Background: Lumbar spinal stenosis (LSS) is a common degenerative condition of the spine, which is
a major cause of pain and functional disability for the elderly. Neurogenic claudication symptoms are a
hallmark of LSS, where patients develop low back or leg pain when walking or standing that is relieved
by sitting or lumbar flexion. The treatment of LSS generally begins with conservative management such
as physical therapy, home exercise programs, and oral analgesics. Once these therapies fail, patients
commonly move forward with interventional pain treatment options such as epidural steroid injections
(ESIs) or MILD® as the next step.
Objective: To assess improvement of function and reduction in pain for Medicare beneficiaries following
treatment with MILD (treatment group) in LSS patients with neurogenic claudication and verified
ligamentum flavum hypertrophy and to compare to a control group receiving ESIs.
Study Design: Prospective, multi-center, randomized controlled clinical trial.
Setting: Twenty-six US interventional pain management centers.
Methods: Patients in this trial were randomized one to one into 2 study arms. A total of 302 patients
were enrolled, with 149 randomized to MILD and 153 to the active control. 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 ESI 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 is
the 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. This report presents safety and efficacy results
at 1-year follow-up. Outcomes at 2 years will be collected and reported for patients in the MILD group only.
Results: At 1-year follow-up, ODI, NPRS, and all 3 ZCQ domains (Symptom Severity, Physical Function
and Patient Satisfaction) demonstrated statistically significant superiority of MILD versus the active
control. For primary efficacy, the 58.0% ODI responder rate in the MILD group was higher than the
27.1% responder rate in the epidural steroid group (P < 0.001). The primary safety endpoint was
achieved, demonstrating that there is no difference in safety between MILD and ESIs (P = 1.00).
Limitations: There was a 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 adjunctive pain
therapy study restrictions. Study enrollment was not limited to patients that had never received ESI therapy.
Conclusions: One-year results of this randomized controlled clinical trial demonstrate that MILD is
statistically superior to ESIs in the treatment of LSS patients with neurogenic claudication and verified
central stenosis due to ligamentum flavum hypertrophy. Primary and secondary efficacy outcome
measures achieved statistical superiority in the MILD group compared to the control group. With 95%
of patients in this study presenting with 5 or more LSS co-factors, it is important to note that patients
with spinal co-morbidities also experienced statistically significant improved function that was durable
through 1 year.
Key words: MILD, minimally invasive lumbar decompression, interlaminar epidural steroid injections,
ESI neurogenic claudication, ligamentum flavum, ENCORE, PILD, CED Study, LSS
Real world adverse events of interspinous spacers using Manufacturer and User Facility Device Experience data