Reliability of facet fluid on preoperative MRI for prediction of segmental instability after decompression surgery for degenerative lumbar spinal stenosis.

Background: The purpose of this study is to determine whether preoperative facet fluid on MRI can help predict segmental instability (SI) after decompression surgery.

Methods: We analyzed 34 patients (14 men and 20 women, a total of 37 segments) who underwent decompression for degenerative lumbar spinal stenosis from June 2011 to August 2019 at a single institution. Mean age at the time of operation was 67.8. Postoperative assessment was performed uniformly 12 months (11~15 months) after the surgery. Preoperative facet fluid on MRI, pre- and postoperative slip percentage, and segmental motion on lumbar lateral neutral and flexion-extension (LFE) radiographic images were measured. Visual Analog Scale (VAS) and necessities of interventional procedure or medication was also assessed for clinical outcomes.

Results: No significant association was found between preoperative facet fluid indices and pre- or postoperative slip percentage (P=0.134) and segmental motion (P=0.936). There were no significant association also between facet fluid indices and VAS of back or leg (P=0.997 and P=0.437 respectively).

Conclusions: Preoperative facet fluid is not a predictive index of postoperative segmental instability or clinical outcome. Without segmental instability on LFE radiographic images, the presence of facet fluid in MRI is not an absolute indication for fusion.