This study will explore the use of OP-1 Putty in conjunction with surgical treatment for the treatment of spinal decompression and lumbar spinal fusion.

It is postulated that the addition of OP-1 Putty to autogenous bone will prove beneficial in the treatment of patients requiring decompression and lumbar spinal fusion. The Investigational system is intended to stimulate bone growth. It is indicated as an adjunct or a replacement for autograft in spinal fusion.

Inclusion Criteria:

1. The subject has a diagnosis of Degenerative Lumbar Spondylolisthesis of Grade I or II with Spinal Stenosis demonstrated by medical history, physical examination a n d radiographic imaging.
2. The subject is a candidate for decompression and spinal fusion with the use of autograft from the iliac crest.
3. The subject requires one level lumbar fusion (L-3 to S-1).
4. The subject has a preoperative Oswestry Disability Index of 30-100.

Exclusion Criteria:

1. The subject has active spinal and/or systemic infection.
2. The subject is morbidly obese.
3. The subject has a known sensitivity to any component of the OP-1 Putty.
4. The subject has spinal instability measured on flexion / extension radiographs of greater than 50% translation of the vertebrae and greater than or equal to 20 degrees of angular motion.
5. The subject uses tobacco or nicotine or is prescribed steroids such as cortisone.