Spine Journal - 2026-09-25 - Journal Article
Preoperative versus Postoperative MRI Comparisons After the MILD Procedure vs. Open Decompression for Lumbar Spinal Stenosis: Multicenter Cohort Study.
Jones MR, Fandos LM, Daitch JS, Thompson S, Beall DP, Yeddu A, Pannozzo P, Krishnan R, Albert SD, Kohane DJ, Navalgund YA, Abed H, Raikar SV, Spayde E, Costigan WM, Lore V, Lazzari M, Chebrolu S, Estevez H, Ilogu CC, Seale JA, Chin KR
Topics
Key Takeaway
MILD procedure achieved 0% SedSign reversal and no measurable anatomical decompression on postoperative MRI, versus 100% SedSign reversal and >90% ligamentum flavum removal with open decompression.
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Summary
This multicenter cohort study compared pre- and postoperative MRI findings in 182 patients with LSS and a positive nerve root sedimentation sign (SedSign) treated by either MILD (n=162) or open decompression (n=20). Blinded radiologists assessed SedSign reversal, ligamentum flavum thickness reduction, lamina defect, and multifidus signal changes. MILD produced no SedSign improvement or anatomical decompression on MRI, while open decompression achieved 100% SedSign reversal, >90% ligamentum flavum removal, and 100% lamina defect and multifidus scar signal changes.
Key Limitation
Non-randomized allocation by physician specialty introduces profound selection bias and confounding — MILD patients were managed exclusively by interventional pain physicians while open decompression patients were managed by a single orthopedic surgeon, making group differences in patient selection, disease severity, and surgical indication impossible to control.
Original Abstract
BACKGROUND CONTEXT
The minimally invasive lumbar decompression (MILD) procedure, introduced in 2005, is a percutaneous fluoroscopy-guided technique designed as an alternative to open decompression for patients with lumbar spinal stenosis (LSS) causing neurogenic claudication. MILD specifically targets hypertrophied ligamentum flavum, allowing for expansion of the dural sac to relieve central stenosis, but it is not intended to treat lateral recess or foraminal stenosis. While published studies have reported symptomatic improvement, no study has evaluated pre- and postoperative MRI to assess its effectiveness in achieving anatomical decompression and improving nerve root sedimentation sign (SedSign).
PURPOSE
To compare pre- and postoperative MRI findings in patients undergoing MILD versus open decompression, specifically evaluating changes in SedSign and anatomical decompression for LSS.
STUDY DESIGN/SETTING
Multicenter cohort study conducted at seven centers between 2019 and 2024.
PATIENT SAMPLE
A total of 182 patients with LSS and a positive SedSign on preoperative MRI underwent either MILD (n = 162) by interventional pain management (IPM) physicians or open decompression (n = 20) by an orthopedic spine surgeon. All patients received postoperative MRI for assessment.
OUTCOME MEASURES
Measures included pre- and postoperative MRI assessments evaluating SedSign improvements, decrease in ligamentum flavum thickness, presence of a lamina defect and multifidus muscle scar signal changes.
METHODS
Patients were assigned to treatment based on the specialty of the consulting physician: IPM physicians performed MILD (Group 1), and an orthopedic spine surgeon performed open decompression (Group 2). Blinded radiologists reviewed pre- and postoperative MRI scans to assess SedSign and anatomical changes. Interobserver and intraobserver reliability were analyzed using Cohen kappa statistics.
RESULTS
Group 1 demonstrated no SedSign improvement or anatomical changes. Group 2 achieved 100% SedSign reversal, >90% ligamentum flavum removal, 100% lamina defect and multifidus muscle scar signal changes postoperatively. No complications were reported in either group.
CONCLUSION
The MILD procedure did not produce anatomical decompression or SedSign reversal on MRI, whereas open decompression reliably achieved both. Secondary anatomical changes, such as scar tissue and muscle signal alterations, were observed only in the open surgery group. These findings suggest that while MILD is tissue-sparing, it may be insufficient for achieving anatomical goals in patients with central LSS. Future percutaneous strategies should aim to combine the anatomical effectiveness of open decompression with the reduced tissue disruption characteristic of less exposure approaches.