rhBMP-2/CRM/CD HORIZON® Spinal System Pilot Study (2-Level)

Inclusion Criteria: 1. Has degenerative disc disease at two adjacent lumbar levels as noted by back pain of discogenic origin, with or without leg pain, with degeneration of the disc confirmed by patient history and radiographic studies to include one or more of the following: * instability; * osteophyte formation; * decreased disc height; * thickening of ligamentous tissue; * disc degeneration or herniation; and/or * facet joint degeneration. 2. Has preoperative Oswestry score \>= 30. 3. Has no greater than Grade 1 spondylolisthesis utilizing Meyerding's Classification (Meyerding, HW, 1932) at either treatment level. 4. Requires fusion at two adjacent lumbar levels from L1 to S1. 5. Is at least 18 years of age, inclusive, at the time of surgery. 6. Has not responded to non-operative treatment( e.g., bed rest, physical therapy, medications, spinal injections, manipulation, and/or TENS) for a period of 6 months. 7. If a female of child-bearing potential, patient is non-pregnant and non-nursing and agrees to not become pregnant for 1 year following surgery. 8. Is willing and able to comply with the study plan and sign the Patient Informed Consent Form. Exclusion Criteria: 1. Has primary diagnosis of a spinal disorder other than degenerative disc disease with Grade 1 or less spondylolisthesis at the involved levels. 2. Has had previous spinal fusion surgical procedure(s) at the involved levels. 3. Requires spinal fusion at more than two lumbar levels. 4. Has a condition that requires postoperative medications that interfere with fusion, such as steroids or prolonged use of nonsteroidal anti-inflammatory drugs, excluding routine perioperative nonsteroidal anti-inflammatory drugs. This does not include low dose aspirin for prophylactic anticoagulation. 5. Has been previously diagnosed with osteopenia, osteomalacia, or osteoporosis, or has any of the following that may be associated with a diagnosis of osteoporosis. (If "Yes" to any of the criteria below, a dual x-ray absorptiometry \[DEXA\] scan will be required to determine eligibility.) * Previously diagnosed with osteopenia, osteomalacia, or osteoporosis. * Postmenopausal non-black female over 60 years of age who weighs less than 140 pounds. * Postmenopausal female who has sustained a nontraumatic hip, spine, or wrist fracture. * Male over the age of 70. * Male over the age of 60 who has sustained a nontraumatic hip or spine fracture. If the level of bone mineral density (BMD) is a T score of -3.5 or lower( i.e., -3.6, - 3.7, etc.) or a T score of -2.5 or lower( i.e., -2.6, * 2.7, etc.) with vertebral crush fracture, then the patient is excluded from the study. 6. Has presence of active malignancy or prior history of malignancy (except for basal cell carcinoma of the skin). 7. Has overt or active bacterial infection, either local or systemic. 8. Has a documented titanium alloy allergy or intolerance. 9. Is mentally incompetent. If questionable, obtain psychiatric consult. 10. Has a Waddell Signs of Inorganic Behavior Score of 3 or greater. 11. Is a prisoner. 12. Is an alcohol and/or drug abuser as defined by currently undergoing treatment for alcohol and/or drug abuse. 13. Has received drugs that may interfere with bone metabolism within two weeks prior to the planned date of spinal fusion surgery( e.g., steroids or methotrexate). 14. Has a history of autoimmune disease. 15. Has a history of exposure to injectable collagen or silicone implants. 16. Has a history of hypersensitivity to protein pharmaceuticals (monoclonal antibodies or gamma globulins) or collagen. 17. Has received treatment with an investigational therapy within 28 days prior to implantation surgery or such treatment is planned during the 16 weeks following rhBMP-2/CRM implantation. 18. Has received any previous exposure to any/all BMPs of either human or animal extraction. 19. Has a history of allergy to bovine products or a history of anaphylaxis. 20. Has history of endocrine or metabolic disorder known to affect osteogenesis (e.g., Paget's disease, renal osteodystrophy, Ehlers-Dalons syndrome, or osteogenesis imperfecta).