Degenerative spondylolisthesis is a forward slippage of a single vertebra over another and generally occurs in patients >40 years of age.1 Spondylolisthesis can be characterized as degenerative, isthmic, dysplastic, traumatic, or pathologic. Degenerative spondylolisthesis represents 25% of all types of spondylolisthesis of the lumbar spine.1
Degenerative spondylolisthesis originates with disk degeneration and narrowing of the disk space. The ligamentum flavum then buckles, causing microinstability of the joint. The facet joints degenerate, which destabilizes the posterior elements and causes spondylolisthesis to occur.1
Degenerative spondylolisthesis is 5 times more likely to occur at the L4-L5 level compared with other levels due to the orientation of the facet joints.1 Degenerative spondylolisthesis is much more common in women, which is thought to be caused by hormonal-related relaxation of the supporting ligaments.1
A lateral radiograph of the lumber spine is the imaging of choice to measure the amount of static anterior listhesis.1 Flexion and extension views of the lumbar spine measure the degree of dynamic instability of the spondylolisthesis, which is an important factor when considering treatment options. Dynamic instability is often defined as sagittal translation of >4 mm or 8% of the vertebral body width with flexion and extension compared with neutral lateral radiographs.1
Chan et al compared the amount of translation between neutral standing, flexion, extension, and supine MRI and found that dynamic instability is best measured by comparing the amount of translation in a neutral standing lateral radiograph to a supine MRI.2 An accurate measure of dynamic translation is important as there is a significant correlation between the amount of dynamic translation measured and the overall improvement of back and leg pain one year after lumbar decompression and instrumented fusion.1-3
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
1. Moore D. Degenerative spondylolisthesis. OrthoBullets website. https://www.orthobullets.com/spine/2039/degenerative-spondylolisthesis. Updated January 19, 2020. Accessed May 11, 2020.
2. Chan V, Marro A, Rempel J, Nataraj A. Determination of dynamic instability in lumbar spondylolisthesis using flexion and extension standing radiographs versus neutral standing radiograph and supine MRI . [published April 26, 2019]. J Neurosurg Spine. doi:10.3171/2019.2.SPINE181389
3. Hendrickson NR, Kelly MP, Ghogawala Z, Pugely AJ. Operative management of degenerative spondylolisthesis. JBJS Rev. 2018;6(8):e4.