Spondylolisthesis

Isthmic spondylolisthesis

The spine condition called isthmic spondylolisthesis occurs when one vertebral body slips forward on the one below it because of a small fracture in a piece of bone that connects the two joints on the back side of the spinal segment.

The fracture in this small piece of bone, called the pars interarticularis, is caused by stress to the bone. While the fracture tends to occur most commonly when an individual is young (around 5 to 7 years old), for most people symptoms typically do not develop until adulthood. There is another spike in occurrence of lower back pain from spondylolisthesis in adolescence.

It is estimated that 5 to 7% of the population has either a fracture in this small piece of bone (a fracture of the pars interarticularis) or a spondylolisthesis (slipped vertebral body), but in most cases there are no symptoms. It has been estimated that 80% of people with a spondylolisthesis will never have symptoms, and if it does become symptomatic, only 15 to 20% will ever need surgical correction.

I was fortunate to meet Dr. Oliver, who took decisive action and decided to treat me by putting a dynamic stabilization system into my vertebra. Following this my recovery has been very rapid

– Olwen / Dublin – Ireland

Isthmic Spondylolisthesis Causes

The pars interarticularis (Latin for “bridge between two joints”) connects the facet joint above to the one below. It is a thin piece of bone with a poor blood supply, which makes it susceptible to stress fractures. There also can be a fracture of the pars interarticularis without a vertebral slip. The fracture itself is known as a spondylolysis. The pars interarticularis may also be referred to as the isthmus.

When this small bone fractures it usually does not cause pain or other symptoms. Trauma is not a common reason for fracturing. The fracture is usually due to cumulative stress, analogous to taking a paper clip and bending it multiple times. It will eventually break apart after enough stress.

Isthmic spondylolisthesis occurs most commonly in the L5-S1 level of the spine, the lowest level of the lumbar spine. It does happen rarely above this level, at L4-L5 or L3-L4, but at these levels trauma (rather than cumulative stress) is a more common cause of the fracture.

A fracture has not ever been found in a newborn so it is not considered a congenital problem. The slip that results from having the fracture is most likely to progress in juvenile or adolescent individuals. Progression of the slippage in adulthood is rare.

At L5-S1 there is not usually a lot of instability associated with the condition because there is a large ligament (the sacral alar ligament) that connects the L5 vertebral body to the sacrum, preventing the progression of slippage of L5 on the sacrum.

 

Degenerative Spondylolisthesis

Degenerative spondylolisthesis is Latin for “slipped vertebral body”, and it is diagnosed when one vertebra slips forward over the one below it. This condition occurs as a consequence of the general aging process in which the bones, joints, and ligaments in the spine become weak and less able to hold the spinal column in alignment.

Degenerative spondylolisthesis is more common in people over age 50, and far more common in individuals older than 65. It is also more common in females than males by a 3:1 margin.

A degenerative spondylolisthesis typically occurs at one of two levels of the lumbar spine:

  • The L4-L5 level of the lower spine (most common location)
  • The L3-L4 level.

Degenerate spondylolisthesis is relatively rare at other levels of the spine, but may occur at two levels or even three levels simultaneously. While not as common as lumbar spondylolisthesis, cervical spondylolisthesis (in the neck) can occur. When degenerative spondylolisthesis does occur in the neck, it is usually a secondary issue to arthritis in the facet joints.

 

Degenerative Spondylolisthesis Causes

Every level of the spine is composed of a disc in the front and paired facet joints in the back. The disc acts as a shock absorber in between the vertebrae, whereas the paired facet joints restrain motion. They allow the spine to bend forwards (flexion) and backwards (extension) but do not allow for a lot of rotation.

As the facet joints age, they can become incompetent and allow too much flexion, allowing one vertebral body to slip forward on the other.

In cases of degenerative spondylolisthesis, the degenerated facet joints tend to increase in size, and enlarged facet joints then encroach upon the spinal canal that runs down the middle of the spinal column, causing canal stenosis.

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