The purpose of this study is to assess the feasibility of a full-scale multicenter randomized, controlled trial comparing the effectiveness of two surgical treatments for a condition associated with lumbar spinal stenosis called degenerative lumbar spondylolisthesis. Both treatments are currently used, but individual surgeons use different selection criteria for each treatment and use the procedures at different rates. The two procedures are decompression with fusion (the most common surgical procedure for spondylolisthesis) and midline-sparing decompression alone (which is also a standard treatment, but is not as widely used for treating spondylolisthesis). The investigators plan to collect the evidence on the following: