What is Spondylolisthesis?

Spinal Vertebral Bone and Intervertebral Disc
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What is Spondylolisthesis?

Spondylolisthesis is a condition in which a vertebra slips out of it's normal position. One spinal bone slides either forward or back, usually forward, relative to the bone beneath it.

Spondylolisthesis may be a cause of, and is often considered to be a form of, spinal instability.

Types of Spondylolisthesis

From cause to slippage characteristics, a number of ways to classify spondylolisthesis exist. But two of the most common, degenerative and spondylolytic, or isthmic, spondylolisthesis, are related to how each originates.

Spondylolytic, or Isthmic, Spondylolisthesis

Spondylolytic spondylolisthesis is generally caused by a stress fracture at a little known site on the back of a spinal bone called the pars interarticularis. The pars interarticularis is a part of the facet joint.

This type of spondylolisthesis most often affects the L5-S1 intervertebral segment.

Left untreated, and certainly once slippage occurs, this stress fracture may develop into spondylolisthesis. Unlike degenerative spondylolisthesis, which is discussed below, the back part of the spinal bone is damaged (by the inciting injury) in cases of spondylolytic spondylolisthesis.

The American Academy of Orthopedic Surgeons says that often pars fracture goes unnoticed until the patient reaches adulthood. After that, they say, degenerative changes that start in the disc may stress the pars fracture further, which, in turn, may cause the spinal bone to slip forward.

Genetics sometimes predisposes people to the initial pars defect, but not always; this type is called dysplastic spondylolisthesis. 

Symptoms of isthmic spondylolisthesis include leg pain and lower back pain. The American Academy of Orthopedic Surgeons says that the most common leg symptom is a vague feeling of weakness that occurs if you've been walking or standing for a while.

Numbness, electrical sensations, weakness and pain are other possible leg symptoms. You may find these disappear when you bend forward or sit, and get worse when you stand or walk. The Academy says this is because sitting and bending opens up the space where nerves are located, thereby relieving pressure.

Degenerative Spondylolisthesis

Degenerative spondylolisthesis is related to changes that occur in the spine as we age. For one thing, the discs start to dry up and become brittle. As this occurs they lose height, and may bulge. According to the American Academy of Orthopedic Surgeons, degenerative changes that affect the disc may give rise to spinal arthritis and/or degenerative spondylolisthesis.

The degenerative process weakens not only the discs but the spinal joints and ligaments as well. The result may be a loss of positional integrity in the spinal column, the Academy says.

Once the bone starts to slip, it may narrow, and put pressure on, the spinal cord. This condition, spinal stenosis, common in people with degenerative spondylolisthesis. It may cause pain, or the numbness, electrical sensations and/or weakness described above in the isthmic spondylolisthesis section. Back pain is a possibility, as well.

Who is At Risk for Spondylolisthesis?

Children involved in sports such as gymnastics, football and diving tend to be at a higher risk for isthmic spondylolisthesis. These sports require repeated spinal hyperextension (bending backwards), which is what causes the pars interarticularis stress fracture.

Degenerative spondylolisthesis tends to mainly occur in non-athletic adults after the age of 40.

A 2018 study identified older age, female gender, larger body mass index (i.e., being overweight or obese) and certain anatomical variations that cause a bent over posture as factors that elevate the risk for this condition. The same study asserts that degenerative spondylolisthesis may be a cause of spinal stenosis.

Grades of Spondylolisthesis

Spondylolisthesis is measured in grades (degrees) of slippage. There are four grades, each representing twenty-five percent slippage.

For example, if a patient is measured to have a grade 2 spondylolisthesis, this means that the two adjacent vertebra maintain a fifty percent contact with one another.

Grades are measured by taking a side view x-ray.

Other diagnostic methods, such as CT scans or MRIs might be used to determine the damage to surrounding tissues.

Spondylolisthesis Treatment

Spondylolisthesis is treated according to the grade. For grades 1 and 2, conservative treatment, including physical therapy, home exercises, stretching and the use a brace are often given. In physical therapy, core strengthening and stabilization exercises are emphasized.

Spondylolisthesis Surgery

If you have a higher grade of spondylolisthesis, your doctor may suggest fusion surgery to help stabilize the spine.

But this treatment may not be effective. A systematic review conducted by the Cochrane Database found that results of studies assessing surgery (and other treatments) for spondylolisthesis conflicted with one another. Because of this, the researchers concluded that some aspects of surgery may be useful, while others are in question. 

As medical technology advances, surgeons have an increasing number of techniques and devices from which to choose when operating on you. And they can mix and match. That said, there is little research on whether or not a combination approach is effective for you, the patient.

A 2018 systematic review published in the journal Spine looked at a variety of fusion techniques that were given to over fifteen hundred patients who went "under the knife" for low grade isthmic spondylolisthesis. They found that adding reduction, which is putting a bone back in place, to a fusion does not help patients' pain or ability to function.

The authors also found no significant difference in the short term (up to three years) between a combination interbody fusion with a pedicle screw installed versus a posteriolateral fusion with a pedicle screw installed.

But after three years, the authors say, the interbody fusion with pedicle screw may indeed be better for pain relief and physical functioning.

And while they found no difference between circumferential fusion and interbody fusion for pain relief and physical functioning, they did mention that circumferential fusion is known for longer time on the operating table, blood loss during surgery, and longer hospital stays.

A Word from VeryWell

It's likely obvious to you that doing your research before saying yes to a suggested surgery may save you time, money and pain.

And don't forget to work your core (according to your physical therapist's instruction, of course.) For many people, remaining dedicated to an exercise program tailored to their condition is all they need to live a spine-healthy life.

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