A treatment is effective if it makes patients feel and function better than they would had they not been treated at all.
With injection therapy, patients get anesthetics, steroids, or both. To decide whether this is effective, researchers compare patients who get these substances to patients who have placebo--or "empty"--injections. If patients who have injection therapy have less pain than those who get placebos, the treatment is "effective."
When weighing a treatment's helpfulness, it's important to ask "for how long?" A recent article said that researchers have mostly looked at the short-term results of injection therapy. In other words, they mostly ask how patients feel within a few weeks or months of treatment. The long-term success of injection therapy has yet to be shown.