Alex Simotas, MD

Hospital for Special Surgery
Board Certified Physiatrist
Specializing In Spine & Sports Medicine

Home > Learning Center > Anatomy > Age, Injury, or Disease of the Spine

Age, Injury, or Disease of the Spine

When is something found on tests like an X-ray, MRI, or CT scan important?  You get these tests back from your doctor and they are often loaded with things like:


Narrowed discs



Slipped vertebra (spondylolisthesis)


Are these important?  Do they mean you have a problematic spine?  How do they come about? Are they a result of past injuries? A spinal degenerative disease?  (And what does that mean?) Or they just of part of aging?

Here are some important initial facts to understand:

All of these are in some way related to spinal degeneration.

Spinal degeneration is a function of age and therefore at least some of these findings may show up on everyone’s tests.

Finding a test result with a report “Normal spine” is as rare as finding someone with absolutely no wrinkles on their skin, even when they have no symptoms.

We know this from studies that have been performed on people who never experience back pain.

What are the causes?

This article will explain how some of these changes come about, and…

how they may or may not lead to symptoms such as pain, weakness or changes in the function of your spine.

Spinal degeneration occurs as a result of changes in cell function due to aging. As will be discussed, “aging” does not mean “overused” or overloaded by repeated use.  In recent years, a basic shift has occurred in the way we understand the spine.  A lot of what was blamed on repetitive injury, are really manifestations of aging changes or adaptions to age.  On the contrary, some forceful weight bearing (or “loading”) and forceful use appears to be important in preserving spinal health.

We have found new causes for pain and loss of function of the back that are not 100 percent visible on currently available radiographic studies. At present, there is no reliable way to image or medically detect these causes that exist elsewhere in our body chemistries and nervous systems.

This shift in science and understanding has lead to changes in treatment.

RADIOLOGICAL STUDIES & SPINAL DEGENERATION: The challenge for the physician.

Radiological studies that include X-rays, CT or MRI scans help doctors to understand the architecture or structure of each person’s spine. Clearly they are important to assess injury and structure.  But, as explained above, they offer limited information.  The challenge for a physician includes:

  • Insuring that the test is performed accurately
  • Deciding what information on each test is relevant to back pain or the condition at hand
  • How to accurately convey this information to the patient


All parts of the body are produced and maintained by living cells, involving a process of upkeep and turnover. The spine is formed of tissues with living cells of numerous types:

  • bone
  • cartilage
  • blood
  • nerve

Lets look at some of the cells and how they might change with age or stress.


As you age, bone turnover slowly shifts towards greater bone cell loss than bone cell production. As a result, bone density or bone strength diminishes in everyone over age 65. This occurs at varying degrees, and women develop higher levels of bone loss with age than men.

When bone loss reaches a moderate level it is called osteopenia. When it is severe, it is called osteoporosis. Regular physical stress on the bones, such as that which occurs with physical activities and exercise, has a positive influence on bone formation and can actually help to slow down or reverse bone loss caused by other factors.


The spinal disc has two very important basic cells that form and regulate its structure:

  • The Nucleus Cells
  • The Anulus Cells

Changes in spinal discs that lead to disc degeneration appear to start with changes in the function of these particular cells.

The main mechanism for this change is a process called apoptosis. Apoptosis is a process that causes the genetically programmed death of a cell unit.


(For a more thorough review of anatomy see article “anatomy of the spine”)

The disc is composed of an inner nucleus and a tough outer layer called the anulus. The nucleus at the center of the disc has nucleus cells. The nucleus is a gel-like substance that is made of water, nucleus cells and special types of collagen proteins.

The nucleus has no direct blood supply. It gets its nutrition and oxygen indirectly through blood vessel endings in the adjacent edges of the vertebral bones called “end plates”.

The endplates are on the top and bottom of each vertebra. The spine relies on loading or compression, to push oxygen and nutrients through the endplates. Without loading, the nucleus of the disc would be starved of nutrition. Loading is very important to the spine.

Some nuclear cell function has been found to decrease early in life. This results in a gradual degradation of the consistency of the nucleus.

This can lead to disc dehydration: loss of water and a tougher consistency. On MRI scans the disc may look narrow and less bright. MRI reports refer to this as reduced disc signal intensity, disc desiccation, or disc dehydration.


The outer disc layer or anulus fibrosis has special anular cells. These cells form and maintain the tough ligament-like fibers that hold the disc and vertebral bodies together. Similar to the nucleus cells, anulus cells appear to deteriorate with age. The start of anular cell loss appears to occur around the same time as the loss of nuclear cells.

Anular cell function loss leads to changes in the collagen fibers allowing them to fray, split and disappear. This leads to a general deterioration of the anulus fibrosis.


