bone doesn’t rub on bone and so the back can be flexible with little or no pain. The intervertebral disc or just the “vertebral disc” is made of two separate kinds of material.  There is an outer portion made of tough material and an inner portion that is gelatinous in nature.

These are the two portions:

• Annulus fibrosus. This forms a tough circular ring made out of concentric sheets of fibers made out of collagen.  The ring completely surrounds the vertebral bodies—on the top of the body and on the bottom of the body.
• Nucleus pulposus. This is the central (interior) part of the disc.  It consists of a loose network of connective tissue fibers suspended in a gel consisting of a mucoprotein.

The role of the annular fibers is to hydraulically seal in the gelatinous nucleus pulposus.  It also distributes the pressure and forces placed upon the disc as part of day-to-day wear and tear.  The outer annulus and the inner nucleus are connected.

They fit like two cylinders, one inside the other.  They are connected by end plates made from collagen.

The disc needs to be hydrated.  Research has shown that the disc is 80 percent water and is really well cushioned.  The percent water goes down with age, but the disc remains hydrate because it is considered the major carrier of the axial load on the body.  Its strength and pliability depend on the disc containing plenty of water.

Discs tend to dehydrate as we age.  They become increasingly stiff, which results in the disc being less compressible.  This is a normal part of aging; however, the disc begins to break down in some people, leading to pain in the back, thorax, or neck.

The degeneration causes what’s known as “micro-motion instability.”  The inflammatory chemicals in the gelatinous inner core of the disc leak out and inflame the nerve roots exiting the spinal column and going out to innervate a part of the body.  In some cases, the disc is injured because of a twisting injury; the injury eventually leads to degeneration.

Part of the disc degenerates is that it has no blood supply and only a few nerve endings.  Without an adequate blood supply, there is no way for the disc to repair itself following an injury.  The degeneration worsens, and there can be chronic pain for many years.  Interestingly, because the inflammatory proteins decrease with age, there is less discogenic pain after 60 years.

One of the most common injuries to the intervertebral disc is called a disc herniation.  This occurs when a portion of the nucleus pulposus comes out through a break in the disc’s annulus portion.  The herniation can occur at any point in the circle that is the disc.

Part of the problem with a herniated disc is age. Discs work best when they are hydrated and, while the disc is 80 percent water at birth, this number goes way down as we age to less than 50 percent by 90 years of age.  The elastin, which makes the tissues stretchable, also changes with age by undergoing chemical cross-linking.  It makes the elastin less stretchy.  Daily activities put pressure on the annulus, which eventually breaks down.

Whenever an axial load is placed on the disc, the nucleus pulposus pushes against a damaged annulus and squirts out of defects in the annulus.  This is the part of the disc that gets removed during a discectomy.  The annulus can also bulge as a person ages, leading to a bulging disc that can no longer use its elasticity to hold in the nucleus pulposus.

A herniated disc can also be caused by an injury such as a fall, a motor vehicle accident, or a sports-related injury.  In such cases, even young people can suffer from a herniated disc when they normally function before the injury.

Other causes of a herniated disc include a sudden heavy strain on the low back, which happens with heavy lifting.  A sudden twisting motion can result in disc herniation.  Even a strong sneeze can result in damage to the annulus and a bulging or herniated disc.

Repetitive motion activities that involve lifting and using the lower back, especially with poor lifting habits or jobs that involve a long exposure to vibration, can cause a gradual breakdown of the annulus and a herniated disc.

The forces in a motor vehicle accident are severe.  Any kind of flexion/extension injury or twisting injury resulting from a car accident can lead to immediate pain in the neck, thorax, or lumbar spine.  In some cases, the damage is done, but the disc doesn’t herniate immediately.  The pain instead comes on after a few days or a few weeks when the nucleus pulposus finally leaks out of the damaged annulus.

The cervical spine and the lumbar spine are areas where a disc herniation is most likely to happen.  In most research studies, it has been found that the level most likely to suffer a herniation is the disk between the fourth and fifth lumbar vertebrae (L4-L5).

Other causes of a disc injury include smoking.  Smoking causes toxins to enter the body, linked to an increased risk of disc degeneration.  Being obese, eating a diet that is not healthy, and not exercising are also risk factors for a damaged disc.

Genetics can play a role in who gets disc disease and who doesn’t.  There are some known genes connected to the predisposition to getting degenerative disc disease.  In such cases, the tendency to have a ruptured or herniated disc will run in the family.

