Prospective, Multi-center Study to Assess Posterolateral Fusion Using FIBERGRAFT

Inclusion Criteria: 1. Signed Informed Consent Form 2. Is at least 18 years of age and skeletally mature. 3. Must have symptomatic spinal stenosis and/or spondylolisthesis or degenerative disc disease (DDD) at one or two adjacent levels from L2-S1, requiring a fusion. 4. Must have completed a minimum of three months of unsuccessful conservative, non-operative care. 5. DDD and spinal stenosis and/or spondylolisthesis must be confirmed by MRI or CT scans. 6. Must score at least 40 points on the Oswestry Disability Index. 7. Must score at least a 4 on a 10 cm Visual Analog Scale for back or leg pain. 8. Must be able to comply with the protocol's follow-up schedule. 9. Must understand and sign the IRB approved informed consent document. Exclusion Criteria: 1. Symptomatic at more than two levels. 2. Previous fusion surgery at any lumbar level with or without instrumentation (prior discectomy, laminotomy, laminectomy or nucleolysis at the index level (\> 6 months) is permitted). 3. Previous total disc replacement at any lumbar level. 4. Undergoing fusion for recurrent stenosis at the level to be treated. 5. Extraspinal cause of back and/or leg pain, or back and/or leg pain of unknown etiology. 6. Spondylolisthesis not able to be reduced to grade I. 7. Lumbar scoliosis greater than 11 degrees. 8. Osteoporosis\*, osteopenia, osteomalacia, Paget's disease, or metabolic or systemic bone disorders that affect bone or wound healing. 9. Use of posterior instrumentation for stabilization is not possible. 10. Intra-operative soft tissue coverage is not possible. 11. Spinal tumors. 12. Active arachnoiditis. 13. Fractures of the epiphyseal plate or fractures for which stabilization of the fracture is not possible. 14. Impaired calcium metabolism. 15. Active systemic infection or surgical site infection. 16. Osteomyelitis at the graft site. 17. Rheumatoid arthritis or other autoimmune disease. 18. Chronic steroid use (used steroids for one month within the last 6 months) or any medical condition that requires treatment with drugs known to interfere with bone healing. 19. Systemic disease such as AIDS, HIV, hepatitis (active), tuberculosis. 20. Morbid obesity defined as body mass index (BMI) \>40 or a weight more than 100 lbs over ideal body weight. 21. Smokers unless the subject agrees to quit at least 2 weeks prior to and for the duration of the study, confirmed by a carboxyhemoglobin test prior to surgery. 22. Psychosocial disorders that would preclude accurate evaluation or has a history of recent substance abuse. 23. Active malignancy except non-melanoma skin cancer; history of any invasive malignancy unless treated and in remission for at least five years. 24. Documented allergies to titanium. 25. Subjects with a history of anaphylaxis, history of multiple allergies, known allergies to bovine collagen, or who are being treated for desensitization to meat products because FIBERGRAFT® BG Matrix contains bovine collagen. 26. Pregnancy/able to become pregnant and not following a reliable contraceptive method, or interested in becoming pregnant in the next two years. 27. Participation in another investigational study within 30 days. 28. Prisoners.