Nearly everyone shows some signs of wear and tear on the spinal discs as they age. Not everyone, however, will have symptoms described as degenerative disc disease. Not actually a disease, degenerative disc disease refers to a condition in which pain is caused from a damaged disc. A wide range of symptoms and severity is associated with this condition.
The discs are like shock absorbers between the bones of the spine and are designed to help the back stay flexible while resisting terrific forces in many different planes of motion. Each disc has two parts:
- A firm, tough outer layer (annulus fibrosus). The outer portion of this layer contains nerves. If the disc tears in this area, it can become quite painful.
- A soft, jelly-like core (nucleus puposus). This part of the disc contains proteins that can cause the tissues they touch to become swollen and tender. If these proteins leak out to the nerves of the outer layer of disc they can cause a great deal of pain.
Unlike other tissues of the body, there is very little blood supply to the disc. Once a disc is injured, it cannot repair itself, and a spiral of degeneration can set in with three stages that appear to occur over 20 to 30 years:
- Acute pain makes normal movement of the back difficult
- The bone where the injury occurred becomes relatively unstable. Over a long period of time, the patient will have back pain that comes and goes.
- The body restabilizes the injured segment of the back. The patient experiences fewer bouts of back pain.
The X-ray below shows degenerated discs on the leftbefore surgery. On the right is an X-ray of the discs after traditional spinal fusion surgery.
The typical person with degenerative disc disease is active, otherwise healthy and in his or her 30s or 40s. Common symptoms of this condition include:
- Pain that is worse when sitting. While seated, the discs of the lower back have three times more load on them than when standing.
- Pain that gets worse when bending, lifting or twisting
- Feeling better while walking or even running than while sitting or standing for long periods of time
- Feeling better changing positions often or lying down
- Periods of severe pain that come and go. These last from a few days to a few months before getting better. They can range from nagging pain to severe, disabling pain.
- Pain can affect the low back, buttocks and thighs or the neck, depending on where the affected disc is, radiating to the arms and hands
- Numbness and tingling in the extremities
- Weakness in the leg muscles or foot drop may be a sign that there is damage to the nerve root
Causes and Risk Factors
Several factors can cause discs to degenerate, including age. Specific factors include:
- The drying out of the disc. When we are born, the disc is about 80% water. As we age, the disc dries out and doesn't absorb shocks as well
- Daily activities and sports cause tears in the outer core of the disc. By the age of 60, most people have some degree of disc degeneration. Not everyone at that age has back pain, however.
- Injuries, which can cause swelling, soreness and instability. This can result in low back pain.
A diagnosis is based on a medical history and a physical examination, as well as the symptoms and the circumstances where the pain started. Magnetic resonance imaging (MRI scan) can show damage to discs, but it alone cannot confirm degenerative disc disease.