Which vacuum phenomenon is more predictive for future junctional disorders?: Intradiscal or Intrafacet?

Recent spine studies focused on identifying whether intradiscal vacuum phenomenon (VP) was associated with spinal instability. However, none of them reported a direct association between VP and spinal instability following fusion for degenerative lumbar spine disorders (DSDs), namely junctional disorders. In the present study, we aimed to evaluate whether the VP was predictive for junctional disorders in patients who underwent short-segment lumbar decompression and fusion for DSDs at a tertiary spine center. We retrospectively reviewed prospectively collected database of patients who underwent short-segment decompression and fusion for DSDs. Pre-operative sagittal and axial computed tomography (CT) scans were evaluated in terms of intradiscal and intrafacet VP at all lumbar levels, respectively. Each VP was scored as 1 point. Then, the total VP score was calculated as the sum of intradiscal VP score and intrafacet VP score. Then, we analyzed the possible predictivity of VP for junctional disorders at final follow-ups of the patients operated for short-segment lumbar decompression and fusion. Patients with junctional disorders had significantly higher total and intrafacet VP scores compared to those without junctional disorders. Total VP score had an OR of 1.217 (p = 0.014) and intrafacet VP score had an OR of 1.465 (p = 0.008). The ROC analysis depicted that the cut-offs value for total and intrafacet VP scores to predict junctional disorders following short-segment lumbar decompression and fusion were 1.5 points and 0.5 point, respectively. Vacuum phenomenon could be associated with junctional disorders in patients who underwent short-segment lumbar decompression and fusion for DSD. Intrafacet VP was more important than intradiscal VP in predicting junctional disorders. Proper surgical planning including the evaluation of both intrafacet and intradiscal VP at all lumbar levels is crucial to decrease the likelihood of junctional disorders.