The phrase “disc disease” is misleading. This condition is a natural consequence of aging. The degeneration refers to alterations in the composition and function of the spinal cartilage, not necessarily to a progressive worsening of the accompanying symptoms.
When degenerative disc disease (DDD) is actively symptomatic, the problems it causes are typically located in the neck and/or lower back. The condition is highly variable in nature.
In some cases, the individual is completely unaware of its presence, and in others symptoms may actually improve depending on how the problem is addressed.
The Structure of the Human Spine
The spinal column is responsible for keeping humans upright, and is the center of our skeletal system. The length of the spine varies by height, but on average it will be 28 inches (71 cm) in men and 24 inches (61 cm) in women.
The Spinal Vertebrae
A total of 26 bony “blocks” or vertebrae separated by cushioning discs form the structure of the spine, which is divided into distinct regions:
- The cervical region or neck is composed of seven vertebrae. It is the most flexible portion of the spine.
- The thoracic region or mid-back includes 12 vertebrae.
- The lumbar region, or lower back, involves five vertebrae.
Below the last lumbar vertebrae, there are five more sacral vertebrae fused into the sacrum bone that run to the mid-buttock region of the body. Below that, lies the coccyx or tailbone. These are the least flexible portions of the overall structure.
If you were to view the spine from the side, it does not make a straight line, but rather follows four curves. The neck (cervical) and lower back (lumbar) portions curve inward, while the upper back (thoracic) and base (sacral) curve outward.
The curves stabilize and strengthen the total spine and help humans to remain balanced in our upright, standing position. The vertebrae grow larger toward the base of the spine because there they carry more weight.
The Function of the Discs
There are 23 discs that lie between the vertebrae that are designed to act as cushions, minimizing the impact of our daily movements on the spinal column. These structures also allow the spine to rotate and to move sideways.
There are no discs present between the skull and the first vertebra, or between the first and second vertebrae themselves.
Often you will see the discs compared to jelly donuts because they have a soft center called the nucleus pulposus. Each disc is a cartilaginous joint that compresses and decompresses (becomes thinner and thicker) as pressure is applied to it throughout the day.
At night, the discs get a chance to rest. Humans will always be slightly taller if measured in the morning than in the evening by a variation of about 1.5-2 cm.
An outer ring, the annulus fibrosus, which is comprised of ligaments, keeps the soft inner core contained so it can serve as a shock absorber.
The Spinal Cord
The spinal cord is encased in the center of the spine for protection. Each vertebra incorporates structures that allow spinal nerves to exit out of the spinal canal and branch outward.
These spinal nerves are responsible for carrying signals from the brain to the muscles and internal organs, and for relaying back sensory information gathered in the body.
This includes the ability to:
- feel heat and cold
- sense vibrations
- distinguish dull and sharp sensations
- sense the position of the limbs (arms and legs)
Additionally, the spinal cord plays a key role in the regulation of blood pressure, heart rate, and body temperature.
If these nerves are damaged, the effect can be extensive. Injuries to the cervical nerves (C1-C8) can result in quadriplegia, affecting the movement of the arms, hands, and legs. Damage to the thoracic nerves (T1-T12) may cause paraplegia, affecting the motion of the legs.
This complex interaction of the brain, spinal cord, and spinal nerves forms the body’s central nervous system. Often the symptoms of degenerative disc disease include neurological deficits like tingling in the extremities when some of these nerves become compressed.
When Degeneration Sets In
As humans age, the discs that separate the spinal vertebrae change in composition and size, leading to greater curvature of the spine. This explains why we become shorter as we get older.
Inflammatory Disc Pain
The principle alteration in the structure of the discs involves protein and water. As both are lost, the discs thin and weaken, losing their flexibility. These diminished capacities make the discs less effective as shock absorbers.
Discs have no way to repair themselves because they do not have their own blood supply. In fact, the discs don’t have many nerve endings, but the adjacent annulus fibrous does.
The proteins that leak out of the interior of the disc are inflammatory in nature, and are thus responsible for one type of pain that accompanies the degenerative process. The pain can also be mechanical, however.
When disc pain is mechanical, a nerve root is being physically compressed, typically as a result of a herniation due to tears in the annulus.
The disc’s inner “jelly” gets forced outward, causing the disc to bulge (herniate) and sometimes to rupture. If enough fluid leaks out of the center of the disc, it may collapse.
The more the distance between the vertebrae shrinks, the less the bones are cushioned from the impact of movement and the less flexible they become.
The collapse and decompression of the spine can lead to spinal stenosis. This narrowing of the spine’s open spaces puts further pressure on the spinal cord and nerves, and happens most commonly in the neck and lower back.
Additionally, the facet joints located between and behind the vertebrae for stabilization may begin to shift. Normally, these joints are in almost constant motion, but with spinal decompression, the bone may begin to overgrow leading to the development of bone spurs.
Bone spurs or osteophytes are the body’s attempts to stop excessive and painful spinal motion, but if the spurs grow into the spinal canal, they begin to press on the nerves causing even more pain.
Thus, the degeneration that begins with water loss in the joints can move through a progressive alteration of healthy spinal function with a cascading set of painful symptoms.
Exacerbating factors in this progression include, but are not limited to:
- being overweight
- having poor posture
- lifting heavy objects on a regular basis
- being subject to repetitive motion
Generally, the progression of degenerative disc disease is so slow people don’t realize the discs in their spines are changing. Rarely is the condition so severe as to require surgery.
On the other end of the spectrum, however, pain may be sufficiently debilitating to limit daily activities. This pain may present in the lower back or neck, but can also radiate into the shoulders, arms, buttocks, and legs. Twisting and reaching upward typically make the discomfort worse.
Diagnosing Degenerative Disc Disease
A diagnosis of degenerative disc disease starts with an extensive medical history. This will include questions about:
- symptoms (past and present)
- the pattern of change in those symptoms
- past injuries or illnesses
- treatment or intervention for past illnesses and injuries
- descriptions of current and past activities
During the course of the examination, the doctor will test for range of motion and look for areas up and down the spine that are tender or that are exhibiting nerve-related damage.
There will also be an assessment of sensations in other areas of the body to detect the presence of:
- tingling or a “pins and needles” feeling
- any numbness that may be present
- weaknesses and diminished reflexes
Other conditions like infections, tumors, fractures, strains, and muscle injuries will be ruled out, often by the use of imaging tests including X-rays and MRIs.
When a determination of degenerative disc disease is made, courses of treatment and intervention will be discussed. Strategies to cope with disc disease always begin with a conservative approach.
It’s important to remember that flare-ups of disc pain are highly episodic and heavily influenced by the presence of inflammation in the body. Early treatment will focus on coping strategies and pain relief with an eye toward behaviour modification and exercise to prevent future incidents.
Only in rarely and unusually severe cases is surgery recommended for degenerative disc disease, and then only after all other avenues have been fully explored.