The purpose of the study is to determine the proper use of lower back screws and rods (instrumentation) and bony fusion in subjects with one level of degenerative spinal narrowing (stenosis) compressing nerves to the legs with one spinal bone slipping forward on another (spondylolisthesis). There are two types of operations that surgeons perform for this problem. Some spinal surgeons remove some bone in the back (laminectomy) to decompress the nerves. Other surgeons perform a laminectomy (decompression) as above, but feel that it is also important to strengthen the back by placing screws and rods into the spine and adding more bone to obtain a new bridge of bone away from the nerves (decompression with instrumented fusion). This study aims to test the hypothesis that adding instrumented fusion to a decompression for this spinal problem will improve long term patient outcomes.

There is considerable debate among spinal surgeons regarding the optimal surgical procedure for lumbar spinal stenosis with a grade I spondylolisthesis. The major question is whether or not instrumented pedicle screw fusion should be undertaken when a decompressive laminectomy is performed to relieve neural compression. This multi-center, randomized, prospective clinical study aims to address this question by testing the hypothesis that adding instrumented fusion to a decompression for this spinal problem will improve long-term patient outcomes.

Inclusion Criteria:

• Symptomatic lumbar spinal stenosis and single level grade I spondylolisthesis (3-14 mm)

Exclusion Criteria:

• History of previous lumbar spinal surgery in region of stenosis
• Gross spinal instability (defined as greater than 3 mm motion on flexion/extension studies)
• Serious medical illness (ASA Class III or higher)
• Spondylolisthesis greater than 14 mm or associated with spondylolysis