Annular Tear of Intervertebral Discs
An annular tear of intervertebral discs occur when the fibrous rings of the annulus fibrosus, or outer portion of the disc become thin, or worn out, to the point that a herniated disc occurs.
Intervertebral discs are what separate the vertebral bones of our spine. They compress downwards to absorb shock during the day, and inflate back to their original size when we lie down for extended periods, such as when we go to sleep. As we get older, the discs begin to lose their size, ability to retain water to hold themselves up, and becomes thinned or frayed at their outer covering. The disc may begin to undergo a process known as degenerative disc disease as we get older, due to degenerative changes to the inside or outside of the disc.
A disc may degenerate due to the watery, gelatin-like material on the inside of the disc, begins to lose its concentration of water, and is not able to compensate for this loss by absorbing more water. Degeneration to the outer layers of the discs, collectively known as the annulus fibrosus, may also occur due to a annular tears of the intervertebral discs. These annular tears often occur for the same reasons that the other joints of the body break down - due to the gradual progression of old age.
As we get older, the two degenerative processes progress at roughly the same rate, with the inside of the disc losing its concentration of water, while the outer annulus begins to gradually thin out. This process may continue and progress to advanced stages of degenerative joint disease, without the patient experiencing chronic back pain, in a majority of cases. Here's how degenerative disc disease could progress without causing middle back pain or lower back pain.
Imagine one of your intervertebral disc as a fully inflated grape in its young age, and more of a shriveled raison in it's advanced age. How could our discs change from one type of shape to another without us experiencing significant side effects. Imagine a fully inflated tire suddenly becoming thin along one portion of its treads, to the point that a complete tear opens up. If the tire were fully inflated, and still rolling down the road, the tire would suddenly pop, or blow out. But this is not what happens to our discs in many cases. In our human spine, the discs begin to slowly deflate themselves as their outer treads (annulus fibrosus) begin to wear out. Because of the lowered water concentration on the inside of the disc, there is not as much pressure on the wall of the disc pushing it outwards. Because of this lowered pressure against the wall of the disc as a result of fluid loss, the reduced pressures against it are not sufficient to tear the walls.
Unfortunately, there are cases where the walls of the intervertebral discs become worn out, or thinned, while there is still a large amount of fluid in the interior of the discs. When this occurs, the discs may become torn from the inside out, or the walls may begin to bulge outwards. When openings open that are big enough for the materials in the nucleus of the disc to flow outwards, this condition may be known as an annular tear of the intervertebral disc, also known as concentric tears. When the pressure on the interior walls of the disc cause it to bulge outwards, rather than tear, it is known as a bulging disc.