Back to Basics: What is Normal Segment Movement?

The greatest performers in any field of human endeavor have two things in common—they ask simple questions, and they obsess on the basics.

Former North American Spine Society (NASS) President and Chief of the Orthopaedic Spine Service at Keck Medicine, University of Southern California, Jeffrey Wang M.D. and his team organized a study to answer or at least provide parameters for what is the baseline question regarding spine instability—and, in turn, diagnosis and treatment of lumbar stenosis and spondylolisthesis.

Dr. Wang and his team led a multicenter group of researchers to tackle this basic but foundational question: What is normal segment movement?

Their work, “Evaluating the Prevalence of Motion Abnormalities at Treatment Levels and Non-Treatment Levels in Lumbar Stenosis and Spondylolisthesis Patients,” appears ahead of print in the March 30, 2023, edition of Spine.

“Regarding patients with spondylolisthesis, there is a common question of whether the segment is unstable or not, and whether a fusion is needed,” explained co-author Jeffrey Wang, M.D. to OTW. “I think most surgeons would plan a lumbar fusion as part of the surgical treatment if the segment was unstable. If there was no instability, then there is more controversy and different surgeons may give different opinions on the necessity of a fusion.”

“This was the first step towards trying to obtain some objective data on the pre-operative instability of patients with lumbar spinal stenosis and spondylolisthesis, and compare them to population norms, in order to determine the presence of instability.”

The investigators looked at the intervertebral motion of 24 lumbar spinal stenosis patients with spondylolisthesis patients treated with spinal fusion in relation to a previously published normative database using well validated measurement technology.

The researchers found a nearly even split of normal and abnormal motion at the treatment levels: 11/24 (45.8%) treatment levels exhibited normal motion, while 13/24 (54.1%) had abnormal motion. In contrast only 12/69 (17.3%) non-treatment levels exhibited abnormal motion. “The fact that we found differences in motion between treatment levels and non-treatment levels is an indicator that the normative database may generalize in a clinically useful manner,” said Dr. Wang.

“The ultimate goal,” said Dr. Wang, “would be to set the normal amount of movement of any given segment for a ‘normal’ population, and then when treating an individual patient, compare the amount of instability present for the treatment patient, to the normal population.”

“It is possible that we may be able to obtain some objective data on whether that segment where a patient is having surgery, has some instability compared to the normal population. This could potentially influence the surgical treatment.”

Co-author Zorica Buser Ph.D., M.B.A., research assistant professor in the Department of Orthopedic Surgery at NYU’s Grossman School of Medicine, said, “The long-term goal would be to develop artificial intelligence to help measure patients being treated and give an objective measurement of the presence of instability, and possibly help determine if a fusion is needed. This could also be used as a screening tool, to detect abnormalities of a patient being treated, compared to the normal population, to determine objectively if there is any instability, which could help guide conservative treatments, in addition to surgical treatments. It could very well end up being part of a screening tool for detecting any abnormalities in patients presenting with spinal problems.”

Dr. Wang added, “I think in the future, we may be able to use this information to detect adjacent level abnormalities and potentially help predict who is at risk for developing adjacent level instability for patients having a lumbar spinal fusion.”