MiDAS III (Mild® Decompression Alternative to Open Surgery): Vertos Mild Patient Evaluation Study

Inclusion Criteria: * Lumbar spinal stenosis (LSS) with neurogenic claudication where the Visual Analog Scale (VAS) of back and leg pain average is ≥ 5. * Prior failure of conservative therapy. * Oswestry Disability Index (ODI) score of ≥ 31%. * Radiologic evidence of LSS, with unilateral or bilateral ligamentum flavum ≥ 4.1mm confirmed by pre-op MRI performed within 6-12 months of baseline visit. * Able to walk ≥ 10 feet before being limited by pain. * Available to complete 24-months of follow-up. * Adults ≥ 50 years of age. Exclusion Criteria: * Prior surgery at intended treatment level. * History of spinal fractures with current related pain symptoms. * Motor deficit or disabling back and/or leg pain from causes other than LSS neurogenic claudication (e.g. acute compression fracture, metabolic neuropathy, vascular claudication symptoms, etc.). * Significant/symptomatic disc protrusion or osteophyte formation judged by the Investigator as possible confounding factor to study results. * Excessive facet hypertrophy judged by the Investigator as possible confounding factor to study results. * Significant symptomatic foraminal stenosis. * Confirmed anterior or retro-listhesis ≥ 3mm. * Bleeding disorders and/or current use of anti-coagulants with the inability to withhold anticoagulants for required time prior to procedure. * Able to walk ≥ 200 yards unaided in erect non-flexed position before being limited by pain. * Able to stand ≥ 15 minutes in erect, non-flexed position before being limited by pain. * Use of acetylsalicylic acid (ASA) and/or non-steroidal anti-inflammatory drug (NSAID) within 7 days of treatment. * Pregnant and/or breastfeeding. * Body mass index (BMI) ≥ 32 as calculated using the patient's weight multiplied by 703 then divided by height in inches squared. * Epidural steroid, systemic steroid or any spine interventional procedure within prior six weeks of study procedure. * Dementia and/or inability to give informed consent and to understand and complete follow-up patient reported outcomes forms. * Inability of the patient to lie prone for any reason with anesthesia support (e.g. chronic obstructive pulmonary disease (COPD), obesity, etc.). * On (or pending) Workman's Compensation or known to be considering litigation associated with back pain. * Unable to tolerate MRI (pacemaker, spinal cord stimulator, etc.). * Intrathecal pump. * Any medical condition determined by the Investigator that would not allow subject to fulfill trial requirements or safely tolerate procedures in this study.