The guy’s desperate. The pain in his knee has made it impossible to play basketball or walk down stairs. In search of a cure, he makes a journey to a healing place, where he’ll undergo a fasting rite, don ceremonial garb, ingest mind-altering substances and be anointed with liquids before a masked healer takes him through a physical ritual intended to vanquish his pain.

Seen through different eyes, the process of modern surgery may look more more spiritual than scientific, said orthopedic surgeon Stuart Green, a professor at the University of California, Irvine. Our hypothetical patient is undergoing arthroscopic knee surgery, and the rituals he’ll participate in — fasting, wearing a hospital gown, undergoing anesthesia, having his surgical site prepared with an iodine solution, and giving himself over to a masked surgeon — foster an expectation that the procedure will provide relief, Green said.

These expectations matter, and we know they matter because of a bizarre research technique called sham surgery. In these fake operations, patients are led to believe that they are having a real surgical procedure — they’re taken through all the regular pre- and post- surgical rituals, from fasting to anesthesia to incisions made in their skin to look like the genuine operation occurred — but the doctor does not actually perform the surgery. If the patient is awake during the “procedure,” the doctor mimics the sounds and sensations of the true surgery, and the patient may be shown a video of someone else’s procedure as if it were his own.

Sham surgeries may sound unethical, but they’re done with participants’ consent and in pursuit of an important question: Does the surgical procedure under consideration really work? In a surprising number of cases, the answer is no.

A 2014 review of 53 trials that compared elective surgical procedures to placebos found that sham surgeries provided some benefit in 74 percent of the trials and worked as well as the real deal in about half. Consider the middle-aged guy going in for surgery to treat his knee pain. Arthroscopic knee surgery has been a common orthopedic procedure in the United States, with about 692,000 of them performed in 2010, but the procedure has proven no better than a sham when done to address degenerative wear and tear, particularly on the meniscus.

Meniscus repair is only one commonly performed orthopedic surgery that has failed to produce better results than a sham surgery. A back operation called vertebroplasty (done to treat compression fractures in the spine) and something called intradiscal electrothermal therapy, a “minimally invasive” treatment for herniated disks and low back pain, have also produced study results that suggest they may be no more effective than a sham at reducing pain in the long term.

Such findings show that these procedures don’t work as promised, but they also indicate that there’s something powerful about believing that you’re having surgery and that it will fix what ails you. Green hypothesizes that a surgery’s placebo effect is proportional to the elaborateness of the rituals surrounding it, the surgeon’s expressed confidence and enthusiasm for the procedure, and a patient’s belief that it will help.

Weirdly enough, surgery’s invasiveness may explain some of its potency. Studies have shown that invasive procedures produce a stronger placebo effect than non-invasive ones, said researcher Jonas Bloch Thorlund of the University of Southern Denmark. A pill can provoke a placebo effect, but an injection produces an even stronger one. Cutting into someone appears to be more powerful still.

Even without a robust placebo effect, an ineffective surgery may seem helpful. Chronic pain often peaks and wanes, which means that if a patient sought treatment when the pain was at its worst, the improvement of symptoms after surgery could be the result of a condition’s natural course, rather than the treatment. That softening of symptoms from an extreme measure of pain is an example of the statistical concept of regression to the mean.

And then there’s what Thorlund calls “car repair” logic — something looks broken, so you try to fix it. A patient comes in with knee pain, and an X-ray or MRI exam shows a tear in the meniscus. The tendency is to assume that the torn meniscus is the cause of the pain and so should be fixed. However, studies show that MRIs can find all kinds of “abnormalities,” such as cartilage damage, even among people without knee pain. One such study looked at the MRI scans of more than 300 knees and found no direct link between meniscus damage and pain. “You can have a meniscal tear without having any problems,” Thorlund said.

Back pain follows a similar pattern. Studies that examined MRIs of people’s backs show that things like slipped, bulging or herniated disks correlate very poorly with pain. Herniated disks and other supposed abnormalities are also common in people without back pain, and it’s telling that studies find that spinal fusion, another popular back surgery used to address disk problems, does not produce better results than nonsurgical interventions.

Given these results, why do these surgeries remain so widespread? Because the ineffectiveness of these procedures can be hard for doctors to see. “Largely, surgeons believe that they are doing the right thing,” writes surgeon Ian Harris in his book “Surgery, the Ultimate Placebo.” Yet in many cases, “the real benefit from surgery is lower and the risks are higher than you or your surgeon think,” he writes. It’s not always a matter of surgeons ignoring the evidence. In some cases, there’s simply a lack of high-quality studies, and that “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,” Harris writes.

Surgeons who perform only real surgeries never see the benefits of sham procedures and so may falsely attribute their patients’ success to the surgery without recognizing that regression to the mean and the placebo effect might also contribute. Patients can also be fooled, Green said, recalling how in one arthroscopic surgery experiment, patients in the placebo group improved so much that they were “flabbergasted” to learn that they’d received the sham treatment.

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? When I posed that question to Thorlund, his answer was a resounding no. Even sham surgery could pose the risk of serious, life-threatening complications. “I don’t think it’s ethical,” he said.