A Pivotal Study of the Premia Spine TOPS™ System

Inclusion Criteria: * Be between 35 and 80 years of age; * Must demonstrate at a single level to be treated (L2/3, L3/4 or L4/5) all three of the following; 1. Degenerative spondylolisthesis or retrolisthesis up to Grade I, as determined by the investigator based on flexion/extension X-rays, 2. At least moderate lumbar spinal stenosis, defined as at least a 25% reduction in either the central canal, the lateral recess space, and/or the foramen when compared to an adjacent level, as determined by the investigator based on MRI, 3. Thickening of the ligamentum flavum and/or scarring of the facet joint capsule as identified by the investigator based on MRI. * Have had at least six (6) months of failed conservative treatment prior to surgery (e.g., physical therapy, use of anti-inflammatory medications at maximum recommended dosage; administration of epidural/facet injections and/or nerve block); * Have an Oswestry Disability Index (ODI) score of at least 40/100 at baseline; * Have leg pain with a VAS score of at least 40/100 for at least one leg at baseline ; * Lower back pain with a VAS score of at least 10 points less than Worst Leg VAS score; * Neurogenic claudication (as defined by worsening leg pain when walking or standing, which is reduced when sitting or bending forward); Exclusion Criteria: * Presence of free fragment disc herniation at the index level or either adjacent level; * Less than 4mm of disc height at the index level; * Spondylolisthesis greater than Grade I; * Back or non-radicular leg pain of unknown etiology; * Stenosis caused by an extruded spinal disc fragment (e.g., herniation) or where the etiology is considered to be congenital, iatrogenic, post-traumatic, or metabolic; * Known allergy or sensitivity to PEEK, titanium, cobalt chrome, and/or polyurethane; * Prior surgery at any lumbar vertebral level with instrumentation; * Prior surgery at the index or adjacent lumbar vertebral level; * Clinically compromised vertebral bodies at the affected level; * Scoliosis greater than ten (10) degrees by major Cobb angle; * BMI \> 40; * Osteoporosis; * Paget's disease, gout, osteomalacia, osteogenesis imperfecta, thyroid and/or parathyroid gland disorder and/or other metabolic bone disease; * Active infection - systemic or local; * Active hepatitis; * AIDS, HIV, Rheumatoid arthritis or other autoimmune disease; * Tuberculosis - active or in the past 3 years; * Active malignancy; * Any medical condition requiring treatment with any drug known to potentially interfere with bone/soft tissue healing or receiving radiation therapy that is expected to continue for the duration of the study; * Cauda equina syndrome or neurogenic bowel/bladder dysfunction; * Vascular claudication due to severe arterial insufficiency of the legs; * Sustained pathologic lumbar fractures of the vertebra or multiple lumbar fractures of the vertebra or hip; * Significant peripheral neuropathy causing decreased sensation in a stocking-like or non-radicular and non-dermatomal distribution in the lower extremities; * Insulin-dependent diabetes mellitus; * Immunologically suppressed, receiving steroids \> 1 month out of the past year; * Current chemical/alcohol dependency; * Current smoker or user of tobacco products; * Pregnant or interested in becoming pregnant; * Currently involved in active spinal litigation; * Currently having a workman's compensation claim; * Currently incarcerated;