Radiographic and Clinical Outcomes Following Unilateral or Bilateral Posterior Fixation in MI-TLIF

Inclusion Criteria: * Age 18-80 years. * Symptomatic single-level lumbar disease including lumbosacral junction. * Unilateral leg-dominant pain non-responsive to conservative management with concordant imaging findings. These include degenerative spondylolisthesis (grade 1 or 2), facet arthropathy +/- lateral disc herniation, recurrent disc herniation, or large central disc herniation. * Back pain of confirmed discogenic origin (single level disease only). * Failed conservative management for a minimum of 3 months. * Negative serum pregnancy test (for women of childbearing potential) Exclusion Criteria: * Severe bilateral leg symptoms. * Prior instrumented arthrodesis at any lumbar level. * History of osteoporosis. * Co-morbidities requiring medication that may interfere with bone or soft tissue healing (i.e., oral or parenteral glucocorticoids, immunosuppressive agent, methotrexate). * Severe co-morbidities (e.g., heart, respiratory, or renal disease). * Recent (\<3 yrs) Co-incident spinal tumor or infection. * Greater than single level symptomatic involvement. * Associated thoracolumbar kyphotic or scoliotic deformity (\>10). * Morbid obesity (BMI \> 40). * History of metal sensitivity/foreign body sensitivity. * Concurrent involvement in another investigational drug or device study that could confound study data. * History of substance abuse (recreational drugs, prescription drugs, or alcohol) that could interfere with protocol assessments and/or with the subject's ability to complete the protocol required follow-up. * Subjects who are pregnant or plan to become pregnant in the next 24 months. * Prisoner.