Dear Dr. Roach: I am an 82-year-old female. I started to have mild low-back pain a year ago, and it escalated to sciatica in my left leg and finally culminated in a pain crisis requiring hospitalization. My treatment goal in the hospital was pain control. Following an epidural injection, I am pretty well controlled with Tylenol and gabapentin 100 mg twice daily. I am no longer using the hydromorphone prescribed in the hospital. 
My CT scan shows significant degenerative changes, including severe arthritis, 8 millimeters of forward slipping of the disc at L4 on L5, and severe central canal stenosis.
I am concerned about the disc slipping. Am I in danger of some sort of sheering action of the spinal cord that would lead to major neurological problems? I appreciate the level of pain control I have now, but must I consider further treatment? — F.G.
Answer: Imagine a stack of boxes. If they are all exactly on top of each other, the stack is stable. However, if one is placed on top of another so that the front of one is stuck over the edge of the other, the stack can become unstable. In the vertebral column, this is called spondylolisthesis, and it almost always happens at L4 on L5. In your case, the major issue is stenosis — the narrowing of the spinal canal, where the spinal cord is.
Fortunately, spondylolisthesis in an adult generally does not progress to the point where the spinal cord is in danger. Surgery is considered only when a person has pain that cannot be controlled, and fortunately, it sounds like you are doing pretty well for pain. You have not mentioned any weakness, which would of course be concerning.
