Before a drug can be marketed, it has to go through rigorous testing to show it is safe and effective. Surgery, though, is different. The Food and Drug Administration does not regulate surgical procedures. So what happens when an operation is subjected to and fails the ultimate test — a clinical trial in which patients are randomly assigned to have it or not?

The expectation is that medical practice will change if an operation turns out not to help.

If only.

It looks as if the onus is on patients to ask what evidence, if any, shows that surgery is better than other options.

Take what happened with spinal fusion, an operation that welds together adjacent vertebrae to relieve back pain from worn-out discs. Unlike most operations, it actually was tested in four clinical trials. The conclusion: Surgery was no better than alternative nonsurgical treatments, like supervised exercise and therapy to help patients deal with their fear of back pain. In both groups, the pain usually diminished or went away.

The studies were completed by the early 2000s and should have been enough to greatly limit or stop the surgery, says Dr. Richard Deyo, professor of evidence-based medicine at the Oregon Health and Sciences University. But that did not happen, according to a recent report. Instead, spinal fusion rates increased — the clinical trials had little effect.