Defining Instability in Degenerative Spondylolisthesis: Surgeon Views

Clin Spine Surg. 2019 Dec;32(10):E434-E439. doi: 10.1097/BSD.0000000000000874.


Study design: Surgeon survey.

Objective: To examine factors influencing surgeons' definition of instability in grade 1 degenerative spondylolisthesis (DS) and assess treatment preferences for both stable and unstable DS.

Summary of background data: DS treatment options are broadly classified as decompression with or without fusion. In surgical decision-making, "instability" is frequently considered as a key factor. However, no consensus on the definition of instability exists.

Methods: A survey was conducted to ascertain the minimum amounts of static translation, dynamic translation, and angulation change that surgeons considered significant for determining instability. The importance of other clinical and radiographic features were also assessed, and respondents' standard treatment for stable and unstable DS.

Results: Out of 226 respondents, 99% deemed dynamic translation moderately to extremely influential for determining instability, whereas only 55% found static translation as important. The most prevalent cut-off values for dynamic (57%) and static translation (32%) were at least 2-4 mm and for angulation change at least 10-15 degrees (43%). Facet angulation was considered moderately to extremely important to determine instability by 69% of the surgeons, disk height by 67%, patient age by 64%, severity of stenosis by 55%, severity of back pain by 50%, patient-reported function by 49%, pelvic incidence by 47%, and severity of neurogenic claudication by 42%.Decompression with fusion was the preferred treatment method for unstable DS in 99% of the respondents. For stable DS, 40% would still perform fusion, whereas 60% preferred treatment with decompression-alone. Those who preferred fusion for stable DS reported significantly lower thresholds for static (P<0.001) and dynamic translation (P=0.004) for their determination of instability.

Conclusions: Clear consensus regarding the definition of instability does not exist. Dynamic translation is the most agreed-upon parameter of influence. Treatment preferences vary for stable DS, but for unstable cases there is broad consensus to perform fusion.

Level of evidence: Level II.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Decompression, Surgical
  • Female
  • Humans
  • Male
  • Preoperative Care
  • Spinal Fusion
  • Spondylolisthesis / pathology*
  • Surgeons*
  • Surveys and Questionnaires