Symptoms and Causes
In about 85% of back pain cases, the origin of the pain is unknown, and imaging studies usually fail to determine its cause. Disk disease, spinal arthritis, and muscle spasms are the most common diagnoses. Other problems can also cause back pain, however.
Lumbar Degenerative Disk Disease/Spondylosis
Osteoarthritis occurs in joints where cartilage is damaged and then destroyed, usually as a result of aging. In reaction to this destruction, the bones associated with the joints develop abnormalities. When osteoarthritis affects the spine, it may damage the cartilage in the disks, the moving joints of the spine, or both. These changes are age-related to some degree. However, the rate at which these changes develop varies between people, and may be accelerated by trauma or excessive wear and tear. The end result of these changes is a gradual loss of spinal structure and function, as well as chronic pain, muscle spasms, and reduced mobility. Depending on which part and how much of the spine is involved, symptoms may be similar to that of a herniated disc, lumbar strain, or spinal stenosis (narrowing of the spinal canal).
Herniated Disk
A herniated disk, sometimes (incorrectly) called a slipped disk, is a common cause of severe back pain and sciatica. A disk in the lumbar area becomes herniated when it ruptures or thins out, and degenerates to the point that the gel within the disk (the nucleus pulposus) pushes outward. The damaged disk can take on many forms:
- A bulge -- The gel has been pushed out slightly from the disk and is evenly distributed around the circumference.
- Protrusion -- The gel has pushed out slightly and asymmetrically in different places.
- Extrusion -- The gel balloons extensively into the area outside the vertebrae or breaks off from the disk.
Leg pain may be worse than the back pain in cases of herniated disks. There is also some debate about how pain develops from a herniated disk and how frequently it causes low back pain. Many people have disks that bulge or protrude and do not suffer back pain. Extrusion (which is less common than the other two conditions) is highly associated with back pain, since the gel is likely to extend out far enough to press against the nerve root, most often the sciatic nerve. Extrusion is very uncommon, however, while sciatic and low-back pain are very common. But there may be other causes of low back pain.
Abnormalities in the Annular Ring. Research has also focused on tears in the annular ring -- the fibrous band that surrounds and protects the disk. The annular ring contains a dense nerve network and high levels of peptides that heighten perception of pain. Tears in the annular ring are a frequent finding in patients with degenerative disk disease. Some cases of chronic low back pain may be caused by inward growth of nerve fibers into the annular ring, which triggers pain within the intervertebral disk.
