When assessing the efficacy of a given surgical procedure, researchers often have some study participants undergo a "sham surgery"—and a surprising number of those patients report improvements in their condition, Christie Aschwanden reports for FiveThirtyEight.

The makings of a sham surgery

According to Aschwanden, researchers conducting surgical efficacy studies have some study participants with a particular condition—such as back or knee pain—undergo a real surgery, while others receive a sham surgery to see if the real procedure is linked to improved patient outcomes.

In the sham surgery group, study participants undergo an imitation of the surgical process going through everything that the actual surgery group does, from fasting to undergoing anesthesia to receiving surgical incisions—but they do not receive the procedure itself. For procedures during which the patient is awake, physicians will imitate the sounds and sensations of the procedure or show patients a video of the procedure that was actually conducted on someone else.

The entire process, Aschwanden adds, is done with the participant's consent.

Research unearths a surgical placebo effect

Research has shown that "in a surprising number of cases," the actual surgery isn't effective—but Aschwanden writes they also show "that there's something powerful about believing that you're having surgery and that it will fix what ails you."  

For instance, a 2014 review of 53 trials that looked at how elective surgical procedures and placebos stacked up found sham surgeries afforded some benefit in about three-quarters of the trials. And in about half of the cases, the sham surgeries worked as well as the actual surgeries.

According to Aschwanden, research suggests arthroscopic surgery for meniscus repairs is one common orthopedic procedure that fails to outperform the sham. Other examples of procedures that seem no more effective than the placebo at reducing pain include vertebroplasty—to treat compression fractures in the spine—and intradiscal electrothermal therapy—performed to treat herniated disks and low back pain.

What makes the sham surgeries seem so helpful?

Orthopedic surgeon Stuart Green, a professor at the University of California, Irvine, has hypothesized that a sham surgery's placebo effect is proportional to the surgeon's confidence and enthusiasm, and the patient's optimism that it'll work.

Research also suggests that sham surgeries for invasive procedures generate a more powerful placebo effect than non-invasive ones, according to Jonas Bloch Thorlund of the University of Southern Denmark.

But factors besides the placebo effect can cause surgery to appear more effective than it is as well, Aschwanden writes. For instance, chronic pain "peaks and wanes," according to Aschwanden, meaning that outcomes that coincide with a surgery could also just be the natural course of the pain.

Why do surgeons keep performing these procedures?

Despite the research, Aschwanden writes that it "can be hard for doctors to see" the ineffectiveness of these commonly performed procedures.

In the book "Surgery, the Ultimate Placebo," surgeon Ian Harris writes, "Largely, surgeons believe that they are doing the right thing." It's not that they are ignoring evidence, Harris adds—it's simply that in some cases, the lack of quality data "allows surgeons to do procedures that have always been done, those that their mentors taught them to do, to do what they think works, and to simply do what everyone else is doing."

And patients themselves can be fooled, Green said, citing one study in which patients told they had undergone an arthroscopic procedure felt so much better that they were "flabbergasted" to learn they received the fake procedure.

Given the evidence, Aschwanden asks, "Could the placebo effect be harnessed for good in the same way that some researchers have used placebo pills to treat ADHD and irritable bowel syndrome?"? For Thorlund, the answer appears to be a clear no given the potential health risks from undergoing a sham surgery, compared with receiving a placebo pill. "I don't think it's ethical," Thorlund  said (Aschwanden, FiveThirtyEight, 7/19).

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