This week’s research review highlights findings from a major multicenter randomized controlled trial evaluating the structural effectiveness of minimally invasive lumbar decompression (MILD) versus open midline decompression surgery in patients with lumbar spinal stenosis (LSS). As MILD gains adoption due to its safety profile, percutaneous nature, and Medicare reimbursement, an important clinical question remains: Does MILD achieve true anatomical decompression?

To address this, the study examined each procedure’s ability to reverse the nerve root sedimentation sign (SedSign)—a validated MRI biomarker of stenosis severity—and to demonstrate measurable postoperative decompression on MRI.

Citation: Ilogu CC, et al. “The efficacy of the MILD procedure for lumbar spinal stenosis: a multicenter randomized controlled trial assessing MRI evidence of ligamentum flavum removal and nerve root sedimentation sign.” The Spine Journal. 2025;25(11):S11–S12.[20]

Study Overview

The multicenter randomized controlled trial enrolled 665 patients across seven centers, all with MRI-confirmed lumbar spinal stenosis and a positive SedSign. Participants were randomized 5:1 into:

• Group 1: MILD (n = 545)

• Group 2: Open midline decompression (n = 120)

Pre- and postoperative MRIs evaluated:

• Ligamentum flavum thickness

• Dural sac dimensions

• SedSign reversal

• Scar tissue formation

• Multifidi muscle signal changes

The imaging assessments demonstrated excellent reliability (ICC = 0.98; Kappa = 1.0), ensuring confidence in anatomical measurements.

Why SedSign Matters

SedSign reflects nerve root crowding due to severe stenosis. Its reversal after surgery correlates strongly with successful anatomical decompression. Because SedSign is objective and reproducible, it is an ideal marker for comparing whether different techniques reliably decompress the spinal canal.

Key Findings

MILD Procedure (Group 1) Findings

• 0% SedSign reversal

• No reduction in ligamentum flavum thickness

• No increase in dural sac size

• No scar tissue formation, consistent with a non-disruptive approach

• No multifidi muscle changes

Postoperative MRI showed no evidence of anatomical decompression after MILD. These results suggest that the percutaneous technique does not adequately remove the ligamentum flavum or enlarge the spinal canal.

Open Midline Decompression (Group 2) Findings

• 100% SedSign reversal (p < 0.001)

• >90% resection of the ligamentum flavum

• Significant dural sac expansion

• Presence of scar tissue and multifidi changes, expected after surgical exposure

• No complications reported

Open surgery consistently demonstrated direct, measurable decompression of neural elements.

Interpretation & Clinical Implications

The findings from Ilogu et al. provide compelling evidence that open midline decompression remains the superior anatomical solution for LSS. While MILD’s minimally invasive design is attractive, the absence of any postoperative MRI changes—particularly the lack of SedSign reversal—raises concerns about its ability to address the true pathology of lumbar stenosis.

Open decompression, on the other hand, reliably removes stenotic tissue and restores canal dimensions, achieving complete SedSign reversal in all cases.

As the field continues to evolve, these results emphasize the need to develop minimally invasive procedures that match the decompressive effectiveness of open surgery while reducing its soft-tissue disruption.