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:

1. The feasibility of the trial protocol, and
2. Preliminary data on the effectiveness of each treatment.

Inclusion Criteria:

• Patients deemed to be surgical candidates with focal (1-2 level) lumbar spinal stenosis (LSS) and associated stable degenerative spondylolisthesis with the following characteristics:

  1. a clinical history of back, buttock and leg pain with walking or standing that is improved when lying, sitting or bending forward
  2. a clinical history of leg symptoms that are greater than or equal to back symptoms with walking or standing, and
  3. greater than 6 months of symptoms with failed conservative care

• aged 50 or over

• sufficient fluency in English or French to provide informed consent and complete questionnaires with or without the need of an interpreter

Exclusion Criteria:

• Greater than 25% listhesis or spinal instability as demonstrated by motion (>5mm of translation) on flexion extension radiographs or non-loaded (MRI/CT or supine x-rays) to loaded imaging (standing radiograph)
• Presence of kyphosis (>0 degrees at the affected level or globally), degenerative scoliosis (>10 degree using the Cobb method) with rotatory or lateral listhesis on preoperative x-rays
• Clinical history of osteoporotic fracture or chronic oral steroid use
• Previous posterior lumbar spinal surgery (excluding prior microdiscectomy)
• Patients who have evidence of neurological disorders that affect physical function (e.g. peripheral neuropathy), neuromuscular disorders (e.g. multiple sclerosis, Parkinson's etc.) or systemic illness (e.g. inflammatory arthritis) that affects physical function