Study of Nucel for One and Two Level Lumbar Interbody Fusion

Inclusion Criteria: 1. Be between 18 and 75 years of age 2. Have clinical and/or radiological evidence of stenosis, spondylolisthesis, spondylosis or degenerative disc disease, or at either one or two levels of lumbar spine. 3. In the opinion of the treating surgeon, must already be a qualified candidate for interbody lumbar fusion surgery with supplemental fixation. 4. Be likely to return for regular follow-ups until the end of the study period. 5. Be willing and able to provide Informed Consent for study participation. Exclusion Criteria: 1. Previous lumbar spine fusion surgery at operative level. 2. Back pain due to acute trauma. 3. Clinical, laboratory and/or radiological evidence of back pain secondary to acute or chronic infection, malignancy, other space occupying lesions and metabolic bone demineralization diseases (e.g. osteomalacia, gout, Paget's disease etc.) 4. No chronic steroid or chronic prescription NSAID use within three (3) months prior to surgery. 5. Any active malignancy, infectious process, or documented chronic autoimmune disease. 6. Any other concurrent medical disease or treatment that might impair normal healing process. 7. Recent history (within past 6 months) of any chemical or alcohol dependence. 8. Morbid obesity (BMI \> 40). 9. Currently a prisoner. 10. Currently experiencing a major mental illness (psychosis, schizophrenia, major affective disorder) which may indicate that the symptoms are psychological rather than of physical origin. 11. Pregnancy at the time of enrollment or planned pregnancy, which would interfere with follow-up imaging.