I am a retired nurse with a new health problem: spinal stenosis. My doctor suggested a steroid injection. But I don't see how this will help. I don't have inflammation, just a too-small spinal opening around the spinal nerves. What's the rationale for this treatment?
Narrowing of the vertebral canal puts pressure on the spinal nerve roots. This can cause microvascular injury and edema (swelling). The sensitive nerve endings respond to these changes with pain messages to the brain.

At the same time, increased blood flow and antiinflammatory cells rush to the area to help with healing and start to accumulate. This creates congestion around the nerve tissue amd adds to the problem.

Antiinflammatory drugs are often used first to help reduce the swelling. These drugs don't make the actual opening any larger. But they do reduce the size of the soft tissues inside the opening, resulting in pain relief.

Epidural steroid injections (ESIs) work well for some patients. It makes sense that patients with the smallest canal openings would have the best results. But a recent study from the University of Louisville School of Medicine found this wasn't true. Patients with large and small openings had the same results. Some got better with ESI and some didn't.

It's likely that other factors predict success of this treatment. More study is needed to find out what these are and plan treatment accordingly.