What Is Spondylolisthesis?

Degenerative disc disease (DDD) is part of the natural process of growing older. As we age, our intervertebral discs lose their flexibility, elasticity, and shock absorbing characteristics. The outer fibers that surround the disc, called the annulus fibrosis, become brittle and are more easily torn. At the same time, the soft gel-like center of the disc, called the nucleus pulposus, starts to dry out and shrink. The combination of damage to the intervertebral discs, the development of bone spurs and the gradual thickening of the ligaments that support the spine can all contribute to degenerative arthritis of the lumbar spine.

To a certain degree, this process happens to everyone. However, not everyone who has degenerative changes in their lumbar spine has pain. Many people who have “normal” backs have MRIs that show disc herniations, degenerative changes, and narrowed spinal canals. Every patient is different, and it is important to realize that not everyone develops symptoms as a result of degenerative disc disease.

Types of spondylolisthesis:

Type I is called dysplastic spondylolisthesis and is secondary to a congenital defect of either the superior sacral or inferior L5 facets or both with gradual slipping of the L5 vertebra.

Type II, isthmic or spondylolytic, in which the lesion is in the isthmus or pars interarticularis, has the greatest clinical importance in persons under the age of 50. If a defect in the pars interarticularis can be identified but no slipping has occurred, the condition is termed spondylolysis. If one vertebra has slipped forward on the other (horizontal translation), it is considered spondylolisthesis.

Type II can be divided into three subcategories:

Type II A is sometimes called Lytic or stress spondylolisthesis and is most likely caused by recurrent microfractures caused by hyperextension. It is also called a “stress fracture” of the pars interarticularis and is much more common in males.
Type II B probably also occurs from microfractures in the pars. However, in contrast to Type II A, the pars interarticularii remain intact but stretched out as the fractures fill in with new bone.
Type II C is very rare and is caused by an acute fracture of the pars. Nuclear imaging may be needed to establish a diagnosis.

Type III is a degenerative spondylolisthesis, and occurs as a result of the degeneration of the lumbar facet joints. The alteration in these joints can allow forward or backward vertebral displacement. This type of spondylolisthesis is most often seen in older patients. In Type III, degenerative spondylolisthesis there is no pars defect and the vertebral slippage is never greater than 30%.

Type IV, traumatic spondylolisthesis, is associated with acute fracture of a posterior element (pedicle, lamina or facets) other than the pars interarticularis.

Type V, pathologic spondylolisthesis, occurs because of a structural weakness of the bone secondary to a disease process such as a tumor or other bone disorder.

How Is Spondylolisthesis Diagnosed?

To determine if spondylolysis is the cause of your symptoms, your doctor may, in addition performing a physical exam, recommend a diagnostic test such as an x-ray, computed tomography (CT) scan or magnetic resonance imaging (MRI). The diagnosis of spondylolisthesis is confirmed by noting the forward position of one vertebral body on another.

A spondylolisthesis also is graded according to the amount that one vertebral body has slipped forward on another. A grade I slip means that the upper vertebra has slipped forward less than 25 percent of the total width of the vertebral body, a grade II slip is between 25 and 50 percent, a grade III slip between 50 and 75 percent, a grade IV slip is more than 75 percent, and in the case of a grade V slip, the upper vertebral body has slid all the way forward off the front of the lower vertebral body, a condition called spondyloptosis.