Because the vertebral disc involves soft tissue, it does not show up on plain film x-rays.  This leaves a CT scan or MRI scan, creating cross-sectional images of the vertebral bodies and the discs.  In such cases, the disc can be seen and identified as to its size and location.

Another test that can be done is a spinal myelogram, which can be done in the cervical, thoracic or lumbar areas, depending on the pain’s location.  It involves injecting dye into the intrathecal space.  The dye shows up on the x-ray.  Places that have a disc herniation will show up as defects in the spinal canal on x-ray film.

There are several choices for treatment in cases of disc disease.  One option is conservative management.  This involves pain control with medications, physical therapy, good posture and lifting techniques, and exercise.  Most patients will get better with conservative measures so that surgery can be avoided.

Another option is removing part of the disc in an endoscopic discectomy.  It is a minimally invasive procedure in which the herniated portion of the disc is removed via an endoscope. The part of the disc that is still contained within the annulus is left within the body.  Most patients get good pain relief with a tiny incision and minimal disruption of tissues.  The procedure can be done with a laser so that the total recovery time is much shorter than other types of back surgery.

Some patients opt for a spinal fusion.  In this procedure, the upper and lower vertebrae at a particular level (or more than one level) are fused together with plates and screws.  This diminishes the pain by making it impossible to move the spine at the affected level.  Unfortunately, this procedure does limit the range of motion of the spine, which can be a problem for some people.

Disc replacement, discussed below, is a procedure where an artificial disc is placed in the intervertebral space after the degenerated disc has been removed.

Artificial disc replacement is a newer procedure done instead of joint fusion, particularly in the lumbar spine area (the area most affected by disc disease). It is used to have a painful lumbar disc, usually from degeneration of the disc.  However, one contraindication of the surgery is arthritis in the facet joints at the level of the surgery to be performed.  If the facet joints are arthritic, there will be continued pain in the lumbar spine even if the surgery is successful.

The US FDA has approved the use of artificial implants only in L3-S1.  Two of these discs are Prodisk-L, which can be used from L4 to S1 only, and Charite.  The FDA approves only one level to be done.  Some doctors are doing multiple levels, but this is considered off-label use for these products.  The spinal vertebrae must be in otherwise great condition to have the surgery.  The spine must be stable and can have no evidence of having scoliosis or curvature of the spine to qualify for surgery.

Artificial discs need to be placed into the damaged disc space using a frontal and central approach.  The patient has opened anteriorly, and the spine is identified by working around the contents of the abdomen and cutting an incision into the retroperitoneal space.  The major blood vessels in the back are moved out of the way to cover up the spine.  Because of the necessity of working with major blood vessels, a general or vascular surgeon acts as one of the surgeons in the procedure and the spinal surgeon.

The disc space is cleaned out in preparation for the artificial disc, and then the new disc is positioned in the intervertebral space.  Following this, the blood vessels are replaced in their original position, and the abdominal contents are replaced in their normal positions.

The purpose of doing artificial disc surgery is to provide cushioning for the spine and ease pain.  The end result is:

• The maintenance of patient flexibility and motion.
• Less stress is placed on the other spinal fragments.
• It can treat low back pain and radiculopathy.

With the advent of the artificial disc replacement, also called a disc arthroplasty, there may be one day a satisfactory alternative to spinal fusion in cases of lumbar, or perhaps cervical, disc degeneration.

Disc arthroplasty is a huge surgery to undergo.  For this reason, there can be complications.  For example, there can be risks due to prolonged anesthesia time. Bleeding complications can occur because major blood vessels are being moved and manipulated.  This is why a vascular surgeon needs to be present during this procedure.  A patient can suffer from ileus or sluggish bowel because the bowels have to be manipulated at the beginning and end of the procedure.  Infection can be a risk and can even involve sepsis or blood infection due to the surgery.

The surgery is being done near the spinal nerves, which are exiting near the facet joints of the back.  Nerve damage in the back or other places of the abdomen can happen with this type of surgery.  Unfortunately, an individual can reject the implant materials, necessitating another surgery to remove the artificial disc and most likely perform a spinal fusion instead.

In one study of 27 patients with complications from a disc arthroplasty, several patients developed abdominal hematomas. In contrast, others suffered a dislocation of the artificial disc, which had to be removed with another type of disc procedure performed instead.

If you or a loved one has a disc injury due to someone else’s negligence and would like to discuss your legal options with an experienced Sacramento Traumatic Injury Attorney, call us at 916.921.6400 or 800.404.5400 for free, friendly advice.

Editor’s Note: This page has been updated for accuracy and relevancy. [cha 7.7.21]