Adjacent segment degeneration or ASD is a condition that often occurs after a spinal fusion or another back surgery is done. ASD affects the intervertebral joint(s) above and below the area addressed by the surgery. ASD can occur anywhere along the spine.

Here’s the clinical definition of ASD: A complication of spine surgery that can be seen on an x-ray, CT scan or MRI as changes in the motion segments (i.e. the vertebral levels, or intervertebral joints) above and below the surgery site.

No one knows for sure if spinal fusion actually causes adjacent segment degeneration. Certainly, there are other factors at work in the development and progression of this condition, particularly advancing age. For example, a 1999 study by Etebar published in the Journal of Neurosurgery looked at 125 fusion patients in which rigid hardware was implanted to correct degenerative instability. The study found that post-menopausal women had an especially high risk for ASD.

What Makes the Joints Degenerate When You Have ASD?

After a fusion surgery, you’ll likely lose the ability to move your spine at the place where the procedure was done. This means you will no longer be able to bend forward, arch back, twist or tilt your spine at the specific level or levels addressed in surgery.

But that motion has to come from somewhere in order to accommodate the things you do hundreds of times during a day – things like sitting, standing, walking, reaching, lifting and more. Usually, it comes from the joints next to or near the surgery site.

You might understand ASD as the result of extra wear and tear on the intervertebral joints above and below your surgery site. These joints have to do double duty in order to make up for the (now) immovable portion of your spine. As such they are subject to extra stress, and this may lead to degenerative changes.

Does ASD Cause Pain?

While degenerative spinal changes associated with ASD do show up on films, they do not necessarily cause symptoms (such as pain). Should symptoms emerge, however, your doctor may diagnose you with adjacent segment disease.

Adjacent segment disease is a progressed form of ASD (adjacent segment degeneration) in which symptoms you did not previously experience show up.

When ASD Starts

Adjacent level degeneration resulting from a fusion surgery takes time to develop. Studies evaluating the incidence (number of new cases of a disease in a year) of ASD may follow spinal surgery patients for up to 20 years. In this way, researchers can give doctors and their patients an idea as to if and when degenerative changes in adjacent segments may develop.

For example, studies show that people who have back surgery when they are young most likely will develop ASD as they age. One example of this may be an adolescent who undergoes spinal fusion for scoliosis.

Will ASD Add to My Medical Problems?

So what will your exact diagnosis be if changes are seen on your films after a spinal fusion? Unfortunately, there is not much research on this topic. A small study done in 1988 by Lee, published in Spine and involving 18 patients found that the most common type of degeneration in cases of ASD was related to facet joint arthritis. Another study by Schlegel done in 1996, also published in Spine and involving 58 patients found incidences of spinal stenosis, disc herniation and spinal instability (an average of) 13.1 years after the surgery.

The good news is the presence of the degenerative changes in your spinal joints after surgery does not necessarily mean another medical issue for you to deal with. Research attempts at correlating the findings from doctors' exams with evidence of degenerative changes in films have resulted in an unclear picture about the degree to which ASD interferes with your lifestyle after the surgery. While some people do need a second surgery or at least conservative treatment for ASD, many times it’s not necessary.