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Natural Disc Height Narrowing Does Not Help with Cervical Spondylolisthesis

Disc Height Narrowing

Goal of the Study?

Disc height narrowing is thought to incur stabilization over time as discs dry out and age. However, in this study1, the researchers were curious to investigate the cervical spine as most previous knowledge of degenerative spondylolisthesis has been performed in the lumbar spine. The cervical spine is structurally different compared to the lumbar spine and has been trickier to ‘fix’ in the case of cervical spondylolisthesis. Often disc height loss will stiffen spinal motion segments, but these researchers were curious about whether the degenerative cascade seen in aging would naturally stabilize as the disc loses height.

Why are they doing this study?

Cervical instability, or dynamic cervical spondylolisthesis, is a common problem for many. This is identified when a cervical vertebra will slip more than 1.8mm on its adjacent vertebra, most often seen in the frontal plane during flexion-extension motion. According to Kirkaldy-Willis’s work on the lumbar spine, a degenerative cascade will naturally stabilize over time. However, the cervical spine appears to behave a little differently. And because these unstable motion segments in the cervical spine contribute to ongoing pain for many, the researchers wanted to see if disc height narrowing stabilized the unstable motion segments naturally. In other words, if left alone, do cervical spines naturally become more stable over time?

 

What was done in this study?

The researchers looked retrospectively at 731 patients who underwent routine radiographs, including cervical flexion-extension x-rays. Additionally, each subject underwent CT or myelogram-CT. The researchers used a 2mm translation of one vertebra on another as an unstable spondylolisthesis. Of the 731 subjects, they identified 101 cases revealing cervical spondylolisthesis. Of these 101 cases, 68 demonstrated anterior translation, while 40 cases slipped posteriorly. If more than two levels were found to translate more than 2 mm, these cases were considered unique and not used and excluded from the data set. Two spinal surgeons evaluated disc height loss by comparing discs of the spondylolisthesis level and grading the disc height compression on a grade scale of 0-4. A zero grade indicated no height loss, a grade 1 indicated 25-50% loss, a grade 3 indicated 50-75% loss, and grade 4 indicated greater than 75% loss of disc height.

 

What did they find?

Disc height narrowing did not reduce the degree of slippage, which was opposed to what the researchers suspected. The researchers found that disc height narrowing was a risk factor for cervical spondylolisthesis. They also found that anterior slippage had more variation compared to posterior translation. Interestingly, disc height narrowing did not have as much effect on increasing the slippage when the translation was posterior compared to anterior.

 

Why do these findings matter?

Cervical spondylolisthesis appears to be different than what has been thought to occur naturally over time in the lumbar spine. Because these findings showed that the natural degenerative changes of the cervical spine did not stabilize the already moving motion vertebra in the cervical spine, time cannot be counted on to help cervical problems related to cervical spondylolisthesis. Solutions focussing on maintaining disc height should be considered in the future as disc height loss encroaches on the spinal canal and intervertebral foramen of the cervical spine.

 

At Dynamic Disc Designs, we create dynamic human anatomy models showing the dynamic disc height loss as it relates to the spinal spacing where nerves reside. Helping patients understand their own anatomy with the postures and activities they perform to maintain disc health is at the roots of our company. Consider taking patient education to the next level with a dynamic disc model.

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