The purpose of this study is to determine if the ACADIA® Facet Replacement System is effective in the treatment of spinal stenosis. The primary objective of the study is to evaluate the overall success rate of the Anatomic Facet Replacement System in patients with spinal stenosis when compared to a posterior spinal fusion control.

Spinal Stenosis continues to be a major cause of back and leg pain. The condition is attributed to narrowing of the space around the nerves in the lumbar spine. This is often caused by the degenerative process in the spine and the facet joints. The current treatment calls for removal of bone around the affected nerve including the facet joints and fusing the posterior of the spine to ensure the segments remain stable.

The ACADIA® Facet Replacement System (AFRS) allows for an anatomic reconstruction of the facet joint after decompression and removal of the degenerated facet. Like the original facet joint, the replacement implant is designed to reproduce facet motion while restoring normal stability and motion.

The ACADIA® Facet Replacement System (AFRS) has been designed on the principals that have allowed other total joint replacement procedures to provide significant patient benefits. These guiding principals include:

• Anatomically based implant design
• Reproducible surgical technique
• Elimination of pain

The ACADIA® Facet Replacement System allows the surgeon to remove the offending bone while preserving the motion of the facet joint.

This study will evaluate the outcomes of patients using the AFRS™ investigation compared to those receiving instrumented posterior fusion procedure. Patients will be required to complete study visits before the procedure and at 6 weeks, 3, 6, 12, 24 months post procedure and annually thereafter as required by FDA. Follow up visits consist of administration of questionnaires, radiographs and neurological assessment.

Inclusion Criteria:

• 21-85 years of age and skeletally mature;
• Have undergone 6 months of non-operative treatment prior to surgery;
• Lateral, lateral recess and/or central canal stenosis;
• Disc height measuring ≥ 4 mm at the operative level;
• Persistent leg, thigh and/or buttock symptoms,including pain,numbness, burning or tingling with a minimum leg pain score of 40mm as measured with the Visual Analogue Scale (VAS) Index;
• A score greater than 2 on a scale of 1-5 on the Zurich Claudication Questionnaire (ZCQ) Symptom Severity (SS) Score-Candidate;
• A score greater than or equal to 2 on a scale of 1-4 on the ZCQ Physical Function (PF) Score;
• A candidate for a decompression with full facetectomy at the operative level
• Candidate for a posterior lumbar fusion;
• Physically and mentally willing and able to comply evaluations;
• Lives in the immediate area and has no plans to relocate;

Exclusion Criteria:

• Previous surgical procedure at the operative or adjacent level except for one of the following: Micro-discectomy, laminectomy, lamino/foraminotomy, rhizotomy, IDET, and/or interspinous spacer;
• Previous lumbar fusion or disc replacement procedure;
• Osteoporosis;
• greater than Grade I spondylolisthesis or retrolisthesis;
• Spondylolisthesis at levels other than at the operative level;
• Scoliosis of the lumbar spine (defined as more than 11 deg Cobb angle) as indicated by plain X-ray films;
• Primary diagnosis of discogenic back pain due to torn, herniated, inflamed or irritated disc or other pathology where the patient exhibits axial back pain from degenerative disc disease;
• Acute traumatic pars fracture at the operative/adjacent level vertebral body;
• Spinal stenosis at more than three lumbar segments;
• Acute trauma to the lumbar spine within the last 24 months;
• Active infection at the operative level, or a systemic infection;
• Physically / mentally compromised;
• Systemic disease that would affect the patient's welfare or the research study.
• Immunologically suppressed or immunocompromised;
• Insulin-Dependent Diabetes Mellitus (Type I Diabetes);
• Currently undergoing long-term steroid therapy;
• Metabolic bone disease;
• Active malignancy: (except non-melanoma skin cancer), unless treated with no clinical signs or symptoms of the malignancy for at least 5 years;
• Known allergy to cobalt chromium or titanium;
• Used any investigational drug or device within the past 30 days;
• Pending litigation related to back pain or injury;
• Is a prisoner.