Comparison of the Aspen Device Versus Pedicle Screws for Supplemental Posterior Fixation in Lumbar Interbody Fusion

Inclusion Criteria: * Age between 18 and 75 years * Scheduled for an elective single-level circumferential lumbar fusion by means of supplemental posterior fusion with fixation (allowing for the placement of ASPEN or pedicle screws) for an anterior or lateral interbody fusion * Diagnosis of primary symptomatic Degenerative Disc Disease (DDD) and/or spondylolisthesis confirmed with appropriate imaging studies and/or positive lumbar discography * Oswestry Disability Index (ODI) v2.1 score \> 30% * Failed at least 3 months of conservative care (non-surgical) OR has clinical signs of neurological deterioration * Signed Informed Consent Form Exclusion Criteria: * Previous fusion at the operative level * Spondylolisthesis Grade 3 or more * Lytic spondylolisthesis * Incompetent or missing posterior arch at the affected level (e.g. complete laminectomy, pars defect) * Requires complete laminectomy at level of surgery * Facet joints at implant level are absent or fractured * Vertebral body compromise or acute fracture at implant level * Body mass Index (BMI) ≥ 35 * Known allergy to titanium * Osteoporosis: Simple Calculated Osteoporosis Risk Estimation (S.C.O.R.E.) \> 6 AND Dual-energy X-ray absorptiometry (DEXA) T-score \< -2.5 * Paget's disease, osteomalacia, or any other metabolic bone disease * Use of medications or any drug known to potentially interfere with bone/soft tissue healing (e.g. chronic systemic steroids) * Planned use of additional segmental fixation (eg. facet screws) * Planned use of Bone Morphogenetic Protein (BMP) for posterolateral fusion\* * Unlikely to comply with the follow-up evaluation schedule * In the opinion of the Investigator, Subject has history of chemical substance dependency or significant psychosocial disturbance that may impact the outcome or study participation * Active participation in a clinical trial of another drug or device * Active systemic infection or any other health condition that would preclude surgery * History of invasive malignancy, except if the subject has received treatment and displayed no clinical signs and symptoms for at least five years * Subject is a prisoner * Pregnant or planning to become pregnant during the length of study participation * Involvement in active litigation related to back problems at the time of screening * Direct involvement in the execution of this protocol * Pre-existing conditions that could interfere with the evaluation of outcome measures (e.g. musculoskeletal, neuromuscular, etc.)