MiDAS ENCORE: Randomized Controlled Clinical
Trial Report of 6-Month Results
Authors: Staats Peter S. 
Published: February 2021

Background: Patients suffering from neurogenic claudication due to lumbar spinal stenosis (LSS)
often experience moderate to severe pain and significant functional disability. Neurogenic claudication
results from progressive degenerative changes in the spine, and most often affects the elderly. Both
the MILD® procedure and epidural steroid injections (ESIs) offer interventional pain treatment options
for LSS patients experiencing neurogenic claudication refractory to more conservative therapies. MILD
provides an alternative to ESIs via minimally invasive lumbar decompression.
Study Design: Prospective, multi-center, randomized controlled clinical trial.
Setting: Twenty-six US interventional pain management centers.
Objective: To compare patient outcomes following treatment with either MILD (treatment group)
or ESIs (active control group) in LSS patients with neurogenic claudication and verified ligamentum
flavum hypertrophy.
Methods: This prospective, multi-center, randomized controlled clinical trial includes 2 study arms
with a 1-to-1 randomization ratio. A total of 302 patients were enrolled, with 149 randomized to
MILD and 153 to the active control. Six-month follow-up has been completed and is presented in
this report. In addition, one year follow-up will be conducted for patients in both study arms, and
supplementary 2 year outcome data will be collected for patients in the MILD group only.
Outcome Measures: Outcomes are assessed using the Oswestry Disability Index (ODI), numeric
pain rating scale (NPRS) and Zurich Claudication Questionnaire (ZCQ). Primary efficacy is the
proportion of ODI responders, tested for statistical superiority of the MILD group versus the active
control group. ODI responders are defined as patients achieving the validated Minimal Important
Change (MIC) of ≥10 point improvement in ODI from baseline to follow-up. Similarly, secondary
efficacy includes proportion of NPRS and ZCQ responders using validated MIC thresholds. Primary
safety is the incidence of device or procedure-related adverse events in each group.
Results: At 6 months, all primary and secondary efficacy results provided statistically significant
evidence that MILD is superior to the active control. For primary efficacy, the proportion of ODI
responders in the MILD group (62.2%) was statistically significantly higher than for the epidural
steroid group (35.7%) (P < 0.001). Further, all secondary efficacy parameters demonstrated statistical
superiority of MILD versus the active control. The primary safety endpoint was achieved, demonstrating
that there is no difference in safety between MILD and ESIs (P = 1.00).
Limitations: Limitations include lack of patient blinding due to considerable differences in treatment
protocols, and a potentially higher non-responder rate for both groups versus standard-of-care due to
study restrictions on adjunctive pain therapies.
Conclusions: Six month follow-up data from this trial demonstrate that the MILD procedure is
statistically superior to epidural steroids, a known active treatment for LSS patients with neurogenic
claudication and verified central stenosis due to ligamentum flavum hypertrophy. The results of all
primary and secondary efficacy outcome measures achieved statistically superior outcomes in the
MILD group versus ESIs. Further, there were no statistically significant differences in the safety profile
between study groups. This prospective, multi-center, randomized controlled clinical trial provides
strong evidence of the effectiveness of MILD versus epidural steroids in this patient population. Key words: MILD, lumbar central spinal stenosis, minimally invasive lumbar decompression, interlaminar epidural steroid
injection, neurogenic claudication, ligamentum flavum, Oswestry Disability Index, ODI, Numeric Pain Rating Scale, NPRS, Zurich
Claudication Questionnaire, ZCQ