Our discs are our 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.
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 affects the low back, buttocks and thighs or the neck, depending on where the affected disc is
Numbness and tingling
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.
Some people appear to have more nerve endings deeper in the outer area of the disc. This may make them more sensitive to back pain.
Diagnosis
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.
