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.  

Anatomy of a Vertebral Disc

The intervertebral disc or just “vertebral disc” is made of two separate kinds of material.  There is an outer portion that is made of a 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 disc.  It consists of a loose network of connective tissue fibers that are 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 place upon the disc itself 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 itself remains hydrate because it is considered to be the major carrier of the axial load on the body.  Its strength and pliability depend on the disc containing plenty of water.  

Disc Degeneration

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, in some people, the disc begins to break down, 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 that are 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 reason why the disc degenerates is because 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 the age of 60 years.  

Causes of Disc Damage

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 annulus portion of the disc.  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.  

Any time an axial load is placed on the disc, the nucleus pulposus pushes against a damage 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 out 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 sports-related injury.  In such cases, even young people can suffer from a herniated disc when they had a normal functioning disc prior to the injury.  

Other causes of a herniated disc include a sudden heavy strain on the low back, such as happens with heavy lifting.  A sudden twisting movement 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 as a result of 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, which has been 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.  

Diagnosing Disc Disease

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, both of which create cross-sectional images of the vertebral bodies and the discs.  In such cases, the disc can be seen and identified as to their 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 location of the pain.  It involves injecting dye into the intrathecal space.  The dye shows up on x-ray.  Places that have a disc herniation will show up as defects in the spinal canal on x-ray film.

Treatment Options in Disc Disease

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 compared to 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.  

Disc Replacement Procedure

Artificial disc replacement is a newer procedure done instead of joint fusion, particularly in the lumbar spine area (which is the area most affected by disc disease). It is used in the situation of having a painful lumbar disc, usually from degeneration of the disc.  One contraindication of the surgery, however, 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 called 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 an off label use for these products.  It is very necessary that the spinal vertebrae be in otherwise great condition in order 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.  

Performance of the Surgery

Artificial discs need to be placed into the damaged disc space using a frontal and central approach.  The patient is 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 because they are covering up the spine.  Because of the necessity of working with major blood vessels, a general or vascular surgeon is acting as one of the surgeons in the procedure along with 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 the 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 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.  

Risks and Complications of a Disc Arthroplasty

The disc arthroplasty is a very big 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 at this procedure.  A patient can suffer from an ileus or sluggish bowel because the bowels have to be manipulated at the beginning and at the end of the procedure.  Infection can be a risk and can even involve a case of sepsis or blood infection as a result of 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 in 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 to perform a spinal fusion instead.  

In one study of 27 patients who had complications from a disc arthroplasty, several patients developed abdominal hematomas, while 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 as a result of someone else's negligence and would like to discuss your legal options with an experienced Sacramento Personal Injury Attorney, contact us online or call us at 916-921-6400 or toll-free at 800-404-5400 to set up a FREE consultation.
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