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Long-Term Safety and Efficacy of Minimally Invasive Lumbar Decompression Procedure for the Treatment of Lumbar Spinal Stenosis With Neurogenic Claudication: 2-Year Results of MiDAS ENCORE
  1. Peter S. Staats, MD, MBA*,
  2. Timothy B. Chafin, MD,
  3. Stanley Golovac, MD,
  4. Christopher K. Kim, MD§,
  5. Sean Li, MD,
  6. William B. Richardson, MD**,
  7. Ricardo Vallejo, MD, PhD††,
  8. Sayed E. Wahezi, MD‡‡,
  9. Edward P. Washabaugh, MD§§ and
  10. Ramsin M. Benyamin, MD††
  1. *From the National Spine and Pain Centers, Shrewsbury, NJ;
  2. Department of Pain Management and Rehabilitation Medicine, Vidant Roanoke-Chowan Hospital, Ahoskie, NC;
  3. Florida Pain Institute, Merritt Island, FL;
  4. §The Center for Pain Relief, Charleston, WV;
  5. Premier Pain Centers, Shrewsbury, NJ;
  6. **Southeastern Spine Institute, Mount Pleasant, SC;
  7. ††Millennium Pain Center, Bloomington, IL;
  8. ‡‡Departments of Physical Medicine and Rehabilitation and Anesthesiology, Albert Einstein College of Medicine at Montefiore, Montefiore Medical Center, Bronx, NY; and
  9. §§Michigan Pain Specialists, Ypsilanti, MI
  1. Address correspondence to: Peter S. Staats, MD, MBA, National Spine and Pain Centers, 170 Avenue at the Common, Ste 6, Shrewsbury, NJ 07702 (e-mail: peterstaats{at}


Background and Objectives This study evaluated the long-term durability of the minimally invasive lumbar decompression (MILD) procedure in terms of functional improvement and pain reduction for patients with lumbar spinal stenosis and neurogenic claudication due to hypertrophic ligamentum flavum. This is a report of 2-year follow-up for MILD study patients.

Methods This prospective, multicenter, randomized controlled clinical study compared outcomes for 143 patients treated with MILD versus 131 treated with epidural steroid injections. Follow-up occurred at 6 months and at 1 year for the randomized phase and at 2 years for MILD subjects only. Oswestry Disability Index, Numeric Pain Rating Scale, and Zurich Claudication Questionnaire were used to evaluate function and pain. Safety was evaluated by assessing incidence of device-/procedure-related adverse events.

Results All outcome measures demonstrated clinically meaningful and statistically significant improvement from baseline through 6-month, 1-year, and 2-year follow-ups. At 2 years, Oswestry Disability Index improved by 22.7 points, Numeric Pain Rating Scale improved by 3.6 points, and Zurich Claudication Questionnaire symptom severity and physical function domains improved by 1.0 and 0.8 points, respectively. There were no serious device-/procedure-related adverse events, and 1.3% experienced a device-/procedure-related adverse event.

Conclusions MILD showed excellent long-term durability, and there was no evidence of spinal instability through 2-year follow-up. Reoperation and spinal fracture rates are lower, and safety is higher for MILD versus other lumbar spine interventions, including interspinous spacers, surgical decompression, and spinal fusion. Given the minimally invasive nature of this procedure, its robust success rate, and durability of outcomes, MILD is an excellent choice for first-line therapy for select patients with central spinal stenosis suffering from neurogenic claudication symptoms with hypertrophic ligamentum flavum.

Clinical Trial Registration This study was registered at, identifier NCT02093520.

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  • P.S.S. and R.M.B. are study principal investigators for MiDAS ENCORE. In this role, they have been responsible for study oversight. Responsibilities include protocol review, assistance with site selection, site investigator support, oversight of patient enrollment and protocol compliance, and adjudication of adverse events.

  • This trial was sponsored by Vertos Medical. The sponsorship includes study-related supplies and expenses, as well as funding for statistical analysis services by an independent provider.

  • The authors declare no conflict of interest.

  • Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (