Is a Persistent Vacuum Phenomenon a Sign of Pseudarthrosis After Posterolateral Spinal Fusion?

The purpose of this study is to evaluate whether the vacuum phenomenon (VP) resolves after posterolateral lumbar fusion, and whether persistence of VP is indicative of failed fusion. We retrospectively reviewed patients with degenerative lumbar spinal stenosis with instability with a positive VP on preoperative computed tomography (CT) who underwent posterolateral lumbar spinal fusion. Lumbar CT and radiographs were evaluated for the presence of VP and fusion at each level. Thirty-six positive VP levels were identified on the preoperative lumbar CT at the levels in the fusion in 18 patients. The mean age at surgery was 67.6 ± 9.4 years and mean follow-up was 1.6 ± 0.86 years. Fusion was seen at 32 levels (88.9%). Of the 15 levels where VP persisted, evidence of fusion was seen in 13 levels and pseudarthrosis was seen at 2. Of the 21 levels where VP disappeared, fusion was seen at 19 levels and pseudarthrosis was seen at 2 .There was no significant difference between the 2 groups (P > .05). We did not find an association between persistence of VP and pseudarthrosis. Persistence of VP after spinal fusion may not be an indicator of pseudarthrosis, and should not be misinterpreted as an indication for additional surgery.