Aspen Spinous Process Fixation System for Use in PLF in Patients With Spondylolisthesis

• Age between 50 and older
• Diagnosis of mild segmental instability on standing radiography lateral film defined as degenerative spondylolisthesis ≤ 4mm in dynamic imaging (i.e., flexion/extension)
• Scheduled for an elective single-level posterior decompression and posterolateral fusion using AspenTM spinous process fixation system
• Oswestry Disability Index (ODI) v 2.1 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:

Pre-operative

• Marked degenerative spondylolisthesis (>4mm)
• Lesions requiring surgery involving two levels
• Prior surgery at index level or adjacent level
• Prior spinal fusion surgery
• Isthmic or 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: SCORE (Simple Calculated Osteoporosis Risk Estimation) will be used to screen subjects requiring DEXA. Subjects with T-score \< -2.5 will be excluded
• 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, anterior/lateral plating, anchored cages)
• Use of Bone Morphogenetic Protein (BMP)*
• 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
• Pregnant or planning to become pregnant during 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.)

Intra-operative Exclusion

• Intra-operative visualization of a > 4mm spondylolisthesis not previously noted radiographically
• Any change in the surgical procedure that violates the inclusion/exclusion criteria. (eg. switching to double level procedure; placing pedicle screws as posterior fixation).