The rings of the anulus begin to fail and tear. These tears (called anular tears) never heal. Over time, anular tears tend to increase in size as more and more rings fail.

The tears to the anulus can be radial or concentric.

  • Radial tears begin in the inner layers and extend towards the outer edge.
  • Concentric tears split and follow the circumference of the disc.

Anular tears seem to start occur during the teenage years, and gradually progress in number and size over time.

75% of all people have radial tears. By age 30, virtually everyone has concentric tears in their lower lumbar discs. Although anular tears occur in everyone, most do not produce any symptoms.


Anular tears can progress. When this occurs, the outer edge of the disc wall may begin to form contour changes called herniation. The thinning of the disc wall allows the nucleus content to move closer to the outside edge.

There are different forms of herniation, representing differences in severity including:

  • Disc bulge
  • Disc protrusion
  • Disc extrusion (also called prolapse)

Disc bulge frequently occurs in discs as they age, and refers to a broad rounding out of the anulus.

Protrusion refers to a more prominent point on the edge of a disc (like a pimple or a bubble on a tire) but it is still contained by some anulus.

Extrusion refers to a larger disc herniation, whereby the nucleus is extruded or pushed out of the anulus.

These herniations are deformities in the disc wall. They can extend outward and result in a narrowing of the space available for the nerve roots in the spinal canal. If there is some nerve compression, it’s more likely to have symptoms. However, all these changes are also common in people who are symptom-free.

It is important to remember that disc bulges do not necessarily form larger herniations. Bulges appear to be part of the process of age-related degeneration of spinal discs, along with anular tears, degeneration, and a loss of anular wall tension. Population studies on people without back pain show that disc bulges are present 20-40% of the time in 20 year olds and 80% of the time in 60 year olds.

Some individuals appear to be more prone to forming larger disc herniations. The nucleus can extend completely through the wall of the disc, resulting in a fragment (or piece) that displaces a spinal nerve. These fragments of disc material are called disc extrusions or sequestrations, and are often given the lay term “ruptured discs.”

These herniations can cause symptoms of nerve compression, such as numbness, weakness, or pain radiating into an arm or leg.


Apoptosis is the programmed death of a cell. It is distinctly different from traumatic cell death which is called necrosis. It is estimated that 50 to 60 billion cells die each day from apoptosis in the average human adult. This process that is constantly occurring with varying rates.

The tendency for apoptosis is pre-programmed into an individual’s genetic code. A group of studies has shown that genetically identical twins have a remarkably similar degree of disc degeneration, no matter what the activity level of each twin. Even if one twin has been sedentary and the other highly active, MRI scans show very similar spines.

Other factors such as smoking, can also influence cell loss and degeneration of the nucleus pulposus, but usually to a smaller degree than genetics. Surprisingly, daily stresses on the spine from work, physical activities, and exercise have a very minor influence on disc degeneration.


Facet joints share some of the load bearing with the spinal disc, while also functioning as stop pads to control the direction and degree of spinal motion. Facet joints also have an independent sensory nerve supply that makes them prone to pain sensation.

Facet joints contain synovial cells that produce a joint fluid, called synovial fluid. These cells increase during states of inflammation and during times of mechanical stress. Throughout the stages of degeneration, a pocket of increased synovial fluid can project from the joint into the spinal canal. This can cause a compression of a spinal nerve and lead to nerve-like symptoms.

The alignment of the spine clearly plays a role in the onset and rate of facet degeneration, in a process that is also mostly genetically predetermined.

Similar to disc tissues, facet joint arthritis appears to be mainly an age-related loss of function of the cells that maintain the cartilage surfaces of the facet joints.

Fortunately most of these conditions respond well to anti-inflammatory treatments.
Occasionally surgery is required to remove them.


Facet degeneration frequently results in changes in the alignment of the vertebrae in the lower back. Degenerative Spondylolisthesis is one such common change. It presents as a slight forward alignment of the L3 orL4 vertebra.

This finding is commonly noted in imaging studies of people after the age of 50. It is present in about twenty percent of people over the age of 70. Women are more prone to this than men.

Degenerative spondylolisthesis is usually well tolerated and may be present for years before it is discovered. It usually results in a reduction of the dimensions of the vertebral canal, and may contribute to the development of lumbar spinal stenosis. Spinal stenosis appears to be a stronger factor in back pain since it is only observed in 20 percent of individuals with no history of back pain.


  • Spine degeneration is mostly due to a genetically influenced process called cell apoptosis.
  • Degenerative anatomic findings on MRI scans are common.
  • Only a few specific findings have been correlated strongly with pain symptoms.
  • Compression forces that are experienced in most forms of exercise are not harmful, and may actually be important to the sustained health of spinal cells.